diff options
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/Kconfig | 170 | ||||
| -rw-r--r-- | kernel/rcu/Kconfig.debug | 65 | ||||
| -rw-r--r-- | kernel/rcu/rcu.h | 168 | ||||
| -rw-r--r-- | kernel/rcu/rcu_segcblist.c | 229 | ||||
| -rw-r--r-- | kernel/rcu/rcu_segcblist.h | 61 | ||||
| -rw-r--r-- | kernel/rcu/rcuscale.c | 412 | ||||
| -rw-r--r-- | kernel/rcu/rcutorture.c | 1896 | ||||
| -rw-r--r-- | kernel/rcu/refscale.c | 535 | ||||
| -rw-r--r-- | kernel/rcu/srcutiny.c | 94 | ||||
| -rw-r--r-- | kernel/rcu/srcutree.c | 1376 | ||||
| -rw-r--r-- | kernel/rcu/sync.c | 8 | ||||
| -rw-r--r-- | kernel/rcu/tasks.h | 1490 | ||||
| -rw-r--r-- | kernel/rcu/tiny.c | 89 | ||||
| -rw-r--r-- | kernel/rcu/tree.c | 2986 | ||||
| -rw-r--r-- | kernel/rcu/tree.h | 126 | ||||
| -rw-r--r-- | kernel/rcu/tree_exp.h | 404 | ||||
| -rw-r--r-- | kernel/rcu/tree_nocb.h | 1805 | ||||
| -rw-r--r-- | kernel/rcu/tree_plugin.h | 1606 | ||||
| -rw-r--r-- | kernel/rcu/tree_stall.h | 454 | ||||
| -rw-r--r-- | kernel/rcu/update.c | 120 |
20 files changed, 9811 insertions, 4283 deletions
diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index cdc57b4f6d48..bdd7eadb33d8 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -8,6 +8,8 @@ menu "RCU Subsystem" config TREE_RCU bool default y if SMP + # Dynticks-idle tracking + select CONTEXT_TRACKING_IDLE help This option selects the RCU implementation that is designed for very large SMP system with hundreds or @@ -51,56 +53,77 @@ config RCU_EXPERT Say N if you are unsure. -config SRCU - bool - help - This option selects the sleepable version of RCU. This version - permits arbitrary sleeping or blocking within RCU read-side critical - sections. - config TINY_SRCU bool - default y if SRCU && TINY_RCU + default y if TINY_RCU help This option selects the single-CPU non-preemptible version of SRCU. config TREE_SRCU bool - default y if SRCU && !TINY_RCU + default y if !TINY_RCU help This option selects the full-fledged version of SRCU. +config NEED_SRCU_NMI_SAFE + def_bool HAVE_NMI && !ARCH_HAS_NMI_SAFE_THIS_CPU_OPS && !TINY_SRCU + config TASKS_RCU_GENERIC def_bool TASKS_RCU || TASKS_RUDE_RCU || TASKS_TRACE_RCU - select SRCU help This option enables generic infrastructure code supporting task-based RCU implementations. Not for manual selection. +config FORCE_TASKS_RCU + bool "Force selection of TASKS_RCU" + depends on RCU_EXPERT + select TASKS_RCU + default n + help + This option force-enables a task-based RCU implementation + that uses only voluntary context switch (not preemption!), + idle, and user-mode execution as quiescent states. Not for + manual selection in most cases. + config TASKS_RCU - def_bool PREEMPTION + bool + default n + select IRQ_WORK + +config FORCE_TASKS_RUDE_RCU + bool "Force selection of Tasks Rude RCU" + depends on RCU_EXPERT + select TASKS_RUDE_RCU + default n help - This option enables a task-based RCU implementation that uses - only voluntary context switch (not preemption!), idle, and - user-mode execution as quiescent states. Not for manual selection. + This option force-enables a task-based RCU implementation + that uses only context switch (including preemption) and + user-mode execution as quiescent states. It forces IPIs and + context switches on all online CPUs, including idle ones, + so use with caution. Not for manual selection in most cases. config TASKS_RUDE_RCU - def_bool 0 - help - This option enables a task-based RCU implementation that uses - only context switch (including preemption) and user-mode - execution as quiescent states. It forces IPIs and context - switches on all online CPUs, including idle ones, so use - with caution. + bool + default n + select IRQ_WORK -config TASKS_TRACE_RCU - def_bool 0 +config FORCE_TASKS_TRACE_RCU + bool "Force selection of Tasks Trace RCU" + depends on RCU_EXPERT + select TASKS_TRACE_RCU + default n help This option enables a task-based RCU implementation that uses explicit rcu_read_lock_trace() read-side markers, and allows - these readers to appear in the idle loop as well as on the CPU - hotplug code paths. It can force IPIs on online CPUs, including - idle ones, so use with caution. + these readers to appear in the idle loop as well as on the + CPU hotplug code paths. It can force IPIs on online CPUs, + including idle ones, so use with caution. Not for manual + selection in most cases. + +config TASKS_TRACE_RCU + bool + default n + select IRQ_WORK config RCU_STALL_COMMON def_bool TREE_RCU @@ -111,7 +134,7 @@ config RCU_STALL_COMMON making these warnings mandatory for the tree variants. config RCU_NEED_SEGCBLIST - def_bool ( TREE_RCU || TREE_SRCU ) + def_bool ( TREE_RCU || TREE_SRCU || TASKS_RCU_GENERIC ) config RCU_FANOUT int "Tree-based hierarchical RCU fanout value" @@ -168,28 +191,10 @@ config RCU_FANOUT_LEAF Take the default if unsure. -config RCU_FAST_NO_HZ - bool "Accelerate last non-dyntick-idle CPU's grace periods" - depends on NO_HZ_COMMON && SMP && RCU_EXPERT - default n - help - This option permits CPUs to enter dynticks-idle state even if - they have RCU callbacks queued, and prevents RCU from waking - these CPUs up more than roughly once every four jiffies (by - default, you can adjust this using the rcutree.rcu_idle_gp_delay - parameter), thus improving energy efficiency. On the other - hand, this option increases the duration of RCU grace periods, - for example, slowing down synchronize_rcu(). - - Say Y if energy efficiency is critically important, and you - don't care about increased grace-period durations. - - Say N if you are unsure. - config RCU_BOOST bool "Enable RCU priority boosting" - depends on RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT - default n + depends on (RT_MUTEXES && PREEMPT_RCU && RCU_EXPERT) || PREEMPT_RT + default y if PREEMPT_RT help This option boosts the priority of preempted RCU readers that block the current preemptible RCU grace period for too long. @@ -212,6 +217,20 @@ config RCU_BOOST_DELAY Accept the default if unsure. +config RCU_EXP_KTHREAD + bool "Perform RCU expedited work in a real-time kthread" + depends on RCU_BOOST && RCU_EXPERT + default !PREEMPT_RT && NR_CPUS <= 32 + help + Use this option to further reduce the latencies of expedited + grace periods at the expense of being more disruptive. + + This option is disabled by default on PREEMPT_RT=y kernels which + disable expedited grace periods after boot by unconditionally + setting rcupdate.rcu_normal_after_boot=1. + + Accept the default if unsure. + config RCU_NOCB_CPU bool "Offload RCU callback processing from boot-selected CPUs" depends on TREE_RCU @@ -240,9 +259,38 @@ config RCU_NOCB_CPU Say Y here if you need reduced OS jitter, despite added overhead. Say N here if you are unsure. +config RCU_NOCB_CPU_DEFAULT_ALL + bool "Offload RCU callback processing from all CPUs by default" + depends on RCU_NOCB_CPU + default n + help + Use this option to offload callback processing from all CPUs + by default, in the absence of the rcu_nocbs or nohz_full boot + parameter. This also avoids the need to use any boot parameters + to achieve the effect of offloading all CPUs on boot. + + Say Y here if you want offload all CPUs by default on boot. + Say N here if you are unsure. + +config RCU_NOCB_CPU_CB_BOOST + bool "Offload RCU callback from real-time kthread" + depends on RCU_NOCB_CPU && RCU_BOOST + default y if PREEMPT_RT + help + Use this option to invoke offloaded callbacks as SCHED_FIFO + to avoid starvation by heavy SCHED_OTHER background load. + Of course, running as SCHED_FIFO during callback floods will + cause the rcuo[ps] kthreads to monopolize the CPU for hundreds + of milliseconds or more. Therefore, when enabling this option, + it is your responsibility to ensure that latency-sensitive + tasks either run with higher priority or run on some other CPU. + + Say Y here if you want to set RT priority for offloading kthreads. + Say N here if you are building a !PREEMPT_RT kernel and are unsure. + config TASKS_TRACE_RCU_READ_MB bool "Tasks Trace RCU readers use memory barriers in user and idle" - depends on RCU_EXPERT + depends on RCU_EXPERT && TASKS_TRACE_RCU default PREEMPT_RT || NR_CPUS < 8 help Use this option to further reduce the number of IPIs sent @@ -258,4 +306,30 @@ config TASKS_TRACE_RCU_READ_MB Say N here if you hate read-side memory barriers. Take the default if you are unsure. +config RCU_LAZY + bool "RCU callback lazy invocation functionality" + depends on RCU_NOCB_CPU + default n + help + To save power, batch RCU callbacks and flush after delay, memory + pressure, or callback list growing too big. + +config RCU_DOUBLE_CHECK_CB_TIME + bool "RCU callback-batch backup time check" + depends on RCU_EXPERT + default n + help + Use this option to provide more precise enforcement of the + rcutree.rcu_resched_ns module parameter in situations where + a single RCU callback might run for hundreds of microseconds, + thus defeating the 32-callback batching used to amortize the + cost of the fine-grained but expensive local_clock() function. + + This option rounds rcutree.rcu_resched_ns up to the next + jiffy, and overrides the 32-callback batching if this limit + is exceeded. + + Say Y here if you need tighter callback-limit enforcement. + Say N here if you are unsure. + endmenu # "RCU Subsystem" diff --git a/kernel/rcu/Kconfig.debug b/kernel/rcu/Kconfig.debug index 1942c1f1bb65..9b0b52e1836f 100644 --- a/kernel/rcu/Kconfig.debug +++ b/kernel/rcu/Kconfig.debug @@ -27,10 +27,6 @@ config RCU_SCALE_TEST tristate "performance tests for RCU" depends on DEBUG_KERNEL select TORTURE_TEST - select SRCU - select TASKS_RCU - select TASKS_RUDE_RCU - select TASKS_TRACE_RCU default n help This option provides a kernel module that runs performance @@ -46,10 +42,6 @@ config RCU_TORTURE_TEST tristate "torture tests for RCU" depends on DEBUG_KERNEL select TORTURE_TEST - select SRCU - select TASKS_RCU - select TASKS_RUDE_RCU - select TASKS_TRACE_RCU default n help This option provides a kernel module that runs torture tests @@ -65,10 +57,6 @@ config RCU_REF_SCALE_TEST tristate "Scalability tests for read-side synchronization (RCU and others)" depends on DEBUG_KERNEL select TORTURE_TEST - select SRCU - select TASKS_RCU - select TASKS_RUDE_RCU - select TASKS_TRACE_RCU default n help This option provides a kernel module that runs performance tests @@ -91,6 +79,57 @@ config RCU_CPU_STALL_TIMEOUT RCU grace period persists, additional CPU stall warnings are printed at more widely spaced intervals. +config RCU_EXP_CPU_STALL_TIMEOUT + int "Expedited RCU CPU stall timeout in milliseconds" + depends on RCU_STALL_COMMON + range 0 300000 + default 0 + help + If a given expedited RCU grace period extends more than the + specified number of milliseconds, a CPU stall warning is printed. + If the RCU grace period persists, additional CPU stall warnings + are printed at more widely spaced intervals. A value of zero + says to use the RCU_CPU_STALL_TIMEOUT value converted from + seconds to milliseconds. + +config RCU_CPU_STALL_CPUTIME + bool "Provide additional RCU stall debug information" + depends on RCU_STALL_COMMON + default n + help + Collect statistics during the sampling period, such as the number of + (hard interrupts, soft interrupts, task switches) and the cputime of + (hard interrupts, soft interrupts, kernel tasks) are added to the + RCU stall report. For multiple continuous RCU stalls, all sampling + periods begin at half of the first RCU stall timeout. + The boot option rcupdate.rcu_cpu_stall_cputime has the same function + as this one, but will override this if it exists. + +config RCU_CPU_STALL_NOTIFIER + bool "Provide RCU CPU-stall notifiers" + depends on RCU_STALL_COMMON + depends on DEBUG_KERNEL + depends on RCU_EXPERT + default n + help + WARNING: You almost certainly do not want this!!! + + Enable RCU CPU-stall notifiers, which are invoked just before + printing the RCU CPU stall warning. As such, bugs in notifier + callbacks can prevent stall warnings from being printed. + And the whole reason that a stall warning is being printed is + that something is hung up somewhere. Therefore, the notifier + callbacks must be written extremely carefully, preferably + containing only lockless code. After all, it is quite possible + that the whole reason that the RCU CPU stall is happening in + the first place is that someone forgot to release whatever lock + that you are thinking of acquiring. In which case, having your + notifier callback acquire that lock will hang, preventing the + RCU CPU stall warning from appearing. + + Say Y here if you want RCU CPU stall notifiers (you don't want them) + Say N if you are unsure. + config RCU_TRACE bool "Enable tracing for RCU" depends on DEBUG_KERNEL @@ -116,7 +155,7 @@ config RCU_EQS_DEBUG config RCU_STRICT_GRACE_PERIOD bool "Provide debug RCU implementation with short grace periods" - depends on DEBUG_KERNEL && RCU_EXPERT + depends on DEBUG_KERNEL && RCU_EXPERT && NR_CPUS <= 4 && !TINY_RCU default n select PREEMPT_COUNT if PREEMPT=n help diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 59ef1ae6dc37..f94f65877f2b 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -10,19 +10,58 @@ #ifndef __LINUX_RCU_H #define __LINUX_RCU_H +#include <linux/slab.h> #include <trace/events/rcu.h> -/* Offset to allow distinguishing irq vs. task-based idle entry/exit. */ -#define DYNTICK_IRQ_NONIDLE ((LONG_MAX / 2) + 1) - - /* * Grace-period counter management. + * + * The two least significant bits contain the control flags. + * The most significant bits contain the grace-period sequence counter. + * + * When both control flags are zero, no grace period is in progress. + * When either bit is non-zero, a grace period has started and is in + * progress. When the grace period completes, the control flags are reset + * to 0 and the grace-period sequence counter is incremented. + * + * However some specific RCU usages make use of custom values. + * + * SRCU special control values: + * + * SRCU_SNP_INIT_SEQ : Invalid/init value set when SRCU node + * is initialized. + * + * SRCU_STATE_IDLE : No SRCU gp is in progress + * + * SRCU_STATE_SCAN1 : State set by rcu_seq_start(). Indicates + * we are scanning the readers on the slot + * defined as inactive (there might well + * be pending readers that will use that + * index, but their number is bounded). + * + * SRCU_STATE_SCAN2 : State set manually via rcu_seq_set_state() + * Indicates we are flipping the readers + * index and then scanning the readers on the + * slot newly designated as inactive (again, + * the number of pending readers that will use + * this inactive index is bounded). + * + * RCU polled GP special control value: + * + * RCU_GET_STATE_COMPLETED : State value indicating an already-completed + * polled GP has completed. This value covers + * both the state and the counter of the + * grace-period sequence number. */ #define RCU_SEQ_CTR_SHIFT 2 #define RCU_SEQ_STATE_MASK ((1 << RCU_SEQ_CTR_SHIFT) - 1) +/* Low-order bit definition for polled grace-period APIs. */ +#define RCU_GET_STATE_COMPLETED 0x1 + +extern int sysctl_sched_rt_runtime; + /* * Return the counter portion of a sequence number previously returned * by rcu_seq_snap() or rcu_seq_current(). @@ -118,6 +157,18 @@ static inline bool rcu_seq_done(unsigned long *sp, unsigned long s) } /* + * Given a snapshot from rcu_seq_snap(), determine whether or not a + * full update-side operation has occurred, but do not allow the + * (ULONG_MAX / 2) safety-factor/guard-band. + */ +static inline bool rcu_seq_done_exact(unsigned long *sp, unsigned long s) +{ + unsigned long cur_s = READ_ONCE(*sp); + + return ULONG_CMP_GE(cur_s, s) || ULONG_CMP_LT(cur_s, s - (2 * RCU_SEQ_STATE_MASK + 1)); +} + +/* * Has a grace period completed since the time the old gp_seq was collected? */ static inline bool rcu_seq_completed_gp(unsigned long old, unsigned long new) @@ -198,6 +249,12 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head) } #endif /* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */ +static inline void debug_rcu_head_callback(struct rcu_head *rhp) +{ + if (unlikely(!rhp->func)) + kmem_dump_obj(rhp); +} + extern int rcu_cpu_stall_suppress_at_boot; static inline bool rcu_stall_is_suppressed_at_boot(void) @@ -205,12 +262,18 @@ static inline bool rcu_stall_is_suppressed_at_boot(void) return rcu_cpu_stall_suppress_at_boot && !rcu_inkernel_boot_has_ended(); } +extern int rcu_cpu_stall_notifiers; + #ifdef CONFIG_RCU_STALL_COMMON extern int rcu_cpu_stall_ftrace_dump; extern int rcu_cpu_stall_suppress; extern int rcu_cpu_stall_timeout; +extern int rcu_exp_cpu_stall_timeout; +extern int rcu_cpu_stall_cputime; +extern bool rcu_exp_stall_task_details __read_mostly; int rcu_jiffies_till_stall_check(void); +int rcu_exp_jiffies_till_stall_check(void); static inline bool rcu_stall_is_suppressed(void) { @@ -271,7 +334,7 @@ void rcu_test_sync_prims(void); */ extern void resched_cpu(int cpu); -#if defined(CONFIG_SRCU) || !defined(CONFIG_TINY_RCU) +#if !defined(CONFIG_TINY_RCU) #include <linux/rcu_node_tree.h> @@ -308,6 +371,8 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt) } } +extern void rcu_init_geometry(void); + /* Returns a pointer to the first leaf rcu_node structure. */ #define rcu_first_leaf_node() (rcu_state.level[rcu_num_lvls - 1]) @@ -322,11 +387,13 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt) * specified state structure (for SRCU) or the only rcu_state structure * (for RCU). */ -#define srcu_for_each_node_breadth_first(sp, rnp) \ +#define _rcu_for_each_node_breadth_first(sp, rnp) \ for ((rnp) = &(sp)->node[0]; \ (rnp) < &(sp)->node[rcu_num_nodes]; (rnp)++) #define rcu_for_each_node_breadth_first(rnp) \ - srcu_for_each_node_breadth_first(&rcu_state, rnp) + _rcu_for_each_node_breadth_first(&rcu_state, rnp) +#define srcu_for_each_node_breadth_first(ssp, rnp) \ + _rcu_for_each_node_breadth_first(ssp->srcu_sup, rnp) /* * Scan the leaves of the rcu_node hierarchy for the rcu_state structure. @@ -358,6 +425,10 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt) (cpu) <= rnp->grphi; \ (cpu) = rcu_find_next_bit((rnp), (cpu) + 1 - (rnp->grplo), (mask))) +#endif /* !defined(CONFIG_TINY_RCU) */ + +#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_TASKS_RCU_GENERIC) + /* * Wrappers for the rcu_node::lock acquire and release. * @@ -378,7 +449,11 @@ do { \ smp_mb__after_unlock_lock(); \ } while (0) -#define raw_spin_unlock_rcu_node(p) raw_spin_unlock(&ACCESS_PRIVATE(p, lock)) +#define raw_spin_unlock_rcu_node(p) \ +do { \ + lockdep_assert_irqs_disabled(); \ + raw_spin_unlock(&ACCESS_PRIVATE(p, lock)); \ +} while (0) #define raw_spin_lock_irq_rcu_node(p) \ do { \ @@ -387,7 +462,10 @@ do { \ } while (0) #define raw_spin_unlock_irq_rcu_node(p) \ - raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock)) +do { \ + lockdep_assert_irqs_disabled(); \ + raw_spin_unlock_irq(&ACCESS_PRIVATE(p, lock)); \ +} while (0) #define raw_spin_lock_irqsave_rcu_node(p, flags) \ do { \ @@ -396,7 +474,10 @@ do { \ } while (0) #define raw_spin_unlock_irqrestore_rcu_node(p, flags) \ - raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) +do { \ + lockdep_assert_irqs_disabled(); \ + raw_spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags); \ +} while (0) #define raw_spin_trylock_rcu_node(p) \ ({ \ @@ -410,31 +491,43 @@ do { \ #define raw_lockdep_assert_held_rcu_node(p) \ lockdep_assert_held(&ACCESS_PRIVATE(p, lock)) -#endif /* #if defined(CONFIG_SRCU) || !defined(CONFIG_TINY_RCU) */ - -#ifdef CONFIG_SRCU -void srcu_init(void); -#else /* #ifdef CONFIG_SRCU */ -static inline void srcu_init(void) { } -#endif /* #else #ifdef CONFIG_SRCU */ +#endif // #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_TASKS_RCU_GENERIC) #ifdef CONFIG_TINY_RCU /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */ static inline bool rcu_gp_is_normal(void) { return true; } static inline bool rcu_gp_is_expedited(void) { return false; } +static inline bool rcu_async_should_hurry(void) { return false; } static inline void rcu_expedite_gp(void) { } static inline void rcu_unexpedite_gp(void) { } -static inline void rcu_request_urgent_qs_task(struct task_struct *t) { } +static inline void rcu_async_hurry(void) { } +static inline void rcu_async_relax(void) { } +static inline bool rcu_cpu_online(int cpu) { return true; } #else /* #ifdef CONFIG_TINY_RCU */ bool rcu_gp_is_normal(void); /* Internal RCU use. */ bool rcu_gp_is_expedited(void); /* Internal RCU use. */ +bool rcu_async_should_hurry(void); /* Internal RCU use. */ void rcu_expedite_gp(void); void rcu_unexpedite_gp(void); +void rcu_async_hurry(void); +void rcu_async_relax(void); void rcupdate_announce_bootup_oddness(void); +bool rcu_cpu_online(int cpu); +#ifdef CONFIG_TASKS_RCU_GENERIC void show_rcu_tasks_gp_kthreads(void); -void rcu_request_urgent_qs_task(struct task_struct *t); +#else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ +static inline void show_rcu_tasks_gp_kthreads(void) {} +#endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ #endif /* #else #ifdef CONFIG_TINY_RCU */ +#ifdef CONFIG_TASKS_RCU +struct task_struct *get_rcu_tasks_gp_kthread(void); +#endif // # ifdef CONFIG_TASKS_RCU + +#ifdef CONFIG_TASKS_RUDE_RCU +struct task_struct *get_rcu_tasks_rude_gp_kthread(void); +#endif // # ifdef CONFIG_TASKS_RUDE_RCU + #define RCU_SCHEDULER_INACTIVE 0 #define RCU_SCHEDULER_INIT 1 #define RCU_SCHEDULER_RUNNING 2 @@ -449,6 +542,14 @@ enum rcutorture_type { INVALID_RCU_FLAVOR }; +#if defined(CONFIG_RCU_LAZY) +unsigned long rcu_lazy_get_jiffies_till_flush(void); +void rcu_lazy_set_jiffies_till_flush(unsigned long j); +#else +static inline unsigned long rcu_lazy_get_jiffies_till_flush(void) { return 0; } +static inline void rcu_lazy_set_jiffies_till_flush(unsigned long j) { } +#endif + #if defined(CONFIG_TREE_RCU) void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, unsigned long *gp_seq); @@ -478,10 +579,6 @@ void do_trace_rcu_torture_read(const char *rcutorturename, static inline void rcu_gp_set_torture_wait(int duration) { } #endif -#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST) -long rcutorture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask); -#endif - #ifdef CONFIG_TINY_SRCU static inline void srcutorture_get_gp_data(enum rcutorture_type test_type, @@ -509,27 +606,36 @@ static inline unsigned long rcu_exp_batches_completed(void) { return 0; } static inline unsigned long srcu_batches_completed(struct srcu_struct *sp) { return 0; } static inline void rcu_force_quiescent_state(void) { } +static inline bool rcu_check_boost_fail(unsigned long gp_state, int *cpup) { return true; } static inline void show_rcu_gp_kthreads(void) { } static inline int rcu_get_gp_kthreads_prio(void) { return 0; } static inline void rcu_fwd_progress_check(unsigned long j) { } +static inline void rcu_gp_slow_register(atomic_t *rgssp) { } +static inline void rcu_gp_slow_unregister(atomic_t *rgssp) { } #else /* #ifdef CONFIG_TINY_RCU */ bool rcu_dynticks_zero_in_eqs(int cpu, int *vp); unsigned long rcu_get_gp_seq(void); unsigned long rcu_exp_batches_completed(void); unsigned long srcu_batches_completed(struct srcu_struct *sp); +bool rcu_check_boost_fail(unsigned long gp_state, int *cpup); void show_rcu_gp_kthreads(void); int rcu_get_gp_kthreads_prio(void); void rcu_fwd_progress_check(unsigned long j); void rcu_force_quiescent_state(void); extern struct workqueue_struct *rcu_gp_wq; +#ifdef CONFIG_RCU_EXP_KTHREAD +extern struct kthread_worker *rcu_exp_gp_kworker; +extern struct kthread_worker *rcu_exp_par_gp_kworker; +#else /* !CONFIG_RCU_EXP_KTHREAD */ extern struct workqueue_struct *rcu_par_gp_wq; +#endif /* CONFIG_RCU_EXP_KTHREAD */ +void rcu_gp_slow_register(atomic_t *rgssp); +void rcu_gp_slow_unregister(atomic_t *rgssp); #endif /* #else #ifdef CONFIG_TINY_RCU */ #ifdef CONFIG_RCU_NOCB_CPU -bool rcu_is_nocb_cpu(int cpu); void rcu_bind_current_to_nocb(void); #else -static inline bool rcu_is_nocb_cpu(int cpu) { return false; } static inline void rcu_bind_current_to_nocb(void) { } #endif @@ -549,4 +655,16 @@ void show_rcu_tasks_trace_gp_kthread(void); static inline void show_rcu_tasks_trace_gp_kthread(void) {} #endif +#ifdef CONFIG_TINY_RCU +static inline bool rcu_cpu_beenfullyonline(int cpu) { return true; } +#else +bool rcu_cpu_beenfullyonline(int cpu); +#endif + +#if defined(CONFIG_RCU_STALL_COMMON) && defined(CONFIG_RCU_CPU_STALL_NOTIFIER) +int rcu_stall_notifier_call_chain(unsigned long val, void *v); +#else // #if defined(CONFIG_RCU_STALL_COMMON) && defined(CONFIG_RCU_CPU_STALL_NOTIFIER) +static inline int rcu_stall_notifier_call_chain(unsigned long val, void *v) { return NOTIFY_DONE; } +#endif // #else // #if defined(CONFIG_RCU_STALL_COMMON) && defined(CONFIG_RCU_CPU_STALL_NOTIFIER) + #endif /* __LINUX_RCU_H */ diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c index 2d2a6b6b9dfb..1693ea22ef1b 100644 --- a/kernel/rcu/rcu_segcblist.c +++ b/kernel/rcu/rcu_segcblist.c @@ -7,10 +7,10 @@ * Authors: Paul E. McKenney <paulmck@linux.ibm.com> */ -#include <linux/types.h> -#include <linux/kernel.h> +#include <linux/cpu.h> #include <linux/interrupt.h> -#include <linux/rcupdate.h> +#include <linux/kernel.h> +#include <linux/types.h> #include "rcu_segcblist.h" @@ -88,23 +88,135 @@ static void rcu_segcblist_set_len(struct rcu_segcblist *rsclp, long v) #endif } +/* Get the length of a segment of the rcu_segcblist structure. */ +long rcu_segcblist_get_seglen(struct rcu_segcblist *rsclp, int seg) +{ + return READ_ONCE(rsclp->seglen[seg]); +} + +/* Return number of callbacks in segmented callback list by summing seglen. */ +long rcu_segcblist_n_segment_cbs(struct rcu_segcblist *rsclp) +{ + long len = 0; + int i; + + for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++) + len += rcu_segcblist_get_seglen(rsclp, i); + + return len; +} + +/* Set the length of a segment of the rcu_segcblist structure. */ +static void rcu_segcblist_set_seglen(struct rcu_segcblist *rsclp, int seg, long v) +{ + WRITE_ONCE(rsclp->seglen[seg], v); +} + +/* Increase the numeric length of a segment by a specified amount. */ +static void rcu_segcblist_add_seglen(struct rcu_segcblist *rsclp, int seg, long v) +{ + WRITE_ONCE(rsclp->seglen[seg], rsclp->seglen[seg] + v); +} + +/* Move from's segment length to to's segment. */ +static void rcu_segcblist_move_seglen(struct rcu_segcblist *rsclp, int from, int to) +{ + long len; + + if (from == to) + return; + + len = rcu_segcblist_get_seglen(rsclp, from); + if (!len) + return; + + rcu_segcblist_add_seglen(rsclp, to, len); + rcu_segcblist_set_seglen(rsclp, from, 0); +} + +/* Increment segment's length. */ +static void rcu_segcblist_inc_seglen(struct rcu_segcblist *rsclp, int seg) +{ + rcu_segcblist_add_seglen(rsclp, seg, 1); +} + /* * Increase the numeric length of an rcu_segcblist structure by the * specified amount, which can be negative. This can cause the ->len * field to disagree with the actual number of callbacks on the structure. * This increase is fully ordered with respect to the callers accesses * both before and after. + * + * So why on earth is a memory barrier required both before and after + * the update to the ->len field??? + * + * The reason is that rcu_barrier() locklessly samples each CPU's ->len + * field, and if a given CPU's field is zero, avoids IPIing that CPU. + * This can of course race with both queuing and invoking of callbacks. + * Failing to correctly handle either of these races could result in + * rcu_barrier() failing to IPI a CPU that actually had callbacks queued + * which rcu_barrier() was obligated to wait on. And if rcu_barrier() + * failed to wait on such a callback, unloading certain kernel modules + * would result in calls to functions whose code was no longer present in + * the kernel, for but one example. + * + * Therefore, ->len transitions from 1->0 and 0->1 have to be carefully + * ordered with respect with both list modifications and the rcu_barrier(). + * + * The queuing case is CASE 1 and the invoking case is CASE 2. + * + * CASE 1: Suppose that CPU 0 has no callbacks queued, but invokes + * call_rcu() just as CPU 1 invokes rcu_barrier(). CPU 0's ->len field + * will transition from 0->1, which is one of the transitions that must + * be handled carefully. Without the full memory barriers after the ->len + * update and at the beginning of rcu_barrier(), the following could happen: + * + * CPU 0 CPU 1 + * + * call_rcu(). + * rcu_barrier() sees ->len as 0. + * set ->len = 1. + * rcu_barrier() does nothing. + * module is unloaded. + * callback invokes unloaded function! + * + * With the full barriers, any case where rcu_barrier() sees ->len as 0 will + * have unambiguously preceded the return from the racing call_rcu(), which + * means that this call_rcu() invocation is OK to not wait on. After all, + * you are supposed to make sure that any problematic call_rcu() invocations + * happen before the rcu_barrier(). + * + * + * CASE 2: Suppose that CPU 0 is invoking its last callback just as + * CPU 1 invokes rcu_barrier(). CPU 0's ->len field will transition from + * 1->0, which is one of the transitions that must be handled carefully. + * Without the full memory barriers before the ->len update and at the + * end of rcu_barrier(), the following could happen: + * + * CPU 0 CPU 1 + * + * start invoking last callback + * set ->len = 0 (reordered) + * rcu_barrier() sees ->len as 0 + * rcu_barrier() does nothing. + * module is unloaded + * callback executing after unloaded! + * + * With the full barriers, any case where rcu_barrier() sees ->len as 0 + * will be fully ordered after the completion of the callback function, + * so that the module unloading operation is completely safe. + * */ -static void rcu_segcblist_add_len(struct rcu_segcblist *rsclp, long v) +void rcu_segcblist_add_len(struct rcu_segcblist *rsclp, long v) { #ifdef CONFIG_RCU_NOCB_CPU - smp_mb__before_atomic(); /* Up to the caller! */ + smp_mb__before_atomic(); // Read header comment above. atomic_long_add(v, &rsclp->len); - smp_mb__after_atomic(); /* Up to the caller! */ + smp_mb__after_atomic(); // Read header comment above. #else - smp_mb(); /* Up to the caller! */ + smp_mb(); // Read header comment above. WRITE_ONCE(rsclp->len, rsclp->len + v); - smp_mb(); /* Up to the caller! */ + smp_mb(); // Read header comment above. #endif } @@ -120,26 +232,6 @@ void rcu_segcblist_inc_len(struct rcu_segcblist *rsclp) } /* - * Exchange the numeric length of the specified rcu_segcblist structure - * with the specified value. This can cause the ->len field to disagree - * with the actual number of callbacks on the structure. This exchange is - * fully ordered with respect to the callers accesses both before and after. - */ -static long rcu_segcblist_xchg_len(struct rcu_segcblist *rsclp, long v) -{ -#ifdef CONFIG_RCU_NOCB_CPU - return atomic_long_xchg(&rsclp->len, v); -#else - long ret = rsclp->len; - - smp_mb(); /* Up to the caller! */ - WRITE_ONCE(rsclp->len, v); - smp_mb(); /* Up to the caller! */ - return ret; -#endif -} - -/* * Initialize an rcu_segcblist structure. */ void rcu_segcblist_init(struct rcu_segcblist *rsclp) @@ -149,10 +241,12 @@ void rcu_segcblist_init(struct rcu_segcblist *rsclp) BUILD_BUG_ON(RCU_NEXT_TAIL + 1 != ARRAY_SIZE(rsclp->gp_seq)); BUILD_BUG_ON(ARRAY_SIZE(rsclp->tails) != ARRAY_SIZE(rsclp->gp_seq)); rsclp->head = NULL; - for (i = 0; i < RCU_CBLIST_NSEGS; i++) + for (i = 0; i < RCU_CBLIST_NSEGS; i++) { rsclp->tails[i] = &rsclp->head; + rcu_segcblist_set_seglen(rsclp, i, 0); + } rcu_segcblist_set_len(rsclp, 0); - rsclp->enabled = 1; + rcu_segcblist_set_flags(rsclp, SEGCBLIST_ENABLED); } /* @@ -163,16 +257,18 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp) { WARN_ON_ONCE(!rcu_segcblist_empty(rsclp)); WARN_ON_ONCE(rcu_segcblist_n_cbs(rsclp)); - rsclp->enabled = 0; + rcu_segcblist_clear_flags(rsclp, SEGCBLIST_ENABLED); } /* - * Mark the specified rcu_segcblist structure as offloaded. This - * structure must be empty. + * Mark the specified rcu_segcblist structure as offloaded (or not) */ -void rcu_segcblist_offload(struct rcu_segcblist *rsclp) +void rcu_segcblist_offload(struct rcu_segcblist *rsclp, bool offload) { - rsclp->offloaded = 1; + if (offload) + rcu_segcblist_set_flags(rsclp, SEGCBLIST_LOCKING | SEGCBLIST_OFFLOADED); + else + rcu_segcblist_clear_flags(rsclp, SEGCBLIST_OFFLOADED); } /* @@ -245,7 +341,7 @@ void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp, struct rcu_head *rhp) { rcu_segcblist_inc_len(rsclp); - smp_mb(); /* Ensure counts are updated before callback is enqueued. */ + rcu_segcblist_inc_seglen(rsclp, RCU_NEXT_TAIL); rhp->next = NULL; WRITE_ONCE(*rsclp->tails[RCU_NEXT_TAIL], rhp); WRITE_ONCE(rsclp->tails[RCU_NEXT_TAIL], &rhp->next); @@ -272,8 +368,9 @@ bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp, smp_mb(); /* Ensure counts are updated before callback is entrained. */ rhp->next = NULL; for (i = RCU_NEXT_TAIL; i > RCU_DONE_TAIL; i--) - if (rsclp->tails[i] != rsclp->tails[i - 1]) + if (!rcu_segcblist_segempty(rsclp, i)) break; + rcu_segcblist_inc_seglen(rsclp, i); WRITE_ONCE(*rsclp->tails[i], rhp); for (; i <= RCU_NEXT_TAIL; i++) WRITE_ONCE(rsclp->tails[i], &rhp->next); @@ -281,21 +378,6 @@ bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp, } /* - * Extract only the counts from the specified rcu_segcblist structure, - * and place them in the specified rcu_cblist structure. This function - * supports both callback orphaning and invocation, hence the separation - * of counts and callbacks. (Callbacks ready for invocation must be - * orphaned and adopted separately from pending callbacks, but counts - * apply to all callbacks. Locking must be used to make sure that - * both orphaned-callbacks lists are consistent.) - */ -void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp, - struct rcu_cblist *rclp) -{ - rclp->len = rcu_segcblist_xchg_len(rsclp, 0); -} - -/* * Extract only those callbacks ready to be invoked from the specified * rcu_segcblist structure and place them in the specified rcu_cblist * structure. @@ -307,6 +389,7 @@ void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp, if (!rcu_segcblist_ready_cbs(rsclp)) return; /* Nothing to do. */ + rclp->len = rcu_segcblist_get_seglen(rsclp, RCU_DONE_TAIL); *rclp->tail = rsclp->head; WRITE_ONCE(rsclp->head, *rsclp->tails[RCU_DONE_TAIL]); WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL); @@ -314,6 +397,7 @@ void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp, for (i = RCU_CBLIST_NSEGS - 1; i >= RCU_DONE_TAIL; i--) if (rsclp->tails[i] == rsclp->tails[RCU_DONE_TAIL]) WRITE_ONCE(rsclp->tails[i], &rsclp->head); + rcu_segcblist_set_seglen(rsclp, RCU_DONE_TAIL, 0); } /* @@ -330,11 +414,15 @@ void rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp, if (!rcu_segcblist_pend_cbs(rsclp)) return; /* Nothing to do. */ + rclp->len = 0; *rclp->tail = *rsclp->tails[RCU_DONE_TAIL]; rclp->tail = rsclp->tails[RCU_NEXT_TAIL]; WRITE_ONCE(*rsclp->tails[RCU_DONE_TAIL], NULL); - for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++) + for (i = RCU_DONE_TAIL + 1; i < RCU_CBLIST_NSEGS; i++) { + rclp->len += rcu_segcblist_get_seglen(rsclp, i); WRITE_ONCE(rsclp->tails[i], rsclp->tails[RCU_DONE_TAIL]); + rcu_segcblist_set_seglen(rsclp, i, 0); + } } /* @@ -345,7 +433,6 @@ void rcu_segcblist_insert_count(struct rcu_segcblist *rsclp, struct rcu_cblist *rclp) { rcu_segcblist_add_len(rsclp, rclp->len); - rclp->len = 0; } /* @@ -359,6 +446,7 @@ void rcu_segcblist_insert_done_cbs(struct rcu_segcblist *rsclp, if (!rclp->head) return; /* No callbacks to move. */ + rcu_segcblist_add_seglen(rsclp, RCU_DONE_TAIL, rclp->len); *rclp->tail = rsclp->head; WRITE_ONCE(rsclp->head, rclp->head); for (i = RCU_DONE_TAIL; i < RCU_CBLIST_NSEGS; i++) @@ -379,6 +467,8 @@ void rcu_segcblist_insert_pend_cbs(struct rcu_segcblist *rsclp, { if (!rclp->head) return; /* Nothing to do. */ + + rcu_segcblist_add_seglen(rsclp, RCU_NEXT_TAIL, rclp->len); WRITE_ONCE(*rsclp->tails[RCU_NEXT_TAIL], rclp->head); WRITE_ONCE(rsclp->tails[RCU_NEXT_TAIL], rclp->tail); } @@ -403,6 +493,7 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq) if (ULONG_CMP_LT(seq, rsclp->gp_seq[i])) break; WRITE_ONCE(rsclp->tails[RCU_DONE_TAIL], rsclp->tails[i]); + rcu_segcblist_move_seglen(rsclp, i, RCU_DONE_TAIL); } /* If no callbacks moved, nothing more need be done. */ @@ -414,15 +505,16 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq) WRITE_ONCE(rsclp->tails[j], rsclp->tails[RCU_DONE_TAIL]); /* - * Callbacks moved, so clean up the misordered ->tails[] pointers - * that now point into the middle of the list of ready-to-invoke - * callbacks. The overall effect is to copy down the later pointers - * into the gap that was created by the now-ready segments. + * Callbacks moved, so there might be an empty RCU_WAIT_TAIL + * and a non-empty RCU_NEXT_READY_TAIL. If so, copy the + * RCU_NEXT_READY_TAIL segment to fill the RCU_WAIT_TAIL gap + * created by the now-ready-to-invoke segments. */ for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) { if (rsclp->tails[j] == rsclp->tails[RCU_NEXT_TAIL]) break; /* No more callbacks. */ WRITE_ONCE(rsclp->tails[j], rsclp->tails[i]); + rcu_segcblist_move_seglen(rsclp, i, j); rsclp->gp_seq[j] = rsclp->gp_seq[i]; } } @@ -444,7 +536,7 @@ void rcu_segcblist_advance(struct rcu_segcblist *rsclp, unsigned long seq) */ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq) { - int i; + int i, j; WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp)); if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)) @@ -459,7 +551,7 @@ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq) * as their ->gp_seq[] grace-period completion sequence number. */ for (i = RCU_NEXT_READY_TAIL; i > RCU_DONE_TAIL; i--) - if (rsclp->tails[i] != rsclp->tails[i - 1] && + if (!rcu_segcblist_segempty(rsclp, i) && ULONG_CMP_LT(rsclp->gp_seq[i], seq)) break; @@ -487,6 +579,10 @@ bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq) if (rcu_segcblist_restempty(rsclp, i) || ++i >= RCU_NEXT_TAIL) return false; + /* Accounting: everything below i is about to get merged into i. */ + for (j = i + 1; j <= RCU_NEXT_TAIL; j++) + rcu_segcblist_move_seglen(rsclp, j, i); + /* * Merge all later callbacks, including newly arrived callbacks, * into the segment located by the for-loop above. Assign "seq" @@ -514,13 +610,24 @@ void rcu_segcblist_merge(struct rcu_segcblist *dst_rsclp, struct rcu_cblist donecbs; struct rcu_cblist pendcbs; + lockdep_assert_cpus_held(); + rcu_cblist_init(&donecbs); rcu_cblist_init(&pendcbs); - rcu_segcblist_extract_count(src_rsclp, &donecbs); + rcu_segcblist_extract_done_cbs(src_rsclp, &donecbs); rcu_segcblist_extract_pend_cbs(src_rsclp, &pendcbs); + + /* + * No need smp_mb() before setting length to 0, because CPU hotplug + * lock excludes rcu_barrier. + */ + rcu_segcblist_set_len(src_rsclp, 0); + rcu_segcblist_insert_count(dst_rsclp, &donecbs); + rcu_segcblist_insert_count(dst_rsclp, &pendcbs); rcu_segcblist_insert_done_cbs(dst_rsclp, &donecbs); rcu_segcblist_insert_pend_cbs(dst_rsclp, &pendcbs); + rcu_segcblist_init(src_rsclp); } diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h index 492262bcb591..4fe877f5f654 100644 --- a/kernel/rcu/rcu_segcblist.h +++ b/kernel/rcu/rcu_segcblist.h @@ -15,6 +15,11 @@ static inline long rcu_cblist_n_cbs(struct rcu_cblist *rclp) return READ_ONCE(rclp->len); } +long rcu_segcblist_get_seglen(struct rcu_segcblist *rsclp, int seg); + +/* Return number of callbacks in segmented callback list by summing seglen. */ +long rcu_segcblist_n_segment_cbs(struct rcu_segcblist *rsclp); + void rcu_cblist_init(struct rcu_cblist *rclp); void rcu_cblist_enqueue(struct rcu_cblist *rclp, struct rcu_head *rhp); void rcu_cblist_flush_enqueue(struct rcu_cblist *drclp, @@ -50,19 +55,53 @@ static inline long rcu_segcblist_n_cbs(struct rcu_segcblist *rsclp) #endif } +static inline void rcu_segcblist_set_flags(struct rcu_segcblist *rsclp, + int flags) +{ + WRITE_ONCE(rsclp->flags, rsclp->flags | flags); +} + +static inline void rcu_segcblist_clear_flags(struct rcu_segcblist *rsclp, + int flags) +{ + WRITE_ONCE(rsclp->flags, rsclp->flags & ~flags); +} + +static inline bool rcu_segcblist_test_flags(struct rcu_segcblist *rsclp, + int flags) +{ + return READ_ONCE(rsclp->flags) & flags; +} + /* * Is the specified rcu_segcblist enabled, for example, not corresponding * to an offline CPU? */ static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp) { - return rsclp->enabled; + return rcu_segcblist_test_flags(rsclp, SEGCBLIST_ENABLED); } -/* Is the specified rcu_segcblist offloaded? */ +/* + * Is the specified rcu_segcblist NOCB offloaded (or in the middle of the + * [de]offloading process)? + */ static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp) { - return IS_ENABLED(CONFIG_RCU_NOCB_CPU) && rsclp->offloaded; + if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) && + rcu_segcblist_test_flags(rsclp, SEGCBLIST_LOCKING)) + return true; + + return false; +} + +static inline bool rcu_segcblist_completely_offloaded(struct rcu_segcblist *rsclp) +{ + if (IS_ENABLED(CONFIG_RCU_NOCB_CPU) && + !rcu_segcblist_test_flags(rsclp, SEGCBLIST_RCU_CORE)) + return true; + + return false; } /* @@ -75,10 +114,22 @@ static inline bool rcu_segcblist_restempty(struct rcu_segcblist *rsclp, int seg) return !READ_ONCE(*READ_ONCE(rsclp->tails[seg])); } +/* + * Is the specified segment of the specified rcu_segcblist structure + * empty of callbacks? + */ +static inline bool rcu_segcblist_segempty(struct rcu_segcblist *rsclp, int seg) +{ + if (seg == RCU_DONE_TAIL) + return &rsclp->head == rsclp->tails[RCU_DONE_TAIL]; + return rsclp->tails[seg - 1] == rsclp->tails[seg]; +} + void rcu_segcblist_inc_len(struct rcu_segcblist *rsclp); +void rcu_segcblist_add_len(struct rcu_segcblist *rsclp, long v); void rcu_segcblist_init(struct rcu_segcblist *rsclp); void rcu_segcblist_disable(struct rcu_segcblist *rsclp); -void rcu_segcblist_offload(struct rcu_segcblist *rsclp); +void rcu_segcblist_offload(struct rcu_segcblist *rsclp, bool offload); bool rcu_segcblist_ready_cbs(struct rcu_segcblist *rsclp); bool rcu_segcblist_pend_cbs(struct rcu_segcblist *rsclp); struct rcu_head *rcu_segcblist_first_cb(struct rcu_segcblist *rsclp); @@ -88,8 +139,6 @@ void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp, struct rcu_head *rhp); bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp, struct rcu_head *rhp); -void rcu_segcblist_extract_count(struct rcu_segcblist *rsclp, - struct rcu_cblist *rclp); void rcu_segcblist_extract_done_cbs(struct rcu_segcblist *rsclp, struct rcu_cblist *rclp); void rcu_segcblist_extract_pend_cbs(struct rcu_segcblist *rsclp, diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c index 06491d5530db..ffdb30495e3c 100644 --- a/kernel/rcu/rcuscale.c +++ b/kernel/rcu/rcuscale.c @@ -50,8 +50,8 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.ibm.com>"); pr_alert("%s" SCALE_FLAG " %s\n", scale_type, s) #define VERBOSE_SCALEOUT_STRING(s) \ do { if (verbose) pr_alert("%s" SCALE_FLAG " %s\n", scale_type, s); } while (0) -#define VERBOSE_SCALEOUT_ERRSTRING(s) \ - do { if (verbose) pr_alert("%s" SCALE_FLAG "!!! %s\n", scale_type, s); } while (0) +#define SCALEOUT_ERRSTRING(s) \ + pr_alert("%s" SCALE_FLAG "!!! %s\n", scale_type, s) /* * The intended use cases for the nreaders and nwriters module parameters @@ -84,17 +84,20 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.ibm.com>"); #endif torture_param(bool, gp_async, false, "Use asynchronous GP wait primitives"); -torture_param(int, gp_async_max, 1000, "Max # outstanding waits per reader"); +torture_param(int, gp_async_max, 1000, "Max # outstanding waits per writer"); torture_param(bool, gp_exp, false, "Use expedited GP wait primitives"); torture_param(int, holdoff, 10, "Holdoff time before test start (s)"); +torture_param(int, minruntime, 0, "Minimum run time (s)"); torture_param(int, nreaders, -1, "Number of RCU reader threads"); torture_param(int, nwriters, -1, "Number of RCU updater threads"); torture_param(bool, shutdown, RCUSCALE_SHUTDOWN, "Shutdown at end of scalability tests."); torture_param(int, verbose, 1, "Enable verbose debugging printk()s"); torture_param(int, writer_holdoff, 0, "Holdoff (us) between GPs, zero to disable"); +torture_param(int, writer_holdoff_jiffies, 0, "Holdoff (jiffies) between GPs, zero to disable"); torture_param(int, kfree_rcu_test, 0, "Do we run a kfree_rcu() scale test?"); torture_param(int, kfree_mult, 1, "Multiple of kfree_obj size to allocate."); +torture_param(int, kfree_by_call_rcu, 0, "Use call_rcu() to emulate kfree_rcu()?"); static char *scale_type = "rcu"; module_param(scale_type, charp, 0444); @@ -138,6 +141,7 @@ struct rcu_scale_ops { void (*gp_barrier)(void); void (*sync)(void); void (*exp_sync)(void); + struct task_struct *(*rso_gp_kthread)(void); const char *name; }; @@ -175,7 +179,7 @@ static struct rcu_scale_ops rcu_ops = { .get_gp_seq = rcu_get_gp_seq, .gp_diff = rcu_seq_diff, .exp_completed = rcu_exp_batches_completed, - .async = call_rcu, + .async = call_rcu_hurry, .gp_barrier = rcu_barrier, .sync = synchronize_rcu, .exp_sync = synchronize_rcu_expedited, @@ -268,6 +272,8 @@ static struct rcu_scale_ops srcud_ops = { .name = "srcud" }; +#ifdef CONFIG_TASKS_RCU + /* * Definitions for RCU-tasks scalability testing. */ @@ -292,9 +298,58 @@ static struct rcu_scale_ops tasks_ops = { .gp_barrier = rcu_barrier_tasks, .sync = synchronize_rcu_tasks, .exp_sync = synchronize_rcu_tasks, + .rso_gp_kthread = get_rcu_tasks_gp_kthread, .name = "tasks" }; +#define TASKS_OPS &tasks_ops, + +#else // #ifdef CONFIG_TASKS_RCU + +#define TASKS_OPS + +#endif // #else // #ifdef CONFIG_TASKS_RCU + +#ifdef CONFIG_TASKS_RUDE_RCU + +/* + * Definitions for RCU-tasks-rude scalability testing. + */ + +static int tasks_rude_scale_read_lock(void) +{ + return 0; +} + +static void tasks_rude_scale_read_unlock(int idx) +{ +} + +static struct rcu_scale_ops tasks_rude_ops = { + .ptype = RCU_TASKS_RUDE_FLAVOR, + .init = rcu_sync_scale_init, + .readlock = tasks_rude_scale_read_lock, + .readunlock = tasks_rude_scale_read_unlock, + .get_gp_seq = rcu_no_completed, + .gp_diff = rcu_seq_diff, + .async = call_rcu_tasks_rude, + .gp_barrier = rcu_barrier_tasks_rude, + .sync = synchronize_rcu_tasks_rude, + .exp_sync = synchronize_rcu_tasks_rude, + .rso_gp_kthread = get_rcu_tasks_rude_gp_kthread, + .name = "tasks-rude" +}; + +#define TASKS_RUDE_OPS &tasks_rude_ops, + +#else // #ifdef CONFIG_TASKS_RUDE_RCU + +#define TASKS_RUDE_OPS + +#endif // #else // #ifdef CONFIG_TASKS_RUDE_RCU + +#ifdef CONFIG_TASKS_TRACE_RCU + /* * Definitions for RCU-tasks-trace scalability testing. */ @@ -321,9 +376,18 @@ static struct rcu_scale_ops tasks_tracing_ops = { .gp_barrier = rcu_barrier_tasks_trace, .sync = synchronize_rcu_tasks_trace, .exp_sync = synchronize_rcu_tasks_trace, + .rso_gp_kthread = get_rcu_tasks_trace_gp_kthread, .name = "tasks-tracing" }; +#define TASKS_TRACING_OPS &tasks_tracing_ops, + +#else // #ifdef CONFIG_TASKS_TRACE_RCU + +#define TASKS_TRACING_OPS + +#endif // #else // #ifdef CONFIG_TASKS_TRACE_RCU + static unsigned long rcuscale_seq_diff(unsigned long new, unsigned long old) { if (!cur_ops->gp_diff) @@ -389,20 +453,23 @@ rcu_scale_writer(void *arg) { int i = 0; int i_max; + unsigned long jdone; long me = (long)arg; struct rcu_head *rhp = NULL; bool started = false, done = false, alldone = false; u64 t; + DEFINE_TORTURE_RANDOM(tr); u64 *wdp; u64 *wdpp = writer_durations[me]; VERBOSE_SCALEOUT_STRING("rcu_scale_writer task started"); WARN_ON(!wdpp); set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids)); + current->flags |= PF_NO_SETAFFINITY; sched_set_fifo_low(current); if (holdoff) - schedule_timeout_uninterruptible(holdoff * HZ); + schedule_timeout_idle(holdoff * HZ); /* * Wait until rcu_end_inkernel_boot() is called for normal GP tests @@ -423,9 +490,12 @@ rcu_scale_writer(void *arg) } } + jdone = jiffies + minruntime * HZ; do { if (writer_holdoff) udelay(writer_holdoff); + if (writer_holdoff_jiffies) + schedule_timeout_idle(torture_random(&tr) % writer_holdoff_jiffies + 1); wdp = &wdpp[i]; *wdp = ktime_get_mono_fast_ns(); if (gp_async) { @@ -453,7 +523,7 @@ retry: if (!started && atomic_read(&n_rcu_scale_writer_started) >= nrealwriters) started = true; - if (!done && i >= MIN_MEAS) { + if (!done && i >= MIN_MEAS && time_after(jiffies, jdone)) { done = true; sched_set_normal(current, 0); pr_alert("%s%s rcu_scale_writer %ld has %d measurements\n", @@ -487,7 +557,7 @@ retry: if (gp_async) { cur_ops->gp_barrier(); } - writer_n_durations[me] = i_max; + writer_n_durations[me] = i_max + 1; torture_kthread_stopping("rcu_scale_writer"); return 0; } @@ -496,91 +566,8 @@ static void rcu_scale_print_module_parms(struct rcu_scale_ops *cur_ops, const char *tag) { pr_alert("%s" SCALE_FLAG - "--- %s: nreaders=%d nwriters=%d verbose=%d shutdown=%d\n", - scale_type, tag, nrealreaders, nrealwriters, verbose, shutdown); -} - -static void -rcu_scale_cleanup(void) -{ - int i; - int j; - int ngps = 0; - u64 *wdp; - u64 *wdpp; - - /* - * Would like warning at start, but everything is expedited - * during the mid-boot phase, so have to wait till the end. - */ - if (rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp) - VERBOSE_SCALEOUT_ERRSTRING("All grace periods expedited, no normal ones to measure!"); - if (rcu_gp_is_normal() && gp_exp) - VERBOSE_SCALEOUT_ERRSTRING("All grace periods normal, no expedited ones to measure!"); - if (gp_exp && gp_async) - VERBOSE_SCALEOUT_ERRSTRING("No expedited async GPs, so went with async!"); - - if (torture_cleanup_begin()) - return; - if (!cur_ops) { - torture_cleanup_end(); - return; - } - - if (reader_tasks) { - for (i = 0; i < nrealreaders; i++) - torture_stop_kthread(rcu_scale_reader, - reader_tasks[i]); - kfree(reader_tasks); - } - - if (writer_tasks) { - for (i = 0; i < nrealwriters; i++) { - torture_stop_kthread(rcu_scale_writer, - writer_tasks[i]); - if (!writer_n_durations) - continue; - j = writer_n_durations[i]; - pr_alert("%s%s writer %d gps: %d\n", - scale_type, SCALE_FLAG, i, j); - ngps += j; - } - pr_alert("%s%s start: %llu end: %llu duration: %llu gps: %d batches: %ld\n", - scale_type, SCALE_FLAG, - t_rcu_scale_writer_started, t_rcu_scale_writer_finished, - t_rcu_scale_writer_finished - - t_rcu_scale_writer_started, - ngps, - rcuscale_seq_diff(b_rcu_gp_test_finished, - b_rcu_gp_test_started)); - for (i = 0; i < nrealwriters; i++) { - if (!writer_durations) - break; - if (!writer_n_durations) - continue; - wdpp = writer_durations[i]; - if (!wdpp) - continue; - for (j = 0; j <= writer_n_durations[i]; j++) { - wdp = &wdpp[j]; - pr_alert("%s%s %4d writer-duration: %5d %llu\n", - scale_type, SCALE_FLAG, - i, j, *wdp); - if (j % 100 == 0) - schedule_timeout_uninterruptible(1); - } - kfree(writer_durations[i]); - } - kfree(writer_tasks); - kfree(writer_durations); - kfree(writer_n_durations); - } - - /* Do torture-type-specific cleanup operations. */ - if (cur_ops->cleanup != NULL) - cur_ops->cleanup(); - - torture_cleanup_end(); + "--- %s: gp_async=%d gp_async_max=%d gp_exp=%d holdoff=%d minruntime=%d nreaders=%d nwriters=%d writer_holdoff=%d writer_holdoff_jiffies=%d verbose=%d shutdown=%d\n", + scale_type, tag, gp_async, gp_async_max, gp_exp, holdoff, minruntime, nrealreaders, nrealwriters, writer_holdoff, writer_holdoff_jiffies, verbose, shutdown); } /* @@ -603,21 +590,6 @@ static int compute_real(int n) } /* - * RCU scalability shutdown kthread. Just waits to be awakened, then shuts - * down system. - */ -static int -rcu_scale_shutdown(void *arg) -{ - wait_event(shutdown_wq, - atomic_read(&n_rcu_scale_writer_finished) >= nrealwriters); - smp_mb(); /* Wake before output. */ - rcu_scale_cleanup(); - kernel_power_off(); - return -EINVAL; -} - -/* * kfree_rcu() scalability tests: Start a kfree_rcu() loop on all CPUs for number * of iterations and measure total time and number of GP for all iterations to complete. */ @@ -625,17 +597,29 @@ rcu_scale_shutdown(void *arg) torture_param(int, kfree_nthreads, -1, "Number of threads running loops of kfree_rcu()."); torture_param(int, kfree_alloc_num, 8000, "Number of allocations and frees done in an iteration."); torture_param(int, kfree_loops, 10, "Number of loops doing kfree_alloc_num allocations and frees."); +torture_param(bool, kfree_rcu_test_double, false, "Do we run a kfree_rcu() double-argument scale test?"); +torture_param(bool, kfree_rcu_test_single, false, "Do we run a kfree_rcu() single-argument scale test?"); static struct task_struct **kfree_reader_tasks; static int kfree_nrealthreads; static atomic_t n_kfree_scale_thread_started; static atomic_t n_kfree_scale_thread_ended; +static struct task_struct *kthread_tp; +static u64 kthread_stime; struct kfree_obj { char kfree_obj[8]; struct rcu_head rh; }; +/* Used if doing RCU-kfree'ing via call_rcu(). */ +static void kfree_call_rcu(struct rcu_head *rh) +{ + struct kfree_obj *obj = container_of(rh, struct kfree_obj, rh); + + kfree(obj); +} + static int kfree_scale_thread(void *arg) { @@ -644,10 +628,13 @@ kfree_scale_thread(void *arg) struct kfree_obj *alloc_ptr; u64 start_time, end_time; long long mem_begin, mem_during = 0; + bool kfree_rcu_test_both; + DEFINE_TORTURE_RANDOM(tr); VERBOSE_SCALEOUT_STRING("kfree_scale_thread task started"); set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids)); set_user_nice(current, MAX_NICE); + kfree_rcu_test_both = (kfree_rcu_test_single == kfree_rcu_test_double); start_time = ktime_get_mono_fast_ns(); @@ -670,7 +657,20 @@ kfree_scale_thread(void *arg) if (!alloc_ptr) return -ENOMEM; - kfree_rcu(alloc_ptr, rh); + if (kfree_by_call_rcu) { + call_rcu(&(alloc_ptr->rh), kfree_call_rcu); + continue; + } + + // By default kfree_rcu_test_single and kfree_rcu_test_double are + // initialized to false. If both have the same value (false or true) + // both are randomly tested, otherwise only the one with value true + // is tested. + if ((kfree_rcu_test_single && !kfree_rcu_test_double) || + (kfree_rcu_test_both && torture_random(&tr) & 0x800)) + kfree_rcu_mightsleep(alloc_ptr); + else + kfree_rcu(alloc_ptr, rh); } cond_resched(); @@ -723,8 +723,8 @@ kfree_scale_cleanup(void) static int kfree_scale_shutdown(void *arg) { - wait_event(shutdown_wq, - atomic_read(&n_kfree_scale_thread_ended) >= kfree_nrealthreads); + wait_event_idle(shutdown_wq, + atomic_read(&n_kfree_scale_thread_ended) >= kfree_nrealthreads); smp_mb(); /* Wake before output. */ @@ -733,11 +733,62 @@ kfree_scale_shutdown(void *arg) return -EINVAL; } +// Used if doing RCU-kfree'ing via call_rcu(). +static unsigned long jiffies_at_lazy_cb; +static struct rcu_head lazy_test1_rh; +static int rcu_lazy_test1_cb_called; +static void call_rcu_lazy_test1(struct rcu_head *rh) +{ + jiffies_at_lazy_cb = jiffies; + WRITE_ONCE(rcu_lazy_test1_cb_called, 1); +} + static int __init kfree_scale_init(void) { - long i; int firsterr = 0; + long i; + unsigned long jif_start; + unsigned long orig_jif; + + pr_alert("%s" SCALE_FLAG + "--- kfree_rcu_test: kfree_mult=%d kfree_by_call_rcu=%d kfree_nthreads=%d kfree_alloc_num=%d kfree_loops=%d kfree_rcu_test_double=%d kfree_rcu_test_single=%d\n", + scale_type, kfree_mult, kfree_by_call_rcu, kfree_nthreads, kfree_alloc_num, kfree_loops, kfree_rcu_test_double, kfree_rcu_test_single); + + // Also, do a quick self-test to ensure laziness is as much as + // expected. + if (kfree_by_call_rcu && !IS_ENABLED(CONFIG_RCU_LAZY)) { + pr_alert("CONFIG_RCU_LAZY is disabled, falling back to kfree_rcu() for delayed RCU kfree'ing\n"); + kfree_by_call_rcu = 0; + } + + if (kfree_by_call_rcu) { + /* do a test to check the timeout. */ + orig_jif = rcu_lazy_get_jiffies_till_flush(); + + rcu_lazy_set_jiffies_till_flush(2 * HZ); + rcu_barrier(); + + jif_start = jiffies; + jiffies_at_lazy_cb = 0; + call_rcu(&lazy_test1_rh, call_rcu_lazy_test1); + + smp_cond_load_relaxed(&rcu_lazy_test1_cb_called, VAL == 1); + + rcu_lazy_set_jiffies_till_flush(orig_jif); + + if (WARN_ON_ONCE(jiffies_at_lazy_cb - jif_start < 2 * HZ)) { + pr_alert("ERROR: call_rcu() CBs are not being lazy as expected!\n"); + WARN_ON_ONCE(1); + return -1; + } + + if (WARN_ON_ONCE(jiffies_at_lazy_cb - jif_start > 3 * HZ)) { + pr_alert("ERROR: call_rcu() CBs are being too lazy!\n"); + WARN_ON_ONCE(1); + return -1; + } + } kfree_nrealthreads = compute_real(kfree_nthreads); /* Start up the kthreads. */ @@ -745,12 +796,14 @@ kfree_scale_init(void) init_waitqueue_head(&shutdown_wq); firsterr = torture_create_kthread(kfree_scale_shutdown, NULL, shutdown_task); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; schedule_timeout_uninterruptible(1); } - pr_alert("kfree object size=%zu\n", kfree_mult * sizeof(struct kfree_obj)); + pr_alert("kfree object size=%zu, kfree_by_call_rcu=%d\n", + kfree_mult * sizeof(struct kfree_obj), + kfree_by_call_rcu); kfree_reader_tasks = kcalloc(kfree_nrealthreads, sizeof(kfree_reader_tasks[0]), GFP_KERNEL); @@ -762,7 +815,7 @@ kfree_scale_init(void) for (i = 0; i < kfree_nrealthreads; i++) { firsterr = torture_create_kthread(kfree_scale_thread, (void *)i, kfree_reader_tasks[i]); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; } @@ -778,13 +831,127 @@ unwind: return firsterr; } +static void +rcu_scale_cleanup(void) +{ + int i; + int j; + int ngps = 0; + u64 *wdp; + u64 *wdpp; + + /* + * Would like warning at start, but everything is expedited + * during the mid-boot phase, so have to wait till the end. + */ + if (rcu_gp_is_expedited() && !rcu_gp_is_normal() && !gp_exp) + SCALEOUT_ERRSTRING("All grace periods expedited, no normal ones to measure!"); + if (rcu_gp_is_normal() && gp_exp) + SCALEOUT_ERRSTRING("All grace periods normal, no expedited ones to measure!"); + if (gp_exp && gp_async) + SCALEOUT_ERRSTRING("No expedited async GPs, so went with async!"); + + // If built-in, just report all of the GP kthread's CPU time. + if (IS_BUILTIN(CONFIG_RCU_SCALE_TEST) && !kthread_tp && cur_ops->rso_gp_kthread) + kthread_tp = cur_ops->rso_gp_kthread(); + if (kthread_tp) { + u32 ns; + u64 us; + + kthread_stime = kthread_tp->stime - kthread_stime; + us = div_u64_rem(kthread_stime, 1000, &ns); + pr_info("rcu_scale: Grace-period kthread CPU time: %llu.%03u us\n", us, ns); + show_rcu_gp_kthreads(); + } + if (kfree_rcu_test) { + kfree_scale_cleanup(); + return; + } + + if (torture_cleanup_begin()) + return; + if (!cur_ops) { + torture_cleanup_end(); + return; + } + + if (reader_tasks) { + for (i = 0; i < nrealreaders; i++) + torture_stop_kthread(rcu_scale_reader, + reader_tasks[i]); + kfree(reader_tasks); + } + + if (writer_tasks) { + for (i = 0; i < nrealwriters; i++) { + torture_stop_kthread(rcu_scale_writer, + writer_tasks[i]); + if (!writer_n_durations) + continue; + j = writer_n_durations[i]; + pr_alert("%s%s writer %d gps: %d\n", + scale_type, SCALE_FLAG, i, j); + ngps += j; + } + pr_alert("%s%s start: %llu end: %llu duration: %llu gps: %d batches: %ld\n", + scale_type, SCALE_FLAG, + t_rcu_scale_writer_started, t_rcu_scale_writer_finished, + t_rcu_scale_writer_finished - + t_rcu_scale_writer_started, + ngps, + rcuscale_seq_diff(b_rcu_gp_test_finished, + b_rcu_gp_test_started)); + for (i = 0; i < nrealwriters; i++) { + if (!writer_durations) + break; + if (!writer_n_durations) + continue; + wdpp = writer_durations[i]; + if (!wdpp) + continue; + for (j = 0; j < writer_n_durations[i]; j++) { + wdp = &wdpp[j]; + pr_alert("%s%s %4d writer-duration: %5d %llu\n", + scale_type, SCALE_FLAG, + i, j, *wdp); + if (j % 100 == 0) + schedule_timeout_uninterruptible(1); + } + kfree(writer_durations[i]); + } + kfree(writer_tasks); + kfree(writer_durations); + kfree(writer_n_durations); + } + + /* Do torture-type-specific cleanup operations. */ + if (cur_ops->cleanup != NULL) + cur_ops->cleanup(); + + torture_cleanup_end(); +} + +/* + * RCU scalability shutdown kthread. Just waits to be awakened, then shuts + * down system. + */ +static int +rcu_scale_shutdown(void *arg) +{ + wait_event_idle(shutdown_wq, atomic_read(&n_rcu_scale_writer_finished) >= nrealwriters); + smp_mb(); /* Wake before output. */ + rcu_scale_cleanup(); + kernel_power_off(); + return -EINVAL; +} + static int __init rcu_scale_init(void) { long i; int firsterr = 0; static struct rcu_scale_ops *scale_ops[] = { - &rcu_ops, &srcu_ops, &srcud_ops, &tasks_ops, &tasks_tracing_ops + &rcu_ops, &srcu_ops, &srcud_ops, TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS }; if (!torture_init_begin(scale_type, verbose)) @@ -809,6 +976,11 @@ rcu_scale_init(void) if (cur_ops->init) cur_ops->init(); + if (cur_ops->rso_gp_kthread) { + kthread_tp = cur_ops->rso_gp_kthread(); + if (kthread_tp) + kthread_stime = kthread_tp->stime; + } if (kfree_rcu_test) return kfree_scale_init(); @@ -825,21 +997,21 @@ rcu_scale_init(void) init_waitqueue_head(&shutdown_wq); firsterr = torture_create_kthread(rcu_scale_shutdown, NULL, shutdown_task); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; schedule_timeout_uninterruptible(1); } reader_tasks = kcalloc(nrealreaders, sizeof(reader_tasks[0]), GFP_KERNEL); if (reader_tasks == NULL) { - VERBOSE_SCALEOUT_ERRSTRING("out of memory"); + SCALEOUT_ERRSTRING("out of memory"); firsterr = -ENOMEM; goto unwind; } for (i = 0; i < nrealreaders; i++) { firsterr = torture_create_kthread(rcu_scale_reader, (void *)i, reader_tasks[i]); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; } while (atomic_read(&n_rcu_scale_reader_started) < nrealreaders) @@ -852,7 +1024,7 @@ rcu_scale_init(void) kcalloc(nrealwriters, sizeof(*writer_n_durations), GFP_KERNEL); if (!writer_tasks || !writer_durations || !writer_n_durations) { - VERBOSE_SCALEOUT_ERRSTRING("out of memory"); + SCALEOUT_ERRSTRING("out of memory"); firsterr = -ENOMEM; goto unwind; } @@ -866,7 +1038,7 @@ rcu_scale_init(void) } firsterr = torture_create_kthread(rcu_scale_writer, (void *)i, writer_tasks[i]); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; } torture_init_end(); diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 528ed10b78fd..7567ca8e743c 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -21,6 +21,7 @@ #include <linux/spinlock.h> #include <linux/smp.h> #include <linux/rcupdate_wait.h> +#include <linux/rcu_notifier.h> #include <linux/interrupt.h> #include <linux/sched/signal.h> #include <uapi/linux/sched/types.h> @@ -46,6 +47,7 @@ #include <linux/oom.h> #include <linux/tick.h> #include <linux/rcupdate_trace.h> +#include <linux/nmi.h> #include "rcu.h" @@ -53,15 +55,18 @@ MODULE_LICENSE("GPL"); MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.ibm.com> and Josh Triplett <josh@joshtriplett.org>"); /* Bits for ->extendables field, extendables param, and related definitions. */ -#define RCUTORTURE_RDR_SHIFT 8 /* Put SRCU index in upper bits. */ -#define RCUTORTURE_RDR_MASK ((1 << RCUTORTURE_RDR_SHIFT) - 1) +#define RCUTORTURE_RDR_SHIFT_1 8 /* Put SRCU index in upper bits. */ +#define RCUTORTURE_RDR_MASK_1 (1 << RCUTORTURE_RDR_SHIFT_1) +#define RCUTORTURE_RDR_SHIFT_2 9 /* Put SRCU index in upper bits. */ +#define RCUTORTURE_RDR_MASK_2 (1 << RCUTORTURE_RDR_SHIFT_2) #define RCUTORTURE_RDR_BH 0x01 /* Extend readers by disabling bh. */ #define RCUTORTURE_RDR_IRQ 0x02 /* ... disabling interrupts. */ #define RCUTORTURE_RDR_PREEMPT 0x04 /* ... disabling preemption. */ #define RCUTORTURE_RDR_RBH 0x08 /* ... rcu_read_lock_bh(). */ #define RCUTORTURE_RDR_SCHED 0x10 /* ... rcu_read_lock_sched(). */ -#define RCUTORTURE_RDR_RCU 0x20 /* ... entering another RCU reader. */ -#define RCUTORTURE_RDR_NBITS 6 /* Number of bits defined above. */ +#define RCUTORTURE_RDR_RCU_1 0x20 /* ... entering another RCU reader. */ +#define RCUTORTURE_RDR_RCU_2 0x40 /* ... entering another RCU reader. */ +#define RCUTORTURE_RDR_NBITS 7 /* Number of bits defined above. */ #define RCUTORTURE_MAX_EXTEND \ (RCUTORTURE_RDR_BH | RCUTORTURE_RDR_IRQ | RCUTORTURE_RDR_PREEMPT | \ RCUTORTURE_RDR_RBH | RCUTORTURE_RDR_SCHED) @@ -71,82 +76,92 @@ MODULE_AUTHOR("Paul E. McKenney <paulmck@linux.ibm.com> and Josh Triplett <josh@ torture_param(int, extendables, RCUTORTURE_MAX_EXTEND, "Extend readers by disabling bh (1), irqs (2), or preempt (4)"); -torture_param(int, fqs_duration, 0, - "Duration of fqs bursts (us), 0 to disable"); +torture_param(int, fqs_duration, 0, "Duration of fqs bursts (us), 0 to disable"); torture_param(int, fqs_holdoff, 0, "Holdoff time within fqs bursts (us)"); torture_param(int, fqs_stutter, 3, "Wait time between fqs bursts (s)"); -torture_param(bool, fwd_progress, 1, "Test grace-period forward progress"); +torture_param(int, fwd_progress, 1, "Number of grace-period forward progress tasks (0 to disable)"); torture_param(int, fwd_progress_div, 4, "Fraction of CPU stall to wait"); -torture_param(int, fwd_progress_holdoff, 60, - "Time between forward-progress tests (s)"); -torture_param(bool, fwd_progress_need_resched, 1, - "Hide cond_resched() behind need_resched()"); +torture_param(int, fwd_progress_holdoff, 60, "Time between forward-progress tests (s)"); +torture_param(bool, fwd_progress_need_resched, 1, "Hide cond_resched() behind need_resched()"); torture_param(bool, gp_cond, false, "Use conditional/async GP wait primitives"); +torture_param(bool, gp_cond_exp, false, "Use conditional/async expedited GP wait primitives"); +torture_param(bool, gp_cond_full, false, "Use conditional/async full-state GP wait primitives"); +torture_param(bool, gp_cond_exp_full, false, + "Use conditional/async full-stateexpedited GP wait primitives"); torture_param(bool, gp_exp, false, "Use expedited GP wait primitives"); -torture_param(bool, gp_normal, false, - "Use normal (non-expedited) GP wait primitives"); +torture_param(bool, gp_normal, false, "Use normal (non-expedited) GP wait primitives"); +torture_param(bool, gp_poll, false, "Use polling GP wait primitives"); +torture_param(bool, gp_poll_exp, false, "Use polling expedited GP wait primitives"); +torture_param(bool, gp_poll_full, false, "Use polling full-state GP wait primitives"); +torture_param(bool, gp_poll_exp_full, false, "Use polling full-state expedited GP wait primitives"); torture_param(bool, gp_sync, false, "Use synchronous GP wait primitives"); torture_param(int, irqreader, 1, "Allow RCU readers from irq handlers"); torture_param(int, leakpointer, 0, "Leak pointer dereferences from readers"); -torture_param(int, n_barrier_cbs, 0, - "# of callbacks/kthreads for barrier testing"); +torture_param(int, n_barrier_cbs, 0, "# of callbacks/kthreads for barrier testing"); torture_param(int, nfakewriters, 4, "Number of RCU fake writer threads"); torture_param(int, nreaders, -1, "Number of RCU reader threads"); -torture_param(int, object_debug, 0, - "Enable debug-object double call_rcu() testing"); +torture_param(int, object_debug, 0, "Enable debug-object double call_rcu() testing"); torture_param(int, onoff_holdoff, 0, "Time after boot before CPU hotplugs (s)"); -torture_param(int, onoff_interval, 0, - "Time between CPU hotplugs (jiffies), 0=disable"); -torture_param(int, read_exit_delay, 13, - "Delay between read-then-exit episodes (s)"); -torture_param(int, read_exit_burst, 16, - "# of read-then-exit bursts per episode, zero to disable"); +torture_param(int, onoff_interval, 0, "Time between CPU hotplugs (jiffies), 0=disable"); +torture_param(int, nocbs_nthreads, 0, "Number of NOCB toggle threads, 0 to disable"); +torture_param(int, nocbs_toggle, 1000, "Time between toggling nocb state (ms)"); +torture_param(int, read_exit_delay, 13, "Delay between read-then-exit episodes (s)"); +torture_param(int, read_exit_burst, 16, "# of read-then-exit bursts per episode, zero to disable"); torture_param(int, shuffle_interval, 3, "Number of seconds between shuffles"); torture_param(int, shutdown_secs, 0, "Shutdown time (s), <= zero to disable."); torture_param(int, stall_cpu, 0, "Stall duration (s), zero to disable."); -torture_param(int, stall_cpu_holdoff, 10, - "Time to wait before starting stall (s)."); +torture_param(int, stall_cpu_holdoff, 10, "Time to wait before starting stall (s)."); +torture_param(bool, stall_no_softlockup, false, "Avoid softlockup warning during cpu stall."); torture_param(int, stall_cpu_irqsoff, 0, "Disable interrupts while stalling."); torture_param(int, stall_cpu_block, 0, "Sleep while stalling."); -torture_param(int, stall_gp_kthread, 0, - "Grace-period kthread stall duration (s)."); -torture_param(int, stat_interval, 60, - "Number of seconds between stats printk()s"); +torture_param(int, stall_gp_kthread, 0, "Grace-period kthread stall duration (s)."); +torture_param(int, stat_interval, 60, "Number of seconds between stats printk()s"); torture_param(int, stutter, 5, "Number of seconds to run/halt test"); torture_param(int, test_boost, 1, "Test RCU prio boost: 0=no, 1=maybe, 2=yes."); -torture_param(int, test_boost_duration, 4, - "Duration of each boost test, seconds."); -torture_param(int, test_boost_interval, 7, - "Interval between boost tests, seconds."); -torture_param(bool, test_no_idle_hz, true, - "Test support for tickless idle CPUs"); -torture_param(int, verbose, 1, - "Enable verbose debugging printk()s"); +torture_param(int, test_boost_duration, 4, "Duration of each boost test, seconds."); +torture_param(int, test_boost_interval, 7, "Interval between boost tests, seconds."); +torture_param(int, test_nmis, 0, "End-test NMI tests, 0 to disable."); +torture_param(bool, test_no_idle_hz, true, "Test support for tickless idle CPUs"); +torture_param(int, test_srcu_lockdep, 0, "Test specified SRCU deadlock scenario."); +torture_param(int, verbose, 1, "Enable verbose debugging printk()s"); static char *torture_type = "rcu"; module_param(torture_type, charp, 0444); MODULE_PARM_DESC(torture_type, "Type of RCU to torture (rcu, srcu, ...)"); +static int nrealnocbers; static int nrealreaders; static struct task_struct *writer_task; static struct task_struct **fakewriter_tasks; static struct task_struct **reader_tasks; +static struct task_struct **nocb_tasks; static struct task_struct *stats_task; static struct task_struct *fqs_task; static struct task_struct *boost_tasks[NR_CPUS]; static struct task_struct *stall_task; -static struct task_struct *fwd_prog_task; +static struct task_struct **fwd_prog_tasks; static struct task_struct **barrier_cbs_tasks; static struct task_struct *barrier_task; static struct task_struct *read_exit_task; #define RCU_TORTURE_PIPE_LEN 10 +// Mailbox-like structure to check RCU global memory ordering. +struct rcu_torture_reader_check { + unsigned long rtc_myloops; + int rtc_chkrdr; + unsigned long rtc_chkloops; + int rtc_ready; + struct rcu_torture_reader_check *rtc_assigner; +} ____cacheline_internodealigned_in_smp; + +// Update-side data structure used to check RCU readers. struct rcu_torture { struct rcu_head rtort_rcu; int rtort_pipe_count; struct list_head rtort_free; int rtort_mbtest; + struct rcu_torture_reader_check *rtort_chkp; }; static LIST_HEAD(rcu_torture_freelist); @@ -157,14 +172,16 @@ static DEFINE_SPINLOCK(rcu_torture_lock); static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_count); static DEFINE_PER_CPU(long [RCU_TORTURE_PIPE_LEN + 1], rcu_torture_batch); static atomic_t rcu_torture_wcount[RCU_TORTURE_PIPE_LEN + 1]; +static struct rcu_torture_reader_check *rcu_torture_reader_mbchk; static atomic_t n_rcu_torture_alloc; static atomic_t n_rcu_torture_alloc_fail; static atomic_t n_rcu_torture_free; static atomic_t n_rcu_torture_mberror; +static atomic_t n_rcu_torture_mbchk_fail; +static atomic_t n_rcu_torture_mbchk_tries; static atomic_t n_rcu_torture_error; static long n_rcu_torture_barrier_error; static long n_rcu_torture_boost_ktrerror; -static long n_rcu_torture_boost_rterror; static long n_rcu_torture_boost_failure; static long n_rcu_torture_boosts; static atomic_long_t n_rcu_torture_timers; @@ -174,6 +191,8 @@ static unsigned long n_read_exits; static struct list_head rcu_torture_removed; static unsigned long shutdown_jiffies; static unsigned long start_gp_seq; +static atomic_long_t n_nocb_offload; +static atomic_long_t n_nocb_deoffload; static int rcu_torture_writer_state; #define RTWS_FIXED_DELAY 0 @@ -182,10 +201,24 @@ static int rcu_torture_writer_state; #define RTWS_DEF_FREE 3 #define RTWS_EXP_SYNC 4 #define RTWS_COND_GET 5 -#define RTWS_COND_SYNC 6 -#define RTWS_SYNC 7 -#define RTWS_STUTTER 8 -#define RTWS_STOPPING 9 +#define RTWS_COND_GET_FULL 6 +#define RTWS_COND_GET_EXP 7 +#define RTWS_COND_GET_EXP_FULL 8 +#define RTWS_COND_SYNC 9 +#define RTWS_COND_SYNC_FULL 10 +#define RTWS_COND_SYNC_EXP 11 +#define RTWS_COND_SYNC_EXP_FULL 12 +#define RTWS_POLL_GET 13 +#define RTWS_POLL_GET_FULL 14 +#define RTWS_POLL_GET_EXP 15 +#define RTWS_POLL_GET_EXP_FULL 16 +#define RTWS_POLL_WAIT 17 +#define RTWS_POLL_WAIT_FULL 18 +#define RTWS_POLL_WAIT_EXP 19 +#define RTWS_POLL_WAIT_EXP_FULL 20 +#define RTWS_SYNC 21 +#define RTWS_STUTTER 22 +#define RTWS_STOPPING 23 static const char * const rcu_torture_writer_state_names[] = { "RTWS_FIXED_DELAY", "RTWS_DELAY", @@ -193,7 +226,21 @@ static const char * const rcu_torture_writer_state_names[] = { "RTWS_DEF_FREE", "RTWS_EXP_SYNC", "RTWS_COND_GET", + "RTWS_COND_GET_FULL", + "RTWS_COND_GET_EXP", + "RTWS_COND_GET_EXP_FULL", "RTWS_COND_SYNC", + "RTWS_COND_SYNC_FULL", + "RTWS_COND_SYNC_EXP", + "RTWS_COND_SYNC_EXP_FULL", + "RTWS_POLL_GET", + "RTWS_POLL_GET_FULL", + "RTWS_POLL_GET_EXP", + "RTWS_POLL_GET_EXP_FULL", + "RTWS_POLL_WAIT", + "RTWS_POLL_WAIT_FULL", + "RTWS_POLL_WAIT_EXP", + "RTWS_POLL_WAIT_EXP_FULL", "RTWS_SYNC", "RTWS_STUTTER", "RTWS_STOPPING", @@ -220,12 +267,6 @@ static const char *rcu_torture_writer_state_getname(void) return rcu_torture_writer_state_names[i]; } -#if defined(CONFIG_RCU_BOOST) && !defined(CONFIG_HOTPLUG_CPU) -#define rcu_can_boost() 1 -#else /* #if defined(CONFIG_RCU_BOOST) && !defined(CONFIG_HOTPLUG_CPU) */ -#define rcu_can_boost() 0 -#endif /* #else #if defined(CONFIG_RCU_BOOST) && !defined(CONFIG_HOTPLUG_CPU) */ - #ifdef CONFIG_RCU_TRACE static u64 notrace rcu_trace_clock_local(void) { @@ -259,7 +300,7 @@ static atomic_t barrier_cbs_invoked; /* Barrier callbacks invoked. */ static wait_queue_head_t *barrier_cbs_wq; /* Coordinate barrier testing. */ static DECLARE_WAIT_QUEUE_HEAD(barrier_wq); -static bool rcu_fwd_cb_nodelay; /* Short rcu_torture_delay() delays. */ +static atomic_t rcu_fwd_cb_nodelay; /* Short rcu_torture_delay() delays. */ /* * Allocate an element from the rcu_tortures pool. @@ -306,23 +347,46 @@ struct rcu_torture_ops { void (*read_delay)(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp); void (*readunlock)(int idx); + int (*readlock_held)(void); unsigned long (*get_gp_seq)(void); unsigned long (*gp_diff)(unsigned long new, unsigned long old); void (*deferred_free)(struct rcu_torture *p); void (*sync)(void); void (*exp_sync)(void); - unsigned long (*get_state)(void); + unsigned long (*get_gp_state_exp)(void); + unsigned long (*start_gp_poll_exp)(void); + void (*start_gp_poll_exp_full)(struct rcu_gp_oldstate *rgosp); + bool (*poll_gp_state_exp)(unsigned long oldstate); + void (*cond_sync_exp)(unsigned long oldstate); + void (*cond_sync_exp_full)(struct rcu_gp_oldstate *rgosp); + unsigned long (*get_comp_state)(void); + void (*get_comp_state_full)(struct rcu_gp_oldstate *rgosp); + bool (*same_gp_state)(unsigned long oldstate1, unsigned long oldstate2); + bool (*same_gp_state_full)(struct rcu_gp_oldstate *rgosp1, struct rcu_gp_oldstate *rgosp2); + unsigned long (*get_gp_state)(void); + void (*get_gp_state_full)(struct rcu_gp_oldstate *rgosp); + unsigned long (*get_gp_completed)(void); + void (*get_gp_completed_full)(struct rcu_gp_oldstate *rgosp); + unsigned long (*start_gp_poll)(void); + void (*start_gp_poll_full)(struct rcu_gp_oldstate *rgosp); + bool (*poll_gp_state)(unsigned long oldstate); + bool (*poll_gp_state_full)(struct rcu_gp_oldstate *rgosp); + bool (*poll_need_2gp)(bool poll, bool poll_full); void (*cond_sync)(unsigned long oldstate); + void (*cond_sync_full)(struct rcu_gp_oldstate *rgosp); call_rcu_func_t call; void (*cb_barrier)(void); void (*fqs)(void); void (*stats)(void); void (*gp_kthread_dbg)(void); + bool (*check_boost_failed)(unsigned long gp_state, int *cpup); int (*stall_dur)(void); + long cbflood_max; int irq_capable; int can_boost; int extendables; int slow_gps; + int no_pi_lock; const char *name; }; @@ -332,7 +396,12 @@ static struct rcu_torture_ops *cur_ops; * Definitions for rcu torture testing. */ -static int rcu_torture_read_lock(void) __acquires(RCU) +static int torture_readlock_not_held(void) +{ + return rcu_read_lock_bh_held() || rcu_read_lock_sched_held(); +} + +static int rcu_torture_read_lock(void) { rcu_read_lock(); return 0; @@ -351,7 +420,7 @@ rcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp) * period, and we want a long delay occasionally to trigger * force_quiescent_state. */ - if (!READ_ONCE(rcu_fwd_cb_nodelay) && + if (!atomic_read(&rcu_fwd_cb_nodelay) && !(torture_random(rrsp) % (nrealreaders * 2000 * longdelay_ms))) { started = cur_ops->get_gp_seq(); ts = rcu_trace_clock_local(); @@ -374,7 +443,7 @@ rcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp) } } -static void rcu_torture_read_unlock(int idx) __releases(RCU) +static void rcu_torture_read_unlock(int idx) { rcu_read_unlock(); } @@ -386,7 +455,12 @@ static bool rcu_torture_pipe_update_one(struct rcu_torture *rp) { int i; + struct rcu_torture_reader_check *rtrcp = READ_ONCE(rp->rtort_chkp); + if (rtrcp) { + WRITE_ONCE(rp->rtort_chkp, NULL); + smp_store_release(&rtrcp->rtc_ready, 1); // Pair with smp_load_acquire(). + } i = READ_ONCE(rp->rtort_pipe_count); if (i > RCU_TORTURE_PIPE_LEN) i = RCU_TORTURE_PIPE_LEN; @@ -442,7 +516,7 @@ static unsigned long rcu_no_completed(void) static void rcu_torture_deferred_free(struct rcu_torture *p) { - call_rcu(&p->rtort_rcu, rcu_torture_cb); + call_rcu_hurry(&p->rtort_rcu, rcu_torture_cb); } static void rcu_sync_torture_init(void) @@ -450,29 +524,54 @@ static void rcu_sync_torture_init(void) INIT_LIST_HEAD(&rcu_torture_removed); } +static bool rcu_poll_need_2gp(bool poll, bool poll_full) +{ + return poll; +} + static struct rcu_torture_ops rcu_ops = { - .ttype = RCU_FLAVOR, - .init = rcu_sync_torture_init, - .readlock = rcu_torture_read_lock, - .read_delay = rcu_read_delay, - .readunlock = rcu_torture_read_unlock, - .get_gp_seq = rcu_get_gp_seq, - .gp_diff = rcu_seq_diff, - .deferred_free = rcu_torture_deferred_free, - .sync = synchronize_rcu, - .exp_sync = synchronize_rcu_expedited, - .get_state = get_state_synchronize_rcu, - .cond_sync = cond_synchronize_rcu, - .call = call_rcu, - .cb_barrier = rcu_barrier, - .fqs = rcu_force_quiescent_state, - .stats = NULL, - .gp_kthread_dbg = show_rcu_gp_kthreads, - .stall_dur = rcu_jiffies_till_stall_check, - .irq_capable = 1, - .can_boost = rcu_can_boost(), - .extendables = RCUTORTURE_MAX_EXTEND, - .name = "rcu" + .ttype = RCU_FLAVOR, + .init = rcu_sync_torture_init, + .readlock = rcu_torture_read_lock, + .read_delay = rcu_read_delay, + .readunlock = rcu_torture_read_unlock, + .readlock_held = torture_readlock_not_held, + .get_gp_seq = rcu_get_gp_seq, + .gp_diff = rcu_seq_diff, + .deferred_free = rcu_torture_deferred_free, + .sync = synchronize_rcu, + .exp_sync = synchronize_rcu_expedited, + .same_gp_state = same_state_synchronize_rcu, + .same_gp_state_full = same_state_synchronize_rcu_full, + .get_comp_state = get_completed_synchronize_rcu, + .get_comp_state_full = get_completed_synchronize_rcu_full, + .get_gp_state = get_state_synchronize_rcu, + .get_gp_state_full = get_state_synchronize_rcu_full, + .get_gp_completed = get_completed_synchronize_rcu, + .get_gp_completed_full = get_completed_synchronize_rcu_full, + .start_gp_poll = start_poll_synchronize_rcu, + .start_gp_poll_full = start_poll_synchronize_rcu_full, + .poll_gp_state = poll_state_synchronize_rcu, + .poll_gp_state_full = poll_state_synchronize_rcu_full, + .poll_need_2gp = rcu_poll_need_2gp, + .cond_sync = cond_synchronize_rcu, + .cond_sync_full = cond_synchronize_rcu_full, + .get_gp_state_exp = get_state_synchronize_rcu, + .start_gp_poll_exp = start_poll_synchronize_rcu_expedited, + .start_gp_poll_exp_full = start_poll_synchronize_rcu_expedited_full, + .poll_gp_state_exp = poll_state_synchronize_rcu, + .cond_sync_exp = cond_synchronize_rcu_expedited, + .call = call_rcu_hurry, + .cb_barrier = rcu_barrier, + .fqs = rcu_force_quiescent_state, + .stats = NULL, + .gp_kthread_dbg = show_rcu_gp_kthreads, + .check_boost_failed = rcu_check_boost_fail, + .stall_dur = rcu_jiffies_till_stall_check, + .irq_capable = 1, + .can_boost = IS_ENABLED(CONFIG_RCU_BOOST), + .extendables = RCUTORTURE_MAX_EXTEND, + .name = "rcu" }; /* @@ -506,6 +605,7 @@ static struct rcu_torture_ops rcu_busted_ops = { .readlock = rcu_torture_read_lock, .read_delay = rcu_read_delay, /* just reuse rcu's version. */ .readunlock = rcu_torture_read_unlock, + .readlock_held = torture_readlock_not_held, .get_gp_seq = rcu_no_completed, .deferred_free = rcu_busted_torture_deferred_free, .sync = synchronize_rcu_busted, @@ -525,10 +625,14 @@ static struct rcu_torture_ops rcu_busted_ops = { DEFINE_STATIC_SRCU(srcu_ctl); static struct srcu_struct srcu_ctld; static struct srcu_struct *srcu_ctlp = &srcu_ctl; +static struct rcu_torture_ops srcud_ops; -static int srcu_torture_read_lock(void) __acquires(srcu_ctlp) +static int srcu_torture_read_lock(void) { - return srcu_read_lock(srcu_ctlp); + if (cur_ops == &srcud_ops) + return srcu_read_lock_nmisafe(srcu_ctlp); + else + return srcu_read_lock(srcu_ctlp); } static void @@ -550,9 +654,17 @@ srcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp) } } -static void srcu_torture_read_unlock(int idx) __releases(srcu_ctlp) +static void srcu_torture_read_unlock(int idx) +{ + if (cur_ops == &srcud_ops) + srcu_read_unlock_nmisafe(srcu_ctlp, idx); + else + srcu_read_unlock(srcu_ctlp, idx); +} + +static int torture_srcu_read_lock_held(void) { - srcu_read_unlock(srcu_ctlp, idx); + return srcu_read_lock_held(srcu_ctlp); } static unsigned long srcu_torture_completed(void) @@ -570,6 +682,21 @@ static void srcu_torture_synchronize(void) synchronize_srcu(srcu_ctlp); } +static unsigned long srcu_torture_get_gp_state(void) +{ + return get_state_synchronize_srcu(srcu_ctlp); +} + +static unsigned long srcu_torture_start_gp_poll(void) +{ + return start_poll_synchronize_srcu(srcu_ctlp); +} + +static bool srcu_torture_poll_gp_state(unsigned long oldstate) +{ + return poll_state_synchronize_srcu(srcu_ctlp, oldstate); +} + static void srcu_torture_call(struct rcu_head *head, rcu_callback_t func) { @@ -597,14 +724,20 @@ static struct rcu_torture_ops srcu_ops = { .readlock = srcu_torture_read_lock, .read_delay = srcu_read_delay, .readunlock = srcu_torture_read_unlock, + .readlock_held = torture_srcu_read_lock_held, .get_gp_seq = srcu_torture_completed, .deferred_free = srcu_torture_deferred_free, .sync = srcu_torture_synchronize, .exp_sync = srcu_torture_synchronize_expedited, + .get_gp_state = srcu_torture_get_gp_state, + .start_gp_poll = srcu_torture_start_gp_poll, + .poll_gp_state = srcu_torture_poll_gp_state, .call = srcu_torture_call, .cb_barrier = srcu_torture_barrier, .stats = srcu_torture_stats, + .cbflood_max = 50000, .irq_capable = 1, + .no_pi_lock = IS_ENABLED(CONFIG_TINY_SRCU), .name = "srcu" }; @@ -629,14 +762,20 @@ static struct rcu_torture_ops srcud_ops = { .readlock = srcu_torture_read_lock, .read_delay = srcu_read_delay, .readunlock = srcu_torture_read_unlock, + .readlock_held = torture_srcu_read_lock_held, .get_gp_seq = srcu_torture_completed, .deferred_free = srcu_torture_deferred_free, .sync = srcu_torture_synchronize, .exp_sync = srcu_torture_synchronize_expedited, + .get_gp_state = srcu_torture_get_gp_state, + .start_gp_poll = srcu_torture_start_gp_poll, + .poll_gp_state = srcu_torture_poll_gp_state, .call = srcu_torture_call, .cb_barrier = srcu_torture_barrier, .stats = srcu_torture_stats, + .cbflood_max = 50000, .irq_capable = 1, + .no_pi_lock = IS_ENABLED(CONFIG_TINY_SRCU), .name = "srcud" }; @@ -648,6 +787,7 @@ static struct rcu_torture_ops busted_srcud_ops = { .readlock = srcu_torture_read_lock, .read_delay = rcu_read_delay, .readunlock = srcu_torture_read_unlock, + .readlock_held = torture_srcu_read_lock_held, .get_gp_seq = srcu_torture_completed, .deferred_free = srcu_torture_deferred_free, .sync = srcu_torture_synchronize, @@ -656,11 +796,56 @@ static struct rcu_torture_ops busted_srcud_ops = { .cb_barrier = srcu_torture_barrier, .stats = srcu_torture_stats, .irq_capable = 1, + .no_pi_lock = IS_ENABLED(CONFIG_TINY_SRCU), .extendables = RCUTORTURE_MAX_EXTEND, .name = "busted_srcud" }; /* + * Definitions for trivial CONFIG_PREEMPT=n-only torture testing. + * This implementation does not necessarily work well with CPU hotplug. + */ + +static void synchronize_rcu_trivial(void) +{ + int cpu; + + for_each_online_cpu(cpu) { + torture_sched_setaffinity(current->pid, cpumask_of(cpu)); + WARN_ON_ONCE(raw_smp_processor_id() != cpu); + } +} + +static int rcu_torture_read_lock_trivial(void) +{ + preempt_disable(); + return 0; +} + +static void rcu_torture_read_unlock_trivial(int idx) +{ + preempt_enable(); +} + +static struct rcu_torture_ops trivial_ops = { + .ttype = RCU_TRIVIAL_FLAVOR, + .init = rcu_sync_torture_init, + .readlock = rcu_torture_read_lock_trivial, + .read_delay = rcu_read_delay, /* just reuse rcu's version. */ + .readunlock = rcu_torture_read_unlock_trivial, + .readlock_held = torture_readlock_not_held, + .get_gp_seq = rcu_no_completed, + .sync = synchronize_rcu_trivial, + .exp_sync = synchronize_rcu_trivial, + .fqs = NULL, + .stats = NULL, + .irq_capable = 1, + .name = "trivial" +}; + +#ifdef CONFIG_TASKS_RCU + +/* * Definitions for RCU-tasks torture testing. */ @@ -680,7 +865,7 @@ static void rcu_tasks_torture_deferred_free(struct rcu_torture *p) static void synchronize_rcu_mult_test(void) { - synchronize_rcu_mult(call_rcu_tasks, call_rcu); + synchronize_rcu_mult(call_rcu_tasks, call_rcu_hurry); } static struct rcu_torture_ops tasks_ops = { @@ -703,46 +888,16 @@ static struct rcu_torture_ops tasks_ops = { .name = "tasks" }; -/* - * Definitions for trivial CONFIG_PREEMPT=n-only torture testing. - * This implementation does not necessarily work well with CPU hotplug. - */ +#define TASKS_OPS &tasks_ops, -static void synchronize_rcu_trivial(void) -{ - int cpu; +#else // #ifdef CONFIG_TASKS_RCU - for_each_online_cpu(cpu) { - rcutorture_sched_setaffinity(current->pid, cpumask_of(cpu)); - WARN_ON_ONCE(raw_smp_processor_id() != cpu); - } -} +#define TASKS_OPS -static int rcu_torture_read_lock_trivial(void) __acquires(RCU) -{ - preempt_disable(); - return 0; -} +#endif // #else #ifdef CONFIG_TASKS_RCU -static void rcu_torture_read_unlock_trivial(int idx) __releases(RCU) -{ - preempt_enable(); -} -static struct rcu_torture_ops trivial_ops = { - .ttype = RCU_TRIVIAL_FLAVOR, - .init = rcu_sync_torture_init, - .readlock = rcu_torture_read_lock_trivial, - .read_delay = rcu_read_delay, /* just reuse rcu's version. */ - .readunlock = rcu_torture_read_unlock_trivial, - .get_gp_seq = rcu_no_completed, - .sync = synchronize_rcu_trivial, - .exp_sync = synchronize_rcu_trivial, - .fqs = NULL, - .stats = NULL, - .irq_capable = 1, - .name = "trivial" -}; +#ifdef CONFIG_TASKS_RUDE_RCU /* * Definitions for rude RCU-tasks torture testing. @@ -766,12 +921,24 @@ static struct rcu_torture_ops tasks_rude_ops = { .call = call_rcu_tasks_rude, .cb_barrier = rcu_barrier_tasks_rude, .gp_kthread_dbg = show_rcu_tasks_rude_gp_kthread, + .cbflood_max = 50000, .fqs = NULL, .stats = NULL, .irq_capable = 1, .name = "tasks-rude" }; +#define TASKS_RUDE_OPS &tasks_rude_ops, + +#else // #ifdef CONFIG_TASKS_RUDE_RCU + +#define TASKS_RUDE_OPS + +#endif // #else #ifdef CONFIG_TASKS_RUDE_RCU + + +#ifdef CONFIG_TASKS_TRACE_RCU + /* * Definitions for tracing RCU-tasks torture testing. */ @@ -798,6 +965,7 @@ static struct rcu_torture_ops tasks_tracing_ops = { .readlock = tasks_tracing_torture_read_lock, .read_delay = srcu_read_delay, /* just reuse srcu's version. */ .readunlock = tasks_tracing_torture_read_unlock, + .readlock_held = rcu_read_lock_trace_held, .get_gp_seq = rcu_no_completed, .deferred_free = rcu_tasks_tracing_torture_deferred_free, .sync = synchronize_rcu_tasks_trace, @@ -805,6 +973,7 @@ static struct rcu_torture_ops tasks_tracing_ops = { .call = call_rcu_tasks_trace, .cb_barrier = rcu_barrier_tasks_trace, .gp_kthread_dbg = show_rcu_tasks_trace_gp_kthread, + .cbflood_max = 50000, .fqs = NULL, .stats = NULL, .irq_capable = 1, @@ -812,6 +981,15 @@ static struct rcu_torture_ops tasks_tracing_ops = { .name = "tasks-tracing" }; +#define TASKS_TRACING_OPS &tasks_tracing_ops, + +#else // #ifdef CONFIG_TASKS_TRACE_RCU + +#define TASKS_TRACING_OPS + +#endif // #else #ifdef CONFIG_TASKS_TRACE_RCU + + static unsigned long rcutorture_seq_diff(unsigned long new, unsigned long old) { if (!cur_ops->gp_diff) @@ -819,32 +997,13 @@ static unsigned long rcutorture_seq_diff(unsigned long new, unsigned long old) return cur_ops->gp_diff(new, old); } -static bool __maybe_unused torturing_tasks(void) -{ - return cur_ops == &tasks_ops || cur_ops == &tasks_rude_ops; -} - /* * RCU torture priority-boost testing. Runs one real-time thread per - * CPU for moderate bursts, repeatedly registering RCU callbacks and - * spinning waiting for them to be invoked. If a given callback takes - * too long to be invoked, we assume that priority inversion has occurred. + * CPU for moderate bursts, repeatedly starting grace periods and waiting + * for them to complete. If a given grace period takes too long, we assume + * that priority inversion has occurred. */ -struct rcu_boost_inflight { - struct rcu_head rcu; - int inflight; -}; - -static void rcu_torture_boost_cb(struct rcu_head *head) -{ - struct rcu_boost_inflight *rbip = - container_of(head, struct rcu_boost_inflight, rcu); - - /* Ensure RCU-core accesses precede clearing ->inflight */ - smp_store_release(&rbip->inflight, 0); -} - static int old_rt_runtime = -1; static void rcu_torture_disable_rt_throttle(void) @@ -871,50 +1030,73 @@ static void rcu_torture_enable_rt_throttle(void) old_rt_runtime = -1; } -static bool rcu_torture_boost_failed(unsigned long start, unsigned long end) +static bool rcu_torture_boost_failed(unsigned long gp_state, unsigned long *start) { - if (end - start > test_boost_duration * HZ - HZ / 2) { + int cpu; + static int dbg_done; + unsigned long end = jiffies; + bool gp_done; + unsigned long j; + static unsigned long last_persist; + unsigned long lp; + unsigned long mininterval = test_boost_duration * HZ - HZ / 2; + + if (end - *start > mininterval) { + // Recheck after checking time to avoid false positives. + smp_mb(); // Time check before grace-period check. + if (cur_ops->poll_gp_state(gp_state)) + return false; // passed, though perhaps just barely + if (cur_ops->check_boost_failed && !cur_ops->check_boost_failed(gp_state, &cpu)) { + // At most one persisted message per boost test. + j = jiffies; + lp = READ_ONCE(last_persist); + if (time_after(j, lp + mininterval) && cmpxchg(&last_persist, lp, j) == lp) + pr_info("Boost inversion persisted: No QS from CPU %d\n", cpu); + return false; // passed on a technicality + } VERBOSE_TOROUT_STRING("rcu_torture_boost boosting failed"); n_rcu_torture_boost_failure++; + if (!xchg(&dbg_done, 1) && cur_ops->gp_kthread_dbg) { + pr_info("Boost inversion thread ->rt_priority %u gp_state %lu jiffies %lu\n", + current->rt_priority, gp_state, end - *start); + cur_ops->gp_kthread_dbg(); + // Recheck after print to flag grace period ending during splat. + gp_done = cur_ops->poll_gp_state(gp_state); + pr_info("Boost inversion: GP %lu %s.\n", gp_state, + gp_done ? "ended already" : "still pending"); - return true; /* failed */ + } + + return true; // failed + } else if (cur_ops->check_boost_failed && !cur_ops->check_boost_failed(gp_state, NULL)) { + *start = jiffies; } - return false; /* passed */ + return false; // passed } static int rcu_torture_boost(void *arg) { - unsigned long call_rcu_time; unsigned long endtime; + unsigned long gp_state; + unsigned long gp_state_time; unsigned long oldstarttime; - struct rcu_boost_inflight rbi = { .inflight = 0 }; VERBOSE_TOROUT_STRING("rcu_torture_boost started"); /* Set real-time priority. */ sched_set_fifo_low(current); - init_rcu_head_on_stack(&rbi.rcu); /* Each pass through the following loop does one boost-test cycle. */ do { - /* Track if the test failed already in this test interval? */ - bool failed = false; + bool failed = false; // Test failed already in this test interval + bool gp_initiated = false; - /* Increment n_rcu_torture_boosts once per boost-test */ - while (!kthread_should_stop()) { - if (mutex_trylock(&boost_mutex)) { - n_rcu_torture_boosts++; - mutex_unlock(&boost_mutex); - break; - } - schedule_timeout_uninterruptible(1); - } if (kthread_should_stop()) goto checkwait; /* Wait for the next test interval. */ - oldstarttime = boost_starttime; + oldstarttime = READ_ONCE(boost_starttime); while (time_before(jiffies, oldstarttime)) { schedule_timeout_interruptible(oldstarttime - jiffies); if (stutter_wait("rcu_torture_boost")) @@ -923,34 +1105,33 @@ static int rcu_torture_boost(void *arg) goto checkwait; } - /* Do one boost-test interval. */ + // Do one boost-test interval. endtime = oldstarttime + test_boost_duration * HZ; - call_rcu_time = jiffies; while (time_before(jiffies, endtime)) { - /* If we don't have a callback in flight, post one. */ - if (!smp_load_acquire(&rbi.inflight)) { - /* RCU core before ->inflight = 1. */ - smp_store_release(&rbi.inflight, 1); - call_rcu(&rbi.rcu, rcu_torture_boost_cb); - /* Check if the boost test failed */ - failed = failed || - rcu_torture_boost_failed(call_rcu_time, - jiffies); - call_rcu_time = jiffies; + // Has current GP gone too long? + if (gp_initiated && !failed && !cur_ops->poll_gp_state(gp_state)) + failed = rcu_torture_boost_failed(gp_state, &gp_state_time); + // If we don't have a grace period in flight, start one. + if (!gp_initiated || cur_ops->poll_gp_state(gp_state)) { + gp_state = cur_ops->start_gp_poll(); + gp_initiated = true; + gp_state_time = jiffies; } - if (stutter_wait("rcu_torture_boost")) + if (stutter_wait("rcu_torture_boost")) { sched_set_fifo_low(current); + // If the grace period already ended, + // we don't know when that happened, so + // start over. + if (cur_ops->poll_gp_state(gp_state)) + gp_initiated = false; + } if (torture_must_stop()) goto checkwait; } - /* - * If boost never happened, then inflight will always be 1, in - * this case the boost check would never happen in the above - * loop so do another one here. - */ - if (!failed && smp_load_acquire(&rbi.inflight)) - rcu_torture_boost_failed(call_rcu_time, jiffies); + // In case the grace period extended beyond the end of the loop. + if (gp_initiated && !failed && !cur_ops->poll_gp_state(gp_state)) + rcu_torture_boost_failed(gp_state, &gp_state_time); /* * Set the start time of the next test interval. @@ -959,15 +1140,17 @@ static int rcu_torture_boost(void *arg) * interval. Besides, we are running at RT priority, * so delays should be relatively rare. */ - while (oldstarttime == boost_starttime && - !kthread_should_stop()) { + while (oldstarttime == READ_ONCE(boost_starttime) && !kthread_should_stop()) { if (mutex_trylock(&boost_mutex)) { - boost_starttime = jiffies + - test_boost_interval * HZ; + if (oldstarttime == boost_starttime) { + WRITE_ONCE(boost_starttime, + jiffies + test_boost_interval * HZ); + n_rcu_torture_boosts++; + } mutex_unlock(&boost_mutex); break; } - schedule_timeout_uninterruptible(1); + schedule_timeout_uninterruptible(HZ / 20); } /* Go do the stutter. */ @@ -976,11 +1159,10 @@ checkwait: if (stutter_wait("rcu_torture_boost")) } while (!torture_must_stop()); /* Clean up and exit. */ - while (!kthread_should_stop() || smp_load_acquire(&rbi.inflight)) { + while (!kthread_should_stop()) { torture_shutdown_absorb("rcu_torture_boost"); - schedule_timeout_uninterruptible(1); + schedule_timeout_uninterruptible(HZ / 20); } - destroy_rcu_head_on_stack(&rbi.rcu); torture_kthread_stopping("rcu_torture_boost"); return 0; } @@ -1002,7 +1184,7 @@ rcu_torture_fqs(void *arg) fqs_resume_time = jiffies + fqs_stutter * HZ; while (time_before(jiffies, fqs_resume_time) && !kthread_should_stop()) { - schedule_timeout_interruptible(1); + schedule_timeout_interruptible(HZ / 20); } fqs_burst_remaining = fqs_duration; while (fqs_burst_remaining > 0 && @@ -1018,44 +1200,69 @@ rcu_torture_fqs(void *arg) return 0; } +// Used by writers to randomly choose from the available grace-period primitives. +static int synctype[ARRAY_SIZE(rcu_torture_writer_state_names)] = { }; +static int nsynctypes; + /* - * RCU torture writer kthread. Repeatedly substitutes a new structure - * for that pointed to by rcu_torture_current, freeing the old structure - * after a series of grace periods (the "pipeline"). + * Determine which grace-period primitives are available. */ -static int -rcu_torture_writer(void *arg) +static void rcu_torture_write_types(void) { - bool can_expedite = !rcu_gp_is_expedited() && !rcu_gp_is_normal(); - int expediting = 0; - unsigned long gp_snap; - bool gp_cond1 = gp_cond, gp_exp1 = gp_exp, gp_normal1 = gp_normal; - bool gp_sync1 = gp_sync; - int i; - int oldnice = task_nice(current); - struct rcu_torture *rp; - struct rcu_torture *old_rp; - static DEFINE_TORTURE_RANDOM(rand); - bool stutter_waited; - int synctype[] = { RTWS_DEF_FREE, RTWS_EXP_SYNC, - RTWS_COND_GET, RTWS_SYNC }; - int nsynctypes = 0; - - VERBOSE_TOROUT_STRING("rcu_torture_writer task started"); - if (!can_expedite) - pr_alert("%s" TORTURE_FLAG - " GP expediting controlled from boot/sysfs for %s.\n", - torture_type, cur_ops->name); + bool gp_cond1 = gp_cond, gp_cond_exp1 = gp_cond_exp, gp_cond_full1 = gp_cond_full; + bool gp_cond_exp_full1 = gp_cond_exp_full, gp_exp1 = gp_exp, gp_poll_exp1 = gp_poll_exp; + bool gp_poll_exp_full1 = gp_poll_exp_full, gp_normal1 = gp_normal, gp_poll1 = gp_poll; + bool gp_poll_full1 = gp_poll_full, gp_sync1 = gp_sync; /* Initialize synctype[] array. If none set, take default. */ - if (!gp_cond1 && !gp_exp1 && !gp_normal1 && !gp_sync1) - gp_cond1 = gp_exp1 = gp_normal1 = gp_sync1 = true; - if (gp_cond1 && cur_ops->get_state && cur_ops->cond_sync) { + if (!gp_cond1 && + !gp_cond_exp1 && + !gp_cond_full1 && + !gp_cond_exp_full1 && + !gp_exp1 && + !gp_poll_exp1 && + !gp_poll_exp_full1 && + !gp_normal1 && + !gp_poll1 && + !gp_poll_full1 && + !gp_sync1) { + gp_cond1 = true; + gp_cond_exp1 = true; + gp_cond_full1 = true; + gp_cond_exp_full1 = true; + gp_exp1 = true; + gp_poll_exp1 = true; + gp_poll_exp_full1 = true; + gp_normal1 = true; + gp_poll1 = true; + gp_poll_full1 = true; + gp_sync1 = true; + } + if (gp_cond1 && cur_ops->get_gp_state && cur_ops->cond_sync) { synctype[nsynctypes++] = RTWS_COND_GET; pr_info("%s: Testing conditional GPs.\n", __func__); - } else if (gp_cond && (!cur_ops->get_state || !cur_ops->cond_sync)) { + } else if (gp_cond && (!cur_ops->get_gp_state || !cur_ops->cond_sync)) { pr_alert("%s: gp_cond without primitives.\n", __func__); } + if (gp_cond_exp1 && cur_ops->get_gp_state_exp && cur_ops->cond_sync_exp) { + synctype[nsynctypes++] = RTWS_COND_GET_EXP; + pr_info("%s: Testing conditional expedited GPs.\n", __func__); + } else if (gp_cond_exp && (!cur_ops->get_gp_state_exp || !cur_ops->cond_sync_exp)) { + pr_alert("%s: gp_cond_exp without primitives.\n", __func__); + } + if (gp_cond_full1 && cur_ops->get_gp_state && cur_ops->cond_sync_full) { + synctype[nsynctypes++] = RTWS_COND_GET_FULL; + pr_info("%s: Testing conditional full-state GPs.\n", __func__); + } else if (gp_cond_full && (!cur_ops->get_gp_state || !cur_ops->cond_sync_full)) { + pr_alert("%s: gp_cond_full without primitives.\n", __func__); + } + if (gp_cond_exp_full1 && cur_ops->get_gp_state_exp && cur_ops->cond_sync_exp_full) { + synctype[nsynctypes++] = RTWS_COND_GET_EXP_FULL; + pr_info("%s: Testing conditional full-state expedited GPs.\n", __func__); + } else if (gp_cond_exp_full && + (!cur_ops->get_gp_state_exp || !cur_ops->cond_sync_exp_full)) { + pr_alert("%s: gp_cond_exp_full without primitives.\n", __func__); + } if (gp_exp1 && cur_ops->exp_sync) { synctype[nsynctypes++] = RTWS_EXP_SYNC; pr_info("%s: Testing expedited GPs.\n", __func__); @@ -1068,14 +1275,109 @@ rcu_torture_writer(void *arg) } else if (gp_normal && !cur_ops->deferred_free) { pr_alert("%s: gp_normal without primitives.\n", __func__); } + if (gp_poll1 && cur_ops->get_comp_state && cur_ops->same_gp_state && + cur_ops->start_gp_poll && cur_ops->poll_gp_state) { + synctype[nsynctypes++] = RTWS_POLL_GET; + pr_info("%s: Testing polling GPs.\n", __func__); + } else if (gp_poll && (!cur_ops->start_gp_poll || !cur_ops->poll_gp_state)) { + pr_alert("%s: gp_poll without primitives.\n", __func__); + } + if (gp_poll_full1 && cur_ops->get_comp_state_full && cur_ops->same_gp_state_full + && cur_ops->start_gp_poll_full && cur_ops->poll_gp_state_full) { + synctype[nsynctypes++] = RTWS_POLL_GET_FULL; + pr_info("%s: Testing polling full-state GPs.\n", __func__); + } else if (gp_poll_full && (!cur_ops->start_gp_poll_full || !cur_ops->poll_gp_state_full)) { + pr_alert("%s: gp_poll_full without primitives.\n", __func__); + } + if (gp_poll_exp1 && cur_ops->start_gp_poll_exp && cur_ops->poll_gp_state_exp) { + synctype[nsynctypes++] = RTWS_POLL_GET_EXP; + pr_info("%s: Testing polling expedited GPs.\n", __func__); + } else if (gp_poll_exp && (!cur_ops->start_gp_poll_exp || !cur_ops->poll_gp_state_exp)) { + pr_alert("%s: gp_poll_exp without primitives.\n", __func__); + } + if (gp_poll_exp_full1 && cur_ops->start_gp_poll_exp_full && cur_ops->poll_gp_state_full) { + synctype[nsynctypes++] = RTWS_POLL_GET_EXP_FULL; + pr_info("%s: Testing polling full-state expedited GPs.\n", __func__); + } else if (gp_poll_exp_full && + (!cur_ops->start_gp_poll_exp_full || !cur_ops->poll_gp_state_full)) { + pr_alert("%s: gp_poll_exp_full without primitives.\n", __func__); + } if (gp_sync1 && cur_ops->sync) { synctype[nsynctypes++] = RTWS_SYNC; pr_info("%s: Testing normal GPs.\n", __func__); } else if (gp_sync && !cur_ops->sync) { pr_alert("%s: gp_sync without primitives.\n", __func__); } +} + +/* + * Do the specified rcu_torture_writer() synchronous grace period, + * while also testing out the polled APIs. Note well that the single-CPU + * grace-period optimizations must be accounted for. + */ +static void do_rtws_sync(struct torture_random_state *trsp, void (*sync)(void)) +{ + unsigned long cookie; + struct rcu_gp_oldstate cookie_full; + bool dopoll; + bool dopoll_full; + unsigned long r = torture_random(trsp); + + dopoll = cur_ops->get_gp_state && cur_ops->poll_gp_state && !(r & 0x300); + dopoll_full = cur_ops->get_gp_state_full && cur_ops->poll_gp_state_full && !(r & 0xc00); + if (dopoll || dopoll_full) + cpus_read_lock(); + if (dopoll) + cookie = cur_ops->get_gp_state(); + if (dopoll_full) + cur_ops->get_gp_state_full(&cookie_full); + if (cur_ops->poll_need_2gp && cur_ops->poll_need_2gp(dopoll, dopoll_full)) + sync(); + sync(); + WARN_ONCE(dopoll && !cur_ops->poll_gp_state(cookie), + "%s: Cookie check 3 failed %pS() online %*pbl.", + __func__, sync, cpumask_pr_args(cpu_online_mask)); + WARN_ONCE(dopoll_full && !cur_ops->poll_gp_state_full(&cookie_full), + "%s: Cookie check 4 failed %pS() online %*pbl", + __func__, sync, cpumask_pr_args(cpu_online_mask)); + if (dopoll || dopoll_full) + cpus_read_unlock(); +} + +/* + * RCU torture writer kthread. Repeatedly substitutes a new structure + * for that pointed to by rcu_torture_current, freeing the old structure + * after a series of grace periods (the "pipeline"). + */ +static int +rcu_torture_writer(void *arg) +{ + bool boot_ended; + bool can_expedite = !rcu_gp_is_expedited() && !rcu_gp_is_normal(); + unsigned long cookie; + struct rcu_gp_oldstate cookie_full; + int expediting = 0; + unsigned long gp_snap; + unsigned long gp_snap1; + struct rcu_gp_oldstate gp_snap_full; + struct rcu_gp_oldstate gp_snap1_full; + int i; + int idx; + int oldnice = task_nice(current); + struct rcu_gp_oldstate rgo[NUM_ACTIVE_RCU_POLL_FULL_OLDSTATE]; + struct rcu_torture *rp; + struct rcu_torture *old_rp; + static DEFINE_TORTURE_RANDOM(rand); + bool stutter_waited; + unsigned long ulo[NUM_ACTIVE_RCU_POLL_OLDSTATE]; + + VERBOSE_TOROUT_STRING("rcu_torture_writer task started"); + if (!can_expedite) + pr_alert("%s" TORTURE_FLAG + " GP expediting controlled from boot/sysfs for %s.\n", + torture_type, cur_ops->name); if (WARN_ONCE(nsynctypes == 0, - "rcu_torture_writer: No update-side primitives.\n")) { + "%s: No update-side primitives.\n", __func__)) { /* * No updates primitives, so don't try updating. * The resulting test won't be testing much, hence the @@ -1083,11 +1385,12 @@ rcu_torture_writer(void *arg) */ rcu_torture_writer_state = RTWS_STOPPING; torture_kthread_stopping("rcu_torture_writer"); + return 0; } do { rcu_torture_writer_state = RTWS_FIXED_DELAY; - schedule_timeout_uninterruptible(1); + torture_hrtimeout_us(500, 1000, &rand); rp = rcu_torture_alloc(); if (rp == NULL) continue; @@ -1107,6 +1410,38 @@ rcu_torture_writer(void *arg) atomic_inc(&rcu_torture_wcount[i]); WRITE_ONCE(old_rp->rtort_pipe_count, old_rp->rtort_pipe_count + 1); + + // Make sure readers block polled grace periods. + if (cur_ops->get_gp_state && cur_ops->poll_gp_state) { + idx = cur_ops->readlock(); + cookie = cur_ops->get_gp_state(); + WARN_ONCE(cur_ops->poll_gp_state(cookie), + "%s: Cookie check 1 failed %s(%d) %lu->%lu\n", + __func__, + rcu_torture_writer_state_getname(), + rcu_torture_writer_state, + cookie, cur_ops->get_gp_state()); + if (cur_ops->get_gp_completed) { + cookie = cur_ops->get_gp_completed(); + WARN_ON_ONCE(!cur_ops->poll_gp_state(cookie)); + } + cur_ops->readunlock(idx); + } + if (cur_ops->get_gp_state_full && cur_ops->poll_gp_state_full) { + idx = cur_ops->readlock(); + cur_ops->get_gp_state_full(&cookie_full); + WARN_ONCE(cur_ops->poll_gp_state_full(&cookie_full), + "%s: Cookie check 5 failed %s(%d) online %*pbl\n", + __func__, + rcu_torture_writer_state_getname(), + rcu_torture_writer_state, + cpumask_pr_args(cpu_online_mask)); + if (cur_ops->get_gp_completed_full) { + cur_ops->get_gp_completed_full(&cookie_full); + WARN_ON_ONCE(!cur_ops->poll_gp_state_full(&cookie_full)); + } + cur_ops->readunlock(idx); + } switch (synctype[torture_random(&rand) % nsynctypes]) { case RTWS_DEF_FREE: rcu_torture_writer_state = RTWS_DEF_FREE; @@ -1114,23 +1449,103 @@ rcu_torture_writer(void *arg) break; case RTWS_EXP_SYNC: rcu_torture_writer_state = RTWS_EXP_SYNC; - cur_ops->exp_sync(); + do_rtws_sync(&rand, cur_ops->exp_sync); rcu_torture_pipe_update(old_rp); break; case RTWS_COND_GET: rcu_torture_writer_state = RTWS_COND_GET; - gp_snap = cur_ops->get_state(); - i = torture_random(&rand) % 16; - if (i != 0) - schedule_timeout_interruptible(i); - udelay(torture_random(&rand) % 1000); + gp_snap = cur_ops->get_gp_state(); + torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand); rcu_torture_writer_state = RTWS_COND_SYNC; cur_ops->cond_sync(gp_snap); rcu_torture_pipe_update(old_rp); break; + case RTWS_COND_GET_EXP: + rcu_torture_writer_state = RTWS_COND_GET_EXP; + gp_snap = cur_ops->get_gp_state_exp(); + torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand); + rcu_torture_writer_state = RTWS_COND_SYNC_EXP; + cur_ops->cond_sync_exp(gp_snap); + rcu_torture_pipe_update(old_rp); + break; + case RTWS_COND_GET_FULL: + rcu_torture_writer_state = RTWS_COND_GET_FULL; + cur_ops->get_gp_state_full(&gp_snap_full); + torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand); + rcu_torture_writer_state = RTWS_COND_SYNC_FULL; + cur_ops->cond_sync_full(&gp_snap_full); + rcu_torture_pipe_update(old_rp); + break; + case RTWS_COND_GET_EXP_FULL: + rcu_torture_writer_state = RTWS_COND_GET_EXP_FULL; + cur_ops->get_gp_state_full(&gp_snap_full); + torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand); + rcu_torture_writer_state = RTWS_COND_SYNC_EXP_FULL; + cur_ops->cond_sync_exp_full(&gp_snap_full); + rcu_torture_pipe_update(old_rp); + break; + case RTWS_POLL_GET: + rcu_torture_writer_state = RTWS_POLL_GET; + for (i = 0; i < ARRAY_SIZE(ulo); i++) + ulo[i] = cur_ops->get_comp_state(); + gp_snap = cur_ops->start_gp_poll(); + rcu_torture_writer_state = RTWS_POLL_WAIT; + while (!cur_ops->poll_gp_state(gp_snap)) { + gp_snap1 = cur_ops->get_gp_state(); + for (i = 0; i < ARRAY_SIZE(ulo); i++) + if (cur_ops->poll_gp_state(ulo[i]) || + cur_ops->same_gp_state(ulo[i], gp_snap1)) { + ulo[i] = gp_snap1; + break; + } + WARN_ON_ONCE(i >= ARRAY_SIZE(ulo)); + torture_hrtimeout_jiffies(torture_random(&rand) % 16, + &rand); + } + rcu_torture_pipe_update(old_rp); + break; + case RTWS_POLL_GET_FULL: + rcu_torture_writer_state = RTWS_POLL_GET_FULL; + for (i = 0; i < ARRAY_SIZE(rgo); i++) + cur_ops->get_comp_state_full(&rgo[i]); + cur_ops->start_gp_poll_full(&gp_snap_full); + rcu_torture_writer_state = RTWS_POLL_WAIT_FULL; + while (!cur_ops->poll_gp_state_full(&gp_snap_full)) { + cur_ops->get_gp_state_full(&gp_snap1_full); + for (i = 0; i < ARRAY_SIZE(rgo); i++) + if (cur_ops->poll_gp_state_full(&rgo[i]) || + cur_ops->same_gp_state_full(&rgo[i], + &gp_snap1_full)) { + rgo[i] = gp_snap1_full; + break; + } + WARN_ON_ONCE(i >= ARRAY_SIZE(rgo)); + torture_hrtimeout_jiffies(torture_random(&rand) % 16, + &rand); + } + rcu_torture_pipe_update(old_rp); + break; + case RTWS_POLL_GET_EXP: + rcu_torture_writer_state = RTWS_POLL_GET_EXP; + gp_snap = cur_ops->start_gp_poll_exp(); + rcu_torture_writer_state = RTWS_POLL_WAIT_EXP; + while (!cur_ops->poll_gp_state_exp(gp_snap)) + torture_hrtimeout_jiffies(torture_random(&rand) % 16, + &rand); + rcu_torture_pipe_update(old_rp); + break; + case RTWS_POLL_GET_EXP_FULL: + rcu_torture_writer_state = RTWS_POLL_GET_EXP_FULL; + cur_ops->start_gp_poll_exp_full(&gp_snap_full); + rcu_torture_writer_state = RTWS_POLL_WAIT_EXP_FULL; + while (!cur_ops->poll_gp_state_full(&gp_snap_full)) + torture_hrtimeout_jiffies(torture_random(&rand) % 16, + &rand); + rcu_torture_pipe_update(old_rp); + break; case RTWS_SYNC: rcu_torture_writer_state = RTWS_SYNC; - cur_ops->sync(); + do_rtws_sync(&rand, cur_ops->sync); rcu_torture_pipe_update(old_rp); break; default: @@ -1155,18 +1570,21 @@ rcu_torture_writer(void *arg) !rcu_gp_is_normal(); } rcu_torture_writer_state = RTWS_STUTTER; + boot_ended = rcu_inkernel_boot_has_ended(); stutter_waited = stutter_wait("rcu_torture_writer"); if (stutter_waited && - !READ_ONCE(rcu_fwd_cb_nodelay) && + !atomic_read(&rcu_fwd_cb_nodelay) && !cur_ops->slow_gps && !torture_must_stop() && - rcu_inkernel_boot_has_ended()) + boot_ended) for (i = 0; i < ARRAY_SIZE(rcu_tortures); i++) if (list_empty(&rcu_tortures[i].rtort_free) && rcu_access_pointer(rcu_torture_current) != &rcu_tortures[i]) { - rcu_ftrace_dump(DUMP_ALL); + tracing_off(); + show_rcu_gp_kthreads(); WARN(1, "%s: rtort_pipe_count: %d\n", __func__, rcu_tortures[i].rtort_pipe_count); + rcu_ftrace_dump(DUMP_ALL); } if (stutter_waited) sched_set_normal(current, oldnice); @@ -1194,26 +1612,91 @@ rcu_torture_writer(void *arg) static int rcu_torture_fakewriter(void *arg) { + unsigned long gp_snap; + struct rcu_gp_oldstate gp_snap_full; DEFINE_TORTURE_RANDOM(rand); VERBOSE_TOROUT_STRING("rcu_torture_fakewriter task started"); set_user_nice(current, MAX_NICE); + if (WARN_ONCE(nsynctypes == 0, + "%s: No update-side primitives.\n", __func__)) { + /* + * No updates primitives, so don't try updating. + * The resulting test won't be testing much, hence the + * above WARN_ONCE(). + */ + torture_kthread_stopping("rcu_torture_fakewriter"); + return 0; + } + do { - schedule_timeout_uninterruptible(1 + torture_random(&rand)%10); - udelay(torture_random(&rand) & 0x3ff); + torture_hrtimeout_jiffies(torture_random(&rand) % 10, &rand); if (cur_ops->cb_barrier != NULL && torture_random(&rand) % (nfakewriters * 8) == 0) { cur_ops->cb_barrier(); - } else if (gp_normal == gp_exp) { - if (cur_ops->sync && torture_random(&rand) & 0x80) - cur_ops->sync(); - else if (cur_ops->exp_sync) + } else { + switch (synctype[torture_random(&rand) % nsynctypes]) { + case RTWS_DEF_FREE: + break; + case RTWS_EXP_SYNC: cur_ops->exp_sync(); - } else if (gp_normal && cur_ops->sync) { - cur_ops->sync(); - } else if (cur_ops->exp_sync) { - cur_ops->exp_sync(); + break; + case RTWS_COND_GET: + gp_snap = cur_ops->get_gp_state(); + torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand); + cur_ops->cond_sync(gp_snap); + break; + case RTWS_COND_GET_EXP: + gp_snap = cur_ops->get_gp_state_exp(); + torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand); + cur_ops->cond_sync_exp(gp_snap); + break; + case RTWS_COND_GET_FULL: + cur_ops->get_gp_state_full(&gp_snap_full); + torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand); + cur_ops->cond_sync_full(&gp_snap_full); + break; + case RTWS_COND_GET_EXP_FULL: + cur_ops->get_gp_state_full(&gp_snap_full); + torture_hrtimeout_jiffies(torture_random(&rand) % 16, &rand); + cur_ops->cond_sync_exp_full(&gp_snap_full); + break; + case RTWS_POLL_GET: + gp_snap = cur_ops->start_gp_poll(); + while (!cur_ops->poll_gp_state(gp_snap)) { + torture_hrtimeout_jiffies(torture_random(&rand) % 16, + &rand); + } + break; + case RTWS_POLL_GET_FULL: + cur_ops->start_gp_poll_full(&gp_snap_full); + while (!cur_ops->poll_gp_state_full(&gp_snap_full)) { + torture_hrtimeout_jiffies(torture_random(&rand) % 16, + &rand); + } + break; + case RTWS_POLL_GET_EXP: + gp_snap = cur_ops->start_gp_poll_exp(); + while (!cur_ops->poll_gp_state_exp(gp_snap)) { + torture_hrtimeout_jiffies(torture_random(&rand) % 16, + &rand); + } + break; + case RTWS_POLL_GET_EXP_FULL: + cur_ops->start_gp_poll_exp_full(&gp_snap_full); + while (!cur_ops->poll_gp_state_full(&gp_snap_full)) { + torture_hrtimeout_jiffies(torture_random(&rand) % 16, + &rand); + } + break; + case RTWS_SYNC: + cur_ops->sync(); + break; + default: + WARN_ON_ONCE(1); + break; + } } stutter_wait("rcu_torture_fakewriter"); } while (!torture_must_stop()); @@ -1227,6 +1710,62 @@ static void rcu_torture_timer_cb(struct rcu_head *rhp) kfree(rhp); } +// Set up and carry out testing of RCU's global memory ordering +static void rcu_torture_reader_do_mbchk(long myid, struct rcu_torture *rtp, + struct torture_random_state *trsp) +{ + unsigned long loops; + int noc = torture_num_online_cpus(); + int rdrchked; + int rdrchker; + struct rcu_torture_reader_check *rtrcp; // Me. + struct rcu_torture_reader_check *rtrcp_assigner; // Assigned us to do checking. + struct rcu_torture_reader_check *rtrcp_chked; // Reader being checked. + struct rcu_torture_reader_check *rtrcp_chker; // Reader doing checking when not me. + + if (myid < 0) + return; // Don't try this from timer handlers. + + // Increment my counter. + rtrcp = &rcu_torture_reader_mbchk[myid]; + WRITE_ONCE(rtrcp->rtc_myloops, rtrcp->rtc_myloops + 1); + + // Attempt to assign someone else some checking work. + rdrchked = torture_random(trsp) % nrealreaders; + rtrcp_chked = &rcu_torture_reader_mbchk[rdrchked]; + rdrchker = torture_random(trsp) % nrealreaders; + rtrcp_chker = &rcu_torture_reader_mbchk[rdrchker]; + if (rdrchked != myid && rdrchked != rdrchker && noc >= rdrchked && noc >= rdrchker && + smp_load_acquire(&rtrcp->rtc_chkrdr) < 0 && // Pairs with smp_store_release below. + !READ_ONCE(rtp->rtort_chkp) && + !smp_load_acquire(&rtrcp_chker->rtc_assigner)) { // Pairs with smp_store_release below. + rtrcp->rtc_chkloops = READ_ONCE(rtrcp_chked->rtc_myloops); + WARN_ON_ONCE(rtrcp->rtc_chkrdr >= 0); + rtrcp->rtc_chkrdr = rdrchked; + WARN_ON_ONCE(rtrcp->rtc_ready); // This gets set after the grace period ends. + if (cmpxchg_relaxed(&rtrcp_chker->rtc_assigner, NULL, rtrcp) || + cmpxchg_relaxed(&rtp->rtort_chkp, NULL, rtrcp)) + (void)cmpxchg_relaxed(&rtrcp_chker->rtc_assigner, rtrcp, NULL); // Back out. + } + + // If assigned some completed work, do it! + rtrcp_assigner = READ_ONCE(rtrcp->rtc_assigner); + if (!rtrcp_assigner || !smp_load_acquire(&rtrcp_assigner->rtc_ready)) + return; // No work or work not yet ready. + rdrchked = rtrcp_assigner->rtc_chkrdr; + if (WARN_ON_ONCE(rdrchked < 0)) + return; + rtrcp_chked = &rcu_torture_reader_mbchk[rdrchked]; + loops = READ_ONCE(rtrcp_chked->rtc_myloops); + atomic_inc(&n_rcu_torture_mbchk_tries); + if (ULONG_CMP_LT(loops, rtrcp_assigner->rtc_chkloops)) + atomic_inc(&n_rcu_torture_mbchk_fail); + rtrcp_assigner->rtc_chkloops = loops + ULONG_MAX / 2; + rtrcp_assigner->rtc_ready = 0; + smp_store_release(&rtrcp->rtc_assigner, NULL); // Someone else can assign us work. + smp_store_release(&rtrcp_assigner->rtc_chkrdr, -1); // Assigner can again assign. +} + /* * Do one extension of an RCU read-side critical section using the * current reader state in readstate (set to zero for initial entry @@ -1241,46 +1780,64 @@ static void rcutorture_one_extend(int *readstate, int newstate, struct rt_read_seg *rtrsp) { unsigned long flags; - int idxnew = -1; - int idxold = *readstate; + int idxnew1 = -1; + int idxnew2 = -1; + int idxold1 = *readstate; + int idxold2 = idxold1; int statesnew = ~*readstate & newstate; int statesold = *readstate & ~newstate; - WARN_ON_ONCE(idxold < 0); - WARN_ON_ONCE((idxold >> RCUTORTURE_RDR_SHIFT) > 1); + WARN_ON_ONCE(idxold2 < 0); + WARN_ON_ONCE((idxold2 >> RCUTORTURE_RDR_SHIFT_2) > 1); rtrsp->rt_readstate = newstate; /* First, put new protection in place to avoid critical-section gap. */ if (statesnew & RCUTORTURE_RDR_BH) local_bh_disable(); + if (statesnew & RCUTORTURE_RDR_RBH) + rcu_read_lock_bh(); if (statesnew & RCUTORTURE_RDR_IRQ) local_irq_disable(); if (statesnew & RCUTORTURE_RDR_PREEMPT) preempt_disable(); - if (statesnew & RCUTORTURE_RDR_RBH) - rcu_read_lock_bh(); if (statesnew & RCUTORTURE_RDR_SCHED) rcu_read_lock_sched(); - if (statesnew & RCUTORTURE_RDR_RCU) - idxnew = cur_ops->readlock() << RCUTORTURE_RDR_SHIFT; + if (statesnew & RCUTORTURE_RDR_RCU_1) + idxnew1 = (cur_ops->readlock() & 0x1) << RCUTORTURE_RDR_SHIFT_1; + if (statesnew & RCUTORTURE_RDR_RCU_2) + idxnew2 = (cur_ops->readlock() & 0x1) << RCUTORTURE_RDR_SHIFT_2; - /* Next, remove old protection, irq first due to bh conflict. */ + /* + * Next, remove old protection, in decreasing order of strength + * to avoid unlock paths that aren't safe in the stronger + * context. Namely: BH can not be enabled with disabled interrupts. + * Additionally PREEMPT_RT requires that BH is enabled in preemptible + * context. + */ if (statesold & RCUTORTURE_RDR_IRQ) local_irq_enable(); - if (statesold & RCUTORTURE_RDR_BH) - local_bh_enable(); if (statesold & RCUTORTURE_RDR_PREEMPT) preempt_enable(); - if (statesold & RCUTORTURE_RDR_RBH) - rcu_read_unlock_bh(); if (statesold & RCUTORTURE_RDR_SCHED) rcu_read_unlock_sched(); - if (statesold & RCUTORTURE_RDR_RCU) { - bool lockit = !statesnew && !(torture_random(trsp) & 0xffff); + if (statesold & RCUTORTURE_RDR_BH) + local_bh_enable(); + if (statesold & RCUTORTURE_RDR_RBH) + rcu_read_unlock_bh(); + if (statesold & RCUTORTURE_RDR_RCU_2) { + cur_ops->readunlock((idxold2 >> RCUTORTURE_RDR_SHIFT_2) & 0x1); + WARN_ON_ONCE(idxnew2 != -1); + idxold2 = 0; + } + if (statesold & RCUTORTURE_RDR_RCU_1) { + bool lockit; + lockit = !cur_ops->no_pi_lock && !statesnew && !(torture_random(trsp) & 0xffff); if (lockit) raw_spin_lock_irqsave(¤t->pi_lock, flags); - cur_ops->readunlock(idxold >> RCUTORTURE_RDR_SHIFT); + cur_ops->readunlock((idxold1 >> RCUTORTURE_RDR_SHIFT_1) & 0x1); + WARN_ON_ONCE(idxnew1 != -1); + idxold1 = 0; if (lockit) raw_spin_unlock_irqrestore(¤t->pi_lock, flags); } @@ -1290,13 +1847,19 @@ static void rcutorture_one_extend(int *readstate, int newstate, cur_ops->read_delay(trsp, rtrsp); /* Update the reader state. */ - if (idxnew == -1) - idxnew = idxold & ~RCUTORTURE_RDR_MASK; - WARN_ON_ONCE(idxnew < 0); - WARN_ON_ONCE((idxnew >> RCUTORTURE_RDR_SHIFT) > 1); - *readstate = idxnew | newstate; - WARN_ON_ONCE((*readstate >> RCUTORTURE_RDR_SHIFT) < 0); - WARN_ON_ONCE((*readstate >> RCUTORTURE_RDR_SHIFT) > 1); + if (idxnew1 == -1) + idxnew1 = idxold1 & RCUTORTURE_RDR_MASK_1; + WARN_ON_ONCE(idxnew1 < 0); + if (WARN_ON_ONCE((idxnew1 >> RCUTORTURE_RDR_SHIFT_1) > 1)) + pr_info("Unexpected idxnew1 value of %#x\n", idxnew1); + if (idxnew2 == -1) + idxnew2 = idxold2 & RCUTORTURE_RDR_MASK_2; + WARN_ON_ONCE(idxnew2 < 0); + WARN_ON_ONCE((idxnew2 >> RCUTORTURE_RDR_SHIFT_2) > 1); + *readstate = idxnew1 | idxnew2 | newstate; + WARN_ON_ONCE(*readstate < 0); + if (WARN_ON_ONCE((*readstate >> RCUTORTURE_RDR_SHIFT_2) > 1)) + pr_info("Unexpected idxnew2 value of %#x\n", idxnew2); } /* Return the biggest extendables mask given current RCU and boot parameters. */ @@ -1306,7 +1869,7 @@ static int rcutorture_extend_mask_max(void) WARN_ON_ONCE(extendables & ~RCUTORTURE_MAX_EXTEND); mask = extendables & RCUTORTURE_MAX_EXTEND & cur_ops->extendables; - mask = mask | RCUTORTURE_RDR_RCU; + mask = mask | RCUTORTURE_RDR_RCU_1 | RCUTORTURE_RDR_RCU_2; return mask; } @@ -1315,21 +1878,47 @@ static int rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp) { int mask = rcutorture_extend_mask_max(); - unsigned long randmask1 = torture_random(trsp) >> 8; + unsigned long randmask1 = torture_random(trsp); unsigned long randmask2 = randmask1 >> 3; + unsigned long preempts = RCUTORTURE_RDR_PREEMPT | RCUTORTURE_RDR_SCHED; + unsigned long preempts_irq = preempts | RCUTORTURE_RDR_IRQ; + unsigned long bhs = RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH; - WARN_ON_ONCE(mask >> RCUTORTURE_RDR_SHIFT); + WARN_ON_ONCE(mask >> RCUTORTURE_RDR_SHIFT_1); /* Mostly only one bit (need preemption!), sometimes lots of bits. */ if (!(randmask1 & 0x7)) mask = mask & randmask2; else mask = mask & (1 << (randmask2 % RCUTORTURE_RDR_NBITS)); - /* Can't enable bh w/irq disabled. */ - if ((mask & RCUTORTURE_RDR_IRQ) && - ((!(mask & RCUTORTURE_RDR_BH) && (oldmask & RCUTORTURE_RDR_BH)) || - (!(mask & RCUTORTURE_RDR_RBH) && (oldmask & RCUTORTURE_RDR_RBH)))) - mask |= RCUTORTURE_RDR_BH | RCUTORTURE_RDR_RBH; - return mask ?: RCUTORTURE_RDR_RCU; + + // Can't have nested RCU reader without outer RCU reader. + if (!(mask & RCUTORTURE_RDR_RCU_1) && (mask & RCUTORTURE_RDR_RCU_2)) { + if (oldmask & RCUTORTURE_RDR_RCU_1) + mask &= ~RCUTORTURE_RDR_RCU_2; + else + mask |= RCUTORTURE_RDR_RCU_1; + } + + /* + * Can't enable bh w/irq disabled. + */ + if (mask & RCUTORTURE_RDR_IRQ) + mask |= oldmask & bhs; + + /* + * Ideally these sequences would be detected in debug builds + * (regardless of RT), but until then don't stop testing + * them on non-RT. + */ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { + /* Can't modify BH in atomic context */ + if (oldmask & preempts_irq) + mask &= ~bhs; + if ((oldmask | mask) & preempts_irq) + mask |= oldmask & bhs; + } + + return mask ?: RCUTORTURE_RDR_RCU_1; } /* @@ -1348,7 +1937,7 @@ rcutorture_loop_extend(int *readstate, struct torture_random_state *trsp, if (!((mask - 1) & mask)) return rtrsp; /* Current RCU reader not extendable. */ /* Bias towards larger numbers of loops. */ - i = (torture_random(trsp) >> 3); + i = torture_random(trsp); i = ((i | (i >> 3)) & RCUTORTURE_RDR_MAX_LOOPS) + 1; for (j = 0; j < i; j++) { mask = rcutorture_extend_mask(*readstate, trsp); @@ -1362,8 +1951,11 @@ rcutorture_loop_extend(int *readstate, struct torture_random_state *trsp, * no data to read. Can be invoked both from process context and * from a timer handler. */ -static bool rcu_torture_one_read(struct torture_random_state *trsp) +static bool rcu_torture_one_read(struct torture_random_state *trsp, long myid) { + bool checkpolling = !(torture_random(trsp) & 0xfff); + unsigned long cookie; + struct rcu_gp_oldstate cookie_full; int i; unsigned long started; unsigned long completed; @@ -1379,14 +1971,16 @@ static bool rcu_torture_one_read(struct torture_random_state *trsp) WARN_ON_ONCE(!rcu_is_watching()); newstate = rcutorture_extend_mask(readstate, trsp); rcutorture_one_extend(&readstate, newstate, trsp, rtrsp++); + if (checkpolling) { + if (cur_ops->get_gp_state && cur_ops->poll_gp_state) + cookie = cur_ops->get_gp_state(); + if (cur_ops->get_gp_state_full && cur_ops->poll_gp_state_full) + cur_ops->get_gp_state_full(&cookie_full); + } started = cur_ops->get_gp_seq(); ts = rcu_trace_clock_local(); p = rcu_dereference_check(rcu_torture_current, - rcu_read_lock_bh_held() || - rcu_read_lock_sched_held() || - srcu_read_lock_held(srcu_ctlp) || - rcu_read_lock_trace_held() || - torturing_tasks()); + !cur_ops->readlock_held || cur_ops->readlock_held()); if (p == NULL) { /* Wait for rcu_torture_writer to get underway */ rcutorture_one_extend(&readstate, 0, trsp, rtrsp); @@ -1394,6 +1988,7 @@ static bool rcu_torture_one_read(struct torture_random_state *trsp) } if (p->rtort_mbtest == 0) atomic_inc(&n_rcu_torture_mberror); + rcu_torture_reader_do_mbchk(myid, p, trsp); rtrsp = rcutorture_loop_extend(&readstate, trsp, rtrsp); preempt_disable(); pipe_count = READ_ONCE(p->rtort_pipe_count); @@ -1415,8 +2010,24 @@ static bool rcu_torture_one_read(struct torture_random_state *trsp) } __this_cpu_inc(rcu_torture_batch[completed]); preempt_enable(); + if (checkpolling) { + if (cur_ops->get_gp_state && cur_ops->poll_gp_state) + WARN_ONCE(cur_ops->poll_gp_state(cookie), + "%s: Cookie check 2 failed %s(%d) %lu->%lu\n", + __func__, + rcu_torture_writer_state_getname(), + rcu_torture_writer_state, + cookie, cur_ops->get_gp_state()); + if (cur_ops->get_gp_state_full && cur_ops->poll_gp_state_full) + WARN_ONCE(cur_ops->poll_gp_state_full(&cookie_full), + "%s: Cookie check 6 failed %s(%d) online %*pbl\n", + __func__, + rcu_torture_writer_state_getname(), + rcu_torture_writer_state, + cpumask_pr_args(cpu_online_mask)); + } rcutorture_one_extend(&readstate, 0, trsp, rtrsp); - WARN_ON_ONCE(readstate & RCUTORTURE_RDR_MASK); + WARN_ON_ONCE(readstate); // This next splat is expected behavior if leakpointer, especially // for CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels. WARN_ON_ONCE(leakpointer && READ_ONCE(p->rtort_pipe_count) > 1); @@ -1443,7 +2054,7 @@ static DEFINE_TORTURE_RANDOM_PERCPU(rcu_torture_timer_rand); static void rcu_torture_timer(struct timer_list *unused) { atomic_long_inc(&n_rcu_torture_timers); - (void)rcu_torture_one_read(this_cpu_ptr(&rcu_torture_timer_rand)); + (void)rcu_torture_one_read(this_cpu_ptr(&rcu_torture_timer_rand), -1); /* Test call_rcu() invocation from interrupt handler. */ if (cur_ops->call) { @@ -1479,13 +2090,13 @@ rcu_torture_reader(void *arg) if (!timer_pending(&t)) mod_timer(&t, jiffies + 1); } - if (!rcu_torture_one_read(&rand) && !torture_must_stop()) + if (!rcu_torture_one_read(&rand, myid) && !torture_must_stop()) schedule_timeout_interruptible(HZ); if (time_after(jiffies, lastsleep) && !torture_must_stop()) { - schedule_timeout_interruptible(1); + torture_hrtimeout_us(500, 1000, &rand); lastsleep = jiffies + 10; } - while (num_online_cpus() < mynumonline && !torture_must_stop()) + while (torture_num_online_cpus() < mynumonline && !torture_must_stop()) schedule_timeout_interruptible(HZ / 5); stutter_wait("rcu_torture_reader"); } while (!torture_must_stop()); @@ -1499,6 +2110,53 @@ rcu_torture_reader(void *arg) } /* + * Randomly Toggle CPUs' callback-offload state. This uses hrtimers to + * increase race probabilities and fuzzes the interval between toggling. + */ +static int rcu_nocb_toggle(void *arg) +{ + int cpu; + int maxcpu = -1; + int oldnice = task_nice(current); + long r; + DEFINE_TORTURE_RANDOM(rand); + ktime_t toggle_delay; + unsigned long toggle_fuzz; + ktime_t toggle_interval = ms_to_ktime(nocbs_toggle); + + VERBOSE_TOROUT_STRING("rcu_nocb_toggle task started"); + while (!rcu_inkernel_boot_has_ended()) + schedule_timeout_interruptible(HZ / 10); + for_each_possible_cpu(cpu) + maxcpu = cpu; + WARN_ON(maxcpu < 0); + if (toggle_interval > ULONG_MAX) + toggle_fuzz = ULONG_MAX >> 3; + else + toggle_fuzz = toggle_interval >> 3; + if (toggle_fuzz <= 0) + toggle_fuzz = NSEC_PER_USEC; + do { + r = torture_random(&rand); + cpu = (r >> 1) % (maxcpu + 1); + if (r & 0x1) { + rcu_nocb_cpu_offload(cpu); + atomic_long_inc(&n_nocb_offload); + } else { + rcu_nocb_cpu_deoffload(cpu); + atomic_long_inc(&n_nocb_deoffload); + } + toggle_delay = torture_random(&rand) % toggle_fuzz + toggle_interval; + set_current_state(TASK_INTERRUPTIBLE); + schedule_hrtimeout(&toggle_delay, HRTIMER_MODE_REL); + if (stutter_wait("rcu_nocb_toggle")) + sched_set_normal(current, oldnice); + } while (!torture_must_stop()); + torture_kthread_stopping("rcu_nocb_toggle"); + return 0; +} + +/* * Print torture statistics. Caller must ensure that there is only * one call to this function at a given time!!! This is normally * accomplished by relying on the module system to only have one copy @@ -1524,7 +2182,7 @@ rcu_torture_stats_print(void) batchsummary[i] += READ_ONCE(per_cpu(rcu_torture_batch, cpu)[i]); } } - for (i = RCU_TORTURE_PIPE_LEN - 1; i >= 0; i--) { + for (i = RCU_TORTURE_PIPE_LEN; i >= 0; i--) { if (pipesummary[i] != 0) break; } @@ -1539,11 +2197,11 @@ rcu_torture_stats_print(void) atomic_read(&n_rcu_torture_alloc), atomic_read(&n_rcu_torture_alloc_fail), atomic_read(&n_rcu_torture_free)); - pr_cont("rtmbe: %d rtbe: %ld rtbke: %ld rtbre: %ld ", + pr_cont("rtmbe: %d rtmbkf: %d/%d rtbe: %ld rtbke: %ld ", atomic_read(&n_rcu_torture_mberror), + atomic_read(&n_rcu_torture_mbchk_fail), atomic_read(&n_rcu_torture_mbchk_tries), n_rcu_torture_barrier_error, - n_rcu_torture_boost_ktrerror, - n_rcu_torture_boost_rterror); + n_rcu_torture_boost_ktrerror); pr_cont("rtbf: %ld rtb: %ld nt: %ld ", n_rcu_torture_boost_failure, n_rcu_torture_boosts, @@ -1553,20 +2211,22 @@ rcu_torture_stats_print(void) data_race(n_barrier_successes), data_race(n_barrier_attempts), data_race(n_rcu_torture_barrier_error)); - pr_cont("read-exits: %ld\n", data_race(n_read_exits)); + pr_cont("read-exits: %ld ", data_race(n_read_exits)); // Statistic. + pr_cont("nocb-toggles: %ld:%ld\n", + atomic_long_read(&n_nocb_offload), atomic_long_read(&n_nocb_deoffload)); pr_alert("%s%s ", torture_type, TORTURE_FLAG); if (atomic_read(&n_rcu_torture_mberror) || + atomic_read(&n_rcu_torture_mbchk_fail) || n_rcu_torture_barrier_error || n_rcu_torture_boost_ktrerror || - n_rcu_torture_boost_rterror || n_rcu_torture_boost_failure || - i > 1) { + n_rcu_torture_boost_failure || i > 1) { pr_cont("%s", "!!! "); atomic_inc(&n_rcu_torture_error); WARN_ON_ONCE(atomic_read(&n_rcu_torture_mberror)); + WARN_ON_ONCE(atomic_read(&n_rcu_torture_mbchk_fail)); WARN_ON_ONCE(n_rcu_torture_barrier_error); // rcu_barrier() WARN_ON_ONCE(n_rcu_torture_boost_ktrerror); // no boost kthread - WARN_ON_ONCE(n_rcu_torture_boost_rterror); // can't set RT prio - WARN_ON_ONCE(n_rcu_torture_boost_failure); // RCU boost failed + WARN_ON_ONCE(n_rcu_torture_boost_failure); // boost failed (TIMER_SOFTIRQ RT prio?) WARN_ON_ONCE(i > 1); // Too-short grace period } pr_cont("Reader Pipe: "); @@ -1600,10 +2260,10 @@ rcu_torture_stats_print(void) srcutorture_get_gp_data(cur_ops->ttype, srcu_ctlp, &flags, &gp_seq); wtp = READ_ONCE(writer_task); - pr_alert("??? Writer stall state %s(%d) g%lu f%#x ->state %#lx cpu %d\n", + pr_alert("??? Writer stall state %s(%d) g%lu f%#x ->state %#x cpu %d\n", rcu_torture_writer_state_getname(), rcu_torture_writer_state, gp_seq, flags, - wtp == NULL ? ~0UL : wtp->state, + wtp == NULL ? ~0U : wtp->__state, wtp == NULL ? -1 : (int)task_cpu(wtp)); if (!splatted && wtp) { sched_show_task(wtp); @@ -1633,6 +2293,56 @@ rcu_torture_stats(void *arg) return 0; } +/* Test mem_dump_obj() and friends. */ +static void rcu_torture_mem_dump_obj(void) +{ + struct rcu_head *rhp; + struct kmem_cache *kcp; + static int z; + + kcp = kmem_cache_create("rcuscale", 136, 8, SLAB_STORE_USER, NULL); + if (WARN_ON_ONCE(!kcp)) + return; + rhp = kmem_cache_alloc(kcp, GFP_KERNEL); + if (WARN_ON_ONCE(!rhp)) { + kmem_cache_destroy(kcp); + return; + } + pr_alert("mem_dump_obj() slab test: rcu_torture_stats = %px, &rhp = %px, rhp = %px, &z = %px\n", stats_task, &rhp, rhp, &z); + pr_alert("mem_dump_obj(ZERO_SIZE_PTR):"); + mem_dump_obj(ZERO_SIZE_PTR); + pr_alert("mem_dump_obj(NULL):"); + mem_dump_obj(NULL); + pr_alert("mem_dump_obj(%px):", &rhp); + mem_dump_obj(&rhp); + pr_alert("mem_dump_obj(%px):", rhp); + mem_dump_obj(rhp); + pr_alert("mem_dump_obj(%px):", &rhp->func); + mem_dump_obj(&rhp->func); + pr_alert("mem_dump_obj(%px):", &z); + mem_dump_obj(&z); + kmem_cache_free(kcp, rhp); + kmem_cache_destroy(kcp); + rhp = kmalloc(sizeof(*rhp), GFP_KERNEL); + if (WARN_ON_ONCE(!rhp)) + return; + pr_alert("mem_dump_obj() kmalloc test: rcu_torture_stats = %px, &rhp = %px, rhp = %px\n", stats_task, &rhp, rhp); + pr_alert("mem_dump_obj(kmalloc %px):", rhp); + mem_dump_obj(rhp); + pr_alert("mem_dump_obj(kmalloc %px):", &rhp->func); + mem_dump_obj(&rhp->func); + kfree(rhp); + rhp = vmalloc(4096); + if (WARN_ON_ONCE(!rhp)) + return; + pr_alert("mem_dump_obj() vmalloc test: rcu_torture_stats = %px, &rhp = %px, rhp = %px\n", stats_task, &rhp, rhp); + pr_alert("mem_dump_obj(vmalloc %px):", rhp); + mem_dump_obj(rhp); + pr_alert("mem_dump_obj(vmalloc %px):", &rhp->func); + mem_dump_obj(&rhp->func); + vfree(rhp); +} + static void rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag) { @@ -1647,7 +2357,9 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag) "stall_cpu_block=%d " "n_barrier_cbs=%d " "onoff_interval=%d onoff_holdoff=%d " - "read_exit_delay=%d read_exit_burst=%d\n", + "read_exit_delay=%d read_exit_burst=%d " + "nocbs_nthreads=%d nocbs_toggle=%d " + "test_nmis=%d\n", torture_type, tag, nrealreaders, nfakewriters, stat_interval, verbose, test_no_idle_hz, shuffle_interval, stutter, irqreader, fqs_duration, fqs_holdoff, fqs_stutter, @@ -1657,7 +2369,9 @@ rcu_torture_print_module_parms(struct rcu_torture_ops *cur_ops, const char *tag) stall_cpu_block, n_barrier_cbs, onoff_interval, onoff_holdoff, - read_exit_delay, read_exit_burst); + read_exit_delay, read_exit_burst, + nocbs_nthreads, nocbs_toggle, + test_nmis); } static int rcutorture_booster_cleanup(unsigned int cpu) @@ -1684,13 +2398,25 @@ static int rcutorture_booster_init(unsigned int cpu) if (boost_tasks[cpu] != NULL) return 0; /* Already created, nothing more to do. */ + // Testing RCU priority boosting requires rcutorture do + // some serious abuse. Counter this by running ksoftirqd + // at higher priority. + if (IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)) { + struct sched_param sp; + struct task_struct *t; + + t = per_cpu(ksoftirqd, cpu); + WARN_ON_ONCE(!t); + sp.sched_priority = 2; + sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); + } + /* Don't allow time recalculation while creating a new task. */ mutex_lock(&boost_mutex); rcu_torture_disable_rt_throttle(); VERBOSE_TOROUT_STRING("Creating rcu_torture_boost task"); - boost_tasks[cpu] = kthread_create_on_node(rcu_torture_boost, NULL, - cpu_to_node(cpu), - "rcu_torture_boost"); + boost_tasks[cpu] = kthread_run_on_cpu(rcu_torture_boost, NULL, + cpu, "rcu_torture_boost_%u"); if (IS_ERR(boost_tasks[cpu])) { retval = PTR_ERR(boost_tasks[cpu]); VERBOSE_TOROUT_STRING("rcu_torture_boost task create failed"); @@ -1699,12 +2425,20 @@ static int rcutorture_booster_init(unsigned int cpu) mutex_unlock(&boost_mutex); return retval; } - kthread_bind(boost_tasks[cpu], cpu); - wake_up_process(boost_tasks[cpu]); mutex_unlock(&boost_mutex); return 0; } +static int rcu_torture_stall_nf(struct notifier_block *nb, unsigned long v, void *ptr) +{ + pr_info("%s: v=%lu, duration=%lu.\n", __func__, v, (unsigned long)ptr); + return NOTIFY_OK; +} + +static struct notifier_block rcu_torture_stall_block = { + .notifier_call = rcu_torture_stall_nf, +}; + /* * CPU-stall kthread. It waits as specified by stall_cpu_holdoff, then * induces a CPU stall for the time specified by stall_cpu. @@ -1712,9 +2446,16 @@ static int rcutorture_booster_init(unsigned int cpu) static int rcu_torture_stall(void *args) { int idx; + int ret; unsigned long stop_at; VERBOSE_TOROUT_STRING("rcu_torture_stall task started"); + if (rcu_cpu_stall_notifiers) { + ret = rcu_stall_chain_notifier_register(&rcu_torture_stall_block); + if (ret) + pr_info("%s: rcu_stall_chain_notifier_register() returned %d, %sexpected.\n", + __func__, ret, !IS_ENABLED(CONFIG_RCU_STALL_COMMON) ? "un" : ""); + } if (stall_cpu_holdoff > 0) { VERBOSE_TOROUT_STRING("rcu_torture_stall begin holdoff"); schedule_timeout_interruptible(stall_cpu_holdoff * HZ); @@ -1738,19 +2479,31 @@ static int rcu_torture_stall(void *args) local_irq_disable(); else if (!stall_cpu_block) preempt_disable(); - pr_alert("rcu_torture_stall start on CPU %d.\n", - raw_smp_processor_id()); + pr_alert("%s start on CPU %d.\n", + __func__, raw_smp_processor_id()); while (ULONG_CMP_LT((unsigned long)ktime_get_seconds(), stop_at)) - if (stall_cpu_block) + if (stall_cpu_block) { +#ifdef CONFIG_PREEMPTION + preempt_schedule(); +#else schedule_timeout_uninterruptible(HZ); +#endif + } else if (stall_no_softlockup) { + touch_softlockup_watchdog(); + } if (stall_cpu_irqsoff) local_irq_enable(); else if (!stall_cpu_block) preempt_enable(); cur_ops->readunlock(idx); } - pr_alert("rcu_torture_stall end.\n"); + pr_alert("%s end.\n", __func__); + if (rcu_cpu_stall_notifiers && !ret) { + ret = rcu_stall_chain_notifier_unregister(&rcu_torture_stall_block); + if (ret) + pr_info("%s: rcu_stall_chain_notifier_unregister() returned %d.\n", __func__, ret); + } torture_shutdown_absorb("rcu_torture_stall"); while (!kthread_should_stop()) schedule_timeout_interruptible(10 * HZ); @@ -1814,10 +2567,13 @@ struct rcu_fwd { unsigned long rcu_fwd_startat; struct rcu_launder_hist n_launders_hist[N_LAUNDERS_HIST]; unsigned long rcu_launder_gp_seq_start; + int rcu_fwd_id; }; static DEFINE_MUTEX(rcu_fwd_mutex); static struct rcu_fwd *rcu_fwds; +static unsigned long rcu_fwd_seq; +static atomic_long_t rcu_fwd_max_cbs; static bool rcu_fwd_emergency_stop; static void rcu_torture_fwd_cb_hist(struct rcu_fwd *rfp) @@ -1830,8 +2586,8 @@ static void rcu_torture_fwd_cb_hist(struct rcu_fwd *rfp) for (i = ARRAY_SIZE(rfp->n_launders_hist) - 1; i > 0; i--) if (rfp->n_launders_hist[i].n_launders > 0) break; - pr_alert("%s: Callback-invocation histogram (duration %lu jiffies):", - __func__, jiffies - rfp->rcu_fwd_startat); + pr_alert("%s: Callback-invocation histogram %d (duration %lu jiffies):", + __func__, rfp->rcu_fwd_id, jiffies - rfp->rcu_fwd_startat); gps_old = rfp->rcu_launder_gp_seq_start; for (j = 0; j <= i; j++) { gps = rfp->n_launders_hist[j].launder_gp_seq; @@ -1929,6 +2685,7 @@ static void rcu_torture_fwd_prog_nr(struct rcu_fwd *rfp, unsigned long stopat; static DEFINE_TORTURE_RANDOM(trs); + pr_alert("%s: Starting forward-progress test %d\n", __func__, rfp->rcu_fwd_id); if (!cur_ops->sync) return; // Cannot do need_resched() forward progress testing without ->sync. if (cur_ops->call && cur_ops->cb_barrier) { @@ -1937,7 +2694,7 @@ static void rcu_torture_fwd_prog_nr(struct rcu_fwd *rfp, } /* Tight loop containing cond_resched(). */ - WRITE_ONCE(rcu_fwd_cb_nodelay, true); + atomic_inc(&rcu_fwd_cb_nodelay); cur_ops->sync(); /* Later readers see above write. */ if (selfpropcb) { WRITE_ONCE(fcs.stop, 0); @@ -1967,11 +2724,13 @@ static void rcu_torture_fwd_prog_nr(struct rcu_fwd *rfp, cver = READ_ONCE(rcu_torture_current_version) - cver; gps = rcutorture_seq_diff(cur_ops->get_gp_seq(), gps); WARN_ON(!cver && gps < 2); - pr_alert("%s: Duration %ld cver %ld gps %ld\n", __func__, dur, cver, gps); + pr_alert("%s: %d Duration %ld cver %ld gps %ld\n", __func__, + rfp->rcu_fwd_id, dur, cver, gps); } if (selfpropcb) { WRITE_ONCE(fcs.stop, 1); cur_ops->sync(); /* Wait for running CB to complete. */ + pr_alert("%s: Waiting for CBs: %pS() %d\n", __func__, cur_ops->cb_barrier, rfp->rcu_fwd_id); cur_ops->cb_barrier(); /* Wait for queued callbacks. */ } @@ -1980,7 +2739,7 @@ static void rcu_torture_fwd_prog_nr(struct rcu_fwd *rfp, destroy_rcu_head_on_stack(&fcs.rh); } schedule_timeout_uninterruptible(HZ / 10); /* Let kthreads recover. */ - WRITE_ONCE(rcu_fwd_cb_nodelay, false); + atomic_dec(&rcu_fwd_cb_nodelay); } /* Carry out call_rcu() forward-progress testing. */ @@ -2000,13 +2759,14 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp) unsigned long stopat; unsigned long stoppedat; + pr_alert("%s: Starting forward-progress test %d\n", __func__, rfp->rcu_fwd_id); if (READ_ONCE(rcu_fwd_emergency_stop)) return; /* Get out of the way quickly, no GP wait! */ if (!cur_ops->call) return; /* Can't do call_rcu() fwd prog without ->call. */ /* Loop continuously posting RCU callbacks. */ - WRITE_ONCE(rcu_fwd_cb_nodelay, true); + atomic_inc(&rcu_fwd_cb_nodelay); cur_ops->sync(); /* Later readers see above write. */ WRITE_ONCE(rfp->rcu_fwd_startat, jiffies); stopat = rfp->rcu_fwd_startat + MAX_FWD_CB_JIFFIES; @@ -2035,7 +2795,7 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp) rfp->rcu_fwd_cb_head = rfcpn; n_launders++; n_launders_sa++; - } else { + } else if (!cur_ops->cbflood_max || cur_ops->cbflood_max > n_max_cbs) { rfcp = kmalloc(sizeof(*rfcp), GFP_KERNEL); if (WARN_ON_ONCE(!rfcp)) { schedule_timeout_interruptible(1); @@ -2045,8 +2805,11 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp) n_launders_sa = 0; rfcp->rfc_gps = 0; rfcp->rfc_rfp = rfp; + } else { + rfcp = NULL; } - cur_ops->call(&rfcp->rh, rcu_torture_fwd_cb_cr); + if (rfcp) + cur_ops->call(&rfcp->rh, rcu_torture_fwd_cb_cr); rcu_torture_fwd_prog_cond_resched(n_launders + n_max_cbs); if (tick_nohz_full_enabled()) { local_irq_save(flags); @@ -2058,6 +2821,7 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp) n_launders_cb_snap = READ_ONCE(rfp->n_launders_cb); cver = READ_ONCE(rcu_torture_current_version) - cver; gps = rcutorture_seq_diff(cur_ops->get_gp_seq(), gps); + pr_alert("%s: Waiting for CBs: %pS() %d\n", __func__, cur_ops->cb_barrier, rfp->rcu_fwd_id); cur_ops->cb_barrier(); /* Wait for callbacks to be invoked. */ (void)rcu_torture_fwd_prog_cbfree(rfp); @@ -2070,11 +2834,14 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp) n_launders + n_max_cbs - n_launders_cb_snap, n_launders, n_launders_sa, n_max_gps, n_max_cbs, cver, gps); + atomic_long_add(n_max_cbs, &rcu_fwd_max_cbs); + mutex_lock(&rcu_fwd_mutex); // Serialize histograms. rcu_torture_fwd_cb_hist(rfp); + mutex_unlock(&rcu_fwd_mutex); } schedule_timeout_uninterruptible(HZ); /* Let CBs drain. */ tick_dep_clear_task(current, TICK_DEP_BIT_RCU); - WRITE_ONCE(rcu_fwd_cb_nodelay, false); + atomic_dec(&rcu_fwd_cb_nodelay); } @@ -2085,6 +2852,8 @@ static void rcu_torture_fwd_prog_cr(struct rcu_fwd *rfp) static int rcutorture_oom_notify(struct notifier_block *self, unsigned long notused, void *nfreed) { + int i; + long ncbs; struct rcu_fwd *rfp; mutex_lock(&rcu_fwd_mutex); @@ -2095,18 +2864,26 @@ static int rcutorture_oom_notify(struct notifier_block *self, } WARN(1, "%s invoked upon OOM during forward-progress testing.\n", __func__); - rcu_torture_fwd_cb_hist(rfp); - rcu_fwd_progress_check(1 + (jiffies - READ_ONCE(rfp->rcu_fwd_startat)) / 2); + for (i = 0; i < fwd_progress; i++) { + rcu_torture_fwd_cb_hist(&rfp[i]); + rcu_fwd_progress_check(1 + (jiffies - READ_ONCE(rfp[i].rcu_fwd_startat)) / 2); + } WRITE_ONCE(rcu_fwd_emergency_stop, true); smp_mb(); /* Emergency stop before free and wait to avoid hangs. */ - pr_info("%s: Freed %lu RCU callbacks.\n", - __func__, rcu_torture_fwd_prog_cbfree(rfp)); - rcu_barrier(); - pr_info("%s: Freed %lu RCU callbacks.\n", - __func__, rcu_torture_fwd_prog_cbfree(rfp)); - rcu_barrier(); - pr_info("%s: Freed %lu RCU callbacks.\n", - __func__, rcu_torture_fwd_prog_cbfree(rfp)); + ncbs = 0; + for (i = 0; i < fwd_progress; i++) + ncbs += rcu_torture_fwd_prog_cbfree(&rfp[i]); + pr_info("%s: Freed %lu RCU callbacks.\n", __func__, ncbs); + cur_ops->cb_barrier(); + ncbs = 0; + for (i = 0; i < fwd_progress; i++) + ncbs += rcu_torture_fwd_prog_cbfree(&rfp[i]); + pr_info("%s: Freed %lu RCU callbacks.\n", __func__, ncbs); + cur_ops->cb_barrier(); + ncbs = 0; + for (i = 0; i < fwd_progress; i++) + ncbs += rcu_torture_fwd_prog_cbfree(&rfp[i]); + pr_info("%s: Freed %lu RCU callbacks.\n", __func__, ncbs); smp_mb(); /* Frees before return to avoid redoing OOM. */ (*(unsigned long *)nfreed)++; /* Forward progress CBs freed! */ pr_info("%s returning after OOM processing.\n", __func__); @@ -2121,7 +2898,10 @@ static struct notifier_block rcutorture_oom_nb = { /* Carry out grace-period forward-progress testing. */ static int rcu_torture_fwd_prog(void *args) { + bool firsttime = true; + long max_cbs; int oldnice = task_nice(current); + unsigned long oldseq = READ_ONCE(rcu_fwd_seq); struct rcu_fwd *rfp = args; int tested = 0; int tested_tries = 0; @@ -2131,21 +2911,38 @@ static int rcu_torture_fwd_prog(void *args) if (!IS_ENABLED(CONFIG_SMP) || !IS_ENABLED(CONFIG_RCU_BOOST)) set_user_nice(current, MAX_NICE); do { - schedule_timeout_interruptible(fwd_progress_holdoff * HZ); - WRITE_ONCE(rcu_fwd_emergency_stop, false); - if (!IS_ENABLED(CONFIG_TINY_RCU) || - rcu_inkernel_boot_has_ended()) - rcu_torture_fwd_prog_nr(rfp, &tested, &tested_tries); - if (rcu_inkernel_boot_has_ended()) + if (!rfp->rcu_fwd_id) { + schedule_timeout_interruptible(fwd_progress_holdoff * HZ); + WRITE_ONCE(rcu_fwd_emergency_stop, false); + if (!firsttime) { + max_cbs = atomic_long_xchg(&rcu_fwd_max_cbs, 0); + pr_alert("%s n_max_cbs: %ld\n", __func__, max_cbs); + } + firsttime = false; + WRITE_ONCE(rcu_fwd_seq, rcu_fwd_seq + 1); + } else { + while (READ_ONCE(rcu_fwd_seq) == oldseq && !torture_must_stop()) + schedule_timeout_interruptible(HZ / 20); + oldseq = READ_ONCE(rcu_fwd_seq); + } + pr_alert("%s: Starting forward-progress test %d\n", __func__, rfp->rcu_fwd_id); + if (rcu_inkernel_boot_has_ended() && torture_num_online_cpus() > rfp->rcu_fwd_id) rcu_torture_fwd_prog_cr(rfp); + if ((cur_ops->stall_dur && cur_ops->stall_dur() > 0) && + (!IS_ENABLED(CONFIG_TINY_RCU) || + (rcu_inkernel_boot_has_ended() && + torture_num_online_cpus() > rfp->rcu_fwd_id))) + rcu_torture_fwd_prog_nr(rfp, &tested, &tested_tries); /* Avoid slow periods, better to test when busy. */ if (stutter_wait("rcu_torture_fwd_prog")) sched_set_normal(current, oldnice); } while (!torture_must_stop()); /* Short runs might not contain a valid forward-progress attempt. */ - WARN_ON(!tested && tested_tries >= 5); - pr_alert("%s: tested %d tested_tries %d\n", __func__, tested, tested_tries); + if (!rfp->rcu_fwd_id) { + WARN_ON(!tested && tested_tries >= 5); + pr_alert("%s: tested %d tested_tries %d\n", __func__, tested, tested_tries); + } torture_kthread_stopping("rcu_torture_fwd_prog"); return 0; } @@ -2153,18 +2950,29 @@ static int rcu_torture_fwd_prog(void *args) /* If forward-progress checking is requested and feasible, spawn the thread. */ static int __init rcu_torture_fwd_prog_init(void) { + int i; + int ret = 0; struct rcu_fwd *rfp; if (!fwd_progress) return 0; /* Not requested, so don't do it. */ + if (fwd_progress >= nr_cpu_ids) { + VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Limiting fwd_progress to # CPUs.\n"); + fwd_progress = nr_cpu_ids; + } else if (fwd_progress < 0) { + fwd_progress = nr_cpu_ids; + } if ((!cur_ops->sync && !cur_ops->call) || - !cur_ops->stall_dur || cur_ops->stall_dur() <= 0 || cur_ops == &rcu_busted_ops) { + (!cur_ops->cbflood_max && (!cur_ops->stall_dur || cur_ops->stall_dur() <= 0)) || + cur_ops == &rcu_busted_ops) { VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, unsupported by RCU flavor under test"); + fwd_progress = 0; return 0; } if (stall_cpu > 0) { VERBOSE_TOROUT_STRING("rcu_torture_fwd_prog_init: Disabled, conflicts with CPU-stall testing"); - if (IS_MODULE(CONFIG_RCU_TORTURE_TESTS)) + fwd_progress = 0; + if (IS_MODULE(CONFIG_RCU_TORTURE_TEST)) return -EINVAL; /* In module, can fail back to user. */ WARN_ON(1); /* Make sure rcutorture notices conflict. */ return 0; @@ -2173,29 +2981,51 @@ static int __init rcu_torture_fwd_prog_init(void) fwd_progress_holdoff = 1; if (fwd_progress_div <= 0) fwd_progress_div = 4; - rfp = kzalloc(sizeof(*rfp), GFP_KERNEL); - if (!rfp) + rfp = kcalloc(fwd_progress, sizeof(*rfp), GFP_KERNEL); + fwd_prog_tasks = kcalloc(fwd_progress, sizeof(*fwd_prog_tasks), GFP_KERNEL); + if (!rfp || !fwd_prog_tasks) { + kfree(rfp); + kfree(fwd_prog_tasks); + fwd_prog_tasks = NULL; + fwd_progress = 0; return -ENOMEM; - spin_lock_init(&rfp->rcu_fwd_lock); - rfp->rcu_fwd_cb_tail = &rfp->rcu_fwd_cb_head; + } + for (i = 0; i < fwd_progress; i++) { + spin_lock_init(&rfp[i].rcu_fwd_lock); + rfp[i].rcu_fwd_cb_tail = &rfp[i].rcu_fwd_cb_head; + rfp[i].rcu_fwd_id = i; + } mutex_lock(&rcu_fwd_mutex); rcu_fwds = rfp; mutex_unlock(&rcu_fwd_mutex); register_oom_notifier(&rcutorture_oom_nb); - return torture_create_kthread(rcu_torture_fwd_prog, rfp, fwd_prog_task); + for (i = 0; i < fwd_progress; i++) { + ret = torture_create_kthread(rcu_torture_fwd_prog, &rcu_fwds[i], fwd_prog_tasks[i]); + if (ret) { + fwd_progress = i; + return ret; + } + } + return 0; } static void rcu_torture_fwd_prog_cleanup(void) { + int i; struct rcu_fwd *rfp; - torture_stop_kthread(rcu_torture_fwd_prog, fwd_prog_task); - rfp = rcu_fwds; + if (!rcu_fwds || !fwd_prog_tasks) + return; + for (i = 0; i < fwd_progress; i++) + torture_stop_kthread(rcu_torture_fwd_prog, fwd_prog_tasks[i]); + unregister_oom_notifier(&rcutorture_oom_nb); mutex_lock(&rcu_fwd_mutex); + rfp = rcu_fwds; rcu_fwds = NULL; mutex_unlock(&rcu_fwd_mutex); - unregister_oom_notifier(&rcutorture_oom_nb); kfree(rfp); + kfree(fwd_prog_tasks); + fwd_prog_tasks = NULL; } /* Callback function for RCU barrier testing. */ @@ -2362,13 +3192,15 @@ static bool rcu_torture_can_boost(void) if (!(test_boost == 1 && cur_ops->can_boost) && test_boost != 2) return false; + if (!cur_ops->start_gp_poll || !cur_ops->poll_gp_state) + return false; prio = rcu_get_gp_kthreads_prio(); if (!prio) return false; if (prio < 2) { - if (boost_warn_once == 1) + if (boost_warn_once == 1) return false; pr_alert("%s: WARN: RCU kthread priority too low to test boosting. Skipping RCU boost test. Try passing rcutree.kthread_prio > 1 on the kernel command line.\n", KBUILD_MODNAME); @@ -2391,15 +3223,14 @@ static int rcu_torture_read_exit_child(void *trsp_in) set_user_nice(current, MAX_NICE); // Minimize time between reading and exiting. while (!kthread_should_stop()) - schedule_timeout_uninterruptible(1); - (void)rcu_torture_one_read(trsp); + schedule_timeout_uninterruptible(HZ / 20); + (void)rcu_torture_one_read(trsp, -1); return 0; } // Parent kthread which creates and destroys read-exit child kthreads. static int rcu_torture_read_exit(void *unused) { - int count = 0; bool errexit = false; int i; struct task_struct *tsp; @@ -2411,34 +3242,28 @@ static int rcu_torture_read_exit(void *unused) // Each pass through this loop does one read-exit episode. do { - if (++count > read_exit_burst) { - VERBOSE_TOROUT_STRING("rcu_torture_read_exit: End of episode"); - rcu_barrier(); // Wait for task_struct free, avoid OOM. - for (i = 0; i < read_exit_delay; i++) { - schedule_timeout_uninterruptible(HZ); - if (READ_ONCE(read_exit_child_stop)) - break; + VERBOSE_TOROUT_STRING("rcu_torture_read_exit: Start of episode"); + for (i = 0; i < read_exit_burst; i++) { + if (READ_ONCE(read_exit_child_stop)) + break; + stutter_wait("rcu_torture_read_exit"); + // Spawn child. + tsp = kthread_run(rcu_torture_read_exit_child, + &trs, "%s", "rcu_torture_read_exit_child"); + if (IS_ERR(tsp)) { + TOROUT_ERRSTRING("out of memory"); + errexit = true; + break; } - if (!READ_ONCE(read_exit_child_stop)) - VERBOSE_TOROUT_STRING("rcu_torture_read_exit: Start of episode"); - count = 0; - } - if (READ_ONCE(read_exit_child_stop)) - break; - // Spawn child. - tsp = kthread_run(rcu_torture_read_exit_child, - &trs, "%s", - "rcu_torture_read_exit_child"); - if (IS_ERR(tsp)) { - VERBOSE_TOROUT_ERRSTRING("out of memory"); - errexit = true; - tsp = NULL; - break; + cond_resched(); + kthread_stop(tsp); + n_read_exits++; } - cond_resched(); - kthread_stop(tsp); - n_read_exits ++; - stutter_wait("rcu_torture_read_exit"); + VERBOSE_TOROUT_STRING("rcu_torture_read_exit: End of episode"); + rcu_barrier(); // Wait for task_struct free, avoid OOM. + i = 0; + for (; !errexit && !READ_ONCE(read_exit_child_stop) && i < read_exit_delay; i++) + schedule_timeout_uninterruptible(HZ); } while (!errexit && !READ_ONCE(read_exit_child_stop)); // Clean up and exit. @@ -2446,7 +3271,7 @@ static int rcu_torture_read_exit(void *unused) smp_mb(); // Store before wakeup. wake_up(&read_exit_wq); while (!torture_must_stop()) - schedule_timeout_uninterruptible(1); + schedule_timeout_uninterruptible(HZ / 20); torture_kthread_stopping("rcu_torture_read_exit"); return 0; } @@ -2454,7 +3279,7 @@ static int rcu_torture_read_exit(void *unused) static int rcu_torture_read_exit_init(void) { if (read_exit_burst <= 0) - return -EINVAL; + return 0; init_waitqueue_head(&read_exit_wq); read_exit_child_stop = false; read_exit_child_stopped = false; @@ -2472,6 +3297,29 @@ static void rcu_torture_read_exit_cleanup(void) torture_stop_kthread(rcutorture_read_exit, read_exit_task); } +static void rcutorture_test_nmis(int n) +{ +#if IS_BUILTIN(CONFIG_RCU_TORTURE_TEST) + int cpu; + int dumpcpu; + int i; + + for (i = 0; i < n; i++) { + preempt_disable(); + cpu = smp_processor_id(); + dumpcpu = cpu + 1; + if (dumpcpu >= nr_cpu_ids) + dumpcpu = 0; + pr_alert("%s: CPU %d invoking dump_cpu_task(%d)\n", __func__, cpu, dumpcpu); + dump_cpu_task(dumpcpu); + preempt_enable(); + schedule_timeout_uninterruptible(15 * HZ); + } +#else // #if IS_BUILTIN(CONFIG_RCU_TORTURE_TEST) + WARN_ONCE(n, "Non-zero rcutorture.test_nmis=%d permitted only when rcutorture is built in.\n", test_nmis); +#endif // #else // #if IS_BUILTIN(CONFIG_RCU_TORTURE_TEST) +} + static enum cpuhp_state rcutor_hp; static void @@ -2483,15 +3331,21 @@ rcu_torture_cleanup(void) int i; if (torture_cleanup_begin()) { - if (cur_ops->cb_barrier != NULL) + if (cur_ops->cb_barrier != NULL) { + pr_info("%s: Invoking %pS().\n", __func__, cur_ops->cb_barrier); cur_ops->cb_barrier(); + } + rcu_gp_slow_unregister(NULL); return; } if (!cur_ops) { torture_cleanup_end(); + rcu_gp_slow_unregister(NULL); return; } + rcutorture_test_nmis(test_nmis); + if (cur_ops->gp_kthread_dbg) cur_ops->gp_kthread_dbg(); rcu_torture_read_exit_cleanup(); @@ -2500,6 +3354,13 @@ rcu_torture_cleanup(void) torture_stop_kthread(rcu_torture_stall, stall_task); torture_stop_kthread(rcu_torture_writer, writer_task); + if (nocb_tasks) { + for (i = 0; i < nrealnocbers; i++) + torture_stop_kthread(rcu_nocb_toggle, nocb_tasks[i]); + kfree(nocb_tasks); + nocb_tasks = NULL; + } + if (reader_tasks) { for (i = 0; i < nrealreaders; i++) torture_stop_kthread(rcu_torture_reader, @@ -2507,6 +3368,8 @@ rcu_torture_cleanup(void) kfree(reader_tasks); reader_tasks = NULL; } + kfree(rcu_torture_reader_mbchk); + rcu_torture_reader_mbchk = NULL; if (fakewriter_tasks) { for (i = 0; i < nfakewriters; i++) @@ -2523,18 +3386,22 @@ rcu_torture_cleanup(void) rcutorture_seq_diff(gp_seq, start_gp_seq)); torture_stop_kthread(rcu_torture_stats, stats_task); torture_stop_kthread(rcu_torture_fqs, fqs_task); - if (rcu_torture_can_boost()) + if (rcu_torture_can_boost() && rcutor_hp >= 0) cpuhp_remove_state(rcutor_hp); /* * Wait for all RCU callbacks to fire, then do torture-type-specific * cleanup operations. */ - if (cur_ops->cb_barrier != NULL) + if (cur_ops->cb_barrier != NULL) { + pr_info("%s: Invoking %pS().\n", __func__, cur_ops->cb_barrier); cur_ops->cb_barrier(); + } if (cur_ops->cleanup != NULL) cur_ops->cleanup(); + rcu_torture_mem_dump_obj(); + rcu_torture_stats_print(); /* -After- the stats thread is stopped! */ if (err_segs_recorded) { @@ -2572,6 +3439,7 @@ rcu_torture_cleanup(void) else rcu_torture_print_module_parms(cur_ops, "End of test: SUCCESS"); torture_cleanup_end(); + rcu_gp_slow_unregister(&rcu_fwd_cb_nodelay); } #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD @@ -2604,6 +3472,7 @@ static void rcu_test_debug_objects(void) #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD struct rcu_head rh1; struct rcu_head rh2; + struct rcu_head *rhp = kmalloc(sizeof(*rhp), GFP_KERNEL); init_rcu_head_on_stack(&rh1); init_rcu_head_on_stack(&rh2); @@ -2612,10 +3481,14 @@ static void rcu_test_debug_objects(void) /* Try to queue the rh2 pair of callbacks for the same grace period. */ preempt_disable(); /* Prevent preemption from interrupting test. */ rcu_read_lock(); /* Make it impossible to finish a grace period. */ - call_rcu(&rh1, rcu_torture_leak_cb); /* Start grace period. */ + call_rcu_hurry(&rh1, rcu_torture_leak_cb); /* Start grace period. */ local_irq_disable(); /* Make it harder to start a new grace period. */ - call_rcu(&rh2, rcu_torture_leak_cb); - call_rcu(&rh2, rcu_torture_err_cb); /* Duplicate callback. */ + call_rcu_hurry(&rh2, rcu_torture_leak_cb); + call_rcu_hurry(&rh2, rcu_torture_err_cb); /* Duplicate callback. */ + if (rhp) { + call_rcu_hurry(rhp, rcu_torture_leak_cb); + call_rcu_hurry(rhp, rcu_torture_err_cb); /* Another duplicate callback. */ + } local_irq_enable(); rcu_read_unlock(); preempt_enable(); @@ -2625,6 +3498,7 @@ static void rcu_test_debug_objects(void) pr_alert("%s: WARN: Duplicate call_rcu() test complete.\n", KBUILD_MODNAME); destroy_rcu_head_on_stack(&rh1); destroy_rcu_head_on_stack(&rh2); + kfree(rhp); #else /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ pr_alert("%s: !CONFIG_DEBUG_OBJECTS_RCU_HEAD, not testing duplicate call_rcu()\n", KBUILD_MODNAME); #endif /* #else #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */ @@ -2638,6 +3512,188 @@ static void rcutorture_sync(void) cur_ops->sync(); } +static DEFINE_MUTEX(mut0); +static DEFINE_MUTEX(mut1); +static DEFINE_MUTEX(mut2); +static DEFINE_MUTEX(mut3); +static DEFINE_MUTEX(mut4); +static DEFINE_MUTEX(mut5); +static DEFINE_MUTEX(mut6); +static DEFINE_MUTEX(mut7); +static DEFINE_MUTEX(mut8); +static DEFINE_MUTEX(mut9); + +static DECLARE_RWSEM(rwsem0); +static DECLARE_RWSEM(rwsem1); +static DECLARE_RWSEM(rwsem2); +static DECLARE_RWSEM(rwsem3); +static DECLARE_RWSEM(rwsem4); +static DECLARE_RWSEM(rwsem5); +static DECLARE_RWSEM(rwsem6); +static DECLARE_RWSEM(rwsem7); +static DECLARE_RWSEM(rwsem8); +static DECLARE_RWSEM(rwsem9); + +DEFINE_STATIC_SRCU(srcu0); +DEFINE_STATIC_SRCU(srcu1); +DEFINE_STATIC_SRCU(srcu2); +DEFINE_STATIC_SRCU(srcu3); +DEFINE_STATIC_SRCU(srcu4); +DEFINE_STATIC_SRCU(srcu5); +DEFINE_STATIC_SRCU(srcu6); +DEFINE_STATIC_SRCU(srcu7); +DEFINE_STATIC_SRCU(srcu8); +DEFINE_STATIC_SRCU(srcu9); + +static int srcu_lockdep_next(const char *f, const char *fl, const char *fs, const char *fu, int i, + int cyclelen, int deadlock) +{ + int j = i + 1; + + if (j >= cyclelen) + j = deadlock ? 0 : -1; + if (j >= 0) + pr_info("%s: %s(%d), %s(%d), %s(%d)\n", f, fl, i, fs, j, fu, i); + else + pr_info("%s: %s(%d), %s(%d)\n", f, fl, i, fu, i); + return j; +} + +// Test lockdep on SRCU-based deadlock scenarios. +static void rcu_torture_init_srcu_lockdep(void) +{ + int cyclelen; + int deadlock; + bool err = false; + int i; + int j; + int idx; + struct mutex *muts[] = { &mut0, &mut1, &mut2, &mut3, &mut4, + &mut5, &mut6, &mut7, &mut8, &mut9 }; + struct rw_semaphore *rwsems[] = { &rwsem0, &rwsem1, &rwsem2, &rwsem3, &rwsem4, + &rwsem5, &rwsem6, &rwsem7, &rwsem8, &rwsem9 }; + struct srcu_struct *srcus[] = { &srcu0, &srcu1, &srcu2, &srcu3, &srcu4, + &srcu5, &srcu6, &srcu7, &srcu8, &srcu9 }; + int testtype; + + if (!test_srcu_lockdep) + return; + + deadlock = test_srcu_lockdep / 1000; + testtype = (test_srcu_lockdep / 10) % 100; + cyclelen = test_srcu_lockdep % 10; + WARN_ON_ONCE(ARRAY_SIZE(muts) != ARRAY_SIZE(srcus)); + if (WARN_ONCE(deadlock != !!deadlock, + "%s: test_srcu_lockdep=%d and deadlock digit %d must be zero or one.\n", + __func__, test_srcu_lockdep, deadlock)) + err = true; + if (WARN_ONCE(cyclelen <= 0, + "%s: test_srcu_lockdep=%d and cycle-length digit %d must be greater than zero.\n", + __func__, test_srcu_lockdep, cyclelen)) + err = true; + if (err) + goto err_out; + + if (testtype == 0) { + pr_info("%s: test_srcu_lockdep = %05d: SRCU %d-way %sdeadlock.\n", + __func__, test_srcu_lockdep, cyclelen, deadlock ? "" : "non-"); + if (deadlock && cyclelen == 1) + pr_info("%s: Expect hang.\n", __func__); + for (i = 0; i < cyclelen; i++) { + j = srcu_lockdep_next(__func__, "srcu_read_lock", "synchronize_srcu", + "srcu_read_unlock", i, cyclelen, deadlock); + idx = srcu_read_lock(srcus[i]); + if (j >= 0) + synchronize_srcu(srcus[j]); + srcu_read_unlock(srcus[i], idx); + } + return; + } + + if (testtype == 1) { + pr_info("%s: test_srcu_lockdep = %05d: SRCU/mutex %d-way %sdeadlock.\n", + __func__, test_srcu_lockdep, cyclelen, deadlock ? "" : "non-"); + for (i = 0; i < cyclelen; i++) { + pr_info("%s: srcu_read_lock(%d), mutex_lock(%d), mutex_unlock(%d), srcu_read_unlock(%d)\n", + __func__, i, i, i, i); + idx = srcu_read_lock(srcus[i]); + mutex_lock(muts[i]); + mutex_unlock(muts[i]); + srcu_read_unlock(srcus[i], idx); + + j = srcu_lockdep_next(__func__, "mutex_lock", "synchronize_srcu", + "mutex_unlock", i, cyclelen, deadlock); + mutex_lock(muts[i]); + if (j >= 0) + synchronize_srcu(srcus[j]); + mutex_unlock(muts[i]); + } + return; + } + + if (testtype == 2) { + pr_info("%s: test_srcu_lockdep = %05d: SRCU/rwsem %d-way %sdeadlock.\n", + __func__, test_srcu_lockdep, cyclelen, deadlock ? "" : "non-"); + for (i = 0; i < cyclelen; i++) { + pr_info("%s: srcu_read_lock(%d), down_read(%d), up_read(%d), srcu_read_unlock(%d)\n", + __func__, i, i, i, i); + idx = srcu_read_lock(srcus[i]); + down_read(rwsems[i]); + up_read(rwsems[i]); + srcu_read_unlock(srcus[i], idx); + + j = srcu_lockdep_next(__func__, "down_write", "synchronize_srcu", + "up_write", i, cyclelen, deadlock); + down_write(rwsems[i]); + if (j >= 0) + synchronize_srcu(srcus[j]); + up_write(rwsems[i]); + } + return; + } + +#ifdef CONFIG_TASKS_TRACE_RCU + if (testtype == 3) { + pr_info("%s: test_srcu_lockdep = %05d: SRCU and Tasks Trace RCU %d-way %sdeadlock.\n", + __func__, test_srcu_lockdep, cyclelen, deadlock ? "" : "non-"); + if (deadlock && cyclelen == 1) + pr_info("%s: Expect hang.\n", __func__); + for (i = 0; i < cyclelen; i++) { + char *fl = i == 0 ? "rcu_read_lock_trace" : "srcu_read_lock"; + char *fs = i == cyclelen - 1 ? "synchronize_rcu_tasks_trace" + : "synchronize_srcu"; + char *fu = i == 0 ? "rcu_read_unlock_trace" : "srcu_read_unlock"; + + j = srcu_lockdep_next(__func__, fl, fs, fu, i, cyclelen, deadlock); + if (i == 0) + rcu_read_lock_trace(); + else + idx = srcu_read_lock(srcus[i]); + if (j >= 0) { + if (i == cyclelen - 1) + synchronize_rcu_tasks_trace(); + else + synchronize_srcu(srcus[j]); + } + if (i == 0) + rcu_read_unlock_trace(); + else + srcu_read_unlock(srcus[i], idx); + } + return; + } +#endif // #ifdef CONFIG_TASKS_TRACE_RCU + +err_out: + pr_info("%s: test_srcu_lockdep = %05d does nothing.\n", __func__, test_srcu_lockdep); + pr_info("%s: test_srcu_lockdep = DNNL.\n", __func__); + pr_info("%s: D: Deadlock if nonzero.\n", __func__); + pr_info("%s: NN: Test number, 0=SRCU, 1=SRCU/mutex, 2=SRCU/rwsem, 3=SRCU/Tasks Trace RCU.\n", __func__); + pr_info("%s: L: Cycle length.\n", __func__); + if (!IS_ENABLED(CONFIG_TASKS_TRACE_RCU)) + pr_info("%s: NN=3 disallowed because kernel is built with CONFIG_TASKS_TRACE_RCU=n\n", __func__); +} + static int __init rcu_torture_init(void) { @@ -2647,9 +3703,9 @@ rcu_torture_init(void) int flags = 0; unsigned long gp_seq = 0; static struct rcu_torture_ops *torture_ops[] = { - &rcu_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops, - &busted_srcud_ops, &tasks_ops, &tasks_rude_ops, - &tasks_tracing_ops, &trivial_ops, + &rcu_ops, &rcu_busted_ops, &srcu_ops, &srcud_ops, &busted_srcud_ops, + TASKS_OPS TASKS_RUDE_OPS TASKS_TRACING_OPS + &trivial_ops, }; if (!torture_init_begin(torture_type, verbose)) @@ -2676,9 +3732,17 @@ rcu_torture_init(void) pr_alert("rcu-torture: ->fqs NULL and non-zero fqs_duration, fqs disabled.\n"); fqs_duration = 0; } + if (nocbs_nthreads != 0 && (cur_ops != &rcu_ops || + !IS_ENABLED(CONFIG_RCU_NOCB_CPU))) { + pr_alert("rcu-torture types: %s and CONFIG_RCU_NOCB_CPU=%d, nocb toggle disabled.\n", + cur_ops->name, IS_ENABLED(CONFIG_RCU_NOCB_CPU)); + nocbs_nthreads = 0; + } if (cur_ops->init) cur_ops->init(); + rcu_torture_init_srcu_lockdep(); + if (nreaders >= 0) { nrealreaders = nreaders; } else { @@ -2710,10 +3774,11 @@ rcu_torture_init(void) atomic_set(&n_rcu_torture_alloc_fail, 0); atomic_set(&n_rcu_torture_free, 0); atomic_set(&n_rcu_torture_mberror, 0); + atomic_set(&n_rcu_torture_mbchk_fail, 0); + atomic_set(&n_rcu_torture_mbchk_tries, 0); atomic_set(&n_rcu_torture_error, 0); n_rcu_torture_barrier_error = 0; n_rcu_torture_boost_ktrerror = 0; - n_rcu_torture_boost_rterror = 0; n_rcu_torture_boost_failure = 0; n_rcu_torture_boosts = 0; for (i = 0; i < RCU_TORTURE_PIPE_LEN + 1; i++) @@ -2729,16 +3794,17 @@ rcu_torture_init(void) /* Start up the kthreads. */ + rcu_torture_write_types(); firsterr = torture_create_kthread(rcu_torture_writer, NULL, writer_task); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; if (nfakewriters > 0) { fakewriter_tasks = kcalloc(nfakewriters, sizeof(fakewriter_tasks[0]), GFP_KERNEL); if (fakewriter_tasks == NULL) { - VERBOSE_TOROUT_ERRSTRING("out of memory"); + TOROUT_ERRSTRING("out of memory"); firsterr = -ENOMEM; goto unwind; } @@ -2746,31 +3812,54 @@ rcu_torture_init(void) for (i = 0; i < nfakewriters; i++) { firsterr = torture_create_kthread(rcu_torture_fakewriter, NULL, fakewriter_tasks[i]); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; } reader_tasks = kcalloc(nrealreaders, sizeof(reader_tasks[0]), GFP_KERNEL); - if (reader_tasks == NULL) { - VERBOSE_TOROUT_ERRSTRING("out of memory"); + rcu_torture_reader_mbchk = kcalloc(nrealreaders, sizeof(*rcu_torture_reader_mbchk), + GFP_KERNEL); + if (!reader_tasks || !rcu_torture_reader_mbchk) { + TOROUT_ERRSTRING("out of memory"); firsterr = -ENOMEM; goto unwind; } for (i = 0; i < nrealreaders; i++) { + rcu_torture_reader_mbchk[i].rtc_chkrdr = -1; firsterr = torture_create_kthread(rcu_torture_reader, (void *)i, reader_tasks[i]); - if (firsterr) + if (torture_init_error(firsterr)) + goto unwind; + } + nrealnocbers = nocbs_nthreads; + if (WARN_ON(nrealnocbers < 0)) + nrealnocbers = 1; + if (WARN_ON(nocbs_toggle < 0)) + nocbs_toggle = HZ; + if (nrealnocbers > 0) { + nocb_tasks = kcalloc(nrealnocbers, sizeof(nocb_tasks[0]), GFP_KERNEL); + if (nocb_tasks == NULL) { + TOROUT_ERRSTRING("out of memory"); + firsterr = -ENOMEM; + goto unwind; + } + } else { + nocb_tasks = NULL; + } + for (i = 0; i < nrealnocbers; i++) { + firsterr = torture_create_kthread(rcu_nocb_toggle, NULL, nocb_tasks[i]); + if (torture_init_error(firsterr)) goto unwind; } if (stat_interval > 0) { firsterr = torture_create_kthread(rcu_torture_stats, NULL, stats_task); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; } if (test_no_idle_hz && shuffle_interval > 0) { firsterr = torture_shuffle_init(shuffle_interval * HZ); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; } if (stutter < 0) @@ -2780,16 +3869,18 @@ rcu_torture_init(void) t = cur_ops->stall_dur ? cur_ops->stall_dur() : stutter * HZ; firsterr = torture_stutter_init(stutter * HZ, t); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; } if (fqs_duration < 0) fqs_duration = 0; - if (fqs_duration) { + if (fqs_holdoff < 0) + fqs_holdoff = 0; + if (fqs_duration && fqs_holdoff) { /* Create the fqs thread */ firsterr = torture_create_kthread(rcu_torture_fqs, NULL, fqs_task); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; } if (test_boost_interval < 1) @@ -2803,33 +3894,34 @@ rcu_torture_init(void) firsterr = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "RCU_TORTURE", rcutorture_booster_init, rcutorture_booster_cleanup); - if (firsterr < 0) - goto unwind; rcutor_hp = firsterr; + if (torture_init_error(firsterr)) + goto unwind; } shutdown_jiffies = jiffies + shutdown_secs * HZ; firsterr = torture_shutdown_init(shutdown_secs, rcu_torture_cleanup); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; firsterr = torture_onoff_init(onoff_holdoff * HZ, onoff_interval, rcutorture_sync); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; firsterr = rcu_torture_stall_init(); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; firsterr = rcu_torture_fwd_prog_init(); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; firsterr = rcu_torture_barrier_init(); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; firsterr = rcu_torture_read_exit_init(); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; if (object_debug) rcu_test_debug_objects(); torture_init_end(); + rcu_gp_slow_register(&rcu_fwd_cb_nodelay); return 0; unwind: diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c index 23ff36a66f97..2c2648a3ad30 100644 --- a/kernel/rcu/refscale.c +++ b/kernel/rcu/refscale.c @@ -44,10 +44,24 @@ pr_alert("%s" SCALE_FLAG s, scale_type, ## x) #define VERBOSE_SCALEOUT(s, x...) \ - do { if (verbose) pr_alert("%s" SCALE_FLAG s, scale_type, ## x); } while (0) + do { \ + if (verbose) \ + pr_alert("%s" SCALE_FLAG s "\n", scale_type, ## x); \ + } while (0) -#define VERBOSE_SCALEOUT_ERRSTRING(s, x...) \ - do { if (verbose) pr_alert("%s" SCALE_FLAG "!!! " s, scale_type, ## x); } while (0) +static atomic_t verbose_batch_ctr; + +#define VERBOSE_SCALEOUT_BATCH(s, x...) \ +do { \ + if (verbose && \ + (verbose_batched <= 0 || \ + !(atomic_inc_return(&verbose_batch_ctr) % verbose_batched))) { \ + schedule_timeout_uninterruptible(1); \ + pr_alert("%s" SCALE_FLAG s "\n", scale_type, ## x); \ + } \ +} while (0) + +#define SCALEOUT_ERRSTRING(s, x...) pr_alert("%s" SCALE_FLAG "!!! " s "\n", scale_type, ## x) MODULE_LICENSE("GPL"); MODULE_AUTHOR("Joel Fernandes (Google) <joel@joelfernandes.org>"); @@ -57,10 +71,13 @@ module_param(scale_type, charp, 0444); MODULE_PARM_DESC(scale_type, "Type of test (rcu, srcu, refcnt, rwsem, rwlock."); torture_param(int, verbose, 0, "Enable verbose debugging printk()s"); +torture_param(int, verbose_batched, 0, "Batch verbose debugging printk()s"); // Wait until there are multiple CPUs before starting test. torture_param(int, holdoff, IS_BUILTIN(CONFIG_RCU_REF_SCALE_TEST) ? 10 : 0, "Holdoff time before test start (s)"); +// Number of typesafe_lookup structures, that is, the degree of concurrency. +torture_param(long, lookup_instances, 0, "Number of typesafe_lookup structures."); // Number of loops per experiment, all readers execute operations concurrently. torture_param(long, loops, 10000, "Number of loops per experiment."); // Number of readers, with -1 defaulting to about 75% of the CPUs. @@ -109,7 +126,7 @@ static int exp_idx; // Operations vector for selecting different types of tests. struct ref_scale_ops { - void (*init)(void); + bool (*init)(void); void (*cleanup)(void); void (*readsection)(const int nloops); void (*delaysection)(const int nloops, const int udl, const int ndl); @@ -147,8 +164,9 @@ static void ref_rcu_delay_section(const int nloops, const int udl, const int ndl } } -static void rcu_sync_scale_init(void) +static bool rcu_sync_scale_init(void) { + return true; } static struct ref_scale_ops rcu_ops = { @@ -192,6 +210,8 @@ static struct ref_scale_ops srcu_ops = { .name = "srcu" }; +#ifdef CONFIG_TASKS_RCU + // Definitions for RCU Tasks ref scale testing: Empty read markers. // These definitions also work for RCU Rude readers. static void rcu_tasks_ref_scale_read_section(const int nloops) @@ -217,6 +237,16 @@ static struct ref_scale_ops rcu_tasks_ops = { .name = "rcu-tasks" }; +#define RCU_TASKS_OPS &rcu_tasks_ops, + +#else // #ifdef CONFIG_TASKS_RCU + +#define RCU_TASKS_OPS + +#endif // #else // #ifdef CONFIG_TASKS_RCU + +#ifdef CONFIG_TASKS_TRACE_RCU + // Definitions for RCU Tasks Trace ref scale testing. static void rcu_trace_ref_scale_read_section(const int nloops) { @@ -246,6 +276,14 @@ static struct ref_scale_ops rcu_trace_ops = { .name = "rcu-trace" }; +#define RCU_TRACE_OPS &rcu_trace_ops, + +#else // #ifdef CONFIG_TASKS_TRACE_RCU + +#define RCU_TRACE_OPS + +#endif // #else // #ifdef CONFIG_TASKS_TRACE_RCU + // Definitions for reference count static atomic_t refcnt; @@ -280,9 +318,10 @@ static struct ref_scale_ops refcnt_ops = { // Definitions for rwlock static rwlock_t test_rwlock; -static void ref_rwlock_init(void) +static bool ref_rwlock_init(void) { rwlock_init(&test_rwlock); + return true; } static void ref_rwlock_section(const int nloops) @@ -316,9 +355,10 @@ static struct ref_scale_ops rwlock_ops = { // Definitions for rwsem static struct rw_semaphore test_rwsem; -static void ref_rwsem_init(void) +static bool ref_rwsem_init(void) { init_rwsem(&test_rwsem); + return true; } static void ref_rwsem_section(const int nloops) @@ -349,6 +389,408 @@ static struct ref_scale_ops rwsem_ops = { .name = "rwsem" }; +// Definitions for global spinlock +static DEFINE_RAW_SPINLOCK(test_lock); + +static void ref_lock_section(const int nloops) +{ + int i; + + preempt_disable(); + for (i = nloops; i >= 0; i--) { + raw_spin_lock(&test_lock); + raw_spin_unlock(&test_lock); + } + preempt_enable(); +} + +static void ref_lock_delay_section(const int nloops, const int udl, const int ndl) +{ + int i; + + preempt_disable(); + for (i = nloops; i >= 0; i--) { + raw_spin_lock(&test_lock); + un_delay(udl, ndl); + raw_spin_unlock(&test_lock); + } + preempt_enable(); +} + +static struct ref_scale_ops lock_ops = { + .readsection = ref_lock_section, + .delaysection = ref_lock_delay_section, + .name = "lock" +}; + +// Definitions for global irq-save spinlock + +static void ref_lock_irq_section(const int nloops) +{ + unsigned long flags; + int i; + + preempt_disable(); + for (i = nloops; i >= 0; i--) { + raw_spin_lock_irqsave(&test_lock, flags); + raw_spin_unlock_irqrestore(&test_lock, flags); + } + preempt_enable(); +} + +static void ref_lock_irq_delay_section(const int nloops, const int udl, const int ndl) +{ + unsigned long flags; + int i; + + preempt_disable(); + for (i = nloops; i >= 0; i--) { + raw_spin_lock_irqsave(&test_lock, flags); + un_delay(udl, ndl); + raw_spin_unlock_irqrestore(&test_lock, flags); + } + preempt_enable(); +} + +static struct ref_scale_ops lock_irq_ops = { + .readsection = ref_lock_irq_section, + .delaysection = ref_lock_irq_delay_section, + .name = "lock-irq" +}; + +// Definitions acquire-release. +static DEFINE_PER_CPU(unsigned long, test_acqrel); + +static void ref_acqrel_section(const int nloops) +{ + unsigned long x; + int i; + + preempt_disable(); + for (i = nloops; i >= 0; i--) { + x = smp_load_acquire(this_cpu_ptr(&test_acqrel)); + smp_store_release(this_cpu_ptr(&test_acqrel), x + 1); + } + preempt_enable(); +} + +static void ref_acqrel_delay_section(const int nloops, const int udl, const int ndl) +{ + unsigned long x; + int i; + + preempt_disable(); + for (i = nloops; i >= 0; i--) { + x = smp_load_acquire(this_cpu_ptr(&test_acqrel)); + un_delay(udl, ndl); + smp_store_release(this_cpu_ptr(&test_acqrel), x + 1); + } + preempt_enable(); +} + +static struct ref_scale_ops acqrel_ops = { + .readsection = ref_acqrel_section, + .delaysection = ref_acqrel_delay_section, + .name = "acqrel" +}; + +static volatile u64 stopopts; + +static void ref_clock_section(const int nloops) +{ + u64 x = 0; + int i; + + preempt_disable(); + for (i = nloops; i >= 0; i--) + x += ktime_get_real_fast_ns(); + preempt_enable(); + stopopts = x; +} + +static void ref_clock_delay_section(const int nloops, const int udl, const int ndl) +{ + u64 x = 0; + int i; + + preempt_disable(); + for (i = nloops; i >= 0; i--) { + x += ktime_get_real_fast_ns(); + un_delay(udl, ndl); + } + preempt_enable(); + stopopts = x; +} + +static struct ref_scale_ops clock_ops = { + .readsection = ref_clock_section, + .delaysection = ref_clock_delay_section, + .name = "clock" +}; + +static void ref_jiffies_section(const int nloops) +{ + u64 x = 0; + int i; + + preempt_disable(); + for (i = nloops; i >= 0; i--) + x += jiffies; + preempt_enable(); + stopopts = x; +} + +static void ref_jiffies_delay_section(const int nloops, const int udl, const int ndl) +{ + u64 x = 0; + int i; + + preempt_disable(); + for (i = nloops; i >= 0; i--) { + x += jiffies; + un_delay(udl, ndl); + } + preempt_enable(); + stopopts = x; +} + +static struct ref_scale_ops jiffies_ops = { + .readsection = ref_jiffies_section, + .delaysection = ref_jiffies_delay_section, + .name = "jiffies" +}; + +//////////////////////////////////////////////////////////////////////// +// +// Methods leveraging SLAB_TYPESAFE_BY_RCU. +// + +// Item to look up in a typesafe manner. Array of pointers to these. +struct refscale_typesafe { + atomic_t rts_refctr; // Used by all flavors + spinlock_t rts_lock; + seqlock_t rts_seqlock; + unsigned int a; + unsigned int b; +}; + +static struct kmem_cache *typesafe_kmem_cachep; +static struct refscale_typesafe **rtsarray; +static long rtsarray_size; +static DEFINE_TORTURE_RANDOM_PERCPU(refscale_rand); +static bool (*rts_acquire)(struct refscale_typesafe *rtsp, unsigned int *start); +static bool (*rts_release)(struct refscale_typesafe *rtsp, unsigned int start); + +// Conditionally acquire an explicit in-structure reference count. +static bool typesafe_ref_acquire(struct refscale_typesafe *rtsp, unsigned int *start) +{ + return atomic_inc_not_zero(&rtsp->rts_refctr); +} + +// Unconditionally release an explicit in-structure reference count. +static bool typesafe_ref_release(struct refscale_typesafe *rtsp, unsigned int start) +{ + if (!atomic_dec_return(&rtsp->rts_refctr)) { + WRITE_ONCE(rtsp->a, rtsp->a + 1); + kmem_cache_free(typesafe_kmem_cachep, rtsp); + } + return true; +} + +// Unconditionally acquire an explicit in-structure spinlock. +static bool typesafe_lock_acquire(struct refscale_typesafe *rtsp, unsigned int *start) +{ + spin_lock(&rtsp->rts_lock); + return true; +} + +// Unconditionally release an explicit in-structure spinlock. +static bool typesafe_lock_release(struct refscale_typesafe *rtsp, unsigned int start) +{ + spin_unlock(&rtsp->rts_lock); + return true; +} + +// Unconditionally acquire an explicit in-structure sequence lock. +static bool typesafe_seqlock_acquire(struct refscale_typesafe *rtsp, unsigned int *start) +{ + *start = read_seqbegin(&rtsp->rts_seqlock); + return true; +} + +// Conditionally release an explicit in-structure sequence lock. Return +// true if this release was successful, that is, if no retry is required. +static bool typesafe_seqlock_release(struct refscale_typesafe *rtsp, unsigned int start) +{ + return !read_seqretry(&rtsp->rts_seqlock, start); +} + +// Do a read-side critical section with the specified delay in +// microseconds and nanoseconds inserted so as to increase probability +// of failure. +static void typesafe_delay_section(const int nloops, const int udl, const int ndl) +{ + unsigned int a; + unsigned int b; + int i; + long idx; + struct refscale_typesafe *rtsp; + unsigned int start; + + for (i = nloops; i >= 0; i--) { + preempt_disable(); + idx = torture_random(this_cpu_ptr(&refscale_rand)) % rtsarray_size; + preempt_enable(); +retry: + rcu_read_lock(); + rtsp = rcu_dereference(rtsarray[idx]); + a = READ_ONCE(rtsp->a); + if (!rts_acquire(rtsp, &start)) { + rcu_read_unlock(); + goto retry; + } + if (a != READ_ONCE(rtsp->a)) { + (void)rts_release(rtsp, start); + rcu_read_unlock(); + goto retry; + } + un_delay(udl, ndl); + b = READ_ONCE(rtsp->a); + // Remember, seqlock read-side release can fail. + if (!rts_release(rtsp, start)) { + rcu_read_unlock(); + goto retry; + } + WARN_ONCE(a != b, "Re-read of ->a changed from %u to %u.\n", a, b); + b = rtsp->b; + rcu_read_unlock(); + WARN_ON_ONCE(a * a != b); + } +} + +// Because the acquisition and release methods are expensive, there +// is no point in optimizing away the un_delay() function's two checks. +// Thus simply define typesafe_read_section() as a simple wrapper around +// typesafe_delay_section(). +static void typesafe_read_section(const int nloops) +{ + typesafe_delay_section(nloops, 0, 0); +} + +// Allocate and initialize one refscale_typesafe structure. +static struct refscale_typesafe *typesafe_alloc_one(void) +{ + struct refscale_typesafe *rtsp; + + rtsp = kmem_cache_alloc(typesafe_kmem_cachep, GFP_KERNEL); + if (!rtsp) + return NULL; + atomic_set(&rtsp->rts_refctr, 1); + WRITE_ONCE(rtsp->a, rtsp->a + 1); + WRITE_ONCE(rtsp->b, rtsp->a * rtsp->a); + return rtsp; +} + +// Slab-allocator constructor for refscale_typesafe structures created +// out of a new slab of system memory. +static void refscale_typesafe_ctor(void *rtsp_in) +{ + struct refscale_typesafe *rtsp = rtsp_in; + + spin_lock_init(&rtsp->rts_lock); + seqlock_init(&rtsp->rts_seqlock); + preempt_disable(); + rtsp->a = torture_random(this_cpu_ptr(&refscale_rand)); + preempt_enable(); +} + +static struct ref_scale_ops typesafe_ref_ops; +static struct ref_scale_ops typesafe_lock_ops; +static struct ref_scale_ops typesafe_seqlock_ops; + +// Initialize for a typesafe test. +static bool typesafe_init(void) +{ + long idx; + long si = lookup_instances; + + typesafe_kmem_cachep = kmem_cache_create("refscale_typesafe", + sizeof(struct refscale_typesafe), sizeof(void *), + SLAB_TYPESAFE_BY_RCU, refscale_typesafe_ctor); + if (!typesafe_kmem_cachep) + return false; + if (si < 0) + si = -si * nr_cpu_ids; + else if (si == 0) + si = nr_cpu_ids; + rtsarray_size = si; + rtsarray = kcalloc(si, sizeof(*rtsarray), GFP_KERNEL); + if (!rtsarray) + return false; + for (idx = 0; idx < rtsarray_size; idx++) { + rtsarray[idx] = typesafe_alloc_one(); + if (!rtsarray[idx]) + return false; + } + if (cur_ops == &typesafe_ref_ops) { + rts_acquire = typesafe_ref_acquire; + rts_release = typesafe_ref_release; + } else if (cur_ops == &typesafe_lock_ops) { + rts_acquire = typesafe_lock_acquire; + rts_release = typesafe_lock_release; + } else if (cur_ops == &typesafe_seqlock_ops) { + rts_acquire = typesafe_seqlock_acquire; + rts_release = typesafe_seqlock_release; + } else { + WARN_ON_ONCE(1); + return false; + } + return true; +} + +// Clean up after a typesafe test. +static void typesafe_cleanup(void) +{ + long idx; + + if (rtsarray) { + for (idx = 0; idx < rtsarray_size; idx++) + kmem_cache_free(typesafe_kmem_cachep, rtsarray[idx]); + kfree(rtsarray); + rtsarray = NULL; + rtsarray_size = 0; + } + kmem_cache_destroy(typesafe_kmem_cachep); + typesafe_kmem_cachep = NULL; + rts_acquire = NULL; + rts_release = NULL; +} + +// The typesafe_init() function distinguishes these structures by address. +static struct ref_scale_ops typesafe_ref_ops = { + .init = typesafe_init, + .cleanup = typesafe_cleanup, + .readsection = typesafe_read_section, + .delaysection = typesafe_delay_section, + .name = "typesafe_ref" +}; + +static struct ref_scale_ops typesafe_lock_ops = { + .init = typesafe_init, + .cleanup = typesafe_cleanup, + .readsection = typesafe_read_section, + .delaysection = typesafe_delay_section, + .name = "typesafe_lock" +}; + +static struct ref_scale_ops typesafe_seqlock_ops = { + .init = typesafe_init, + .cleanup = typesafe_cleanup, + .readsection = typesafe_read_section, + .delaysection = typesafe_delay_section, + .name = "typesafe_seqlock" +}; + static void rcu_scale_one_reader(void) { if (readdelay <= 0) @@ -368,14 +810,14 @@ ref_scale_reader(void *arg) u64 start; s64 duration; - VERBOSE_SCALEOUT("ref_scale_reader %ld: task started", me); - set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids)); + VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: task started", me); + WARN_ON_ONCE(set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids))); set_user_nice(current, MAX_NICE); atomic_inc(&n_init); if (holdoff) schedule_timeout_interruptible(holdoff * HZ); repeat: - VERBOSE_SCALEOUT("ref_scale_reader %ld: waiting to start next experiment on cpu %d", me, smp_processor_id()); + VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: waiting to start next experiment on cpu %d", me, raw_smp_processor_id()); // Wait for signal that this reader can start. wait_event(rt->wq, (atomic_read(&nreaders_exp) && smp_load_acquire(&rt->start_reader)) || @@ -385,14 +827,14 @@ repeat: goto end; // Make sure that the CPU is affinitized appropriately during testing. - WARN_ON_ONCE(smp_processor_id() != me); + WARN_ON_ONCE(raw_smp_processor_id() != me); WRITE_ONCE(rt->start_reader, 0); if (!atomic_dec_return(&n_started)) while (atomic_read_acquire(&n_started)) cpu_relax(); - VERBOSE_SCALEOUT("ref_scale_reader %ld: experiment %d started", me, exp_idx); + VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: experiment %d started", me, exp_idx); // To reduce noise, do an initial cache-warming invocation, check @@ -421,8 +863,8 @@ repeat: if (atomic_dec_and_test(&nreaders_exp)) wake_up(&main_wq); - VERBOSE_SCALEOUT("ref_scale_reader %ld: experiment %d ended, (readers remaining=%d)", - me, exp_idx, atomic_read(&nreaders_exp)); + VERBOSE_SCALEOUT_BATCH("ref_scale_reader %ld: experiment %d ended, (readers remaining=%d)", + me, exp_idx, atomic_read(&nreaders_exp)); if (!torture_must_stop()) goto repeat; @@ -452,7 +894,7 @@ static u64 process_durations(int n) char *buf; u64 sum = 0; - buf = kmalloc(128 + nreaders * 32, GFP_KERNEL); + buf = kmalloc(800 + 64, GFP_KERNEL); if (!buf) return 0; buf[0] = 0; @@ -465,13 +907,15 @@ static u64 process_durations(int n) if (i % 5 == 0) strcat(buf, "\n"); + if (strlen(buf) >= 800) { + pr_alert("%s", buf); + buf[0] = 0; + } strcat(buf, buf1); sum += rt->last_duration_ns; } - strcat(buf, "\n"); - - SCALEOUT("%s\n", buf); + pr_alert("%s\n", buf); kfree(buf); return sum; @@ -485,7 +929,6 @@ static u64 process_durations(int n) // point all the timestamps are printed. static int main_func(void *arg) { - bool errexit = false; int exp, r; char buf1[64]; char *buf; @@ -496,10 +939,10 @@ static int main_func(void *arg) VERBOSE_SCALEOUT("main_func task started"); result_avg = kzalloc(nruns * sizeof(*result_avg), GFP_KERNEL); - buf = kzalloc(64 + nruns * 32, GFP_KERNEL); + buf = kzalloc(800 + 64, GFP_KERNEL); if (!result_avg || !buf) { - VERBOSE_SCALEOUT_ERRSTRING("out of memory"); - errexit = true; + SCALEOUT_ERRSTRING("out of memory"); + goto oom_exit; } if (holdoff) schedule_timeout_interruptible(holdoff * HZ); @@ -511,8 +954,6 @@ static int main_func(void *arg) // Start exp readers up per experiment for (exp = 0; exp < nruns && !torture_must_stop(); exp++) { - if (errexit) - break; if (torture_must_stop()) goto end; @@ -546,26 +987,23 @@ static int main_func(void *arg) // Print the average of all experiments SCALEOUT("END OF TEST. Calculating average duration per loop (nanoseconds)...\n"); - if (!errexit) { - buf[0] = 0; - strcat(buf, "\n"); - strcat(buf, "Runs\tTime(ns)\n"); - } - + pr_alert("Runs\tTime(ns)\n"); for (exp = 0; exp < nruns; exp++) { u64 avg; u32 rem; - if (errexit) - break; avg = div_u64_rem(result_avg[exp], 1000, &rem); sprintf(buf1, "%d\t%llu.%03u\n", exp + 1, avg, rem); strcat(buf, buf1); + if (strlen(buf) >= 800) { + pr_alert("%s", buf); + buf[0] = 0; + } } - if (!errexit) - SCALEOUT("%s", buf); + pr_alert("%s", buf); +oom_exit: // This will shutdown everything including us. if (shutdown) { shutdown_start = 1; @@ -587,8 +1025,8 @@ static void ref_scale_print_module_parms(struct ref_scale_ops *cur_ops, const char *tag) { pr_alert("%s" SCALE_FLAG - "--- %s: verbose=%d shutdown=%d holdoff=%d loops=%ld nreaders=%d nruns=%d readdelay=%d\n", scale_type, tag, - verbose, shutdown, holdoff, loops, nreaders, nruns, readdelay); + "--- %s: verbose=%d verbose_batched=%d shutdown=%d holdoff=%d lookup_instances=%ld loops=%ld nreaders=%d nruns=%d readdelay=%d\n", scale_type, tag, + verbose, verbose_batched, shutdown, holdoff, lookup_instances, loops, nreaders, nruns, readdelay); } static void @@ -625,7 +1063,7 @@ ref_scale_cleanup(void) static int ref_scale_shutdown(void *arg) { - wait_event(shutdown_wq, shutdown_start); + wait_event_idle(shutdown_wq, shutdown_start); smp_mb(); // Wake before output. ref_scale_cleanup(); @@ -640,8 +1078,9 @@ ref_scale_init(void) long i; int firsterr = 0; static struct ref_scale_ops *scale_ops[] = { - &rcu_ops, &srcu_ops, &rcu_trace_ops, &rcu_tasks_ops, - &refcnt_ops, &rwlock_ops, &rwsem_ops, + &rcu_ops, &srcu_ops, RCU_TRACE_OPS RCU_TASKS_OPS &refcnt_ops, &rwlock_ops, + &rwsem_ops, &lock_ops, &lock_irq_ops, &acqrel_ops, &clock_ops, &jiffies_ops, + &typesafe_ref_ops, &typesafe_lock_ops, &typesafe_seqlock_ops, }; if (!torture_init_begin(scale_type, verbose)) @@ -663,7 +1102,10 @@ ref_scale_init(void) goto unwind; } if (cur_ops->init) - cur_ops->init(); + if (!cur_ops->init()) { + firsterr = -EUCLEAN; + goto unwind; + } ref_scale_print_module_parms(cur_ops, "Start of test"); @@ -672,7 +1114,7 @@ ref_scale_init(void) init_waitqueue_head(&shutdown_wq); firsterr = torture_create_kthread(ref_scale_shutdown, NULL, shutdown_task); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; schedule_timeout_uninterruptible(1); } @@ -689,26 +1131,25 @@ ref_scale_init(void) reader_tasks = kcalloc(nreaders, sizeof(reader_tasks[0]), GFP_KERNEL); if (!reader_tasks) { - VERBOSE_SCALEOUT_ERRSTRING("out of memory"); + SCALEOUT_ERRSTRING("out of memory"); firsterr = -ENOMEM; goto unwind; } - VERBOSE_SCALEOUT("Starting %d reader threads\n", nreaders); + VERBOSE_SCALEOUT("Starting %d reader threads", nreaders); for (i = 0; i < nreaders; i++) { + init_waitqueue_head(&reader_tasks[i].wq); firsterr = torture_create_kthread(ref_scale_reader, (void *)i, reader_tasks[i].task); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; - - init_waitqueue_head(&(reader_tasks[i].wq)); } // Main Task init_waitqueue_head(&main_wq); firsterr = torture_create_kthread(main_func, NULL, main_task); - if (firsterr) + if (torture_init_error(firsterr)) goto unwind; torture_init_end(); diff --git a/kernel/rcu/srcutiny.c b/kernel/rcu/srcutiny.c index 6208c1dae5c9..c38e5933a5d6 100644 --- a/kernel/rcu/srcutiny.c +++ b/kernel/rcu/srcutiny.c @@ -34,6 +34,7 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp) ssp->srcu_gp_running = false; ssp->srcu_gp_waiting = false; ssp->srcu_idx = 0; + ssp->srcu_idx_max = 0; INIT_WORK(&ssp->srcu_work, srcu_drive_gp); INIT_LIST_HEAD(&ssp->srcu_work.entry); return 0; @@ -84,6 +85,8 @@ void cleanup_srcu_struct(struct srcu_struct *ssp) WARN_ON(ssp->srcu_gp_waiting); WARN_ON(ssp->srcu_cb_head); WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail); + WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max); + WARN_ON(ssp->srcu_idx & 0x1); } EXPORT_SYMBOL_GPL(cleanup_srcu_struct); @@ -93,10 +96,10 @@ EXPORT_SYMBOL_GPL(cleanup_srcu_struct); */ void __srcu_read_unlock(struct srcu_struct *ssp, int idx) { - int newval = ssp->srcu_lock_nesting[idx] - 1; + int newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1; WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval); - if (!newval && READ_ONCE(ssp->srcu_gp_waiting)) + if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task()) swake_up_one(&ssp->srcu_wq); } EXPORT_SYMBOL_GPL(__srcu_read_unlock); @@ -114,7 +117,7 @@ void srcu_drive_gp(struct work_struct *wp) struct srcu_struct *ssp; ssp = container_of(wp, struct srcu_struct, srcu_work); - if (ssp->srcu_gp_running || !READ_ONCE(ssp->srcu_cb_head)) + if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) return; /* Already running or nothing to do. */ /* Remove recently arrived callbacks and wait for readers. */ @@ -124,16 +127,18 @@ void srcu_drive_gp(struct work_struct *wp) ssp->srcu_cb_head = NULL; ssp->srcu_cb_tail = &ssp->srcu_cb_head; local_irq_enable(); - idx = ssp->srcu_idx; - WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx); + idx = (ssp->srcu_idx & 0x2) / 2; + WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx])); WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ + WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); /* Invoke the callbacks we removed above. */ while (lh) { rhp = lh; lh = lh->next; + debug_rcu_head_callback(rhp); local_bh_disable(); rhp->func(rhp); local_bh_enable(); @@ -146,11 +151,27 @@ void srcu_drive_gp(struct work_struct *wp) * straighten that out. */ WRITE_ONCE(ssp->srcu_gp_running, false); - if (READ_ONCE(ssp->srcu_cb_head)) + if (ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) schedule_work(&ssp->srcu_work); } EXPORT_SYMBOL_GPL(srcu_drive_gp); +static void srcu_gp_start_if_needed(struct srcu_struct *ssp) +{ + unsigned long cookie; + + cookie = get_state_synchronize_srcu(ssp); + if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) + return; + WRITE_ONCE(ssp->srcu_idx_max, cookie); + if (!READ_ONCE(ssp->srcu_gp_running)) { + if (likely(srcu_init_done)) + schedule_work(&ssp->srcu_work); + else if (list_empty(&ssp->srcu_work.entry)) + list_add(&ssp->srcu_work.entry, &srcu_boot_list); + } +} + /* * Enqueue an SRCU callback on the specified srcu_struct structure, * initiating grace-period processing if it is not already running. @@ -166,12 +187,7 @@ void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, *ssp->srcu_cb_tail = rhp; ssp->srcu_cb_tail = &rhp->next; local_irq_restore(flags); - if (!READ_ONCE(ssp->srcu_gp_running)) { - if (likely(srcu_init_done)) - schedule_work(&ssp->srcu_work); - else if (list_empty(&ssp->srcu_work.entry)) - list_add(&ssp->srcu_work.entry, &srcu_boot_list); - } + srcu_gp_start_if_needed(ssp); } EXPORT_SYMBOL_GPL(call_srcu); @@ -182,6 +198,18 @@ void synchronize_srcu(struct srcu_struct *ssp) { struct rcu_synchronize rs; + srcu_lock_sync(&ssp->dep_map); + + RCU_LOCKDEP_WARN(lockdep_is_held(ssp) || + lock_is_held(&rcu_bh_lock_map) || + lock_is_held(&rcu_lock_map) || + lock_is_held(&rcu_sched_lock_map), + "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section"); + + if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) + return; + + might_sleep(); init_rcu_head_on_stack(&rs.head); init_completion(&rs.completion); call_srcu(ssp, &rs.head, wakeme_after_rcu); @@ -190,6 +218,48 @@ void synchronize_srcu(struct srcu_struct *ssp) } EXPORT_SYMBOL_GPL(synchronize_srcu); +/* + * get_state_synchronize_srcu - Provide an end-of-grace-period cookie + */ +unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp) +{ + unsigned long ret; + + barrier(); + ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1; + barrier(); + return ret; +} +EXPORT_SYMBOL_GPL(get_state_synchronize_srcu); + +/* + * start_poll_synchronize_srcu - Provide cookie and start grace period + * + * The difference between this and get_state_synchronize_srcu() is that + * this function ensures that the poll_state_synchronize_srcu() will + * eventually return the value true. + */ +unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp) +{ + unsigned long ret = get_state_synchronize_srcu(ssp); + + srcu_gp_start_if_needed(ssp); + return ret; +} +EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); + +/* + * poll_state_synchronize_srcu - Has cookie's grace period ended? + */ +bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) +{ + unsigned long cur_s = READ_ONCE(ssp->srcu_idx); + + barrier(); + return ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3); +} +EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu); + /* Lockdep diagnostics. */ void __init rcu_scheduler_starting(void) { diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 0f23d20d485a..0351a4e83529 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -24,6 +24,7 @@ #include <linux/smp.h> #include <linux/delay.h> #include <linux/module.h> +#include <linux/slab.h> #include <linux/srcu.h> #include "rcu.h" @@ -38,6 +39,35 @@ module_param(exp_holdoff, ulong, 0444); static ulong counter_wrap_check = (ULONG_MAX >> 2); module_param(counter_wrap_check, ulong, 0444); +/* + * Control conversion to SRCU_SIZE_BIG: + * 0: Don't convert at all. + * 1: Convert at init_srcu_struct() time. + * 2: Convert when rcutorture invokes srcu_torture_stats_print(). + * 3: Decide at boot time based on system shape (default). + * 0x1x: Convert when excessive contention encountered. + */ +#define SRCU_SIZING_NONE 0 +#define SRCU_SIZING_INIT 1 +#define SRCU_SIZING_TORTURE 2 +#define SRCU_SIZING_AUTO 3 +#define SRCU_SIZING_CONTEND 0x10 +#define SRCU_SIZING_IS(x) ((convert_to_big & ~SRCU_SIZING_CONTEND) == x) +#define SRCU_SIZING_IS_NONE() (SRCU_SIZING_IS(SRCU_SIZING_NONE)) +#define SRCU_SIZING_IS_INIT() (SRCU_SIZING_IS(SRCU_SIZING_INIT)) +#define SRCU_SIZING_IS_TORTURE() (SRCU_SIZING_IS(SRCU_SIZING_TORTURE)) +#define SRCU_SIZING_IS_CONTEND() (convert_to_big & SRCU_SIZING_CONTEND) +static int convert_to_big = SRCU_SIZING_AUTO; +module_param(convert_to_big, int, 0444); + +/* Number of CPUs to trigger init_srcu_struct()-time transition to big. */ +static int big_cpu_lim __read_mostly = 128; +module_param(big_cpu_lim, int, 0444); + +/* Contention events per jiffy to initiate transition to big. */ +static int small_contention_lim __read_mostly = 100; +module_param(small_contention_lim, int, 0444); + /* Early-boot callback-management, so early that no lock is required! */ static LIST_HEAD(srcu_boot_list); static bool __read_mostly srcu_init_done; @@ -48,39 +78,90 @@ static void process_srcu(struct work_struct *work); static void srcu_delay_timer(struct timer_list *t); /* Wrappers for lock acquisition and release, see raw_spin_lock_rcu_node(). */ -#define spin_lock_rcu_node(p) \ -do { \ - spin_lock(&ACCESS_PRIVATE(p, lock)); \ - smp_mb__after_unlock_lock(); \ +#define spin_lock_rcu_node(p) \ +do { \ + spin_lock(&ACCESS_PRIVATE(p, lock)); \ + smp_mb__after_unlock_lock(); \ } while (0) #define spin_unlock_rcu_node(p) spin_unlock(&ACCESS_PRIVATE(p, lock)) -#define spin_lock_irq_rcu_node(p) \ -do { \ - spin_lock_irq(&ACCESS_PRIVATE(p, lock)); \ - smp_mb__after_unlock_lock(); \ +#define spin_lock_irq_rcu_node(p) \ +do { \ + spin_lock_irq(&ACCESS_PRIVATE(p, lock)); \ + smp_mb__after_unlock_lock(); \ } while (0) -#define spin_unlock_irq_rcu_node(p) \ +#define spin_unlock_irq_rcu_node(p) \ spin_unlock_irq(&ACCESS_PRIVATE(p, lock)) -#define spin_lock_irqsave_rcu_node(p, flags) \ -do { \ - spin_lock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \ - smp_mb__after_unlock_lock(); \ +#define spin_lock_irqsave_rcu_node(p, flags) \ +do { \ + spin_lock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \ + smp_mb__after_unlock_lock(); \ } while (0) -#define spin_unlock_irqrestore_rcu_node(p, flags) \ - spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) \ +#define spin_trylock_irqsave_rcu_node(p, flags) \ +({ \ + bool ___locked = spin_trylock_irqsave(&ACCESS_PRIVATE(p, lock), flags); \ + \ + if (___locked) \ + smp_mb__after_unlock_lock(); \ + ___locked; \ +}) + +#define spin_unlock_irqrestore_rcu_node(p, flags) \ + spin_unlock_irqrestore(&ACCESS_PRIVATE(p, lock), flags) \ /* - * Initialize SRCU combining tree. Note that statically allocated + * Initialize SRCU per-CPU data. Note that statically allocated * srcu_struct structures might already have srcu_read_lock() and * srcu_read_unlock() running against them. So if the is_static parameter * is set, don't initialize ->srcu_lock_count[] and ->srcu_unlock_count[]. */ -static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static) +static void init_srcu_struct_data(struct srcu_struct *ssp) +{ + int cpu; + struct srcu_data *sdp; + + /* + * Initialize the per-CPU srcu_data array, which feeds into the + * leaves of the srcu_node tree. + */ + WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) != + ARRAY_SIZE(sdp->srcu_unlock_count)); + for_each_possible_cpu(cpu) { + sdp = per_cpu_ptr(ssp->sda, cpu); + spin_lock_init(&ACCESS_PRIVATE(sdp, lock)); + rcu_segcblist_init(&sdp->srcu_cblist); + sdp->srcu_cblist_invoking = false; + sdp->srcu_gp_seq_needed = ssp->srcu_sup->srcu_gp_seq; + sdp->srcu_gp_seq_needed_exp = ssp->srcu_sup->srcu_gp_seq; + sdp->mynode = NULL; + sdp->cpu = cpu; + INIT_WORK(&sdp->work, srcu_invoke_callbacks); + timer_setup(&sdp->delay_work, srcu_delay_timer, 0); + sdp->ssp = ssp; + } +} + +/* Invalid seq state, used during snp node initialization */ +#define SRCU_SNP_INIT_SEQ 0x2 + +/* + * Check whether sequence number corresponding to snp node, + * is invalid. + */ +static inline bool srcu_invl_snp_seq(unsigned long s) +{ + return s == SRCU_SNP_INIT_SEQ; +} + +/* + * Allocated and initialize SRCU combining tree. Returns @true if + * allocation succeeded and @false otherwise. + */ +static bool init_srcu_struct_nodes(struct srcu_struct *ssp, gfp_t gfp_flags) { int cpu; int i; @@ -90,10 +171,16 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static) struct srcu_node *snp; struct srcu_node *snp_first; + /* Initialize geometry if it has not already been initialized. */ + rcu_init_geometry(); + ssp->srcu_sup->node = kcalloc(rcu_num_nodes, sizeof(*ssp->srcu_sup->node), gfp_flags); + if (!ssp->srcu_sup->node) + return false; + /* Work out the overall tree geometry. */ - ssp->level[0] = &ssp->node[0]; + ssp->srcu_sup->level[0] = &ssp->srcu_sup->node[0]; for (i = 1; i < rcu_num_lvls; i++) - ssp->level[i] = ssp->level[i - 1] + num_rcu_lvl[i - 1]; + ssp->srcu_sup->level[i] = ssp->srcu_sup->level[i - 1] + num_rcu_lvl[i - 1]; rcu_init_levelspread(levelspread, num_rcu_lvl); /* Each pass through this loop initializes one srcu_node structure. */ @@ -102,23 +189,23 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static) WARN_ON_ONCE(ARRAY_SIZE(snp->srcu_have_cbs) != ARRAY_SIZE(snp->srcu_data_have_cbs)); for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++) { - snp->srcu_have_cbs[i] = 0; + snp->srcu_have_cbs[i] = SRCU_SNP_INIT_SEQ; snp->srcu_data_have_cbs[i] = 0; } - snp->srcu_gp_seq_needed_exp = 0; + snp->srcu_gp_seq_needed_exp = SRCU_SNP_INIT_SEQ; snp->grplo = -1; snp->grphi = -1; - if (snp == &ssp->node[0]) { + if (snp == &ssp->srcu_sup->node[0]) { /* Root node, special case. */ snp->srcu_parent = NULL; continue; } /* Non-root node. */ - if (snp == ssp->level[level + 1]) + if (snp == ssp->srcu_sup->level[level + 1]) level++; - snp->srcu_parent = ssp->level[level - 1] + - (snp - ssp->level[level]) / + snp->srcu_parent = ssp->srcu_sup->level[level - 1] + + (snp - ssp->srcu_sup->level[level]) / levelspread[level - 1]; } @@ -126,64 +213,73 @@ static void init_srcu_struct_nodes(struct srcu_struct *ssp, bool is_static) * Initialize the per-CPU srcu_data array, which feeds into the * leaves of the srcu_node tree. */ - WARN_ON_ONCE(ARRAY_SIZE(sdp->srcu_lock_count) != - ARRAY_SIZE(sdp->srcu_unlock_count)); level = rcu_num_lvls - 1; - snp_first = ssp->level[level]; + snp_first = ssp->srcu_sup->level[level]; for_each_possible_cpu(cpu) { sdp = per_cpu_ptr(ssp->sda, cpu); - spin_lock_init(&ACCESS_PRIVATE(sdp, lock)); - rcu_segcblist_init(&sdp->srcu_cblist); - sdp->srcu_cblist_invoking = false; - sdp->srcu_gp_seq_needed = ssp->srcu_gp_seq; - sdp->srcu_gp_seq_needed_exp = ssp->srcu_gp_seq; sdp->mynode = &snp_first[cpu / levelspread[level]]; for (snp = sdp->mynode; snp != NULL; snp = snp->srcu_parent) { if (snp->grplo < 0) snp->grplo = cpu; snp->grphi = cpu; } - sdp->cpu = cpu; - INIT_WORK(&sdp->work, srcu_invoke_callbacks); - timer_setup(&sdp->delay_work, srcu_delay_timer, 0); - sdp->ssp = ssp; - sdp->grpmask = 1 << (cpu - sdp->mynode->grplo); - if (is_static) - continue; - - /* Dynamically allocated, better be no srcu_read_locks()! */ - for (i = 0; i < ARRAY_SIZE(sdp->srcu_lock_count); i++) { - sdp->srcu_lock_count[i] = 0; - sdp->srcu_unlock_count[i] = 0; - } + sdp->grpmask = 1UL << (cpu - sdp->mynode->grplo); } + smp_store_release(&ssp->srcu_sup->srcu_size_state, SRCU_SIZE_WAIT_BARRIER); + return true; } /* * Initialize non-compile-time initialized fields, including the - * associated srcu_node and srcu_data structures. The is_static - * parameter is passed through to init_srcu_struct_nodes(), and - * also tells us that ->sda has already been wired up to srcu_data. + * associated srcu_node and srcu_data structures. The is_static parameter + * tells us that ->sda has already been wired up to srcu_data. */ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) { - mutex_init(&ssp->srcu_cb_mutex); - mutex_init(&ssp->srcu_gp_mutex); + if (!is_static) + ssp->srcu_sup = kzalloc(sizeof(*ssp->srcu_sup), GFP_KERNEL); + if (!ssp->srcu_sup) + return -ENOMEM; + if (!is_static) + spin_lock_init(&ACCESS_PRIVATE(ssp->srcu_sup, lock)); + ssp->srcu_sup->srcu_size_state = SRCU_SIZE_SMALL; + ssp->srcu_sup->node = NULL; + mutex_init(&ssp->srcu_sup->srcu_cb_mutex); + mutex_init(&ssp->srcu_sup->srcu_gp_mutex); ssp->srcu_idx = 0; - ssp->srcu_gp_seq = 0; - ssp->srcu_barrier_seq = 0; - mutex_init(&ssp->srcu_barrier_mutex); - atomic_set(&ssp->srcu_barrier_cpu_cnt, 0); - INIT_DELAYED_WORK(&ssp->work, process_srcu); + ssp->srcu_sup->srcu_gp_seq = 0; + ssp->srcu_sup->srcu_barrier_seq = 0; + mutex_init(&ssp->srcu_sup->srcu_barrier_mutex); + atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 0); + INIT_DELAYED_WORK(&ssp->srcu_sup->work, process_srcu); + ssp->srcu_sup->sda_is_static = is_static; if (!is_static) ssp->sda = alloc_percpu(struct srcu_data); if (!ssp->sda) - return -ENOMEM; - init_srcu_struct_nodes(ssp, is_static); - ssp->srcu_gp_seq_needed_exp = 0; - ssp->srcu_last_gp_end = ktime_get_mono_fast_ns(); - smp_store_release(&ssp->srcu_gp_seq_needed, 0); /* Init done. */ + goto err_free_sup; + init_srcu_struct_data(ssp); + ssp->srcu_sup->srcu_gp_seq_needed_exp = 0; + ssp->srcu_sup->srcu_last_gp_end = ktime_get_mono_fast_ns(); + if (READ_ONCE(ssp->srcu_sup->srcu_size_state) == SRCU_SIZE_SMALL && SRCU_SIZING_IS_INIT()) { + if (!init_srcu_struct_nodes(ssp, GFP_ATOMIC)) + goto err_free_sda; + WRITE_ONCE(ssp->srcu_sup->srcu_size_state, SRCU_SIZE_BIG); + } + ssp->srcu_sup->srcu_ssp = ssp; + smp_store_release(&ssp->srcu_sup->srcu_gp_seq_needed, 0); /* Init done. */ return 0; + +err_free_sda: + if (!is_static) { + free_percpu(ssp->sda); + ssp->sda = NULL; + } +err_free_sup: + if (!is_static) { + kfree(ssp->srcu_sup); + ssp->srcu_sup = NULL; + } + return -ENOMEM; } #ifdef CONFIG_DEBUG_LOCK_ALLOC @@ -194,7 +290,6 @@ int __init_srcu_struct(struct srcu_struct *ssp, const char *name, /* Don't re-initialize a lock while it is held. */ debug_check_no_locks_freed((void *)ssp, sizeof(*ssp)); lockdep_init_map(&ssp->dep_map, name, key, 0); - spin_lock_init(&ACCESS_PRIVATE(ssp, lock)); return init_srcu_struct_fields(ssp, false); } EXPORT_SYMBOL_GPL(__init_srcu_struct); @@ -211,7 +306,6 @@ EXPORT_SYMBOL_GPL(__init_srcu_struct); */ int init_srcu_struct(struct srcu_struct *ssp) { - spin_lock_init(&ACCESS_PRIVATE(ssp, lock)); return init_srcu_struct_fields(ssp, false); } EXPORT_SYMBOL_GPL(init_srcu_struct); @@ -219,6 +313,86 @@ EXPORT_SYMBOL_GPL(init_srcu_struct); #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ /* + * Initiate a transition to SRCU_SIZE_BIG with lock held. + */ +static void __srcu_transition_to_big(struct srcu_struct *ssp) +{ + lockdep_assert_held(&ACCESS_PRIVATE(ssp->srcu_sup, lock)); + smp_store_release(&ssp->srcu_sup->srcu_size_state, SRCU_SIZE_ALLOC); +} + +/* + * Initiate an idempotent transition to SRCU_SIZE_BIG. + */ +static void srcu_transition_to_big(struct srcu_struct *ssp) +{ + unsigned long flags; + + /* Double-checked locking on ->srcu_size-state. */ + if (smp_load_acquire(&ssp->srcu_sup->srcu_size_state) != SRCU_SIZE_SMALL) + return; + spin_lock_irqsave_rcu_node(ssp->srcu_sup, flags); + if (smp_load_acquire(&ssp->srcu_sup->srcu_size_state) != SRCU_SIZE_SMALL) { + spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags); + return; + } + __srcu_transition_to_big(ssp); + spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags); +} + +/* + * Check to see if the just-encountered contention event justifies + * a transition to SRCU_SIZE_BIG. + */ +static void spin_lock_irqsave_check_contention(struct srcu_struct *ssp) +{ + unsigned long j; + + if (!SRCU_SIZING_IS_CONTEND() || ssp->srcu_sup->srcu_size_state) + return; + j = jiffies; + if (ssp->srcu_sup->srcu_size_jiffies != j) { + ssp->srcu_sup->srcu_size_jiffies = j; + ssp->srcu_sup->srcu_n_lock_retries = 0; + } + if (++ssp->srcu_sup->srcu_n_lock_retries <= small_contention_lim) + return; + __srcu_transition_to_big(ssp); +} + +/* + * Acquire the specified srcu_data structure's ->lock, but check for + * excessive contention, which results in initiation of a transition + * to SRCU_SIZE_BIG. But only if the srcutree.convert_to_big module + * parameter permits this. + */ +static void spin_lock_irqsave_sdp_contention(struct srcu_data *sdp, unsigned long *flags) +{ + struct srcu_struct *ssp = sdp->ssp; + + if (spin_trylock_irqsave_rcu_node(sdp, *flags)) + return; + spin_lock_irqsave_rcu_node(ssp->srcu_sup, *flags); + spin_lock_irqsave_check_contention(ssp); + spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, *flags); + spin_lock_irqsave_rcu_node(sdp, *flags); +} + +/* + * Acquire the specified srcu_struct structure's ->lock, but check for + * excessive contention, which results in initiation of a transition + * to SRCU_SIZE_BIG. But only if the srcutree.convert_to_big module + * parameter permits this. + */ +static void spin_lock_irqsave_ssp_contention(struct srcu_struct *ssp, unsigned long *flags) +{ + if (spin_trylock_irqsave_rcu_node(ssp->srcu_sup, *flags)) + return; + spin_lock_irqsave_rcu_node(ssp->srcu_sup, *flags); + spin_lock_irqsave_check_contention(ssp); +} + +/* * First-use initialization of statically allocated srcu_struct * structure. Wiring up the combining tree is more than can be * done with compile-time initialization, so this check is added @@ -231,15 +405,15 @@ static void check_init_srcu_struct(struct srcu_struct *ssp) unsigned long flags; /* The smp_load_acquire() pairs with the smp_store_release(). */ - if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_gp_seq_needed))) /*^^^*/ + if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_sup->srcu_gp_seq_needed))) /*^^^*/ return; /* Already initialized. */ - spin_lock_irqsave_rcu_node(ssp, flags); - if (!rcu_seq_state(ssp->srcu_gp_seq_needed)) { - spin_unlock_irqrestore_rcu_node(ssp, flags); + spin_lock_irqsave_rcu_node(ssp->srcu_sup, flags); + if (!rcu_seq_state(ssp->srcu_sup->srcu_gp_seq_needed)) { + spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags); return; } init_srcu_struct_fields(ssp, true); - spin_unlock_irqrestore_rcu_node(ssp, flags); + spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags); } /* @@ -254,7 +428,7 @@ static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx) for_each_possible_cpu(cpu) { struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); - sum += READ_ONCE(cpuc->srcu_lock_count[idx]); + sum += atomic_long_read(&cpuc->srcu_lock_count[idx]); } return sum; } @@ -266,13 +440,18 @@ static unsigned long srcu_readers_lock_idx(struct srcu_struct *ssp, int idx) static unsigned long srcu_readers_unlock_idx(struct srcu_struct *ssp, int idx) { int cpu; + unsigned long mask = 0; unsigned long sum = 0; for_each_possible_cpu(cpu) { struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); - sum += READ_ONCE(cpuc->srcu_unlock_count[idx]); + sum += atomic_long_read(&cpuc->srcu_unlock_count[idx]); + if (IS_ENABLED(CONFIG_PROVE_RCU)) + mask = mask | READ_ONCE(cpuc->srcu_nmi_safety); } + WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && (mask & (mask >> 1)), + "Mixed NMI-safe readers for srcu_struct at %ps.\n", ssp); return sum; } @@ -301,24 +480,59 @@ static bool srcu_readers_active_idx_check(struct srcu_struct *ssp, int idx) /* * If the locks are the same as the unlocks, then there must have - * been no readers on this index at some time in between. This does - * not mean that there are no more readers, as one could have read - * the current index but not have incremented the lock counter yet. + * been no readers on this index at some point in this function. + * But there might be more readers, as a task might have read + * the current ->srcu_idx but not yet have incremented its CPU's + * ->srcu_lock_count[idx] counter. In fact, it is possible + * that most of the tasks have been preempted between fetching + * ->srcu_idx and incrementing ->srcu_lock_count[idx]. And there + * could be almost (ULONG_MAX / sizeof(struct task_struct)) tasks + * in a system whose address space was fully populated with memory. + * Call this quantity Nt. + * + * So suppose that the updater is preempted at this point in the + * code for a long time. That now-preempted updater has already + * flipped ->srcu_idx (possibly during the preceding grace period), + * done an smp_mb() (again, possibly during the preceding grace + * period), and summed up the ->srcu_unlock_count[idx] counters. + * How many times can a given one of the aforementioned Nt tasks + * increment the old ->srcu_idx value's ->srcu_lock_count[idx] + * counter, in the absence of nesting? + * + * It can clearly do so once, given that it has already fetched + * the old value of ->srcu_idx and is just about to use that value + * to index its increment of ->srcu_lock_count[idx]. But as soon as + * it leaves that SRCU read-side critical section, it will increment + * ->srcu_unlock_count[idx], which must follow the updater's above + * read from that same value. Thus, as soon the reading task does + * an smp_mb() and a later fetch from ->srcu_idx, that task will be + * guaranteed to get the new index. Except that the increment of + * ->srcu_unlock_count[idx] in __srcu_read_unlock() is after the + * smp_mb(), and the fetch from ->srcu_idx in __srcu_read_lock() + * is before the smp_mb(). Thus, that task might not see the new + * value of ->srcu_idx until the -second- __srcu_read_lock(), + * which in turn means that this task might well increment + * ->srcu_lock_count[idx] for the old value of ->srcu_idx twice, + * not just once. + * + * However, it is important to note that a given smp_mb() takes + * effect not just for the task executing it, but also for any + * later task running on that same CPU. * - * So suppose that the updater is preempted here for so long - * that more than ULONG_MAX non-nested readers come and go in - * the meantime. It turns out that this cannot result in overflow - * because if a reader modifies its unlock count after we read it - * above, then that reader's next load of ->srcu_idx is guaranteed - * to get the new value, which will cause it to operate on the - * other bank of counters, where it cannot contribute to the - * overflow of these counters. This means that there is a maximum - * of 2*NR_CPUS increments, which cannot overflow given current - * systems, especially not on 64-bit systems. + * That is, there can be almost Nt + Nc further increments of + * ->srcu_lock_count[idx] for the old index, where Nc is the number + * of CPUs. But this is OK because the size of the task_struct + * structure limits the value of Nt and current systems limit Nc + * to a few thousand. * - * OK, how about nesting? This does impose a limit on nesting - * of floor(ULONG_MAX/NR_CPUS/2), which should be sufficient, - * especially on 64-bit systems. + * OK, but what about nesting? This does impose a limit on + * nesting of half of the size of the task_struct structure + * (measured in bytes), which should be sufficient. A late 2022 + * TREE01 rcutorture run reported this size to be no less than + * 9408 bytes, allowing up to 4704 levels of nesting, which is + * comfortably beyond excessive. Especially on 64-bit systems, + * which are unlikely to be configured with an address space fully + * populated with memory, at least not anytime soon. */ return srcu_readers_lock_idx(ssp, idx) == unlocks; } @@ -340,15 +554,60 @@ static bool srcu_readers_active(struct srcu_struct *ssp) for_each_possible_cpu(cpu) { struct srcu_data *cpuc = per_cpu_ptr(ssp->sda, cpu); - sum += READ_ONCE(cpuc->srcu_lock_count[0]); - sum += READ_ONCE(cpuc->srcu_lock_count[1]); - sum -= READ_ONCE(cpuc->srcu_unlock_count[0]); - sum -= READ_ONCE(cpuc->srcu_unlock_count[1]); + sum += atomic_long_read(&cpuc->srcu_lock_count[0]); + sum += atomic_long_read(&cpuc->srcu_lock_count[1]); + sum -= atomic_long_read(&cpuc->srcu_unlock_count[0]); + sum -= atomic_long_read(&cpuc->srcu_unlock_count[1]); } return sum; } -#define SRCU_INTERVAL 1 +/* + * We use an adaptive strategy for synchronize_srcu() and especially for + * synchronize_srcu_expedited(). We spin for a fixed time period + * (defined below, boot time configurable) to allow SRCU readers to exit + * their read-side critical sections. If there are still some readers + * after one jiffy, we repeatedly block for one jiffy time periods. + * The blocking time is increased as the grace-period age increases, + * with max blocking time capped at 10 jiffies. + */ +#define SRCU_DEFAULT_RETRY_CHECK_DELAY 5 + +static ulong srcu_retry_check_delay = SRCU_DEFAULT_RETRY_CHECK_DELAY; +module_param(srcu_retry_check_delay, ulong, 0444); + +#define SRCU_INTERVAL 1 // Base delay if no expedited GPs pending. +#define SRCU_MAX_INTERVAL 10 // Maximum incremental delay from slow readers. + +#define SRCU_DEFAULT_MAX_NODELAY_PHASE_LO 3UL // Lowmark on default per-GP-phase + // no-delay instances. +#define SRCU_DEFAULT_MAX_NODELAY_PHASE_HI 1000UL // Highmark on default per-GP-phase + // no-delay instances. + +#define SRCU_UL_CLAMP_LO(val, low) ((val) > (low) ? (val) : (low)) +#define SRCU_UL_CLAMP_HI(val, high) ((val) < (high) ? (val) : (high)) +#define SRCU_UL_CLAMP(val, low, high) SRCU_UL_CLAMP_HI(SRCU_UL_CLAMP_LO((val), (low)), (high)) +// per-GP-phase no-delay instances adjusted to allow non-sleeping poll upto +// one jiffies time duration. Mult by 2 is done to factor in the srcu_get_delay() +// called from process_srcu(). +#define SRCU_DEFAULT_MAX_NODELAY_PHASE_ADJUSTED \ + (2UL * USEC_PER_SEC / HZ / SRCU_DEFAULT_RETRY_CHECK_DELAY) + +// Maximum per-GP-phase consecutive no-delay instances. +#define SRCU_DEFAULT_MAX_NODELAY_PHASE \ + SRCU_UL_CLAMP(SRCU_DEFAULT_MAX_NODELAY_PHASE_ADJUSTED, \ + SRCU_DEFAULT_MAX_NODELAY_PHASE_LO, \ + SRCU_DEFAULT_MAX_NODELAY_PHASE_HI) + +static ulong srcu_max_nodelay_phase = SRCU_DEFAULT_MAX_NODELAY_PHASE; +module_param(srcu_max_nodelay_phase, ulong, 0444); + +// Maximum consecutive no-delay instances. +#define SRCU_DEFAULT_MAX_NODELAY (SRCU_DEFAULT_MAX_NODELAY_PHASE > 100 ? \ + SRCU_DEFAULT_MAX_NODELAY_PHASE : 100) + +static ulong srcu_max_nodelay = SRCU_DEFAULT_MAX_NODELAY; +module_param(srcu_max_nodelay, ulong, 0444); /* * Return grace-period delay, zero if there are expedited grace @@ -356,10 +615,25 @@ static bool srcu_readers_active(struct srcu_struct *ssp) */ static unsigned long srcu_get_delay(struct srcu_struct *ssp) { - if (ULONG_CMP_LT(READ_ONCE(ssp->srcu_gp_seq), - READ_ONCE(ssp->srcu_gp_seq_needed_exp))) - return 0; - return SRCU_INTERVAL; + unsigned long gpstart; + unsigned long j; + unsigned long jbase = SRCU_INTERVAL; + struct srcu_usage *sup = ssp->srcu_sup; + + if (ULONG_CMP_LT(READ_ONCE(sup->srcu_gp_seq), READ_ONCE(sup->srcu_gp_seq_needed_exp))) + jbase = 0; + if (rcu_seq_state(READ_ONCE(sup->srcu_gp_seq))) { + j = jiffies - 1; + gpstart = READ_ONCE(sup->srcu_gp_start); + if (time_after(j, gpstart)) + jbase += j - gpstart; + if (!jbase) { + WRITE_ONCE(sup->srcu_n_exp_nodelay, READ_ONCE(sup->srcu_n_exp_nodelay) + 1); + if (READ_ONCE(sup->srcu_n_exp_nodelay) > srcu_max_nodelay_phase) + jbase = 1; + } + } + return jbase > SRCU_MAX_INTERVAL ? SRCU_MAX_INTERVAL : jbase; } /** @@ -372,12 +646,13 @@ static unsigned long srcu_get_delay(struct srcu_struct *ssp) void cleanup_srcu_struct(struct srcu_struct *ssp) { int cpu; + struct srcu_usage *sup = ssp->srcu_sup; if (WARN_ON(!srcu_get_delay(ssp))) return; /* Just leak it! */ if (WARN_ON(srcu_readers_active(ssp))) return; /* Just leak it! */ - flush_delayed_work(&ssp->work); + flush_delayed_work(&sup->work); for_each_possible_cpu(cpu) { struct srcu_data *sdp = per_cpu_ptr(ssp->sda, cpu); @@ -386,17 +661,49 @@ void cleanup_srcu_struct(struct srcu_struct *ssp) if (WARN_ON(rcu_segcblist_n_cbs(&sdp->srcu_cblist))) return; /* Forgot srcu_barrier(), so just leak it! */ } - if (WARN_ON(rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) != SRCU_STATE_IDLE) || + if (WARN_ON(rcu_seq_state(READ_ONCE(sup->srcu_gp_seq)) != SRCU_STATE_IDLE) || + WARN_ON(rcu_seq_current(&sup->srcu_gp_seq) != sup->srcu_gp_seq_needed) || WARN_ON(srcu_readers_active(ssp))) { - pr_info("%s: Active srcu_struct %p state: %d\n", - __func__, ssp, rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq))); + pr_info("%s: Active srcu_struct %p read state: %d gp state: %lu/%lu\n", + __func__, ssp, rcu_seq_state(READ_ONCE(sup->srcu_gp_seq)), + rcu_seq_current(&sup->srcu_gp_seq), sup->srcu_gp_seq_needed); return; /* Caller forgot to stop doing call_srcu()? */ } - free_percpu(ssp->sda); - ssp->sda = NULL; + kfree(sup->node); + sup->node = NULL; + sup->srcu_size_state = SRCU_SIZE_SMALL; + if (!sup->sda_is_static) { + free_percpu(ssp->sda); + ssp->sda = NULL; + kfree(sup); + ssp->srcu_sup = NULL; + } } EXPORT_SYMBOL_GPL(cleanup_srcu_struct); +#ifdef CONFIG_PROVE_RCU +/* + * Check for consistent NMI safety. + */ +void srcu_check_nmi_safety(struct srcu_struct *ssp, bool nmi_safe) +{ + int nmi_safe_mask = 1 << nmi_safe; + int old_nmi_safe_mask; + struct srcu_data *sdp; + + /* NMI-unsafe use in NMI is a bad sign */ + WARN_ON_ONCE(!nmi_safe && in_nmi()); + sdp = raw_cpu_ptr(ssp->sda); + old_nmi_safe_mask = READ_ONCE(sdp->srcu_nmi_safety); + if (!old_nmi_safe_mask) { + WRITE_ONCE(sdp->srcu_nmi_safety, nmi_safe_mask); + return; + } + WARN_ONCE(old_nmi_safe_mask != nmi_safe_mask, "CPU %d old state %d new state %d\n", sdp->cpu, old_nmi_safe_mask, nmi_safe_mask); +} +EXPORT_SYMBOL_GPL(srcu_check_nmi_safety); +#endif /* CONFIG_PROVE_RCU */ + /* * Counts the new reader in the appropriate per-CPU element of the * srcu_struct. @@ -407,7 +714,7 @@ int __srcu_read_lock(struct srcu_struct *ssp) int idx; idx = READ_ONCE(ssp->srcu_idx) & 0x1; - this_cpu_inc(ssp->sda->srcu_lock_count[idx]); + this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter); smp_mb(); /* B */ /* Avoid leaking the critical section. */ return idx; } @@ -421,38 +728,59 @@ EXPORT_SYMBOL_GPL(__srcu_read_lock); void __srcu_read_unlock(struct srcu_struct *ssp, int idx) { smp_mb(); /* C */ /* Avoid leaking the critical section. */ - this_cpu_inc(ssp->sda->srcu_unlock_count[idx]); + this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter); } EXPORT_SYMBOL_GPL(__srcu_read_unlock); +#ifdef CONFIG_NEED_SRCU_NMI_SAFE + /* - * We use an adaptive strategy for synchronize_srcu() and especially for - * synchronize_srcu_expedited(). We spin for a fixed time period - * (defined below) to allow SRCU readers to exit their read-side critical - * sections. If there are still some readers after a few microseconds, - * we repeatedly block for 1-millisecond time periods. + * Counts the new reader in the appropriate per-CPU element of the + * srcu_struct, but in an NMI-safe manner using RMW atomics. + * Returns an index that must be passed to the matching srcu_read_unlock(). */ -#define SRCU_RETRY_CHECK_DELAY 5 +int __srcu_read_lock_nmisafe(struct srcu_struct *ssp) +{ + int idx; + struct srcu_data *sdp = raw_cpu_ptr(ssp->sda); + + idx = READ_ONCE(ssp->srcu_idx) & 0x1; + atomic_long_inc(&sdp->srcu_lock_count[idx]); + smp_mb__after_atomic(); /* B */ /* Avoid leaking the critical section. */ + return idx; +} +EXPORT_SYMBOL_GPL(__srcu_read_lock_nmisafe); + +/* + * Removes the count for the old reader from the appropriate per-CPU + * element of the srcu_struct. Note that this may well be a different + * CPU than that which was incremented by the corresponding srcu_read_lock(). + */ +void __srcu_read_unlock_nmisafe(struct srcu_struct *ssp, int idx) +{ + struct srcu_data *sdp = raw_cpu_ptr(ssp->sda); + + smp_mb__before_atomic(); /* C */ /* Avoid leaking the critical section. */ + atomic_long_inc(&sdp->srcu_unlock_count[idx]); +} +EXPORT_SYMBOL_GPL(__srcu_read_unlock_nmisafe); + +#endif // CONFIG_NEED_SRCU_NMI_SAFE /* * Start an SRCU grace period. */ static void srcu_gp_start(struct srcu_struct *ssp) { - struct srcu_data *sdp = this_cpu_ptr(ssp->sda); int state; - lockdep_assert_held(&ACCESS_PRIVATE(ssp, lock)); - WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)); - spin_lock_rcu_node(sdp); /* Interrupts already disabled. */ - rcu_segcblist_advance(&sdp->srcu_cblist, - rcu_seq_current(&ssp->srcu_gp_seq)); - (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, - rcu_seq_snap(&ssp->srcu_gp_seq)); - spin_unlock_rcu_node(sdp); /* Interrupts remain disabled. */ + lockdep_assert_held(&ACCESS_PRIVATE(ssp->srcu_sup, lock)); + WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed)); + WRITE_ONCE(ssp->srcu_sup->srcu_gp_start, jiffies); + WRITE_ONCE(ssp->srcu_sup->srcu_n_exp_nodelay, 0); smp_mb(); /* Order prior store to ->srcu_gp_seq_needed vs. GP start. */ - rcu_seq_start(&ssp->srcu_gp_seq); - state = rcu_seq_state(ssp->srcu_gp_seq); + rcu_seq_start(&ssp->srcu_sup->srcu_gp_seq); + state = rcu_seq_state(ssp->srcu_sup->srcu_gp_seq); WARN_ON_ONCE(state != SRCU_STATE_SCAN1); } @@ -496,7 +824,7 @@ static void srcu_schedule_cbs_snp(struct srcu_struct *ssp, struct srcu_node *snp int cpu; for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) { - if (!(mask & (1 << (cpu - snp->grplo)))) + if (!(mask & (1UL << (cpu - snp->grplo)))) continue; srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, cpu), delay); } @@ -513,7 +841,7 @@ static void srcu_schedule_cbs_snp(struct srcu_struct *ssp, struct srcu_node *snp */ static void srcu_gp_end(struct srcu_struct *ssp) { - unsigned long cbdelay; + unsigned long cbdelay = 1; bool cbs; bool last_lvl; int cpu; @@ -522,71 +850,92 @@ static void srcu_gp_end(struct srcu_struct *ssp) int idx; unsigned long mask; struct srcu_data *sdp; + unsigned long sgsne; struct srcu_node *snp; + int ss_state; + struct srcu_usage *sup = ssp->srcu_sup; /* Prevent more than one additional grace period. */ - mutex_lock(&ssp->srcu_cb_mutex); + mutex_lock(&sup->srcu_cb_mutex); /* End the current grace period. */ - spin_lock_irq_rcu_node(ssp); - idx = rcu_seq_state(ssp->srcu_gp_seq); + spin_lock_irq_rcu_node(sup); + idx = rcu_seq_state(sup->srcu_gp_seq); WARN_ON_ONCE(idx != SRCU_STATE_SCAN2); - cbdelay = srcu_get_delay(ssp); - WRITE_ONCE(ssp->srcu_last_gp_end, ktime_get_mono_fast_ns()); - rcu_seq_end(&ssp->srcu_gp_seq); - gpseq = rcu_seq_current(&ssp->srcu_gp_seq); - if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, gpseq)) - WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, gpseq); - spin_unlock_irq_rcu_node(ssp); - mutex_unlock(&ssp->srcu_gp_mutex); + if (ULONG_CMP_LT(READ_ONCE(sup->srcu_gp_seq), READ_ONCE(sup->srcu_gp_seq_needed_exp))) + cbdelay = 0; + + WRITE_ONCE(sup->srcu_last_gp_end, ktime_get_mono_fast_ns()); + rcu_seq_end(&sup->srcu_gp_seq); + gpseq = rcu_seq_current(&sup->srcu_gp_seq); + if (ULONG_CMP_LT(sup->srcu_gp_seq_needed_exp, gpseq)) + WRITE_ONCE(sup->srcu_gp_seq_needed_exp, gpseq); + spin_unlock_irq_rcu_node(sup); + mutex_unlock(&sup->srcu_gp_mutex); /* A new grace period can start at this point. But only one. */ /* Initiate callback invocation as needed. */ - idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs); - srcu_for_each_node_breadth_first(ssp, snp) { - spin_lock_irq_rcu_node(snp); - cbs = false; - last_lvl = snp >= ssp->level[rcu_num_lvls - 1]; - if (last_lvl) - cbs = snp->srcu_have_cbs[idx] == gpseq; - snp->srcu_have_cbs[idx] = gpseq; - rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1); - if (ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, gpseq)) - WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq); - mask = snp->srcu_data_have_cbs[idx]; - snp->srcu_data_have_cbs[idx] = 0; - spin_unlock_irq_rcu_node(snp); - if (cbs) - srcu_schedule_cbs_snp(ssp, snp, mask, cbdelay); - - /* Occasionally prevent srcu_data counter wrap. */ - if (!(gpseq & counter_wrap_check) && last_lvl) - for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) { - sdp = per_cpu_ptr(ssp->sda, cpu); - spin_lock_irqsave_rcu_node(sdp, flags); - if (ULONG_CMP_GE(gpseq, - sdp->srcu_gp_seq_needed + 100)) - sdp->srcu_gp_seq_needed = gpseq; - if (ULONG_CMP_GE(gpseq, - sdp->srcu_gp_seq_needed_exp + 100)) - sdp->srcu_gp_seq_needed_exp = gpseq; - spin_unlock_irqrestore_rcu_node(sdp, flags); - } + ss_state = smp_load_acquire(&sup->srcu_size_state); + if (ss_state < SRCU_SIZE_WAIT_BARRIER) { + srcu_schedule_cbs_sdp(per_cpu_ptr(ssp->sda, get_boot_cpu_id()), + cbdelay); + } else { + idx = rcu_seq_ctr(gpseq) % ARRAY_SIZE(snp->srcu_have_cbs); + srcu_for_each_node_breadth_first(ssp, snp) { + spin_lock_irq_rcu_node(snp); + cbs = false; + last_lvl = snp >= sup->level[rcu_num_lvls - 1]; + if (last_lvl) + cbs = ss_state < SRCU_SIZE_BIG || snp->srcu_have_cbs[idx] == gpseq; + snp->srcu_have_cbs[idx] = gpseq; + rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1); + sgsne = snp->srcu_gp_seq_needed_exp; + if (srcu_invl_snp_seq(sgsne) || ULONG_CMP_LT(sgsne, gpseq)) + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, gpseq); + if (ss_state < SRCU_SIZE_BIG) + mask = ~0; + else + mask = snp->srcu_data_have_cbs[idx]; + snp->srcu_data_have_cbs[idx] = 0; + spin_unlock_irq_rcu_node(snp); + if (cbs) + srcu_schedule_cbs_snp(ssp, snp, mask, cbdelay); + } } + /* Occasionally prevent srcu_data counter wrap. */ + if (!(gpseq & counter_wrap_check)) + for_each_possible_cpu(cpu) { + sdp = per_cpu_ptr(ssp->sda, cpu); + spin_lock_irqsave_rcu_node(sdp, flags); + if (ULONG_CMP_GE(gpseq, sdp->srcu_gp_seq_needed + 100)) + sdp->srcu_gp_seq_needed = gpseq; + if (ULONG_CMP_GE(gpseq, sdp->srcu_gp_seq_needed_exp + 100)) + sdp->srcu_gp_seq_needed_exp = gpseq; + spin_unlock_irqrestore_rcu_node(sdp, flags); + } + /* Callback initiation done, allow grace periods after next. */ - mutex_unlock(&ssp->srcu_cb_mutex); + mutex_unlock(&sup->srcu_cb_mutex); /* Start a new grace period if needed. */ - spin_lock_irq_rcu_node(ssp); - gpseq = rcu_seq_current(&ssp->srcu_gp_seq); + spin_lock_irq_rcu_node(sup); + gpseq = rcu_seq_current(&sup->srcu_gp_seq); if (!rcu_seq_state(gpseq) && - ULONG_CMP_LT(gpseq, ssp->srcu_gp_seq_needed)) { + ULONG_CMP_LT(gpseq, sup->srcu_gp_seq_needed)) { srcu_gp_start(ssp); - spin_unlock_irq_rcu_node(ssp); + spin_unlock_irq_rcu_node(sup); srcu_reschedule(ssp, 0); } else { - spin_unlock_irq_rcu_node(ssp); + spin_unlock_irq_rcu_node(sup); + } + + /* Transition to big if needed. */ + if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) { + if (ss_state == SRCU_SIZE_ALLOC) + init_srcu_struct_nodes(ssp, GFP_KERNEL); + else + smp_store_release(&sup->srcu_size_state, ss_state + 1); } } @@ -601,23 +950,27 @@ static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp unsigned long s) { unsigned long flags; + unsigned long sgsne; - for (; snp != NULL; snp = snp->srcu_parent) { - if (rcu_seq_done(&ssp->srcu_gp_seq, s) || - ULONG_CMP_GE(READ_ONCE(snp->srcu_gp_seq_needed_exp), s)) - return; - spin_lock_irqsave_rcu_node(snp, flags); - if (ULONG_CMP_GE(snp->srcu_gp_seq_needed_exp, s)) { + if (snp) + for (; snp != NULL; snp = snp->srcu_parent) { + sgsne = READ_ONCE(snp->srcu_gp_seq_needed_exp); + if (WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_sup->srcu_gp_seq, s)) || + (!srcu_invl_snp_seq(sgsne) && ULONG_CMP_GE(sgsne, s))) + return; + spin_lock_irqsave_rcu_node(snp, flags); + sgsne = snp->srcu_gp_seq_needed_exp; + if (!srcu_invl_snp_seq(sgsne) && ULONG_CMP_GE(sgsne, s)) { + spin_unlock_irqrestore_rcu_node(snp, flags); + return; + } + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s); spin_unlock_irqrestore_rcu_node(snp, flags); - return; } - WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s); - spin_unlock_irqrestore_rcu_node(snp, flags); - } - spin_lock_irqsave_rcu_node(ssp, flags); - if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s)) - WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s); - spin_unlock_irqrestore_rcu_node(ssp, flags); + spin_lock_irqsave_ssp_contention(ssp, &flags); + if (ULONG_CMP_LT(ssp->srcu_sup->srcu_gp_seq_needed_exp, s)) + WRITE_ONCE(ssp->srcu_sup->srcu_gp_seq_needed_exp, s); + spin_unlock_irqrestore_rcu_node(ssp->srcu_sup, flags); } /* @@ -629,67 +982,85 @@ static void srcu_funnel_exp_start(struct srcu_struct *ssp, struct srcu_node *snp * * Note that this function also does the work of srcu_funnel_exp_start(), * in some cases by directly invoking it. + * + * The srcu read lock should be hold around this function. And s is a seq snap + * after holding that lock. */ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp, unsigned long s, bool do_norm) { unsigned long flags; int idx = rcu_seq_ctr(s) % ARRAY_SIZE(sdp->mynode->srcu_have_cbs); - struct srcu_node *snp = sdp->mynode; + unsigned long sgsne; + struct srcu_node *snp; + struct srcu_node *snp_leaf; unsigned long snp_seq; + struct srcu_usage *sup = ssp->srcu_sup; - /* Each pass through the loop does one level of the srcu_node tree. */ - for (; snp != NULL; snp = snp->srcu_parent) { - if (rcu_seq_done(&ssp->srcu_gp_seq, s) && snp != sdp->mynode) - return; /* GP already done and CBs recorded. */ - spin_lock_irqsave_rcu_node(snp, flags); - if (ULONG_CMP_GE(snp->srcu_have_cbs[idx], s)) { + /* Ensure that snp node tree is fully initialized before traversing it */ + if (smp_load_acquire(&sup->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER) + snp_leaf = NULL; + else + snp_leaf = sdp->mynode; + + if (snp_leaf) + /* Each pass through the loop does one level of the srcu_node tree. */ + for (snp = snp_leaf; snp != NULL; snp = snp->srcu_parent) { + if (WARN_ON_ONCE(rcu_seq_done(&sup->srcu_gp_seq, s)) && snp != snp_leaf) + return; /* GP already done and CBs recorded. */ + spin_lock_irqsave_rcu_node(snp, flags); snp_seq = snp->srcu_have_cbs[idx]; - if (snp == sdp->mynode && snp_seq == s) - snp->srcu_data_have_cbs[idx] |= sdp->grpmask; - spin_unlock_irqrestore_rcu_node(snp, flags); - if (snp == sdp->mynode && snp_seq != s) { - srcu_schedule_cbs_sdp(sdp, do_norm - ? SRCU_INTERVAL - : 0); + if (!srcu_invl_snp_seq(snp_seq) && ULONG_CMP_GE(snp_seq, s)) { + if (snp == snp_leaf && snp_seq == s) + snp->srcu_data_have_cbs[idx] |= sdp->grpmask; + spin_unlock_irqrestore_rcu_node(snp, flags); + if (snp == snp_leaf && snp_seq != s) { + srcu_schedule_cbs_sdp(sdp, do_norm ? SRCU_INTERVAL : 0); + return; + } + if (!do_norm) + srcu_funnel_exp_start(ssp, snp, s); return; } - if (!do_norm) - srcu_funnel_exp_start(ssp, snp, s); - return; + snp->srcu_have_cbs[idx] = s; + if (snp == snp_leaf) + snp->srcu_data_have_cbs[idx] |= sdp->grpmask; + sgsne = snp->srcu_gp_seq_needed_exp; + if (!do_norm && (srcu_invl_snp_seq(sgsne) || ULONG_CMP_LT(sgsne, s))) + WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s); + spin_unlock_irqrestore_rcu_node(snp, flags); } - snp->srcu_have_cbs[idx] = s; - if (snp == sdp->mynode) - snp->srcu_data_have_cbs[idx] |= sdp->grpmask; - if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s)) - WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s); - spin_unlock_irqrestore_rcu_node(snp, flags); - } /* Top of tree, must ensure the grace period will be started. */ - spin_lock_irqsave_rcu_node(ssp, flags); - if (ULONG_CMP_LT(ssp->srcu_gp_seq_needed, s)) { + spin_lock_irqsave_ssp_contention(ssp, &flags); + if (ULONG_CMP_LT(sup->srcu_gp_seq_needed, s)) { /* * Record need for grace period s. Pair with load * acquire setting up for initialization. */ - smp_store_release(&ssp->srcu_gp_seq_needed, s); /*^^^*/ + smp_store_release(&sup->srcu_gp_seq_needed, s); /*^^^*/ } - if (!do_norm && ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s)) - WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s); + if (!do_norm && ULONG_CMP_LT(sup->srcu_gp_seq_needed_exp, s)) + WRITE_ONCE(sup->srcu_gp_seq_needed_exp, s); - /* If grace period not already done and none in progress, start it. */ - if (!rcu_seq_done(&ssp->srcu_gp_seq, s) && - rcu_seq_state(ssp->srcu_gp_seq) == SRCU_STATE_IDLE) { - WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)); + /* If grace period not already in progress, start it. */ + if (!WARN_ON_ONCE(rcu_seq_done(&sup->srcu_gp_seq, s)) && + rcu_seq_state(sup->srcu_gp_seq) == SRCU_STATE_IDLE) { + WARN_ON_ONCE(ULONG_CMP_GE(sup->srcu_gp_seq, sup->srcu_gp_seq_needed)); srcu_gp_start(ssp); + + // And how can that list_add() in the "else" clause + // possibly be safe for concurrent execution? Well, + // it isn't. And it does not have to be. After all, it + // can only be executed during early boot when there is only + // the one boot CPU running with interrupts still disabled. if (likely(srcu_init_done)) - queue_delayed_work(rcu_gp_wq, &ssp->work, - srcu_get_delay(ssp)); - else if (list_empty(&ssp->work.work.entry)) - list_add(&ssp->work.work.entry, &srcu_boot_list); + queue_delayed_work(rcu_gp_wq, &sup->work, + !!srcu_get_delay(ssp)); + else if (list_empty(&sup->work.work.entry)) + list_add(&sup->work.work.entry, &srcu_boot_list); } - spin_unlock_irqrestore_rcu_node(ssp, flags); + spin_unlock_irqrestore_rcu_node(sup, flags); } /* @@ -699,12 +1070,16 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp, */ static bool try_check_zero(struct srcu_struct *ssp, int idx, int trycount) { + unsigned long curdelay; + + curdelay = !srcu_get_delay(ssp); + for (;;) { if (srcu_readers_active_idx_check(ssp, idx)) return true; - if (--trycount + !srcu_get_delay(ssp) <= 0) + if ((--trycount + curdelay) <= 0) return false; - udelay(SRCU_RETRY_CHECK_DELAY); + udelay(srcu_retry_check_delay); } } @@ -716,23 +1091,44 @@ static bool try_check_zero(struct srcu_struct *ssp, int idx, int trycount) static void srcu_flip(struct srcu_struct *ssp) { /* - * Ensure that if this updater saw a given reader's increment - * from __srcu_read_lock(), that reader was using an old value - * of ->srcu_idx. Also ensure that if a given reader sees the - * new value of ->srcu_idx, this updater's earlier scans cannot - * have seen that reader's increments (which is OK, because this - * grace period need not wait on that reader). + * Because the flip of ->srcu_idx is executed only if the + * preceding call to srcu_readers_active_idx_check() found that + * the ->srcu_unlock_count[] and ->srcu_lock_count[] sums matched + * and because that summing uses atomic_long_read(), there is + * ordering due to a control dependency between that summing and + * the WRITE_ONCE() in this call to srcu_flip(). This ordering + * ensures that if this updater saw a given reader's increment from + * __srcu_read_lock(), that reader was using a value of ->srcu_idx + * from before the previous call to srcu_flip(), which should be + * quite rare. This ordering thus helps forward progress because + * the grace period could otherwise be delayed by additional + * calls to __srcu_read_lock() using that old (soon to be new) + * value of ->srcu_idx. + * + * This sum-equality check and ordering also ensures that if + * a given call to __srcu_read_lock() uses the new value of + * ->srcu_idx, this updater's earlier scans cannot have seen + * that reader's increments, which is all to the good, because + * this grace period need not wait on that reader. After all, + * if those earlier scans had seen that reader, there would have + * been a sum mismatch and this code would not be reached. + * + * This means that the following smp_mb() is redundant, but + * it stays until either (1) Compilers learn about this sort of + * control dependency or (2) Some production workload running on + * a production system is unduly delayed by this slowpath smp_mb(). */ smp_mb(); /* E */ /* Pairs with B and C. */ - WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); + WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); // Flip the counter. /* * Ensure that if the updater misses an __srcu_read_unlock() - * increment, that task's next __srcu_read_lock() will see the - * above counter update. Note that both this memory barrier - * and the one in srcu_readers_active_idx_check() provide the - * guarantee for __srcu_read_lock(). + * increment, that task's __srcu_read_lock() following its next + * __srcu_read_lock() or __srcu_read_unlock() will see the above + * counter update. Note that both this memory barrier and the + * one in srcu_readers_active_idx_check() provide the guarantee + * for __srcu_read_lock(). */ smp_mb(); /* D */ /* Pairs with C. */ } @@ -777,25 +1173,25 @@ static bool srcu_might_be_idle(struct srcu_struct *ssp) spin_unlock_irqrestore_rcu_node(sdp, flags); /* - * No local callbacks, so probabalistically probe global state. + * No local callbacks, so probabilistically probe global state. * Exact information would require acquiring locks, which would - * kill scalability, hence the probabalistic nature of the probe. + * kill scalability, hence the probabilistic nature of the probe. */ /* First, see if enough time has passed since the last GP. */ t = ktime_get_mono_fast_ns(); - tlast = READ_ONCE(ssp->srcu_last_gp_end); + tlast = READ_ONCE(ssp->srcu_sup->srcu_last_gp_end); if (exp_holdoff == 0 || time_in_range_open(t, tlast, tlast + exp_holdoff)) return false; /* Too soon after last GP. */ /* Next, check for probable idleness. */ - curseq = rcu_seq_current(&ssp->srcu_gp_seq); + curseq = rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq); smp_mb(); /* Order ->srcu_gp_seq with ->srcu_gp_seq_needed. */ - if (ULONG_CMP_LT(curseq, READ_ONCE(ssp->srcu_gp_seq_needed))) + if (ULONG_CMP_LT(curseq, READ_ONCE(ssp->srcu_sup->srcu_gp_seq_needed))) return false; /* Grace period in progress, so not idle. */ smp_mb(); /* Order ->srcu_gp_seq with prior access. */ - if (curseq != rcu_seq_current(&ssp->srcu_gp_seq)) + if (curseq != rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq)) return false; /* GP # changed, so not idle. */ return true; /* With reasonable probability, idle! */ } @@ -808,6 +1204,93 @@ static void srcu_leak_callback(struct rcu_head *rhp) } /* + * Start an SRCU grace period, and also queue the callback if non-NULL. + */ +static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp, + struct rcu_head *rhp, bool do_norm) +{ + unsigned long flags; + int idx; + bool needexp = false; + bool needgp = false; + unsigned long s; + struct srcu_data *sdp; + struct srcu_node *sdp_mynode; + int ss_state; + + check_init_srcu_struct(ssp); + /* + * While starting a new grace period, make sure we are in an + * SRCU read-side critical section so that the grace-period + * sequence number cannot wrap around in the meantime. + */ + idx = __srcu_read_lock_nmisafe(ssp); + ss_state = smp_load_acquire(&ssp->srcu_sup->srcu_size_state); + if (ss_state < SRCU_SIZE_WAIT_CALL) + sdp = per_cpu_ptr(ssp->sda, get_boot_cpu_id()); + else + sdp = raw_cpu_ptr(ssp->sda); + spin_lock_irqsave_sdp_contention(sdp, &flags); + if (rhp) + rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp); + /* + * The snapshot for acceleration must be taken _before_ the read of the + * current gp sequence used for advancing, otherwise advancing may fail + * and acceleration may then fail too. + * + * This could happen if: + * + * 1) The RCU_WAIT_TAIL segment has callbacks (gp_num = X + 4) and the + * RCU_NEXT_READY_TAIL also has callbacks (gp_num = X + 8). + * + * 2) The grace period for RCU_WAIT_TAIL is seen as started but not + * completed so rcu_seq_current() returns X + SRCU_STATE_SCAN1. + * + * 3) This value is passed to rcu_segcblist_advance() which can't move + * any segment forward and fails. + * + * 4) srcu_gp_start_if_needed() still proceeds with callback acceleration. + * But then the call to rcu_seq_snap() observes the grace period for the + * RCU_WAIT_TAIL segment as completed and the subsequent one for the + * RCU_NEXT_READY_TAIL segment as started (ie: X + 4 + SRCU_STATE_SCAN1) + * so it returns a snapshot of the next grace period, which is X + 12. + * + * 5) The value of X + 12 is passed to rcu_segcblist_accelerate() but the + * freshly enqueued callback in RCU_NEXT_TAIL can't move to + * RCU_NEXT_READY_TAIL which already has callbacks for a previous grace + * period (gp_num = X + 8). So acceleration fails. + */ + s = rcu_seq_snap(&ssp->srcu_sup->srcu_gp_seq); + if (rhp) { + rcu_segcblist_advance(&sdp->srcu_cblist, + rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq)); + WARN_ON_ONCE(!rcu_segcblist_accelerate(&sdp->srcu_cblist, s)); + } + if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) { + sdp->srcu_gp_seq_needed = s; + needgp = true; + } + if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) { + sdp->srcu_gp_seq_needed_exp = s; + needexp = true; + } + spin_unlock_irqrestore_rcu_node(sdp, flags); + + /* Ensure that snp node tree is fully initialized before traversing it */ + if (ss_state < SRCU_SIZE_WAIT_BARRIER) + sdp_mynode = NULL; + else + sdp_mynode = sdp->mynode; + + if (needgp) + srcu_funnel_gp_start(ssp, sdp, s, do_norm); + else if (needexp) + srcu_funnel_exp_start(ssp, sdp_mynode, s); + __srcu_read_unlock_nmisafe(ssp, idx); + return s; +} + +/* * Enqueue an SRCU callback on the srcu_data structure associated with * the current CPU and the specified srcu_struct structure, initiating * grace-period processing if it is not already running. @@ -838,14 +1321,6 @@ static void srcu_leak_callback(struct rcu_head *rhp) static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, rcu_callback_t func, bool do_norm) { - unsigned long flags; - int idx; - bool needexp = false; - bool needgp = false; - unsigned long s; - struct srcu_data *sdp; - - check_init_srcu_struct(ssp); if (debug_rcu_head_queue(rhp)) { /* Probable double call_srcu(), so leak the callback. */ WRITE_ONCE(rhp->func, srcu_leak_callback); @@ -853,28 +1328,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, return; } rhp->func = func; - idx = srcu_read_lock(ssp); - sdp = raw_cpu_ptr(ssp->sda); - spin_lock_irqsave_rcu_node(sdp, flags); - rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp); - rcu_segcblist_advance(&sdp->srcu_cblist, - rcu_seq_current(&ssp->srcu_gp_seq)); - s = rcu_seq_snap(&ssp->srcu_gp_seq); - (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s); - if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) { - sdp->srcu_gp_seq_needed = s; - needgp = true; - } - if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) { - sdp->srcu_gp_seq_needed_exp = s; - needexp = true; - } - spin_unlock_irqrestore_rcu_node(sdp, flags); - if (needgp) - srcu_funnel_gp_start(ssp, sdp, s, do_norm); - else if (needexp) - srcu_funnel_exp_start(ssp, sdp->mynode, s); - srcu_read_unlock(ssp, idx); + (void)srcu_gp_start_if_needed(ssp, rhp, do_norm); } /** @@ -908,6 +1362,8 @@ static void __synchronize_srcu(struct srcu_struct *ssp, bool do_norm) { struct rcu_synchronize rcu; + srcu_lock_sync(&ssp->dep_map); + RCU_LOCKDEP_WARN(lockdep_is_held(ssp) || lock_is_held(&rcu_bh_lock_map) || lock_is_held(&rcu_lock_map) || @@ -989,6 +1445,9 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited); * synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are * passed the same srcu_struct structure. * + * Implementation of these memory-ordering guarantees is similar to + * that of synchronize_rcu(). + * * If SRCU is likely idle, expedite the first request. This semantic * was provided by Classic SRCU, and is relied upon by its users, so TREE * SRCU must also provide it. Note that detecting idleness is heuristic @@ -1003,6 +1462,77 @@ void synchronize_srcu(struct srcu_struct *ssp) } EXPORT_SYMBOL_GPL(synchronize_srcu); +/** + * get_state_synchronize_srcu - Provide an end-of-grace-period cookie + * @ssp: srcu_struct to provide cookie for. + * + * This function returns a cookie that can be passed to + * poll_state_synchronize_srcu(), which will return true if a full grace + * period has elapsed in the meantime. It is the caller's responsibility + * to make sure that grace period happens, for example, by invoking + * call_srcu() after return from get_state_synchronize_srcu(). + */ +unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp) +{ + // Any prior manipulation of SRCU-protected data must happen + // before the load from ->srcu_gp_seq. + smp_mb(); + return rcu_seq_snap(&ssp->srcu_sup->srcu_gp_seq); +} +EXPORT_SYMBOL_GPL(get_state_synchronize_srcu); + +/** + * start_poll_synchronize_srcu - Provide cookie and start grace period + * @ssp: srcu_struct to provide cookie for. + * + * This function returns a cookie that can be passed to + * poll_state_synchronize_srcu(), which will return true if a full grace + * period has elapsed in the meantime. Unlike get_state_synchronize_srcu(), + * this function also ensures that any needed SRCU grace period will be + * started. This convenience does come at a cost in terms of CPU overhead. + */ +unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp) +{ + return srcu_gp_start_if_needed(ssp, NULL, true); +} +EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu); + +/** + * poll_state_synchronize_srcu - Has cookie's grace period ended? + * @ssp: srcu_struct to provide cookie for. + * @cookie: Return value from get_state_synchronize_srcu() or start_poll_synchronize_srcu(). + * + * This function takes the cookie that was returned from either + * get_state_synchronize_srcu() or start_poll_synchronize_srcu(), and + * returns @true if an SRCU grace period elapsed since the time that the + * cookie was created. + * + * Because cookies are finite in size, wrapping/overflow is possible. + * This is more pronounced on 32-bit systems where cookies are 32 bits, + * where in theory wrapping could happen in about 14 hours assuming + * 25-microsecond expedited SRCU grace periods. However, a more likely + * overflow lower bound is on the order of 24 days in the case of + * one-millisecond SRCU grace periods. Of course, wrapping in a 64-bit + * system requires geologic timespans, as in more than seven million years + * even for expedited SRCU grace periods. + * + * Wrapping/overflow is much more of an issue for CONFIG_SMP=n systems + * that also have CONFIG_PREEMPTION=n, which selects Tiny SRCU. This uses + * a 16-bit cookie, which rcutorture routinely wraps in a matter of a + * few minutes. If this proves to be a problem, this counter will be + * expanded to the same size as for Tree SRCU. + */ +bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie) +{ + if (!rcu_seq_done(&ssp->srcu_sup->srcu_gp_seq, cookie)) + return false; + // Ensure that the end of the SRCU grace period happens before + // any subsequent code that the caller might execute. + smp_mb(); // ^^^ + return true; +} +EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu); + /* * Callback function for srcu_barrier() use. */ @@ -1013,8 +1543,30 @@ static void srcu_barrier_cb(struct rcu_head *rhp) sdp = container_of(rhp, struct srcu_data, srcu_barrier_head); ssp = sdp->ssp; - if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt)) - complete(&ssp->srcu_barrier_completion); + if (atomic_dec_and_test(&ssp->srcu_sup->srcu_barrier_cpu_cnt)) + complete(&ssp->srcu_sup->srcu_barrier_completion); +} + +/* + * Enqueue an srcu_barrier() callback on the specified srcu_data + * structure's ->cblist. but only if that ->cblist already has at least one + * callback enqueued. Note that if a CPU already has callbacks enqueue, + * it must have already registered the need for a future grace period, + * so all we need do is enqueue a callback that will use the same grace + * period as the last callback already in the queue. + */ +static void srcu_barrier_one_cpu(struct srcu_struct *ssp, struct srcu_data *sdp) +{ + spin_lock_irq_rcu_node(sdp); + atomic_inc(&ssp->srcu_sup->srcu_barrier_cpu_cnt); + sdp->srcu_barrier_head.func = srcu_barrier_cb; + debug_rcu_head_queue(&sdp->srcu_barrier_head); + if (!rcu_segcblist_entrain(&sdp->srcu_cblist, + &sdp->srcu_barrier_head)) { + debug_rcu_head_unqueue(&sdp->srcu_barrier_head); + atomic_dec(&ssp->srcu_sup->srcu_barrier_cpu_cnt); + } + spin_unlock_irq_rcu_node(sdp); } /** @@ -1024,51 +1576,37 @@ static void srcu_barrier_cb(struct rcu_head *rhp) void srcu_barrier(struct srcu_struct *ssp) { int cpu; - struct srcu_data *sdp; - unsigned long s = rcu_seq_snap(&ssp->srcu_barrier_seq); + int idx; + unsigned long s = rcu_seq_snap(&ssp->srcu_sup->srcu_barrier_seq); check_init_srcu_struct(ssp); - mutex_lock(&ssp->srcu_barrier_mutex); - if (rcu_seq_done(&ssp->srcu_barrier_seq, s)) { + mutex_lock(&ssp->srcu_sup->srcu_barrier_mutex); + if (rcu_seq_done(&ssp->srcu_sup->srcu_barrier_seq, s)) { smp_mb(); /* Force ordering following return. */ - mutex_unlock(&ssp->srcu_barrier_mutex); + mutex_unlock(&ssp->srcu_sup->srcu_barrier_mutex); return; /* Someone else did our work for us. */ } - rcu_seq_start(&ssp->srcu_barrier_seq); - init_completion(&ssp->srcu_barrier_completion); + rcu_seq_start(&ssp->srcu_sup->srcu_barrier_seq); + init_completion(&ssp->srcu_sup->srcu_barrier_completion); /* Initial count prevents reaching zero until all CBs are posted. */ - atomic_set(&ssp->srcu_barrier_cpu_cnt, 1); + atomic_set(&ssp->srcu_sup->srcu_barrier_cpu_cnt, 1); - /* - * Each pass through this loop enqueues a callback, but only - * on CPUs already having callbacks enqueued. Note that if - * a CPU already has callbacks enqueue, it must have already - * registered the need for a future grace period, so all we - * need do is enqueue a callback that will use the same - * grace period as the last callback already in the queue. - */ - for_each_possible_cpu(cpu) { - sdp = per_cpu_ptr(ssp->sda, cpu); - spin_lock_irq_rcu_node(sdp); - atomic_inc(&ssp->srcu_barrier_cpu_cnt); - sdp->srcu_barrier_head.func = srcu_barrier_cb; - debug_rcu_head_queue(&sdp->srcu_barrier_head); - if (!rcu_segcblist_entrain(&sdp->srcu_cblist, - &sdp->srcu_barrier_head)) { - debug_rcu_head_unqueue(&sdp->srcu_barrier_head); - atomic_dec(&ssp->srcu_barrier_cpu_cnt); - } - spin_unlock_irq_rcu_node(sdp); - } + idx = __srcu_read_lock_nmisafe(ssp); + if (smp_load_acquire(&ssp->srcu_sup->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER) + srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, get_boot_cpu_id())); + else + for_each_possible_cpu(cpu) + srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, cpu)); + __srcu_read_unlock_nmisafe(ssp, idx); /* Remove the initial count, at which point reaching zero can happen. */ - if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt)) - complete(&ssp->srcu_barrier_completion); - wait_for_completion(&ssp->srcu_barrier_completion); + if (atomic_dec_and_test(&ssp->srcu_sup->srcu_barrier_cpu_cnt)) + complete(&ssp->srcu_sup->srcu_barrier_completion); + wait_for_completion(&ssp->srcu_sup->srcu_barrier_completion); - rcu_seq_end(&ssp->srcu_barrier_seq); - mutex_unlock(&ssp->srcu_barrier_mutex); + rcu_seq_end(&ssp->srcu_sup->srcu_barrier_seq); + mutex_unlock(&ssp->srcu_sup->srcu_barrier_mutex); } EXPORT_SYMBOL_GPL(srcu_barrier); @@ -1094,7 +1632,7 @@ static void srcu_advance_state(struct srcu_struct *ssp) { int idx; - mutex_lock(&ssp->srcu_gp_mutex); + mutex_lock(&ssp->srcu_sup->srcu_gp_mutex); /* * Because readers might be delayed for an extended period after @@ -1106,38 +1644,39 @@ static void srcu_advance_state(struct srcu_struct *ssp) * The load-acquire ensures that we see the accesses performed * by the prior grace period. */ - idx = rcu_seq_state(smp_load_acquire(&ssp->srcu_gp_seq)); /* ^^^ */ + idx = rcu_seq_state(smp_load_acquire(&ssp->srcu_sup->srcu_gp_seq)); /* ^^^ */ if (idx == SRCU_STATE_IDLE) { - spin_lock_irq_rcu_node(ssp); - if (ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)) { - WARN_ON_ONCE(rcu_seq_state(ssp->srcu_gp_seq)); - spin_unlock_irq_rcu_node(ssp); - mutex_unlock(&ssp->srcu_gp_mutex); + spin_lock_irq_rcu_node(ssp->srcu_sup); + if (ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed)) { + WARN_ON_ONCE(rcu_seq_state(ssp->srcu_sup->srcu_gp_seq)); + spin_unlock_irq_rcu_node(ssp->srcu_sup); + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; } - idx = rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)); + idx = rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)); if (idx == SRCU_STATE_IDLE) srcu_gp_start(ssp); - spin_unlock_irq_rcu_node(ssp); + spin_unlock_irq_rcu_node(ssp->srcu_sup); if (idx != SRCU_STATE_IDLE) { - mutex_unlock(&ssp->srcu_gp_mutex); + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; /* Someone else started the grace period. */ } } - if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN1) { + if (rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)) == SRCU_STATE_SCAN1) { idx = 1 ^ (ssp->srcu_idx & 1); if (!try_check_zero(ssp, idx, 1)) { - mutex_unlock(&ssp->srcu_gp_mutex); + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; /* readers present, retry later. */ } srcu_flip(ssp); - spin_lock_irq_rcu_node(ssp); - rcu_seq_set_state(&ssp->srcu_gp_seq, SRCU_STATE_SCAN2); - spin_unlock_irq_rcu_node(ssp); + spin_lock_irq_rcu_node(ssp->srcu_sup); + rcu_seq_set_state(&ssp->srcu_sup->srcu_gp_seq, SRCU_STATE_SCAN2); + ssp->srcu_sup->srcu_n_exp_nodelay = 0; + spin_unlock_irq_rcu_node(ssp->srcu_sup); } - if (rcu_seq_state(READ_ONCE(ssp->srcu_gp_seq)) == SRCU_STATE_SCAN2) { + if (rcu_seq_state(READ_ONCE(ssp->srcu_sup->srcu_gp_seq)) == SRCU_STATE_SCAN2) { /* * SRCU read-side critical sections are normally short, @@ -1145,9 +1684,10 @@ static void srcu_advance_state(struct srcu_struct *ssp) */ idx = 1 ^ (ssp->srcu_idx & 1); if (!try_check_zero(ssp, idx, 2)) { - mutex_unlock(&ssp->srcu_gp_mutex); + mutex_unlock(&ssp->srcu_sup->srcu_gp_mutex); return; /* readers present, retry later. */ } + ssp->srcu_sup->srcu_n_exp_nodelay = 0; srcu_gp_end(ssp); /* Releases ->srcu_gp_mutex. */ } } @@ -1160,6 +1700,7 @@ static void srcu_advance_state(struct srcu_struct *ssp) */ static void srcu_invoke_callbacks(struct work_struct *work) { + long len; bool more; struct rcu_cblist ready_cbs; struct rcu_head *rhp; @@ -1171,8 +1712,14 @@ static void srcu_invoke_callbacks(struct work_struct *work) ssp = sdp->ssp; rcu_cblist_init(&ready_cbs); spin_lock_irq_rcu_node(sdp); + WARN_ON_ONCE(!rcu_segcblist_segempty(&sdp->srcu_cblist, RCU_NEXT_TAIL)); rcu_segcblist_advance(&sdp->srcu_cblist, - rcu_seq_current(&ssp->srcu_gp_seq)); + rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq)); + /* + * Although this function is theoretically re-entrant, concurrent + * callbacks invocation is disallowed to avoid executing an SRCU barrier + * too early. + */ if (sdp->srcu_cblist_invoking || !rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) { spin_unlock_irq_rcu_node(sdp); @@ -1182,26 +1729,28 @@ static void srcu_invoke_callbacks(struct work_struct *work) /* We are on the job! Extract and invoke ready callbacks. */ sdp->srcu_cblist_invoking = true; rcu_segcblist_extract_done_cbs(&sdp->srcu_cblist, &ready_cbs); + len = ready_cbs.len; spin_unlock_irq_rcu_node(sdp); rhp = rcu_cblist_dequeue(&ready_cbs); for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) { debug_rcu_head_unqueue(rhp); + debug_rcu_head_callback(rhp); local_bh_disable(); rhp->func(rhp); local_bh_enable(); } + WARN_ON_ONCE(ready_cbs.len); /* * Update counts, accelerate new callbacks, and if needed, * schedule another round of callback invocation. */ spin_lock_irq_rcu_node(sdp); - rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs); - (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, - rcu_seq_snap(&ssp->srcu_gp_seq)); + rcu_segcblist_add_len(&sdp->srcu_cblist, -len); sdp->srcu_cblist_invoking = false; more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist); spin_unlock_irq_rcu_node(sdp); + /* An SRCU barrier or callbacks from previous nesting work pending */ if (more) srcu_schedule_cbs_sdp(sdp, 0); } @@ -1214,20 +1763,20 @@ static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay) { bool pushgp = true; - spin_lock_irq_rcu_node(ssp); - if (ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)) { - if (!WARN_ON_ONCE(rcu_seq_state(ssp->srcu_gp_seq))) { + spin_lock_irq_rcu_node(ssp->srcu_sup); + if (ULONG_CMP_GE(ssp->srcu_sup->srcu_gp_seq, ssp->srcu_sup->srcu_gp_seq_needed)) { + if (!WARN_ON_ONCE(rcu_seq_state(ssp->srcu_sup->srcu_gp_seq))) { /* All requests fulfilled, time to go idle. */ pushgp = false; } - } else if (!rcu_seq_state(ssp->srcu_gp_seq)) { + } else if (!rcu_seq_state(ssp->srcu_sup->srcu_gp_seq)) { /* Outstanding request and no GP. Start one. */ srcu_gp_start(ssp); } - spin_unlock_irq_rcu_node(ssp); + spin_unlock_irq_rcu_node(ssp->srcu_sup); if (pushgp) - queue_delayed_work(rcu_gp_wq, &ssp->work, delay); + queue_delayed_work(rcu_gp_wq, &ssp->srcu_sup->work, delay); } /* @@ -1235,12 +1784,30 @@ static void srcu_reschedule(struct srcu_struct *ssp, unsigned long delay) */ static void process_srcu(struct work_struct *work) { + unsigned long curdelay; + unsigned long j; struct srcu_struct *ssp; + struct srcu_usage *sup; - ssp = container_of(work, struct srcu_struct, work.work); + sup = container_of(work, struct srcu_usage, work.work); + ssp = sup->srcu_ssp; srcu_advance_state(ssp); - srcu_reschedule(ssp, srcu_get_delay(ssp)); + curdelay = srcu_get_delay(ssp); + if (curdelay) { + WRITE_ONCE(sup->reschedule_count, 0); + } else { + j = jiffies; + if (READ_ONCE(sup->reschedule_jiffies) == j) { + WRITE_ONCE(sup->reschedule_count, READ_ONCE(sup->reschedule_count) + 1); + if (READ_ONCE(sup->reschedule_count) > srcu_max_nodelay) + curdelay = 1; + } else { + WRITE_ONCE(sup->reschedule_count, 1); + WRITE_ONCE(sup->reschedule_jiffies, j); + } + } + srcu_reschedule(ssp, curdelay); } void srcutorture_get_gp_data(enum rcutorture_type test_type, @@ -1250,47 +1817,73 @@ void srcutorture_get_gp_data(enum rcutorture_type test_type, if (test_type != SRCU_FLAVOR) return; *flags = 0; - *gp_seq = rcu_seq_current(&ssp->srcu_gp_seq); + *gp_seq = rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq); } EXPORT_SYMBOL_GPL(srcutorture_get_gp_data); +static const char * const srcu_size_state_name[] = { + "SRCU_SIZE_SMALL", + "SRCU_SIZE_ALLOC", + "SRCU_SIZE_WAIT_BARRIER", + "SRCU_SIZE_WAIT_CALL", + "SRCU_SIZE_WAIT_CBS1", + "SRCU_SIZE_WAIT_CBS2", + "SRCU_SIZE_WAIT_CBS3", + "SRCU_SIZE_WAIT_CBS4", + "SRCU_SIZE_BIG", + "SRCU_SIZE_???", +}; + void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf) { int cpu; int idx; unsigned long s0 = 0, s1 = 0; + int ss_state = READ_ONCE(ssp->srcu_sup->srcu_size_state); + int ss_state_idx = ss_state; idx = ssp->srcu_idx & 0x1; - pr_alert("%s%s Tree SRCU g%ld per-CPU(idx=%d):", - tt, tf, rcu_seq_current(&ssp->srcu_gp_seq), idx); - for_each_possible_cpu(cpu) { - unsigned long l0, l1; - unsigned long u0, u1; - long c0, c1; - struct srcu_data *sdp; - - sdp = per_cpu_ptr(ssp->sda, cpu); - u0 = data_race(sdp->srcu_unlock_count[!idx]); - u1 = data_race(sdp->srcu_unlock_count[idx]); - - /* - * Make sure that a lock is always counted if the corresponding - * unlock is counted. - */ - smp_rmb(); - - l0 = data_race(sdp->srcu_lock_count[!idx]); - l1 = data_race(sdp->srcu_lock_count[idx]); - - c0 = l0 - u0; - c1 = l1 - u1; - pr_cont(" %d(%ld,%ld %c)", - cpu, c0, c1, - "C."[rcu_segcblist_empty(&sdp->srcu_cblist)]); - s0 += c0; - s1 += c1; + if (ss_state < 0 || ss_state >= ARRAY_SIZE(srcu_size_state_name)) + ss_state_idx = ARRAY_SIZE(srcu_size_state_name) - 1; + pr_alert("%s%s Tree SRCU g%ld state %d (%s)", + tt, tf, rcu_seq_current(&ssp->srcu_sup->srcu_gp_seq), ss_state, + srcu_size_state_name[ss_state_idx]); + if (!ssp->sda) { + // Called after cleanup_srcu_struct(), perhaps. + pr_cont(" No per-CPU srcu_data structures (->sda == NULL).\n"); + } else { + pr_cont(" per-CPU(idx=%d):", idx); + for_each_possible_cpu(cpu) { + unsigned long l0, l1; + unsigned long u0, u1; + long c0, c1; + struct srcu_data *sdp; + + sdp = per_cpu_ptr(ssp->sda, cpu); + u0 = data_race(atomic_long_read(&sdp->srcu_unlock_count[!idx])); + u1 = data_race(atomic_long_read(&sdp->srcu_unlock_count[idx])); + + /* + * Make sure that a lock is always counted if the corresponding + * unlock is counted. + */ + smp_rmb(); + + l0 = data_race(atomic_long_read(&sdp->srcu_lock_count[!idx])); + l1 = data_race(atomic_long_read(&sdp->srcu_lock_count[idx])); + + c0 = l0 - u0; + c1 = l1 - u1; + pr_cont(" %d(%ld,%ld %c)", + cpu, c0, c1, + "C."[rcu_segcblist_empty(&sdp->srcu_cblist)]); + s0 += c0; + s1 += c1; + } + pr_cont(" T(%ld,%ld)\n", s0, s1); } - pr_cont(" T(%ld,%ld)\n", s0, s1); + if (SRCU_SIZING_IS_TORTURE()) + srcu_transition_to_big(ssp); } EXPORT_SYMBOL_GPL(srcu_torture_stats_print); @@ -1299,21 +1892,44 @@ static int __init srcu_bootup_announce(void) pr_info("Hierarchical SRCU implementation.\n"); if (exp_holdoff != DEFAULT_SRCU_EXP_HOLDOFF) pr_info("\tNon-default auto-expedite holdoff of %lu ns.\n", exp_holdoff); + if (srcu_retry_check_delay != SRCU_DEFAULT_RETRY_CHECK_DELAY) + pr_info("\tNon-default retry check delay of %lu us.\n", srcu_retry_check_delay); + if (srcu_max_nodelay != SRCU_DEFAULT_MAX_NODELAY) + pr_info("\tNon-default max no-delay of %lu.\n", srcu_max_nodelay); + pr_info("\tMax phase no-delay instances is %lu.\n", srcu_max_nodelay_phase); return 0; } early_initcall(srcu_bootup_announce); void __init srcu_init(void) { - struct srcu_struct *ssp; + struct srcu_usage *sup; + + /* Decide on srcu_struct-size strategy. */ + if (SRCU_SIZING_IS(SRCU_SIZING_AUTO)) { + if (nr_cpu_ids >= big_cpu_lim) { + convert_to_big = SRCU_SIZING_INIT; // Don't bother waiting for contention. + pr_info("%s: Setting srcu_struct sizes to big.\n", __func__); + } else { + convert_to_big = SRCU_SIZING_NONE | SRCU_SIZING_CONTEND; + pr_info("%s: Setting srcu_struct sizes based on contention.\n", __func__); + } + } + /* + * Once that is set, call_srcu() can follow the normal path and + * queue delayed work. This must follow RCU workqueues creation + * and timers initialization. + */ srcu_init_done = true; while (!list_empty(&srcu_boot_list)) { - ssp = list_first_entry(&srcu_boot_list, struct srcu_struct, + sup = list_first_entry(&srcu_boot_list, struct srcu_usage, work.work.entry); - check_init_srcu_struct(ssp); - list_del_init(&ssp->work.work.entry); - queue_work(rcu_gp_wq, &ssp->work.work); + list_del_init(&sup->work.work.entry); + if (SRCU_SIZING_IS(SRCU_SIZING_INIT) && + sup->srcu_size_state == SRCU_SIZE_SMALL) + sup->srcu_size_state = SRCU_SIZE_ALLOC; + queue_work(rcu_gp_wq, &sup->work.work); } } @@ -1323,13 +1939,14 @@ void __init srcu_init(void) static int srcu_module_coming(struct module *mod) { int i; + struct srcu_struct *ssp; struct srcu_struct **sspp = mod->srcu_struct_ptrs; - int ret; for (i = 0; i < mod->num_srcu_structs; i++) { - ret = init_srcu_struct(*(sspp++)); - if (WARN_ON_ONCE(ret)) - return ret; + ssp = *(sspp++); + ssp->sda = alloc_percpu(struct srcu_data); + if (WARN_ON_ONCE(!ssp->sda)) + return -ENOMEM; } return 0; } @@ -1338,10 +1955,17 @@ static int srcu_module_coming(struct module *mod) static void srcu_module_going(struct module *mod) { int i; + struct srcu_struct *ssp; struct srcu_struct **sspp = mod->srcu_struct_ptrs; - for (i = 0; i < mod->num_srcu_structs; i++) - cleanup_srcu_struct(*(sspp++)); + for (i = 0; i < mod->num_srcu_structs; i++) { + ssp = *(sspp++); + if (!rcu_seq_state(smp_load_acquire(&ssp->srcu_sup->srcu_gp_seq_needed)) && + !WARN_ON_ONCE(!ssp->srcu_sup->sda_is_static)) + cleanup_srcu_struct(ssp); + if (!WARN_ON(srcu_readers_active(ssp))) + free_percpu(ssp->sda); + } } /* Handle one module, either coming or going. */ diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c index d4558ab7a07d..e550f97779b8 100644 --- a/kernel/rcu/sync.c +++ b/kernel/rcu/sync.c @@ -44,7 +44,7 @@ static void rcu_sync_func(struct rcu_head *rhp); static void rcu_sync_call(struct rcu_sync *rsp) { - call_rcu(&rsp->cb_head, rcu_sync_func); + call_rcu_hurry(&rsp->cb_head, rcu_sync_func); } /** @@ -94,9 +94,9 @@ static void rcu_sync_func(struct rcu_head *rhp) rcu_sync_call(rsp); } else { /* - * We're at least a GP after the last rcu_sync_exit(); eveybody + * We're at least a GP after the last rcu_sync_exit(); everybody * will now have observed the write side critical section. - * Let 'em rip!. + * Let 'em rip! */ WRITE_ONCE(rsp->gp_state, GP_IDLE); } @@ -111,7 +111,7 @@ static void rcu_sync_func(struct rcu_head *rhp) * a slowpath during the update. After this function returns, all * subsequent calls to rcu_sync_is_idle() will return false, which * tells readers to stay off their fastpaths. A later call to - * rcu_sync_exit() re-enables reader slowpaths. + * rcu_sync_exit() re-enables reader fastpaths. * * When called in isolation, rcu_sync_enter() must wait for a grace * period, however, closely spaced calls to rcu_sync_enter() can diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 36607551f966..732ad5b39946 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -6,6 +6,7 @@ */ #ifdef CONFIG_TASKS_RCU_GENERIC +#include "rcu_segcblist.h" //////////////////////////////////////////////////////////////////////// // @@ -13,51 +14,90 @@ struct rcu_tasks; typedef void (*rcu_tasks_gp_func_t)(struct rcu_tasks *rtp); -typedef void (*pregp_func_t)(void); +typedef void (*pregp_func_t)(struct list_head *hop); typedef void (*pertask_func_t)(struct task_struct *t, struct list_head *hop); typedef void (*postscan_func_t)(struct list_head *hop); typedef void (*holdouts_func_t)(struct list_head *hop, bool ndrpt, bool *frptp); typedef void (*postgp_func_t)(struct rcu_tasks *rtp); /** - * Definition for a Tasks-RCU-like mechanism. - * @cbs_head: Head of callback list. - * @cbs_tail: Tail pointer for callback list. - * @cbs_wq: Wait queue allowning new callback to get kthread's attention. - * @cbs_lock: Lock protecting callback list. - * @kthread_ptr: This flavor's grace-period/callback-invocation kthread. + * struct rcu_tasks_percpu - Per-CPU component of definition for a Tasks-RCU-like mechanism. + * @cblist: Callback list. + * @lock: Lock protecting per-CPU callback list. + * @rtp_jiffies: Jiffies counter value for statistics. + * @lazy_timer: Timer to unlazify callbacks. + * @urgent_gp: Number of additional non-lazy grace periods. + * @rtp_n_lock_retries: Rough lock-contention statistic. + * @rtp_work: Work queue for invoking callbacks. + * @rtp_irq_work: IRQ work queue for deferred wakeups. + * @barrier_q_head: RCU callback for barrier operation. + * @rtp_blkd_tasks: List of tasks blocked as readers. + * @cpu: CPU number corresponding to this entry. + * @rtpp: Pointer to the rcu_tasks structure. + */ +struct rcu_tasks_percpu { + struct rcu_segcblist cblist; + raw_spinlock_t __private lock; + unsigned long rtp_jiffies; + unsigned long rtp_n_lock_retries; + struct timer_list lazy_timer; + unsigned int urgent_gp; + struct work_struct rtp_work; + struct irq_work rtp_irq_work; + struct rcu_head barrier_q_head; + struct list_head rtp_blkd_tasks; + int cpu; + struct rcu_tasks *rtpp; +}; + +/** + * struct rcu_tasks - Definition for a Tasks-RCU-like mechanism. + * @cbs_wait: RCU wait allowing a new callback to get kthread's attention. + * @cbs_gbl_lock: Lock protecting callback list. + * @tasks_gp_mutex: Mutex protecting grace period, needed during mid-boot dead zone. * @gp_func: This flavor's grace-period-wait function. * @gp_state: Grace period's most recent state transition (debugging). * @gp_sleep: Per-grace-period sleep to prevent CPU-bound looping. * @init_fract: Initial backoff sleep interval. * @gp_jiffies: Time of last @gp_state transition. * @gp_start: Most recent grace-period start in jiffies. - * @n_gps: Number of grace periods completed since boot. + * @tasks_gp_seq: Number of grace periods completed since boot. * @n_ipis: Number of IPIs sent to encourage grace periods to end. * @n_ipis_fails: Number of IPI-send failures. + * @kthread_ptr: This flavor's grace-period/callback-invocation kthread. + * @lazy_jiffies: Number of jiffies to allow callbacks to be lazy. * @pregp_func: This flavor's pre-grace-period function (optional). * @pertask_func: This flavor's per-task scan function (optional). * @postscan_func: This flavor's post-task scan function (optional). - * @holdout_func: This flavor's holdout-list scan function (optional). + * @holdouts_func: This flavor's holdout-list scan function (optional). * @postgp_func: This flavor's post-grace-period function (optional). * @call_func: This flavor's call_rcu()-equivalent function. + * @rtpcpu: This flavor's rcu_tasks_percpu structure. + * @percpu_enqueue_shift: Shift down CPU ID this much when enqueuing callbacks. + * @percpu_enqueue_lim: Number of per-CPU callback queues in use for enqueuing. + * @percpu_dequeue_lim: Number of per-CPU callback queues in use for dequeuing. + * @percpu_dequeue_gpseq: RCU grace-period number to propagate enqueue limit to dequeuers. + * @barrier_q_mutex: Serialize barrier operations. + * @barrier_q_count: Number of queues being waited on. + * @barrier_q_completion: Barrier wait/wakeup mechanism. + * @barrier_q_seq: Sequence number for barrier operations. * @name: This flavor's textual name. * @kname: This flavor's kthread name. */ struct rcu_tasks { - struct rcu_head *cbs_head; - struct rcu_head **cbs_tail; - struct wait_queue_head cbs_wq; - raw_spinlock_t cbs_lock; + struct rcuwait cbs_wait; + raw_spinlock_t cbs_gbl_lock; + struct mutex tasks_gp_mutex; int gp_state; int gp_sleep; int init_fract; unsigned long gp_jiffies; unsigned long gp_start; - unsigned long n_gps; + unsigned long tasks_gp_seq; unsigned long n_ipis; unsigned long n_ipis_fails; struct task_struct *kthread_ptr; + unsigned long lazy_jiffies; rcu_tasks_gp_func_t gp_func; pregp_func_t pregp_func; pertask_func_t pertask_func; @@ -65,34 +105,79 @@ struct rcu_tasks { holdouts_func_t holdouts_func; postgp_func_t postgp_func; call_rcu_func_t call_func; + struct rcu_tasks_percpu __percpu *rtpcpu; + int percpu_enqueue_shift; + int percpu_enqueue_lim; + int percpu_dequeue_lim; + unsigned long percpu_dequeue_gpseq; + struct mutex barrier_q_mutex; + atomic_t barrier_q_count; + struct completion barrier_q_completion; + unsigned long barrier_q_seq; char *name; char *kname; }; -#define DEFINE_RCU_TASKS(rt_name, gp, call, n) \ -static struct rcu_tasks rt_name = \ -{ \ - .cbs_tail = &rt_name.cbs_head, \ - .cbs_wq = __WAIT_QUEUE_HEAD_INITIALIZER(rt_name.cbs_wq), \ - .cbs_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_lock), \ - .gp_func = gp, \ - .call_func = call, \ - .name = n, \ - .kname = #rt_name, \ +static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp); + +#define DEFINE_RCU_TASKS(rt_name, gp, call, n) \ +static DEFINE_PER_CPU(struct rcu_tasks_percpu, rt_name ## __percpu) = { \ + .lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name ## __percpu.cbs_pcpu_lock), \ + .rtp_irq_work = IRQ_WORK_INIT_HARD(call_rcu_tasks_iw_wakeup), \ +}; \ +static struct rcu_tasks rt_name = \ +{ \ + .cbs_wait = __RCUWAIT_INITIALIZER(rt_name.wait), \ + .cbs_gbl_lock = __RAW_SPIN_LOCK_UNLOCKED(rt_name.cbs_gbl_lock), \ + .tasks_gp_mutex = __MUTEX_INITIALIZER(rt_name.tasks_gp_mutex), \ + .gp_func = gp, \ + .call_func = call, \ + .rtpcpu = &rt_name ## __percpu, \ + .lazy_jiffies = DIV_ROUND_UP(HZ, 4), \ + .name = n, \ + .percpu_enqueue_shift = order_base_2(CONFIG_NR_CPUS), \ + .percpu_enqueue_lim = 1, \ + .percpu_dequeue_lim = 1, \ + .barrier_q_mutex = __MUTEX_INITIALIZER(rt_name.barrier_q_mutex), \ + .barrier_q_seq = (0UL - 50UL) << RCU_SEQ_CTR_SHIFT, \ + .kname = #rt_name, \ } +#ifdef CONFIG_TASKS_RCU /* Track exiting tasks in order to allow them to be waited for. */ DEFINE_STATIC_SRCU(tasks_rcu_exit_srcu); +/* Report delay in synchronize_srcu() completion in rcu_tasks_postscan(). */ +static void tasks_rcu_exit_srcu_stall(struct timer_list *unused); +static DEFINE_TIMER(tasks_rcu_exit_srcu_stall_timer, tasks_rcu_exit_srcu_stall); +#endif + /* Avoid IPIing CPUs early in the grace period. */ #define RCU_TASK_IPI_DELAY (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) ? HZ / 2 : 0) static int rcu_task_ipi_delay __read_mostly = RCU_TASK_IPI_DELAY; module_param(rcu_task_ipi_delay, int, 0644); /* Control stall timeouts. Disable with <= 0, otherwise jiffies till stall. */ +#define RCU_TASK_BOOT_STALL_TIMEOUT (HZ * 30) #define RCU_TASK_STALL_TIMEOUT (HZ * 60 * 10) static int rcu_task_stall_timeout __read_mostly = RCU_TASK_STALL_TIMEOUT; module_param(rcu_task_stall_timeout, int, 0644); +#define RCU_TASK_STALL_INFO (HZ * 10) +static int rcu_task_stall_info __read_mostly = RCU_TASK_STALL_INFO; +module_param(rcu_task_stall_info, int, 0644); +static int rcu_task_stall_info_mult __read_mostly = 3; +module_param(rcu_task_stall_info_mult, int, 0444); + +static int rcu_task_enqueue_lim __read_mostly = -1; +module_param(rcu_task_enqueue_lim, int, 0444); + +static bool rcu_task_cb_adjust; +static int rcu_task_contend_lim __read_mostly = 100; +module_param(rcu_task_contend_lim, int, 0444); +static int rcu_task_collapse_lim __read_mostly = 10; +module_param(rcu_task_collapse_lim, int, 0444); +static int rcu_task_lazy_lim __read_mostly = 32; +module_param(rcu_task_lazy_lim, int, 0444); /* RCU tasks grace-period state for debugging. */ #define RTGS_INIT 0 @@ -128,6 +213,8 @@ static const char * const rcu_tasks_gp_state_names[] = { // // Generic code. +static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp); + /* Record grace-period phase and time. */ static void set_tasks_gp_state(struct rcu_tasks *rtp, int newstate) { @@ -148,47 +235,383 @@ static const char *tasks_gp_state_getname(struct rcu_tasks *rtp) } #endif /* #ifndef CONFIG_TINY_RCU */ +// Initialize per-CPU callback lists for the specified flavor of +// Tasks RCU. Do not enqueue callbacks before this function is invoked. +static void cblist_init_generic(struct rcu_tasks *rtp) +{ + int cpu; + unsigned long flags; + int lim; + int shift; + + if (rcu_task_enqueue_lim < 0) { + rcu_task_enqueue_lim = 1; + rcu_task_cb_adjust = true; + } else if (rcu_task_enqueue_lim == 0) { + rcu_task_enqueue_lim = 1; + } + lim = rcu_task_enqueue_lim; + + if (lim > nr_cpu_ids) + lim = nr_cpu_ids; + shift = ilog2(nr_cpu_ids / lim); + if (((nr_cpu_ids - 1) >> shift) >= lim) + shift++; + WRITE_ONCE(rtp->percpu_enqueue_shift, shift); + WRITE_ONCE(rtp->percpu_dequeue_lim, lim); + smp_store_release(&rtp->percpu_enqueue_lim, lim); + for_each_possible_cpu(cpu) { + struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); + + WARN_ON_ONCE(!rtpcp); + if (cpu) + raw_spin_lock_init(&ACCESS_PRIVATE(rtpcp, lock)); + local_irq_save(flags); // serialize initialization + if (rcu_segcblist_empty(&rtpcp->cblist)) + rcu_segcblist_init(&rtpcp->cblist); + local_irq_restore(flags); + INIT_WORK(&rtpcp->rtp_work, rcu_tasks_invoke_cbs_wq); + rtpcp->cpu = cpu; + rtpcp->rtpp = rtp; + if (!rtpcp->rtp_blkd_tasks.next) + INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks); + } + + pr_info("%s: Setting shift to %d and lim to %d rcu_task_cb_adjust=%d.\n", rtp->name, + data_race(rtp->percpu_enqueue_shift), data_race(rtp->percpu_enqueue_lim), rcu_task_cb_adjust); +} + +// Compute wakeup time for lazy callback timer. +static unsigned long rcu_tasks_lazy_time(struct rcu_tasks *rtp) +{ + return jiffies + rtp->lazy_jiffies; +} + +// Timer handler that unlazifies lazy callbacks. +static void call_rcu_tasks_generic_timer(struct timer_list *tlp) +{ + unsigned long flags; + bool needwake = false; + struct rcu_tasks *rtp; + struct rcu_tasks_percpu *rtpcp = from_timer(rtpcp, tlp, lazy_timer); + + rtp = rtpcp->rtpp; + raw_spin_lock_irqsave_rcu_node(rtpcp, flags); + if (!rcu_segcblist_empty(&rtpcp->cblist) && rtp->lazy_jiffies) { + if (!rtpcp->urgent_gp) + rtpcp->urgent_gp = 1; + needwake = true; + mod_timer(&rtpcp->lazy_timer, rcu_tasks_lazy_time(rtp)); + } + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); + if (needwake) + rcuwait_wake_up(&rtp->cbs_wait); +} + +// IRQ-work handler that does deferred wakeup for call_rcu_tasks_generic(). +static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp) +{ + struct rcu_tasks *rtp; + struct rcu_tasks_percpu *rtpcp = container_of(iwp, struct rcu_tasks_percpu, rtp_irq_work); + + rtp = rtpcp->rtpp; + rcuwait_wake_up(&rtp->cbs_wait); +} + // Enqueue a callback for the specified flavor of Tasks RCU. static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func, struct rcu_tasks *rtp) { + int chosen_cpu; unsigned long flags; + bool havekthread = smp_load_acquire(&rtp->kthread_ptr); + int ideal_cpu; + unsigned long j; + bool needadjust = false; bool needwake; + struct rcu_tasks_percpu *rtpcp; rhp->next = NULL; rhp->func = func; - raw_spin_lock_irqsave(&rtp->cbs_lock, flags); - needwake = !rtp->cbs_head; - WRITE_ONCE(*rtp->cbs_tail, rhp); - rtp->cbs_tail = &rhp->next; - raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags); + local_irq_save(flags); + rcu_read_lock(); + ideal_cpu = smp_processor_id() >> READ_ONCE(rtp->percpu_enqueue_shift); + chosen_cpu = cpumask_next(ideal_cpu - 1, cpu_possible_mask); + rtpcp = per_cpu_ptr(rtp->rtpcpu, chosen_cpu); + if (!raw_spin_trylock_rcu_node(rtpcp)) { // irqs already disabled. + raw_spin_lock_rcu_node(rtpcp); // irqs already disabled. + j = jiffies; + if (rtpcp->rtp_jiffies != j) { + rtpcp->rtp_jiffies = j; + rtpcp->rtp_n_lock_retries = 0; + } + if (rcu_task_cb_adjust && ++rtpcp->rtp_n_lock_retries > rcu_task_contend_lim && + READ_ONCE(rtp->percpu_enqueue_lim) != nr_cpu_ids) + needadjust = true; // Defer adjustment to avoid deadlock. + } + // Queuing callbacks before initialization not yet supported. + if (WARN_ON_ONCE(!rcu_segcblist_is_enabled(&rtpcp->cblist))) + rcu_segcblist_init(&rtpcp->cblist); + needwake = (func == wakeme_after_rcu) || + (rcu_segcblist_n_cbs(&rtpcp->cblist) == rcu_task_lazy_lim); + if (havekthread && !needwake && !timer_pending(&rtpcp->lazy_timer)) { + if (rtp->lazy_jiffies) + mod_timer(&rtpcp->lazy_timer, rcu_tasks_lazy_time(rtp)); + else + needwake = rcu_segcblist_empty(&rtpcp->cblist); + } + if (needwake) + rtpcp->urgent_gp = 3; + rcu_segcblist_enqueue(&rtpcp->cblist, rhp); + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); + if (unlikely(needadjust)) { + raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); + if (rtp->percpu_enqueue_lim != nr_cpu_ids) { + WRITE_ONCE(rtp->percpu_enqueue_shift, 0); + WRITE_ONCE(rtp->percpu_dequeue_lim, nr_cpu_ids); + smp_store_release(&rtp->percpu_enqueue_lim, nr_cpu_ids); + pr_info("Switching %s to per-CPU callback queuing.\n", rtp->name); + } + raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); + } + rcu_read_unlock(); /* We can't create the thread unless interrupts are enabled. */ if (needwake && READ_ONCE(rtp->kthread_ptr)) - wake_up(&rtp->cbs_wq); + irq_work_queue(&rtpcp->rtp_irq_work); } -// Wait for a grace period for the specified flavor of Tasks RCU. -static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp) +// RCU callback function for rcu_barrier_tasks_generic(). +static void rcu_barrier_tasks_generic_cb(struct rcu_head *rhp) { - /* Complain if the scheduler has not started. */ - RCU_LOCKDEP_WARN(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE, - "synchronize_rcu_tasks called too soon"); + struct rcu_tasks *rtp; + struct rcu_tasks_percpu *rtpcp; - /* Wait for the grace period. */ - wait_rcu_gp(rtp->call_func); + rtpcp = container_of(rhp, struct rcu_tasks_percpu, barrier_q_head); + rtp = rtpcp->rtpp; + if (atomic_dec_and_test(&rtp->barrier_q_count)) + complete(&rtp->barrier_q_completion); } -/* RCU-tasks kthread that detects grace periods and invokes callbacks. */ -static int __noreturn rcu_tasks_kthread(void *arg) +// Wait for all in-flight callbacks for the specified RCU Tasks flavor. +// Operates in a manner similar to rcu_barrier(). +static void rcu_barrier_tasks_generic(struct rcu_tasks *rtp) +{ + int cpu; + unsigned long flags; + struct rcu_tasks_percpu *rtpcp; + unsigned long s = rcu_seq_snap(&rtp->barrier_q_seq); + + mutex_lock(&rtp->barrier_q_mutex); + if (rcu_seq_done(&rtp->barrier_q_seq, s)) { + smp_mb(); + mutex_unlock(&rtp->barrier_q_mutex); + return; + } + rcu_seq_start(&rtp->barrier_q_seq); + init_completion(&rtp->barrier_q_completion); + atomic_set(&rtp->barrier_q_count, 2); + for_each_possible_cpu(cpu) { + if (cpu >= smp_load_acquire(&rtp->percpu_dequeue_lim)) + break; + rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); + rtpcp->barrier_q_head.func = rcu_barrier_tasks_generic_cb; + raw_spin_lock_irqsave_rcu_node(rtpcp, flags); + if (rcu_segcblist_entrain(&rtpcp->cblist, &rtpcp->barrier_q_head)) + atomic_inc(&rtp->barrier_q_count); + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); + } + if (atomic_sub_and_test(2, &rtp->barrier_q_count)) + complete(&rtp->barrier_q_completion); + wait_for_completion(&rtp->barrier_q_completion); + rcu_seq_end(&rtp->barrier_q_seq); + mutex_unlock(&rtp->barrier_q_mutex); +} + +// Advance callbacks and indicate whether either a grace period or +// callback invocation is needed. +static int rcu_tasks_need_gpcb(struct rcu_tasks *rtp) { + int cpu; + int dequeue_limit; unsigned long flags; - struct rcu_head *list; - struct rcu_head *next; + bool gpdone = poll_state_synchronize_rcu(rtp->percpu_dequeue_gpseq); + long n; + long ncbs = 0; + long ncbsnz = 0; + int needgpcb = 0; + + dequeue_limit = smp_load_acquire(&rtp->percpu_dequeue_lim); + for (cpu = 0; cpu < dequeue_limit; cpu++) { + struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); + + /* Advance and accelerate any new callbacks. */ + if (!rcu_segcblist_n_cbs(&rtpcp->cblist)) + continue; + raw_spin_lock_irqsave_rcu_node(rtpcp, flags); + // Should we shrink down to a single callback queue? + n = rcu_segcblist_n_cbs(&rtpcp->cblist); + if (n) { + ncbs += n; + if (cpu > 0) + ncbsnz += n; + } + rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq)); + (void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq)); + if (rtpcp->urgent_gp > 0 && rcu_segcblist_pend_cbs(&rtpcp->cblist)) { + if (rtp->lazy_jiffies) + rtpcp->urgent_gp--; + needgpcb |= 0x3; + } else if (rcu_segcblist_empty(&rtpcp->cblist)) { + rtpcp->urgent_gp = 0; + } + if (rcu_segcblist_ready_cbs(&rtpcp->cblist)) + needgpcb |= 0x1; + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); + } + + // Shrink down to a single callback queue if appropriate. + // This is done in two stages: (1) If there are no more than + // rcu_task_collapse_lim callbacks on CPU 0 and none on any other + // CPU, limit enqueueing to CPU 0. (2) After an RCU grace period, + // if there has not been an increase in callbacks, limit dequeuing + // to CPU 0. Note the matching RCU read-side critical section in + // call_rcu_tasks_generic(). + if (rcu_task_cb_adjust && ncbs <= rcu_task_collapse_lim) { + raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); + if (rtp->percpu_enqueue_lim > 1) { + WRITE_ONCE(rtp->percpu_enqueue_shift, order_base_2(nr_cpu_ids)); + smp_store_release(&rtp->percpu_enqueue_lim, 1); + rtp->percpu_dequeue_gpseq = get_state_synchronize_rcu(); + gpdone = false; + pr_info("Starting switch %s to CPU-0 callback queuing.\n", rtp->name); + } + raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); + } + if (rcu_task_cb_adjust && !ncbsnz && gpdone) { + raw_spin_lock_irqsave(&rtp->cbs_gbl_lock, flags); + if (rtp->percpu_enqueue_lim < rtp->percpu_dequeue_lim) { + WRITE_ONCE(rtp->percpu_dequeue_lim, 1); + pr_info("Completing switch %s to CPU-0 callback queuing.\n", rtp->name); + } + if (rtp->percpu_dequeue_lim == 1) { + for (cpu = rtp->percpu_dequeue_lim; cpu < nr_cpu_ids; cpu++) { + struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); + + WARN_ON_ONCE(rcu_segcblist_n_cbs(&rtpcp->cblist)); + } + } + raw_spin_unlock_irqrestore(&rtp->cbs_gbl_lock, flags); + } + + return needgpcb; +} + +// Advance callbacks and invoke any that are ready. +static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu *rtpcp) +{ + int cpu; + int cpunext; + int cpuwq; + unsigned long flags; + int len; + struct rcu_head *rhp; + struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); + struct rcu_tasks_percpu *rtpcp_next; + + cpu = rtpcp->cpu; + cpunext = cpu * 2 + 1; + if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) { + rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext); + cpuwq = rcu_cpu_beenfullyonline(cpunext) ? cpunext : WORK_CPU_UNBOUND; + queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work); + cpunext++; + if (cpunext < smp_load_acquire(&rtp->percpu_dequeue_lim)) { + rtpcp_next = per_cpu_ptr(rtp->rtpcpu, cpunext); + cpuwq = rcu_cpu_beenfullyonline(cpunext) ? cpunext : WORK_CPU_UNBOUND; + queue_work_on(cpuwq, system_wq, &rtpcp_next->rtp_work); + } + } + + if (rcu_segcblist_empty(&rtpcp->cblist) || !cpu_possible(cpu)) + return; + raw_spin_lock_irqsave_rcu_node(rtpcp, flags); + rcu_segcblist_advance(&rtpcp->cblist, rcu_seq_current(&rtp->tasks_gp_seq)); + rcu_segcblist_extract_done_cbs(&rtpcp->cblist, &rcl); + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); + len = rcl.len; + for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) { + debug_rcu_head_callback(rhp); + local_bh_disable(); + rhp->func(rhp); + local_bh_enable(); + cond_resched(); + } + raw_spin_lock_irqsave_rcu_node(rtpcp, flags); + rcu_segcblist_add_len(&rtpcp->cblist, -len); + (void)rcu_segcblist_accelerate(&rtpcp->cblist, rcu_seq_snap(&rtp->tasks_gp_seq)); + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); +} + +// Workqueue flood to advance callbacks and invoke any that are ready. +static void rcu_tasks_invoke_cbs_wq(struct work_struct *wp) +{ + struct rcu_tasks *rtp; + struct rcu_tasks_percpu *rtpcp = container_of(wp, struct rcu_tasks_percpu, rtp_work); + + rtp = rtpcp->rtpp; + rcu_tasks_invoke_cbs(rtp, rtpcp); +} + +// Wait for one grace period. +static void rcu_tasks_one_gp(struct rcu_tasks *rtp, bool midboot) +{ + int needgpcb; + + mutex_lock(&rtp->tasks_gp_mutex); + + // If there were none, wait a bit and start over. + if (unlikely(midboot)) { + needgpcb = 0x2; + } else { + mutex_unlock(&rtp->tasks_gp_mutex); + set_tasks_gp_state(rtp, RTGS_WAIT_CBS); + rcuwait_wait_event(&rtp->cbs_wait, + (needgpcb = rcu_tasks_need_gpcb(rtp)), + TASK_IDLE); + mutex_lock(&rtp->tasks_gp_mutex); + } + + if (needgpcb & 0x2) { + // Wait for one grace period. + set_tasks_gp_state(rtp, RTGS_WAIT_GP); + rtp->gp_start = jiffies; + rcu_seq_start(&rtp->tasks_gp_seq); + rtp->gp_func(rtp); + rcu_seq_end(&rtp->tasks_gp_seq); + } + + // Invoke callbacks. + set_tasks_gp_state(rtp, RTGS_INVOKE_CBS); + rcu_tasks_invoke_cbs(rtp, per_cpu_ptr(rtp->rtpcpu, 0)); + mutex_unlock(&rtp->tasks_gp_mutex); +} + +// RCU-tasks kthread that detects grace periods and invokes callbacks. +static int __noreturn rcu_tasks_kthread(void *arg) +{ + int cpu; struct rcu_tasks *rtp = arg; + for_each_possible_cpu(cpu) { + struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); + + timer_setup(&rtpcp->lazy_timer, call_rcu_tasks_generic_timer, 0); + rtpcp->urgent_gp = 1; + } + /* Run on housekeeping CPUs by default. Sysadm can move if desired. */ - housekeeping_affine(current, HK_FLAG_RCU); - WRITE_ONCE(rtp->kthread_ptr, current); // Let GPs start! + housekeeping_affine(current, HK_TYPE_RCU); + smp_store_release(&rtp->kthread_ptr, current); // Let GPs start! /* * Each pass through the following loop makes one check for @@ -197,48 +620,29 @@ static int __noreturn rcu_tasks_kthread(void *arg) * This loop is terminated by the system going down. ;-) */ for (;;) { + // Wait for one grace period and invoke any callbacks + // that are ready. + rcu_tasks_one_gp(rtp, false); - /* Pick up any new callbacks. */ - raw_spin_lock_irqsave(&rtp->cbs_lock, flags); - smp_mb__after_spinlock(); // Order updates vs. GP. - list = rtp->cbs_head; - rtp->cbs_head = NULL; - rtp->cbs_tail = &rtp->cbs_head; - raw_spin_unlock_irqrestore(&rtp->cbs_lock, flags); - - /* If there were none, wait a bit and start over. */ - if (!list) { - wait_event_interruptible(rtp->cbs_wq, - READ_ONCE(rtp->cbs_head)); - if (!rtp->cbs_head) { - WARN_ON(signal_pending(current)); - set_tasks_gp_state(rtp, RTGS_WAIT_WAIT_CBS); - schedule_timeout_idle(HZ/10); - } - continue; - } - - // Wait for one grace period. - set_tasks_gp_state(rtp, RTGS_WAIT_GP); - rtp->gp_start = jiffies; - rtp->gp_func(rtp); - rtp->n_gps++; - - /* Invoke the callbacks. */ - set_tasks_gp_state(rtp, RTGS_INVOKE_CBS); - while (list) { - next = list->next; - local_bh_disable(); - list->func(list); - local_bh_enable(); - list = next; - cond_resched(); - } - /* Paranoid sleep to keep this from entering a tight loop */ + // Paranoid sleep to keep this from entering a tight loop. schedule_timeout_idle(rtp->gp_sleep); + } +} - set_tasks_gp_state(rtp, RTGS_WAIT_CBS); +// Wait for a grace period for the specified flavor of Tasks RCU. +static void synchronize_rcu_tasks_generic(struct rcu_tasks *rtp) +{ + /* Complain if the scheduler has not started. */ + if (WARN_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INACTIVE, + "synchronize_%s() called too soon", rtp->name)) + return; + + // If the grace-period kthread is running, use it. + if (READ_ONCE(rtp->kthread_ptr)) { + wait_rcu_gp(rtp->call_func); + return; } + rcu_tasks_one_gp(rtp, true); } /* Spawn RCU-tasks grace-period kthread. */ @@ -260,8 +664,15 @@ static void __init rcu_spawn_tasks_kthread_generic(struct rcu_tasks *rtp) static void __init rcu_tasks_bootup_oddness(void) { #if defined(CONFIG_TASKS_RCU) || defined(CONFIG_TASKS_TRACE_RCU) + int rtsimc; + if (rcu_task_stall_timeout != RCU_TASK_STALL_TIMEOUT) pr_info("\tTasks-RCU CPU stall warnings timeout set to %d (rcu_task_stall_timeout).\n", rcu_task_stall_timeout); + rtsimc = clamp(rcu_task_stall_info_mult, 1, 10); + if (rtsimc != rcu_task_stall_info_mult) { + pr_info("\tTasks-RCU CPU stall info multiplier clamped to %d (rcu_task_stall_info_mult).\n", rtsimc); + rcu_task_stall_info_mult = rtsimc; + } #endif /* #ifdef CONFIG_TASKS_RCU */ #ifdef CONFIG_TASKS_RCU pr_info("\tTrampoline variant of Tasks RCU enabled.\n"); @@ -280,14 +691,34 @@ static void __init rcu_tasks_bootup_oddness(void) /* Dump out rcutorture-relevant state common to all RCU-tasks flavors. */ static void show_rcu_tasks_generic_gp_kthread(struct rcu_tasks *rtp, char *s) { - pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c %s\n", + int cpu; + bool havecbs = false; + bool haveurgent = false; + bool haveurgentcbs = false; + + for_each_possible_cpu(cpu) { + struct rcu_tasks_percpu *rtpcp = per_cpu_ptr(rtp->rtpcpu, cpu); + + if (!data_race(rcu_segcblist_empty(&rtpcp->cblist))) + havecbs = true; + if (data_race(rtpcp->urgent_gp)) + haveurgent = true; + if (!data_race(rcu_segcblist_empty(&rtpcp->cblist)) && data_race(rtpcp->urgent_gp)) + haveurgentcbs = true; + if (havecbs && haveurgent && haveurgentcbs) + break; + } + pr_info("%s: %s(%d) since %lu g:%lu i:%lu/%lu %c%c%c%c l:%lu %s\n", rtp->kname, tasks_gp_state_getname(rtp), data_race(rtp->gp_state), jiffies - data_race(rtp->gp_jiffies), - data_race(rtp->n_gps), + data_race(rcu_seq_current(&rtp->tasks_gp_seq)), data_race(rtp->n_ipis_fails), data_race(rtp->n_ipis), ".k"[!!data_race(rtp->kthread_ptr)], - ".C"[!!data_race(rtp->cbs_head)], + ".C"[havecbs], + ".u"[haveurgent], + ".U"[haveurgentcbs], + rtp->lazy_jiffies, s); } #endif // #ifndef CONFIG_TINY_RCU @@ -303,13 +734,18 @@ static void exit_tasks_rcu_finish_trace(struct task_struct *t); /* Wait for one RCU-tasks grace period. */ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) { - struct task_struct *g, *t; - unsigned long lastreport; - LIST_HEAD(holdouts); + struct task_struct *g; int fract; + LIST_HEAD(holdouts); + unsigned long j; + unsigned long lastinfo; + unsigned long lastreport; + bool reported = false; + int rtsi; + struct task_struct *t; set_tasks_gp_state(rtp, RTGS_PRE_WAIT_GP); - rtp->pregp_func(); + rtp->pregp_func(&holdouts); /* * There were callbacks, so we need to wait for an RCU-tasks @@ -318,10 +754,12 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) * and make a list of them in holdouts. */ set_tasks_gp_state(rtp, RTGS_SCAN_TASKLIST); - rcu_read_lock(); - for_each_process_thread(g, t) - rtp->pertask_func(t, &holdouts); - rcu_read_unlock(); + if (rtp->pertask_func) { + rcu_read_lock(); + for_each_process_thread(g, t) + rtp->pertask_func(t, &holdouts); + rcu_read_unlock(); + } set_tasks_gp_state(rtp, RTGS_POST_SCAN_TASKLIST); rtp->postscan_func(&holdouts); @@ -332,30 +770,50 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) * is empty, we are done. */ lastreport = jiffies; + lastinfo = lastreport; + rtsi = READ_ONCE(rcu_task_stall_info); // Start off with initial wait and slowly back off to 1 HZ wait. fract = rtp->init_fract; while (!list_empty(&holdouts)) { + ktime_t exp; bool firstreport; bool needreport; int rtst; - /* Slowly back off waiting for holdouts */ + // Slowly back off waiting for holdouts set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS); - schedule_timeout_idle(fract); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) { + schedule_timeout_idle(fract); + } else { + exp = jiffies_to_nsecs(fract); + __set_current_state(TASK_IDLE); + schedule_hrtimeout_range(&exp, jiffies_to_nsecs(HZ / 2), HRTIMER_MODE_REL_HARD); + } if (fract < HZ) fract++; rtst = READ_ONCE(rcu_task_stall_timeout); needreport = rtst > 0 && time_after(jiffies, lastreport + rtst); - if (needreport) + if (needreport) { lastreport = jiffies; + reported = true; + } firstreport = true; WARN_ON(signal_pending(current)); set_tasks_gp_state(rtp, RTGS_SCAN_HOLDOUTS); rtp->holdouts_func(&holdouts, needreport, &firstreport); + + // Print pre-stall informational messages if needed. + j = jiffies; + if (rtsi > 0 && !reported && time_after(j, lastinfo + rtsi)) { + lastinfo = j; + rtsi = rtsi * rcu_task_stall_info_mult; + pr_info("%s: %s grace period number %lu (since boot) is %lu jiffies old.\n", + __func__, rtp->kname, rtp->tasks_gp_seq, j - rtp->gp_start); + } } set_tasks_gp_state(rtp, RTGS_POST_GP); @@ -369,7 +827,7 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) //////////////////////////////////////////////////////////////////////// // // Simple variant of RCU whose quiescent states are voluntary context -// switch, cond_resched_rcu_qs(), user-space execution, and idle. +// switch, cond_resched_tasks_rcu_qs(), user-space execution, and idle. // As such, grace periods can take one good long time. There are no // read-side primitives similar to rcu_read_lock() and rcu_read_unlock() // because this implementation is intended to get the system into a safe @@ -377,9 +835,49 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp) // Finally, this implementation does not support high call_rcu_tasks() // rates from multiple CPUs. If this is required, per-CPU callback lists // will be needed. +// +// The implementation uses rcu_tasks_wait_gp(), which relies on function +// pointers in the rcu_tasks structure. The rcu_spawn_tasks_kthread() +// function sets these function pointers up so that rcu_tasks_wait_gp() +// invokes these functions in this order: +// +// rcu_tasks_pregp_step(): +// Invokes synchronize_rcu() in order to wait for all in-flight +// t->on_rq and t->nvcsw transitions to complete. This works because +// all such transitions are carried out with interrupts disabled. +// rcu_tasks_pertask(), invoked on every non-idle task: +// For every runnable non-idle task other than the current one, use +// get_task_struct() to pin down that task, snapshot that task's +// number of voluntary context switches, and add that task to the +// holdout list. +// rcu_tasks_postscan(): +// Invoke synchronize_srcu() to ensure that all tasks that were +// in the process of exiting (and which thus might not know to +// synchronize with this RCU Tasks grace period) have completed +// exiting. +// check_all_holdout_tasks(), repeatedly until holdout list is empty: +// Scans the holdout list, attempting to identify a quiescent state +// for each task on the list. If there is a quiescent state, the +// corresponding task is removed from the holdout list. +// rcu_tasks_postgp(): +// Invokes synchronize_rcu() in order to ensure that all prior +// t->on_rq and t->nvcsw transitions are seen by all CPUs and tasks +// to have happened before the end of this RCU Tasks grace period. +// Again, this works because all such transitions are carried out +// with interrupts disabled. +// +// For each exiting task, the exit_tasks_rcu_start() and +// exit_tasks_rcu_finish() functions begin and end, respectively, the SRCU +// read-side critical sections waited for by rcu_tasks_postscan(). +// +// Pre-grace-period update-side code is ordered before the grace +// via the raw_spin_lock.*rcu_node(). Pre-grace-period read-side code +// is ordered before the grace period via synchronize_rcu() call in +// rcu_tasks_pregp_step() and by the scheduler's locks and interrupt +// disabling. /* Pre-grace-period preparation. */ -static void rcu_tasks_pregp_step(void) +static void rcu_tasks_pregp_step(struct list_head *hop) { /* * Wait for all pre-existing t->on_rq and t->nvcsw transitions @@ -397,10 +895,36 @@ static void rcu_tasks_pregp_step(void) synchronize_rcu(); } +/* Check for quiescent states since the pregp's synchronize_rcu() */ +static bool rcu_tasks_is_holdout(struct task_struct *t) +{ + int cpu; + + /* Has the task been seen voluntarily sleeping? */ + if (!READ_ONCE(t->on_rq)) + return false; + + /* + * Idle tasks (or idle injection) within the idle loop are RCU-tasks + * quiescent states. But CPU boot code performed by the idle task + * isn't a quiescent state. + */ + if (is_idle_task(t)) + return false; + + cpu = task_cpu(t); + + /* Idle tasks on offline CPUs are RCU-tasks quiescent states. */ + if (t == idle_task(cpu) && !rcu_cpu_online(cpu)) + return false; + + return true; +} + /* Per-task initial processing. */ static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop) { - if (t != current && READ_ONCE(t->on_rq) && !is_idle_task(t)) { + if (t != current && rcu_tasks_is_holdout(t)) { get_task_struct(t); t->rcu_tasks_nvcsw = READ_ONCE(t->nvcsw); WRITE_ONCE(t->rcu_tasks_holdout, true); @@ -411,14 +935,34 @@ static void rcu_tasks_pertask(struct task_struct *t, struct list_head *hop) /* Processing between scanning taskslist and draining the holdout list. */ static void rcu_tasks_postscan(struct list_head *hop) { + int rtsi = READ_ONCE(rcu_task_stall_info); + + if (!IS_ENABLED(CONFIG_TINY_RCU)) { + tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi; + add_timer(&tasks_rcu_exit_srcu_stall_timer); + } + /* - * Wait for tasks that are in the process of exiting. This - * does only part of the job, ensuring that all tasks that were - * previously exiting reach the point where they have disabled - * preemption, allowing the later synchronize_rcu() to finish - * the job. + * Exiting tasks may escape the tasklist scan. Those are vulnerable + * until their final schedule() with TASK_DEAD state. To cope with + * this, divide the fragile exit path part in two intersecting + * read side critical sections: + * + * 1) An _SRCU_ read side starting before calling exit_notify(), + * which may remove the task from the tasklist, and ending after + * the final preempt_disable() call in do_exit(). + * + * 2) An _RCU_ read side starting with the final preempt_disable() + * call in do_exit() and ending with the final call to schedule() + * with TASK_DEAD state. + * + * This handles the part 1). And postgp will handle part 2) with a + * call to synchronize_rcu(). */ synchronize_srcu(&tasks_rcu_exit_srcu); + + if (!IS_ENABLED(CONFIG_TINY_RCU)) + del_timer_sync(&tasks_rcu_exit_srcu_stall_timer); } /* See if tasks are still holding out, complain if so. */ @@ -429,9 +973,9 @@ static void check_holdout_task(struct task_struct *t, if (!READ_ONCE(t->rcu_tasks_holdout) || t->rcu_tasks_nvcsw != READ_ONCE(t->nvcsw) || - !READ_ONCE(t->on_rq) || + !rcu_tasks_is_holdout(t) || (IS_ENABLED(CONFIG_NO_HZ_FULL) && - !is_idle_task(t) && t->rcu_tasks_idle_cpu >= 0)) { + !is_idle_task(t) && READ_ONCE(t->rcu_tasks_idle_cpu) >= 0)) { WRITE_ONCE(t->rcu_tasks_holdout, false); list_del_init(&t->rcu_tasks_holdout_list); put_task_struct(t); @@ -449,7 +993,7 @@ static void check_holdout_task(struct task_struct *t, t, ".I"[is_idle_task(t)], "N."[cpu < 0 || !tick_nohz_full_cpu(cpu)], t->rcu_tasks_nvcsw, t->nvcsw, t->rcu_tasks_holdout, - t->rcu_tasks_idle_cpu, cpu); + data_race(t->rcu_tasks_idle_cpu), cpu); sched_show_task(t); } @@ -483,7 +1027,10 @@ static void rcu_tasks_postgp(struct rcu_tasks *rtp) * * In addition, this synchronize_rcu() waits for exiting tasks * to complete their final preempt_disable() region of execution, - * cleaning up after the synchronize_srcu() above. + * cleaning up after synchronize_srcu(&tasks_rcu_exit_srcu), + * enforcing the whole region before tasklist removal until + * the final schedule() with TASK_DEAD state to be an RCU TASKS + * read side critical section. */ synchronize_rcu(); } @@ -491,6 +1038,21 @@ static void rcu_tasks_postgp(struct rcu_tasks *rtp) void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func); DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks"); +static void tasks_rcu_exit_srcu_stall(struct timer_list *unused) +{ +#ifndef CONFIG_TINY_RCU + int rtsi; + + rtsi = READ_ONCE(rcu_task_stall_info); + pr_info("%s: %s grace period number %lu (since boot) gp_state: %s is %lu jiffies old.\n", + __func__, rcu_tasks.kname, rcu_tasks.tasks_gp_seq, + tasks_gp_state_getname(&rcu_tasks), jiffies - rcu_tasks.gp_jiffies); + pr_info("Please check any exiting tasks stuck between calls to exit_tasks_rcu_start() and exit_tasks_rcu_finish()\n"); + tasks_rcu_exit_srcu_stall_timer.expires = jiffies + rtsi; + add_timer(&tasks_rcu_exit_srcu_stall_timer); +#endif // #ifndef CONFIG_TINY_RCU +} + /** * call_rcu_tasks() - Queue an RCU for invocation task-based grace period * @rhp: structure to be used for queueing the RCU updates. @@ -500,11 +1062,11 @@ DEFINE_RCU_TASKS(rcu_tasks, rcu_tasks_wait_gp, call_rcu_tasks, "RCU Tasks"); * period elapses, in other words after all currently executing RCU * read-side critical sections have completed. call_rcu_tasks() assumes * that the read-side critical sections end at a voluntary context - * switch (not a preemption!), cond_resched_rcu_qs(), entry into idle, + * switch (not a preemption!), cond_resched_tasks_rcu_qs(), entry into idle, * or transition to usermode execution. As such, there are no read-side * primitives analogous to rcu_read_lock() and rcu_read_unlock() because * this primitive is intended to determine that all tasks have passed - * through a safe state, not so much for data-strcuture synchronization. + * through a safe state, not so much for data-structure synchronization. * * See the description of call_rcu() for more detailed information on * memory ordering guarantees. @@ -547,15 +1109,20 @@ EXPORT_SYMBOL_GPL(synchronize_rcu_tasks); */ void rcu_barrier_tasks(void) { - /* There is only one callback queue, so this is easy. ;-) */ - synchronize_rcu_tasks(); + rcu_barrier_tasks_generic(&rcu_tasks); } EXPORT_SYMBOL_GPL(rcu_barrier_tasks); +static int rcu_tasks_lazy_ms = -1; +module_param(rcu_tasks_lazy_ms, int, 0444); + static int __init rcu_spawn_tasks_kthread(void) { + cblist_init_generic(&rcu_tasks); rcu_tasks.gp_sleep = HZ / 10; rcu_tasks.init_fract = HZ / 10; + if (rcu_tasks_lazy_ms >= 0) + rcu_tasks.lazy_jiffies = msecs_to_jiffies(rcu_tasks_lazy_ms); rcu_tasks.pregp_func = rcu_tasks_pregp_step; rcu_tasks.pertask_func = rcu_tasks_pertask; rcu_tasks.postscan_func = rcu_tasks_postscan; @@ -573,27 +1140,48 @@ void show_rcu_tasks_classic_gp_kthread(void) EXPORT_SYMBOL_GPL(show_rcu_tasks_classic_gp_kthread); #endif // !defined(CONFIG_TINY_RCU) -/* Do the srcu_read_lock() for the above synchronize_srcu(). */ +struct task_struct *get_rcu_tasks_gp_kthread(void) +{ + return rcu_tasks.kthread_ptr; +} +EXPORT_SYMBOL_GPL(get_rcu_tasks_gp_kthread); + +/* + * Contribute to protect against tasklist scan blind spot while the + * task is exiting and may be removed from the tasklist. See + * corresponding synchronize_srcu() for further details. + */ void exit_tasks_rcu_start(void) __acquires(&tasks_rcu_exit_srcu) { - preempt_disable(); current->rcu_tasks_idx = __srcu_read_lock(&tasks_rcu_exit_srcu); - preempt_enable(); } -/* Do the srcu_read_unlock() for the above synchronize_srcu(). */ -void exit_tasks_rcu_finish(void) __releases(&tasks_rcu_exit_srcu) +/* + * Contribute to protect against tasklist scan blind spot while the + * task is exiting and may be removed from the tasklist. See + * corresponding synchronize_srcu() for further details. + */ +void exit_tasks_rcu_stop(void) __releases(&tasks_rcu_exit_srcu) { struct task_struct *t = current; - preempt_disable(); __srcu_read_unlock(&tasks_rcu_exit_srcu, t->rcu_tasks_idx); - preempt_enable(); - exit_tasks_rcu_finish_trace(t); +} + +/* + * Contribute to protect against tasklist scan blind spot while the + * task is exiting and may be removed from the tasklist. See + * corresponding synchronize_srcu() for further details. + */ +void exit_tasks_rcu_finish(void) +{ + exit_tasks_rcu_stop(); + exit_tasks_rcu_finish_trace(current); } #else /* #ifdef CONFIG_TASKS_RCU */ void exit_tasks_rcu_start(void) { } +void exit_tasks_rcu_stop(void) { } void exit_tasks_rcu_finish(void) { exit_tasks_rcu_finish_trace(current); } #endif /* #else #ifdef CONFIG_TASKS_RCU */ @@ -603,10 +1191,15 @@ void exit_tasks_rcu_finish(void) { exit_tasks_rcu_finish_trace(current); } // // "Rude" variant of Tasks RCU, inspired by Steve Rostedt's trick of // passing an empty function to schedule_on_each_cpu(). This approach -// provides an asynchronous call_rcu_tasks_rude() API and batching -// of concurrent calls to the synchronous synchronize_rcu_rude() API. -// This sends IPIs far and wide and induces otherwise unnecessary context -// switches on all online CPUs, whether idle or not. +// provides an asynchronous call_rcu_tasks_rude() API and batching of +// concurrent calls to the synchronous synchronize_rcu_tasks_rude() API. +// This invokes schedule_on_each_cpu() in order to send IPIs far and wide +// and induces otherwise unnecessary context switches on all online CPUs, +// whether idle or not. +// +// Callback handling is provided by the rcu_tasks_kthread() function. +// +// Ordering is provided by the scheduler's context-switch code. // Empty function to allow workqueues to force a context switch. static void rcu_tasks_be_rude(struct work_struct *work) @@ -633,11 +1226,11 @@ DEFINE_RCU_TASKS(rcu_tasks_rude, rcu_tasks_rude_wait_gp, call_rcu_tasks_rude, * period elapses, in other words after all currently executing RCU * read-side critical sections have completed. call_rcu_tasks_rude() * assumes that the read-side critical sections end at context switch, - * cond_resched_rcu_qs(), or transition to usermode execution. As such, - * there are no read-side primitives analogous to rcu_read_lock() and - * rcu_read_unlock() because this primitive is intended to determine - * that all tasks have passed through a safe state, not so much for - * data-strcuture synchronization. + * cond_resched_tasks_rcu_qs(), or transition to usermode execution (as + * usermode execution is schedulable). As such, there are no read-side + * primitives analogous to rcu_read_lock() and rcu_read_unlock() because + * this primitive is intended to determine that all tasks have passed + * through a safe state, not so much for data-structure synchronization. * * See the description of call_rcu() for more detailed information on * memory ordering guarantees. @@ -655,8 +1248,8 @@ EXPORT_SYMBOL_GPL(call_rcu_tasks_rude); * grace period has elapsed, in other words after all currently * executing rcu-tasks read-side critical sections have elapsed. These * read-side critical sections are delimited by calls to schedule(), - * cond_resched_tasks_rcu_qs(), userspace execution, and (in theory, - * anyway) cond_resched(). + * cond_resched_tasks_rcu_qs(), userspace execution (which is a schedulable + * context), and (in theory, anyway) cond_resched(). * * This is a very specialized primitive, intended only for a few uses in * tracing and other situations requiring manipulation of function preambles @@ -680,14 +1273,19 @@ EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_rude); */ void rcu_barrier_tasks_rude(void) { - /* There is only one callback queue, so this is easy. ;-) */ - synchronize_rcu_tasks_rude(); + rcu_barrier_tasks_generic(&rcu_tasks_rude); } EXPORT_SYMBOL_GPL(rcu_barrier_tasks_rude); +int rcu_tasks_rude_lazy_ms = -1; +module_param(rcu_tasks_rude_lazy_ms, int, 0444); + static int __init rcu_spawn_tasks_rude_kthread(void) { + cblist_init_generic(&rcu_tasks_rude); rcu_tasks_rude.gp_sleep = HZ / 10; + if (rcu_tasks_rude_lazy_ms >= 0) + rcu_tasks_rude.lazy_jiffies = msecs_to_jiffies(rcu_tasks_rude_lazy_ms); rcu_spawn_tasks_kthread_generic(&rcu_tasks_rude); return 0; } @@ -699,6 +1297,13 @@ void show_rcu_tasks_rude_gp_kthread(void) } EXPORT_SYMBOL_GPL(show_rcu_tasks_rude_gp_kthread); #endif // !defined(CONFIG_TINY_RCU) + +struct task_struct *get_rcu_tasks_rude_gp_kthread(void) +{ + return rcu_tasks_rude.kthread_ptr; +} +EXPORT_SYMBOL_GPL(get_rcu_tasks_rude_gp_kthread); + #endif /* #ifdef CONFIG_TASKS_RUDE_RCU */ //////////////////////////////////////////////////////////////////////// @@ -713,19 +1318,49 @@ EXPORT_SYMBOL_GPL(show_rcu_tasks_rude_gp_kthread); // 2. Protects code in the idle loop, exception entry/exit, and // CPU-hotplug code paths, similar to the capabilities of SRCU. // -// 3. Avoids expensive read-side instruction, having overhead similar +// 3. Avoids expensive read-side instructions, having overhead similar // to that of Preemptible RCU. // -// There are of course downsides. The grace-period code can send IPIs to -// CPUs, even when those CPUs are in the idle loop or in nohz_full userspace. -// It is necessary to scan the full tasklist, much as for Tasks RCU. There -// is a single callback queue guarded by a single lock, again, much as for -// Tasks RCU. If needed, these downsides can be at least partially remedied. +// There are of course downsides. For example, the grace-period code +// can send IPIs to CPUs, even when those CPUs are in the idle loop or +// in nohz_full userspace. If needed, these downsides can be at least +// partially remedied. // // Perhaps most important, this variant of RCU does not affect the vanilla // flavors, rcu_preempt and rcu_sched. The fact that RCU Tasks Trace // readers can operate from idle, offline, and exception entry/exit in no // way allows rcu_preempt and rcu_sched readers to also do so. +// +// The implementation uses rcu_tasks_wait_gp(), which relies on function +// pointers in the rcu_tasks structure. The rcu_spawn_tasks_trace_kthread() +// function sets these function pointers up so that rcu_tasks_wait_gp() +// invokes these functions in this order: +// +// rcu_tasks_trace_pregp_step(): +// Disables CPU hotplug, adds all currently executing tasks to the +// holdout list, then checks the state of all tasks that blocked +// or were preempted within their current RCU Tasks Trace read-side +// critical section, adding them to the holdout list if appropriate. +// Finally, this function re-enables CPU hotplug. +// The ->pertask_func() pointer is NULL, so there is no per-task processing. +// rcu_tasks_trace_postscan(): +// Invokes synchronize_rcu() to wait for late-stage exiting tasks +// to finish exiting. +// check_all_holdout_tasks_trace(), repeatedly until holdout list is empty: +// Scans the holdout list, attempting to identify a quiescent state +// for each task on the list. If there is a quiescent state, the +// corresponding task is removed from the holdout list. Once this +// list is empty, the grace period has completed. +// rcu_tasks_trace_postgp(): +// Provides the needed full memory barrier and does debug checks. +// +// The exit_tasks_rcu_finish_trace() synchronizes with exiting tasks. +// +// Pre-grace-period update-side code is ordered before the grace period +// via the ->cbs_lock and barriers in rcu_tasks_kthread(). Pre-grace-period +// read-side code is ordered before the grace period by atomic operations +// on .b.need_qs flag of each task involved in this process, or by scheduler +// context-switch ordering (for locked-down non-running readers). // The lockdep state must be outside of #ifdef to be useful. #ifdef CONFIG_DEBUG_LOCK_ALLOC @@ -737,9 +1372,6 @@ EXPORT_SYMBOL_GPL(rcu_trace_lock_map); #ifdef CONFIG_TASKS_TRACE_RCU -static atomic_t trc_n_readers_need_end; // Number of waited-for readers. -static DECLARE_WAIT_QUEUE_HEAD(trc_wait); // List of holdout tasks. - // Record outstanding IPIs to each CPU. No point in sending two... static DEFINE_PER_CPU(bool, trc_ipi_to_cpu); @@ -748,44 +1380,104 @@ static DEFINE_PER_CPU(bool, trc_ipi_to_cpu); static unsigned long n_heavy_reader_attempts; static unsigned long n_heavy_reader_updates; static unsigned long n_heavy_reader_ofl_updates; +static unsigned long n_trc_holdouts; void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func); DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace, "RCU Tasks Trace"); +/* Load from ->trc_reader_special.b.need_qs with proper ordering. */ +static u8 rcu_ld_need_qs(struct task_struct *t) +{ + smp_mb(); // Enforce full grace-period ordering. + return smp_load_acquire(&t->trc_reader_special.b.need_qs); +} + +/* Store to ->trc_reader_special.b.need_qs with proper ordering. */ +static void rcu_st_need_qs(struct task_struct *t, u8 v) +{ + smp_store_release(&t->trc_reader_special.b.need_qs, v); + smp_mb(); // Enforce full grace-period ordering. +} + /* - * This irq_work handler allows rcu_read_unlock_trace() to be invoked - * while the scheduler locks are held. + * Do a cmpxchg() on ->trc_reader_special.b.need_qs, allowing for + * the four-byte operand-size restriction of some platforms. + * Returns the old value, which is often ignored. */ -static void rcu_read_unlock_iw(struct irq_work *iwp) +u8 rcu_trc_cmpxchg_need_qs(struct task_struct *t, u8 old, u8 new) { - wake_up(&trc_wait); + union rcu_special ret; + union rcu_special trs_old = READ_ONCE(t->trc_reader_special); + union rcu_special trs_new = trs_old; + + if (trs_old.b.need_qs != old) + return trs_old.b.need_qs; + trs_new.b.need_qs = new; + ret.s = cmpxchg(&t->trc_reader_special.s, trs_old.s, trs_new.s); + return ret.b.need_qs; } -static DEFINE_IRQ_WORK(rcu_tasks_trace_iw, rcu_read_unlock_iw); +EXPORT_SYMBOL_GPL(rcu_trc_cmpxchg_need_qs); -/* If we are the last reader, wake up the grace-period kthread. */ -void rcu_read_unlock_trace_special(struct task_struct *t, int nesting) +/* + * If we are the last reader, signal the grace-period kthread. + * Also remove from the per-CPU list of blocked tasks. + */ +void rcu_read_unlock_trace_special(struct task_struct *t) { - int nq = t->trc_reader_special.b.need_qs; + unsigned long flags; + struct rcu_tasks_percpu *rtpcp; + union rcu_special trs; - if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && - t->trc_reader_special.b.need_mb) + // Open-coded full-word version of rcu_ld_need_qs(). + smp_mb(); // Enforce full grace-period ordering. + trs = smp_load_acquire(&t->trc_reader_special); + + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && t->trc_reader_special.b.need_mb) smp_mb(); // Pairs with update-side barriers. // Update .need_qs before ->trc_reader_nesting for irq/NMI handlers. - if (nq) - WRITE_ONCE(t->trc_reader_special.b.need_qs, false); - WRITE_ONCE(t->trc_reader_nesting, nesting); - if (nq && atomic_dec_and_test(&trc_n_readers_need_end)) - irq_work_queue(&rcu_tasks_trace_iw); + if (trs.b.need_qs == (TRC_NEED_QS_CHECKED | TRC_NEED_QS)) { + u8 result = rcu_trc_cmpxchg_need_qs(t, TRC_NEED_QS_CHECKED | TRC_NEED_QS, + TRC_NEED_QS_CHECKED); + + WARN_ONCE(result != trs.b.need_qs, "%s: result = %d", __func__, result); + } + if (trs.b.blocked) { + rtpcp = per_cpu_ptr(rcu_tasks_trace.rtpcpu, t->trc_blkd_cpu); + raw_spin_lock_irqsave_rcu_node(rtpcp, flags); + list_del_init(&t->trc_blkd_node); + WRITE_ONCE(t->trc_reader_special.b.blocked, false); + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); + } + WRITE_ONCE(t->trc_reader_nesting, 0); } EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special); +/* Add a newly blocked reader task to its CPU's list. */ +void rcu_tasks_trace_qs_blkd(struct task_struct *t) +{ + unsigned long flags; + struct rcu_tasks_percpu *rtpcp; + + local_irq_save(flags); + rtpcp = this_cpu_ptr(rcu_tasks_trace.rtpcpu); + raw_spin_lock_rcu_node(rtpcp); // irqs already disabled + t->trc_blkd_cpu = smp_processor_id(); + if (!rtpcp->rtp_blkd_tasks.next) + INIT_LIST_HEAD(&rtpcp->rtp_blkd_tasks); + list_add(&t->trc_blkd_node, &rtpcp->rtp_blkd_tasks); + WRITE_ONCE(t->trc_reader_special.b.blocked, true); + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); +} +EXPORT_SYMBOL_GPL(rcu_tasks_trace_qs_blkd); + /* Add a task to the holdout list, if it is not already on the list. */ static void trc_add_holdout(struct task_struct *t, struct list_head *bhp) { if (list_empty(&t->trc_holdout_list)) { get_task_struct(t); list_add(&t->trc_holdout_list, bhp); + n_trc_holdouts++; } } @@ -795,98 +1487,91 @@ static void trc_del_holdout(struct task_struct *t) if (!list_empty(&t->trc_holdout_list)) { list_del_init(&t->trc_holdout_list); put_task_struct(t); + n_trc_holdouts--; } } /* IPI handler to check task state. */ static void trc_read_check_handler(void *t_in) { + int nesting; struct task_struct *t = current; struct task_struct *texp = t_in; // If the task is no longer running on this CPU, leave. - if (unlikely(texp != t)) { - if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end))) - wake_up(&trc_wait); + if (unlikely(texp != t)) goto reset_ipi; // Already on holdout list, so will check later. - } // If the task is not in a read-side critical section, and // if this is the last reader, awaken the grace-period kthread. - if (likely(!t->trc_reader_nesting)) { - if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end))) - wake_up(&trc_wait); - // Mark as checked after decrement to avoid false - // positives on the above WARN_ON_ONCE(). - WRITE_ONCE(t->trc_reader_checked, true); + nesting = READ_ONCE(t->trc_reader_nesting); + if (likely(!nesting)) { + rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); goto reset_ipi; } // If we are racing with an rcu_read_unlock_trace(), try again later. - if (unlikely(t->trc_reader_nesting < 0)) { - if (WARN_ON_ONCE(atomic_dec_and_test(&trc_n_readers_need_end))) - wake_up(&trc_wait); + if (unlikely(nesting < 0)) goto reset_ipi; - } - WRITE_ONCE(t->trc_reader_checked, true); - // Get here if the task is in a read-side critical section. Set - // its state so that it will awaken the grace-period kthread upon - // exit from that critical section. - WARN_ON_ONCE(t->trc_reader_special.b.need_qs); - WRITE_ONCE(t->trc_reader_special.b.need_qs, true); + // Get here if the task is in a read-side critical section. + // Set its state so that it will update state for the grace-period + // kthread upon exit from that critical section. + rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS | TRC_NEED_QS_CHECKED); reset_ipi: // Allow future IPIs to be sent on CPU and for task. // Also order this IPI handler against any later manipulations of // the intended task. - smp_store_release(&per_cpu(trc_ipi_to_cpu, smp_processor_id()), false); // ^^^ + smp_store_release(per_cpu_ptr(&trc_ipi_to_cpu, smp_processor_id()), false); // ^^^ smp_store_release(&texp->trc_ipi_to_cpu, -1); // ^^^ } /* Callback function for scheduler to check locked-down task. */ -static bool trc_inspect_reader(struct task_struct *t, void *arg) +static int trc_inspect_reader(struct task_struct *t, void *bhp_in) { + struct list_head *bhp = bhp_in; int cpu = task_cpu(t); - bool in_qs = false; + int nesting; bool ofl = cpu_is_offline(cpu); - if (task_curr(t)) { - WARN_ON_ONCE(ofl && !is_idle_task(t)); - + if (task_curr(t) && !ofl) { // If no chance of heavyweight readers, do it the hard way. - if (!ofl && !IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) - return false; + if (!IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) + return -EINVAL; // If heavyweight readers are enabled on the remote task, // we can inspect its state despite its currently running. // However, we cannot safely change its state. n_heavy_reader_attempts++; - if (!ofl && // Check for "running" idle tasks on offline CPUs. - !rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting)) - return false; // No quiescent state, do it the hard way. + // Check for "running" idle tasks on offline CPUs. + if (!rcu_dynticks_zero_in_eqs(cpu, &t->trc_reader_nesting)) + return -EINVAL; // No quiescent state, do it the hard way. n_heavy_reader_updates++; - if (ofl) - n_heavy_reader_ofl_updates++; - in_qs = true; + nesting = 0; } else { - in_qs = likely(!t->trc_reader_nesting); + // The task is not running, so C-language access is safe. + nesting = t->trc_reader_nesting; + WARN_ON_ONCE(ofl && task_curr(t) && (t != idle_task(task_cpu(t)))); + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && ofl) + n_heavy_reader_ofl_updates++; } - // Mark as checked. Because this is called from the grace-period - // kthread, also remove the task from the holdout list. - t->trc_reader_checked = true; - trc_del_holdout(t); - - if (in_qs) - return true; // Already in quiescent state, done!!! + // If not exiting a read-side critical section, mark as checked + // so that the grace-period kthread will remove it from the + // holdout list. + if (!nesting) { + rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); + return 0; // In QS, so done. + } + if (nesting < 0) + return -EINVAL; // Reader transitioning, try again later. // The task is in a read-side critical section, so set up its - // state so that it will awaken the grace-period kthread upon exit - // from that critical section. - atomic_inc(&trc_n_readers_need_end); // One more to wait on. - WARN_ON_ONCE(t->trc_reader_special.b.need_qs); - WRITE_ONCE(t->trc_reader_special.b.need_qs, true); - return true; + // state so that it will update state upon exit from that critical + // section. + if (!rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS | TRC_NEED_QS_CHECKED)) + trc_add_holdout(t, bhp); + return 0; } /* Attempt to extract the state for the specified task. */ @@ -901,20 +1586,25 @@ static void trc_wait_for_one_reader(struct task_struct *t, // The current task had better be in a quiescent state. if (t == current) { - t->trc_reader_checked = true; - trc_del_holdout(t); - WARN_ON_ONCE(t->trc_reader_nesting); + rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); + WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting)); return; } // Attempt to nail down the task for inspection. get_task_struct(t); - if (try_invoke_on_locked_down_task(t, trc_inspect_reader, NULL)) { + if (!task_call_func(t, trc_inspect_reader, bhp)) { put_task_struct(t); return; } put_task_struct(t); + // If this task is not yet on the holdout list, then we are in + // an RCU read-side critical section. Otherwise, the invocation of + // trc_add_holdout() that added it to the list did the necessary + // get_task_struct(). Either way, the task cannot be freed out + // from under this code. + // If currently running, send an IPI, either way, add to list. trc_add_holdout(t, bhp); if (task_curr(t) && @@ -926,96 +1616,161 @@ static void trc_wait_for_one_reader(struct task_struct *t, if (per_cpu(trc_ipi_to_cpu, cpu) || t->trc_ipi_to_cpu >= 0) return; - atomic_inc(&trc_n_readers_need_end); per_cpu(trc_ipi_to_cpu, cpu) = true; t->trc_ipi_to_cpu = cpu; rcu_tasks_trace.n_ipis++; - if (smp_call_function_single(cpu, - trc_read_check_handler, t, 0)) { + if (smp_call_function_single(cpu, trc_read_check_handler, t, 0)) { // Just in case there is some other reason for // failure than the target CPU being offline. + WARN_ONCE(1, "%s(): smp_call_function_single() failed for CPU: %d\n", + __func__, cpu); rcu_tasks_trace.n_ipis_fails++; per_cpu(trc_ipi_to_cpu, cpu) = false; - t->trc_ipi_to_cpu = cpu; - if (atomic_dec_and_test(&trc_n_readers_need_end)) { - WARN_ON_ONCE(1); - wake_up(&trc_wait); - } + t->trc_ipi_to_cpu = -1; } } } +/* + * Initialize for first-round processing for the specified task. + * Return false if task is NULL or already taken care of, true otherwise. + */ +static bool rcu_tasks_trace_pertask_prep(struct task_struct *t, bool notself) +{ + // During early boot when there is only the one boot CPU, there + // is no idle task for the other CPUs. Also, the grace-period + // kthread is always in a quiescent state. In addition, just return + // if this task is already on the list. + if (unlikely(t == NULL) || (t == current && notself) || !list_empty(&t->trc_holdout_list)) + return false; + + rcu_st_need_qs(t, 0); + t->trc_ipi_to_cpu = -1; + return true; +} + +/* Do first-round processing for the specified task. */ +static void rcu_tasks_trace_pertask(struct task_struct *t, struct list_head *hop) +{ + if (rcu_tasks_trace_pertask_prep(t, true)) + trc_wait_for_one_reader(t, hop); +} + /* Initialize for a new RCU-tasks-trace grace period. */ -static void rcu_tasks_trace_pregp_step(void) +static void rcu_tasks_trace_pregp_step(struct list_head *hop) { + LIST_HEAD(blkd_tasks); int cpu; - - // Allow for fast-acting IPIs. - atomic_set(&trc_n_readers_need_end, 1); + unsigned long flags; + struct rcu_tasks_percpu *rtpcp; + struct task_struct *t; // There shouldn't be any old IPIs, but... for_each_possible_cpu(cpu) WARN_ON_ONCE(per_cpu(trc_ipi_to_cpu, cpu)); - // Disable CPU hotplug across the tasklist scan. - // This also waits for all readers in CPU-hotplug code paths. + // Disable CPU hotplug across the CPU scan for the benefit of + // any IPIs that might be needed. This also waits for all readers + // in CPU-hotplug code paths. cpus_read_lock(); -} -/* Do first-round processing for the specified task. */ -static void rcu_tasks_trace_pertask(struct task_struct *t, - struct list_head *hop) -{ - // During early boot when there is only the one boot CPU, there - // is no idle task for the other CPUs. Just return. - if (unlikely(t == NULL)) - return; + // These rcu_tasks_trace_pertask_prep() calls are serialized to + // allow safe access to the hop list. + for_each_online_cpu(cpu) { + rcu_read_lock(); + t = cpu_curr_snapshot(cpu); + if (rcu_tasks_trace_pertask_prep(t, true)) + trc_add_holdout(t, hop); + rcu_read_unlock(); + cond_resched_tasks_rcu_qs(); + } - WRITE_ONCE(t->trc_reader_special.b.need_qs, false); - WRITE_ONCE(t->trc_reader_checked, false); - t->trc_ipi_to_cpu = -1; - trc_wait_for_one_reader(t, hop); + // Only after all running tasks have been accounted for is it + // safe to take care of the tasks that have blocked within their + // current RCU tasks trace read-side critical section. + for_each_possible_cpu(cpu) { + rtpcp = per_cpu_ptr(rcu_tasks_trace.rtpcpu, cpu); + raw_spin_lock_irqsave_rcu_node(rtpcp, flags); + list_splice_init(&rtpcp->rtp_blkd_tasks, &blkd_tasks); + while (!list_empty(&blkd_tasks)) { + rcu_read_lock(); + t = list_first_entry(&blkd_tasks, struct task_struct, trc_blkd_node); + list_del_init(&t->trc_blkd_node); + list_add(&t->trc_blkd_node, &rtpcp->rtp_blkd_tasks); + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); + rcu_tasks_trace_pertask(t, hop); + rcu_read_unlock(); + raw_spin_lock_irqsave_rcu_node(rtpcp, flags); + } + raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags); + cond_resched_tasks_rcu_qs(); + } + + // Re-enable CPU hotplug now that the holdout list is populated. + cpus_read_unlock(); } /* - * Do intermediate processing between task and holdout scans and - * pick up the idle tasks. + * Do intermediate processing between task and holdout scans. */ static void rcu_tasks_trace_postscan(struct list_head *hop) { - int cpu; - - for_each_possible_cpu(cpu) - rcu_tasks_trace_pertask(idle_task(cpu), hop); - - // Re-enable CPU hotplug now that the tasklist scan has completed. - cpus_read_unlock(); - // Wait for late-stage exiting tasks to finish exiting. // These might have passed the call to exit_tasks_rcu_finish(). + + // If you remove the following line, update rcu_trace_implies_rcu_gp()!!! synchronize_rcu(); - // Any tasks that exit after this point will set ->trc_reader_checked. + // Any tasks that exit after this point will set + // TRC_NEED_QS_CHECKED in ->trc_reader_special.b.need_qs. +} + +/* Communicate task state back to the RCU tasks trace stall warning request. */ +struct trc_stall_chk_rdr { + int nesting; + int ipi_to_cpu; + u8 needqs; +}; + +static int trc_check_slow_task(struct task_struct *t, void *arg) +{ + struct trc_stall_chk_rdr *trc_rdrp = arg; + + if (task_curr(t) && cpu_online(task_cpu(t))) + return false; // It is running, so decline to inspect it. + trc_rdrp->nesting = READ_ONCE(t->trc_reader_nesting); + trc_rdrp->ipi_to_cpu = READ_ONCE(t->trc_ipi_to_cpu); + trc_rdrp->needqs = rcu_ld_need_qs(t); + return true; } /* Show the state of a task stalling the current RCU tasks trace GP. */ static void show_stalled_task_trace(struct task_struct *t, bool *firstreport) { int cpu; + struct trc_stall_chk_rdr trc_rdr; + bool is_idle_tsk = is_idle_task(t); if (*firstreport) { pr_err("INFO: rcu_tasks_trace detected stalls on tasks:\n"); *firstreport = false; } - // FIXME: This should attempt to use try_invoke_on_nonrunning_task(). cpu = task_cpu(t); - pr_alert("P%d: %c%c%c nesting: %d%c cpu: %d\n", - t->pid, - ".I"[READ_ONCE(t->trc_ipi_to_cpu) > 0], - ".i"[is_idle_task(t)], - ".N"[cpu > 0 && tick_nohz_full_cpu(cpu)], - t->trc_reader_nesting, - " N"[!!t->trc_reader_special.b.need_qs], - cpu); + if (!task_call_func(t, trc_check_slow_task, &trc_rdr)) + pr_alert("P%d: %c%c\n", + t->pid, + ".I"[t->trc_ipi_to_cpu >= 0], + ".i"[is_idle_tsk]); + else + pr_alert("P%d: %c%c%c%c nesting: %d%c%c cpu: %d%s\n", + t->pid, + ".I"[trc_rdr.ipi_to_cpu >= 0], + ".i"[is_idle_tsk], + ".N"[cpu >= 0 && tick_nohz_full_cpu(cpu)], + ".B"[!!data_race(t->trc_reader_special.b.blocked)], + trc_rdr.nesting, + " !CN"[trc_rdr.needqs & 0x3], + " ?"[trc_rdr.needqs > 0x3], + cpu, cpu_online(cpu) ? "" : "(offline)"); sched_show_task(t); } @@ -1035,71 +1790,52 @@ static void check_all_holdout_tasks_trace(struct list_head *hop, { struct task_struct *g, *t; - // Disable CPU hotplug across the holdout list scan. + // Disable CPU hotplug across the holdout list scan for IPIs. cpus_read_lock(); list_for_each_entry_safe(t, g, hop, trc_holdout_list) { // If safe and needed, try to check the current task. if (READ_ONCE(t->trc_ipi_to_cpu) == -1 && - !READ_ONCE(t->trc_reader_checked)) + !(rcu_ld_need_qs(t) & TRC_NEED_QS_CHECKED)) trc_wait_for_one_reader(t, hop); // If check succeeded, remove this task from the list. - if (READ_ONCE(t->trc_reader_checked)) + if (smp_load_acquire(&t->trc_ipi_to_cpu) == -1 && + rcu_ld_need_qs(t) == TRC_NEED_QS_CHECKED) trc_del_holdout(t); else if (needreport) show_stalled_task_trace(t, firstreport); + cond_resched_tasks_rcu_qs(); } // Re-enable CPU hotplug now that the holdout list scan has completed. cpus_read_unlock(); if (needreport) { - if (firstreport) + if (*firstreport) pr_err("INFO: rcu_tasks_trace detected stalls? (Late IPI?)\n"); show_stalled_ipi_trace(); } } +static void rcu_tasks_trace_empty_fn(void *unused) +{ +} + /* Wait for grace period to complete and provide ordering. */ static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp) { - bool firstreport; - struct task_struct *g, *t; - LIST_HEAD(holdouts); - long ret; + int cpu; - // Remove the safety count. - smp_mb__before_atomic(); // Order vs. earlier atomics - atomic_dec(&trc_n_readers_need_end); - smp_mb__after_atomic(); // Order vs. later atomics + // Wait for any lingering IPI handlers to complete. Note that + // if a CPU has gone offline or transitioned to userspace in the + // meantime, all IPI handlers should have been drained beforehand. + // Yes, this assumes that CPUs process IPIs in order. If that ever + // changes, there will need to be a recheck and/or timed wait. + for_each_online_cpu(cpu) + if (WARN_ON_ONCE(smp_load_acquire(per_cpu_ptr(&trc_ipi_to_cpu, cpu)))) + smp_call_function_single(cpu, rcu_tasks_trace_empty_fn, NULL, 1); - // Wait for readers. - set_tasks_gp_state(rtp, RTGS_WAIT_READERS); - for (;;) { - ret = wait_event_idle_exclusive_timeout( - trc_wait, - atomic_read(&trc_n_readers_need_end) == 0, - READ_ONCE(rcu_task_stall_timeout)); - if (ret) - break; // Count reached zero. - // Stall warning time, so make a list of the offenders. - rcu_read_lock(); - for_each_process_thread(g, t) - if (READ_ONCE(t->trc_reader_special.b.need_qs)) - trc_add_holdout(t, &holdouts); - rcu_read_unlock(); - firstreport = true; - list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list) { - if (READ_ONCE(t->trc_reader_special.b.need_qs)) - show_stalled_task_trace(t, &firstreport); - trc_del_holdout(t); // Release task_struct reference. - } - if (firstreport) - pr_err("INFO: rcu_tasks_trace detected stalls? (Counter/taskslist mismatch?)\n"); - show_stalled_ipi_trace(); - pr_err("\t%d holdouts\n", atomic_read(&trc_n_readers_need_end)); - } smp_mb(); // Caller's code must be ordered after wakeup. // Pairs with pretty much every ordering primitive. } @@ -1107,11 +1843,14 @@ static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp) /* Report any needed quiescent state for this exiting task. */ static void exit_tasks_rcu_finish_trace(struct task_struct *t) { - WRITE_ONCE(t->trc_reader_checked, true); - WARN_ON_ONCE(t->trc_reader_nesting); - WRITE_ONCE(t->trc_reader_nesting, 0); - if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs))) - rcu_read_unlock_trace_special(t, 0); + union rcu_special trs = READ_ONCE(t->trc_reader_special); + + rcu_trc_cmpxchg_need_qs(t, 0, TRC_NEED_QS_CHECKED); + WARN_ON_ONCE(READ_ONCE(t->trc_reader_nesting)); + if (WARN_ON_ONCE(rcu_ld_need_qs(t) & TRC_NEED_QS || trs.b.blocked)) + rcu_read_unlock_trace_special(t); + else + WRITE_ONCE(t->trc_reader_nesting, 0); } /** @@ -1119,15 +1858,11 @@ static void exit_tasks_rcu_finish_trace(struct task_struct *t) * @rhp: structure to be used for queueing the RCU updates. * @func: actual callback function to be invoked after the grace period * - * The callback function will be invoked some time after a full grace - * period elapses, in other words after all currently executing RCU - * read-side critical sections have completed. call_rcu_tasks_trace() - * assumes that the read-side critical sections end at context switch, - * cond_resched_rcu_qs(), or transition to usermode execution. As such, - * there are no read-side primitives analogous to rcu_read_lock() and - * rcu_read_unlock() because this primitive is intended to determine - * that all tasks have passed through a safe state, not so much for - * data-strcuture synchronization. + * The callback function will be invoked some time after a trace rcu-tasks + * grace period elapses, in other words after all currently executing + * trace rcu-tasks read-side critical sections have completed. These + * read-side critical sections are delimited by calls to rcu_read_lock_trace() + * and rcu_read_unlock_trace(). * * See the description of call_rcu() for more detailed information on * memory ordering guarantees. @@ -1143,7 +1878,7 @@ EXPORT_SYMBOL_GPL(call_rcu_tasks_trace); * * Control will return to the caller some time after a trace rcu-tasks * grace period has elapsed, in other words after all currently executing - * rcu-tasks read-side critical sections have elapsed. These read-side + * trace rcu-tasks read-side critical sections have elapsed. These read-side * critical sections are delimited by calls to rcu_read_lock_trace() * and rcu_read_unlock_trace(). * @@ -1170,13 +1905,16 @@ EXPORT_SYMBOL_GPL(synchronize_rcu_tasks_trace); */ void rcu_barrier_tasks_trace(void) { - /* There is only one callback queue, so this is easy. ;-) */ - synchronize_rcu_tasks_trace(); + rcu_barrier_tasks_generic(&rcu_tasks_trace); } EXPORT_SYMBOL_GPL(rcu_barrier_tasks_trace); +int rcu_tasks_trace_lazy_ms = -1; +module_param(rcu_tasks_trace_lazy_ms, int, 0444); + static int __init rcu_spawn_tasks_trace_kthread(void) { + cblist_init_generic(&rcu_tasks_trace); if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) { rcu_tasks_trace.gp_sleep = HZ / 10; rcu_tasks_trace.init_fract = HZ / 10; @@ -1188,8 +1926,9 @@ static int __init rcu_spawn_tasks_trace_kthread(void) if (rcu_tasks_trace.init_fract <= 0) rcu_tasks_trace.init_fract = 1; } + if (rcu_tasks_trace_lazy_ms >= 0) + rcu_tasks_trace.lazy_jiffies = msecs_to_jiffies(rcu_tasks_trace_lazy_ms); rcu_tasks_trace.pregp_func = rcu_tasks_trace_pregp_step; - rcu_tasks_trace.pertask_func = rcu_tasks_trace_pertask; rcu_tasks_trace.postscan_func = rcu_tasks_trace_postscan; rcu_tasks_trace.holdouts_func = check_all_holdout_tasks_trace; rcu_tasks_trace.postgp_func = rcu_tasks_trace_postgp; @@ -1202,7 +1941,8 @@ void show_rcu_tasks_trace_gp_kthread(void) { char buf[64]; - sprintf(buf, "N%d h:%lu/%lu/%lu", atomic_read(&trc_n_readers_need_end), + sprintf(buf, "N%lu h:%lu/%lu/%lu", + data_race(n_trc_holdouts), data_race(n_heavy_reader_ofl_updates), data_race(n_heavy_reader_updates), data_race(n_heavy_reader_attempts)); @@ -1211,6 +1951,12 @@ void show_rcu_tasks_trace_gp_kthread(void) EXPORT_SYMBOL_GPL(show_rcu_tasks_trace_gp_kthread); #endif // !defined(CONFIG_TINY_RCU) +struct task_struct *get_rcu_tasks_trace_gp_kthread(void) +{ + return rcu_tasks_trace.kthread_ptr; +} +EXPORT_SYMBOL_GPL(get_rcu_tasks_trace_gp_kthread); + #else /* #ifdef CONFIG_TASKS_TRACE_RCU */ static void exit_tasks_rcu_finish_trace(struct task_struct *t) { } #endif /* #else #ifdef CONFIG_TASKS_TRACE_RCU */ @@ -1224,6 +1970,122 @@ void show_rcu_tasks_gp_kthreads(void) } #endif /* #ifndef CONFIG_TINY_RCU */ +#ifdef CONFIG_PROVE_RCU +struct rcu_tasks_test_desc { + struct rcu_head rh; + const char *name; + bool notrun; + unsigned long runstart; +}; + +static struct rcu_tasks_test_desc tests[] = { + { + .name = "call_rcu_tasks()", + /* If not defined, the test is skipped. */ + .notrun = IS_ENABLED(CONFIG_TASKS_RCU), + }, + { + .name = "call_rcu_tasks_rude()", + /* If not defined, the test is skipped. */ + .notrun = IS_ENABLED(CONFIG_TASKS_RUDE_RCU), + }, + { + .name = "call_rcu_tasks_trace()", + /* If not defined, the test is skipped. */ + .notrun = IS_ENABLED(CONFIG_TASKS_TRACE_RCU) + } +}; + +static void test_rcu_tasks_callback(struct rcu_head *rhp) +{ + struct rcu_tasks_test_desc *rttd = + container_of(rhp, struct rcu_tasks_test_desc, rh); + + pr_info("Callback from %s invoked.\n", rttd->name); + + rttd->notrun = false; +} + +static void rcu_tasks_initiate_self_tests(void) +{ +#ifdef CONFIG_TASKS_RCU + pr_info("Running RCU Tasks wait API self tests\n"); + tests[0].runstart = jiffies; + synchronize_rcu_tasks(); + call_rcu_tasks(&tests[0].rh, test_rcu_tasks_callback); +#endif + +#ifdef CONFIG_TASKS_RUDE_RCU + pr_info("Running RCU Tasks Rude wait API self tests\n"); + tests[1].runstart = jiffies; + synchronize_rcu_tasks_rude(); + call_rcu_tasks_rude(&tests[1].rh, test_rcu_tasks_callback); +#endif + +#ifdef CONFIG_TASKS_TRACE_RCU + pr_info("Running RCU Tasks Trace wait API self tests\n"); + tests[2].runstart = jiffies; + synchronize_rcu_tasks_trace(); + call_rcu_tasks_trace(&tests[2].rh, test_rcu_tasks_callback); +#endif +} + +/* + * Return: 0 - test passed + * 1 - test failed, but have not timed out yet + * -1 - test failed and timed out + */ +static int rcu_tasks_verify_self_tests(void) +{ + int ret = 0; + int i; + unsigned long bst = rcu_task_stall_timeout; + + if (bst <= 0 || bst > RCU_TASK_BOOT_STALL_TIMEOUT) + bst = RCU_TASK_BOOT_STALL_TIMEOUT; + for (i = 0; i < ARRAY_SIZE(tests); i++) { + while (tests[i].notrun) { // still hanging. + if (time_after(jiffies, tests[i].runstart + bst)) { + pr_err("%s has failed boot-time tests.\n", tests[i].name); + ret = -1; + break; + } + ret = 1; + break; + } + } + WARN_ON(ret < 0); + + return ret; +} + +/* + * Repeat the rcu_tasks_verify_self_tests() call once every second until the + * test passes or has timed out. + */ +static struct delayed_work rcu_tasks_verify_work; +static void rcu_tasks_verify_work_fn(struct work_struct *work __maybe_unused) +{ + int ret = rcu_tasks_verify_self_tests(); + + if (ret <= 0) + return; + + /* Test fails but not timed out yet, reschedule another check */ + schedule_delayed_work(&rcu_tasks_verify_work, HZ); +} + +static int rcu_tasks_verify_schedule_work(void) +{ + INIT_DELAYED_WORK(&rcu_tasks_verify_work, rcu_tasks_verify_work_fn); + rcu_tasks_verify_work_fn(NULL); + return 0; +} +late_initcall(rcu_tasks_verify_schedule_work); +#else /* #ifdef CONFIG_PROVE_RCU */ +static void rcu_tasks_initiate_self_tests(void) { } +#endif /* #else #ifdef CONFIG_PROVE_RCU */ + void __init rcu_init_tasks_generic(void) { #ifdef CONFIG_TASKS_RCU @@ -1237,9 +2099,11 @@ void __init rcu_init_tasks_generic(void) #ifdef CONFIG_TASKS_TRACE_RCU rcu_spawn_tasks_trace_kthread(); #endif + + // Run the self-tests. + rcu_tasks_initiate_self_tests(); } #else /* #ifdef CONFIG_TASKS_RCU_GENERIC */ static inline void rcu_tasks_bootup_oddness(void) {} -void show_rcu_tasks_gp_kthreads(void) {} #endif /* #else #ifdef CONFIG_TASKS_RCU_GENERIC */ diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index aa897c3f2e92..fec804b79080 100644 --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -32,17 +32,19 @@ struct rcu_ctrlblk { struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */ struct rcu_head **donetail; /* ->next pointer of last "done" CB. */ struct rcu_head **curtail; /* ->next pointer of last CB. */ + unsigned long gp_seq; /* Grace-period counter. */ }; /* Definition for rcupdate control block. */ static struct rcu_ctrlblk rcu_ctrlblk = { .donetail = &rcu_ctrlblk.rcucblist, .curtail = &rcu_ctrlblk.rcucblist, + .gp_seq = 0 - 300UL, }; void rcu_barrier(void) { - wait_rcu_gp(call_rcu); + wait_rcu_gp(call_rcu_hurry); } EXPORT_SYMBOL(rcu_barrier); @@ -56,6 +58,7 @@ void rcu_qs(void) rcu_ctrlblk.donetail = rcu_ctrlblk.curtail; raise_softirq_irqoff(RCU_SOFTIRQ); } + WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2); local_irq_restore(flags); } @@ -94,6 +97,7 @@ static inline bool rcu_reclaim_tiny(struct rcu_head *head) trace_rcu_invoke_callback("", head); f = head->func; + debug_rcu_head_callback(head); WRITE_ONCE(head->func, (rcu_callback_t)0L); f(head); rcu_lock_release(&rcu_callback_map); @@ -136,8 +140,10 @@ static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused /* * Wait for a grace period to elapse. But it is illegal to invoke * synchronize_rcu() from within an RCU read-side critical section. - * Therefore, any legal call to synchronize_rcu() is a quiescent - * state, and so on a UP system, synchronize_rcu() need do nothing. + * Therefore, any legal call to synchronize_rcu() is a quiescent state, + * and so on a UP system, synchronize_rcu() need do nothing, other than + * let the polled APIs know that another grace period elapsed. + * * (But Lai Jiangshan points out the benefits of doing might_sleep() * to reduce latency.) * @@ -149,9 +155,14 @@ void synchronize_rcu(void) lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map), "Illegal synchronize_rcu() in RCU read-side critical section"); + WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2); } EXPORT_SYMBOL_GPL(synchronize_rcu); +static void tiny_rcu_leak_callback(struct rcu_head *rhp) +{ +} + /* * Post an RCU callback to be invoked after the end of an RCU grace * period. But since we have but one CPU, that would be after any @@ -159,9 +170,20 @@ EXPORT_SYMBOL_GPL(synchronize_rcu); */ void call_rcu(struct rcu_head *head, rcu_callback_t func) { + static atomic_t doublefrees; unsigned long flags; - debug_rcu_head_queue(head); + if (debug_rcu_head_queue(head)) { + if (atomic_inc_return(&doublefrees) < 4) { + pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func); + mem_dump_obj(head); + } + + if (!__is_kvfree_rcu_offset((unsigned long)head->func)) + WRITE_ONCE(head->func, tiny_rcu_leak_callback); + return; + } + head->func = func; head->next = NULL; @@ -177,9 +199,66 @@ void call_rcu(struct rcu_head *head, rcu_callback_t func) } EXPORT_SYMBOL_GPL(call_rcu); +/* + * Store a grace-period-counter "cookie". For more information, + * see the Tree RCU header comment. + */ +void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) +{ + rgosp->rgos_norm = RCU_GET_STATE_COMPLETED; +} +EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full); + +/* + * Return a grace-period-counter "cookie". For more information, + * see the Tree RCU header comment. + */ +unsigned long get_state_synchronize_rcu(void) +{ + return READ_ONCE(rcu_ctrlblk.gp_seq); +} +EXPORT_SYMBOL_GPL(get_state_synchronize_rcu); + +/* + * Return a grace-period-counter "cookie" and ensure that a future grace + * period completes. For more information, see the Tree RCU header comment. + */ +unsigned long start_poll_synchronize_rcu(void) +{ + unsigned long gp_seq = get_state_synchronize_rcu(); + + if (unlikely(is_idle_task(current))) { + /* force scheduling for rcu_qs() */ + resched_cpu(0); + } + return gp_seq; +} +EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu); + +/* + * Return true if the grace period corresponding to oldstate has completed + * and false otherwise. For more information, see the Tree RCU header + * comment. + */ +bool poll_state_synchronize_rcu(unsigned long oldstate) +{ + return oldstate == RCU_GET_STATE_COMPLETED || READ_ONCE(rcu_ctrlblk.gp_seq) != oldstate; +} +EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu); + +#ifdef CONFIG_KASAN_GENERIC +void kvfree_call_rcu(struct rcu_head *head, void *ptr) +{ + if (head) + kasan_record_aux_stack_noalloc(ptr); + + __kvfree_call_rcu(head, ptr); +} +EXPORT_SYMBOL_GPL(kvfree_call_rcu); +#endif + void __init rcu_init(void) { open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); rcu_early_boot_tests(); - srcu_init(); } diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 40e5e3dd253e..b2bccfd37c38 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -31,7 +31,10 @@ #include <linux/bitops.h> #include <linux/export.h> #include <linux/completion.h> +#include <linux/kmemleak.h> #include <linux/moduleparam.h> +#include <linux/panic.h> +#include <linux/panic_notifier.h> #include <linux/percpu.h> #include <linux/notifier.h> #include <linux/cpu.h> @@ -60,6 +63,7 @@ #include <linux/vmalloc.h> #include <linux/mm.h> #include <linux/kasan.h> +#include <linux/context_tracking.h> #include "../time/tick-internal.h" #include "tree.h" @@ -72,36 +76,33 @@ /* Data structures. */ -/* - * Steal a bit from the bottom of ->dynticks for idle entry/exit - * control. Initially this is for TLB flushing. - */ -#define RCU_DYNTICK_CTRL_MASK 0x1 -#define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1) - static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = { - .dynticks_nesting = 1, - .dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE, - .dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR), + .gpwrap = true, +#ifdef CONFIG_RCU_NOCB_CPU + .cblist.flags = SEGCBLIST_RCU_CORE, +#endif }; static struct rcu_state rcu_state = { .level = { &rcu_state.node[0] }, .gp_state = RCU_GP_IDLE, .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT, .barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex), + .barrier_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.barrier_lock), .name = RCU_NAME, .abbr = RCU_ABBR, .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex), .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex), - .ofl_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.ofl_lock), + .ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED, }; /* Dump rcu_node combining tree at boot to verify correct setup. */ static bool dump_tree; module_param(dump_tree, bool, 0444); /* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */ -static bool use_softirq = true; +static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT); +#ifndef CONFIG_PREEMPT_RT module_param(use_softirq, bool, 0444); +#endif /* Control rcu_node-tree auto-balancing at boot time. */ static bool rcu_fanout_exact; module_param(rcu_fanout_exact, bool, 0444); @@ -144,15 +145,22 @@ static int rcu_scheduler_fully_active __read_mostly; static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp, unsigned long gps, unsigned long flags); -static void rcu_init_new_rnp(struct rcu_node *rnp_leaf); -static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf); static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu); static void invoke_rcu_core(void); static void rcu_report_exp_rdp(struct rcu_data *rdp); static void sync_sched_exp_online_cleanup(int cpu); static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp); +static bool rcu_rdp_is_offloaded(struct rcu_data *rdp); +static bool rcu_rdp_cpu_online(struct rcu_data *rdp); +static bool rcu_init_invoked(void); +static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf); +static void rcu_init_new_rnp(struct rcu_node *rnp_leaf); -/* rcuc/rcub kthread realtime priority */ +/* + * rcuc/rcub/rcuop kthread realtime priority. The "rcuop" + * real-time priority(enabling/disabling) is controlled by + * the extra CONFIG_RCU_NOCB_CPU_CB_BOOST configuration. + */ static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0; module_param(kthread_prio, int, 0444); @@ -180,6 +188,17 @@ module_param(rcu_unlock_delay, int, 0444); static int rcu_min_cached_objs = 5; module_param(rcu_min_cached_objs, int, 0444); +// A page shrinker can ask for pages to be freed to make them +// available for other parts of the system. This usually happens +// under low memory conditions, and in that case we should also +// defer page-cache filling for a short time period. +// +// The default value is 5 seconds, which is long enough to reduce +// interference with the shrinker while it asks other systems to +// drain their caches. +static int rcu_delay_page_cache_fill_msec = 5000; +module_param(rcu_delay_page_cache_fill_msec, int, 0444); + /* Retrieve RCU kthreads priority for rcutorture */ int rcu_get_gp_kthreads_prio(void) { @@ -196,18 +215,7 @@ EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio); * the need for long delays to increase some race probabilities with the * need for fast grace periods to increase other race probabilities. */ -#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */ - -/* - * Compute the mask of online CPUs for the specified rcu_node structure. - * This will not be stable unless the rcu_node structure's ->lock is - * held, but the bit corresponding to the current CPU will be stable - * in most contexts. - */ -static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp) -{ - return READ_ONCE(rnp->qsmaskinitnext); -} +#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays for debugging. */ /* * Return true if an RCU grace period is in progress. The READ_ONCE()s @@ -236,58 +244,7 @@ void rcu_softirq_qs(void) { rcu_qs(); rcu_preempt_deferred_qs(current); -} - -/* - * Record entry into an extended quiescent state. This is only to be - * called when not already in an extended quiescent state, that is, - * RCU is watching prior to the call to this function and is no longer - * watching upon return. - */ -static noinstr void rcu_dynticks_eqs_enter(void) -{ - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - int seq; - - /* - * CPUs seeing atomic_add_return() must see prior RCU read-side - * critical sections, and we also must force ordering with the - * next idle sojourn. - */ - rcu_dynticks_task_trace_enter(); // Before ->dynticks update! - seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); - // RCU is no longer watching. Better be in extended quiescent state! - WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && - (seq & RCU_DYNTICK_CTRL_CTR)); - /* Better not have special action (TLB flush) pending! */ - WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && - (seq & RCU_DYNTICK_CTRL_MASK)); -} - -/* - * Record exit from an extended quiescent state. This is only to be - * called from an extended quiescent state, that is, RCU is not watching - * prior to the call to this function and is watching upon return. - */ -static noinstr void rcu_dynticks_eqs_exit(void) -{ - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - int seq; - - /* - * CPUs seeing atomic_add_return() must see prior idle sojourns, - * and we also must force ordering with the next RCU read-side - * critical section. - */ - seq = arch_atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); - // RCU is now watching. Better not be in an extended quiescent state! - rcu_dynticks_task_trace_exit(); // After ->dynticks update! - WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && - !(seq & RCU_DYNTICK_CTRL_CTR)); - if (seq & RCU_DYNTICK_CTRL_MASK) { - arch_atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks); - smp_mb__after_atomic(); /* _exit after clearing mask. */ - } + rcu_tasks_qs(current, false); } /* @@ -302,34 +259,19 @@ static noinstr void rcu_dynticks_eqs_exit(void) */ static void rcu_dynticks_eqs_online(void) { - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - - if (atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR) + if (ct_dynticks() & RCU_DYNTICKS_IDX) return; - atomic_add(RCU_DYNTICK_CTRL_CTR, &rdp->dynticks); -} - -/* - * Is the current CPU in an extended quiescent state? - * - * No ordering, as we are sampling CPU-local information. - */ -static __always_inline bool rcu_dynticks_curr_cpu_in_eqs(void) -{ - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - - return !(arch_atomic_read(&rdp->dynticks) & RCU_DYNTICK_CTRL_CTR); + ct_state_inc(RCU_DYNTICKS_IDX); } /* * Snapshot the ->dynticks counter with full ordering so as to allow * stable comparison of this counter with past and future snapshots. */ -static int rcu_dynticks_snap(struct rcu_data *rdp) +static int rcu_dynticks_snap(int cpu) { - int snap = atomic_add_return(0, &rdp->dynticks); - - return snap & ~RCU_DYNTICK_CTRL_MASK; + smp_mb(); // Fundamental RCU ordering guarantee. + return ct_dynticks_cpu_acquire(cpu); } /* @@ -338,15 +280,7 @@ static int rcu_dynticks_snap(struct rcu_data *rdp) */ static bool rcu_dynticks_in_eqs(int snap) { - return !(snap & RCU_DYNTICK_CTRL_CTR); -} - -/* Return true if the specified CPU is currently idle from an RCU viewpoint. */ -bool rcu_is_idle_cpu(int cpu) -{ - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); - - return rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)); + return !(snap & RCU_DYNTICKS_IDX); } /* @@ -356,7 +290,7 @@ bool rcu_is_idle_cpu(int cpu) */ static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap) { - return snap != rcu_dynticks_snap(rdp); + return snap != rcu_dynticks_snap(rdp->cpu); } /* @@ -365,45 +299,17 @@ static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap) */ bool rcu_dynticks_zero_in_eqs(int cpu, int *vp) { - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); int snap; // If not quiescent, force back to earlier extended quiescent state. - snap = atomic_read(&rdp->dynticks) & ~(RCU_DYNTICK_CTRL_MASK | - RCU_DYNTICK_CTRL_CTR); - + snap = ct_dynticks_cpu(cpu) & ~RCU_DYNTICKS_IDX; smp_rmb(); // Order ->dynticks and *vp reads. if (READ_ONCE(*vp)) return false; // Non-zero, so report failure; smp_rmb(); // Order *vp read and ->dynticks re-read. // If still in the same extended quiescent state, we are good! - return snap == (atomic_read(&rdp->dynticks) & ~RCU_DYNTICK_CTRL_MASK); -} - -/* - * Set the special (bottom) bit of the specified CPU so that it - * will take special action (such as flushing its TLB) on the - * next exit from an extended quiescent state. Returns true if - * the bit was successfully set, or false if the CPU was not in - * an extended quiescent state. - */ -bool rcu_eqs_special_set(int cpu) -{ - int old; - int new; - int new_old; - struct rcu_data *rdp = &per_cpu(rcu_data, cpu); - - new_old = atomic_read(&rdp->dynticks); - do { - old = new_old; - if (old & RCU_DYNTICK_CTRL_CTR) - return false; - new = old | RCU_DYNTICK_CTRL_MASK; - new_old = atomic_cmpxchg(&rdp->dynticks, old, new); - } while (new_old != old); - return true; + return snap == ct_dynticks_cpu(cpu); } /* @@ -419,13 +325,12 @@ bool rcu_eqs_special_set(int cpu) */ notrace void rcu_momentary_dyntick_idle(void) { - int special; + int seq; raw_cpu_write(rcu_data.rcu_need_heavy_qs, false); - special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR, - &this_cpu_ptr(&rcu_data)->dynticks); + seq = ct_state_inc(2 * RCU_DYNTICKS_IDX); /* It is illegal to call this from idle state. */ - WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR)); + WARN_ON_ONCE(!(seq & RCU_DYNTICKS_IDX)); rcu_preempt_deferred_qs(current); } EXPORT_SYMBOL_GPL(rcu_momentary_dyntick_idle); @@ -450,13 +355,13 @@ static int rcu_is_cpu_rrupt_from_idle(void) lockdep_assert_irqs_disabled(); /* Check for counter underflows */ - RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) < 0, + RCU_LOCKDEP_WARN(ct_dynticks_nesting() < 0, "RCU dynticks_nesting counter underflow!"); - RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 0, + RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() <= 0, "RCU dynticks_nmi_nesting counter underflow/zero!"); /* Are we at first interrupt nesting level? */ - nesting = __this_cpu_read(rcu_data.dynticks_nmi_nesting); + nesting = ct_dynticks_nmi_nesting(); if (nesting > 1) return false; @@ -466,7 +371,7 @@ static int rcu_is_cpu_rrupt_from_idle(void) WARN_ON_ONCE(!nesting && !is_idle_task(current)); /* Does CPU appear to be idle from an RCU standpoint? */ - return __this_cpu_read(rcu_data.dynticks_nesting) == 0; + return ct_dynticks_nesting() == 0; } #define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10) @@ -617,187 +522,45 @@ void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, } EXPORT_SYMBOL_GPL(rcutorture_get_gp_data); +#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) /* - * Enter an RCU extended quiescent state, which can be either the - * idle loop or adaptive-tickless usermode execution. - * - * We crowbar the ->dynticks_nmi_nesting field to zero to allow for - * the possibility of usermode upcalls having messed up our count - * of interrupt nesting level during the prior busy period. + * An empty function that will trigger a reschedule on + * IRQ tail once IRQs get re-enabled on userspace/guest resume. */ -static noinstr void rcu_eqs_enter(bool user) +static void late_wakeup_func(struct irq_work *work) { - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - - WARN_ON_ONCE(rdp->dynticks_nmi_nesting != DYNTICK_IRQ_NONIDLE); - WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); - WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && - rdp->dynticks_nesting == 0); - if (rdp->dynticks_nesting != 1) { - // RCU will still be watching, so just do accounting and leave. - rdp->dynticks_nesting--; - return; - } - - lockdep_assert_irqs_disabled(); - instrumentation_begin(); - trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&rdp->dynticks)); - WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current)); - rdp = this_cpu_ptr(&rcu_data); - do_nocb_deferred_wakeup(rdp); - rcu_prepare_for_idle(); - rcu_preempt_deferred_qs(current); - - // instrumentation for the noinstr rcu_dynticks_eqs_enter() - instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks)); - - instrumentation_end(); - WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */ - // RCU is watching here ... - rcu_dynticks_eqs_enter(); - // ... but is no longer watching here. - rcu_dynticks_task_enter(); -} - -/** - * rcu_idle_enter - inform RCU that current CPU is entering idle - * - * Enter idle mode, in other words, -leave- the mode in which RCU - * read-side critical sections can occur. (Though RCU read-side - * critical sections can occur in irq handlers in idle, a possibility - * handled by irq_enter() and irq_exit().) - * - * If you add or remove a call to rcu_idle_enter(), be sure to test with - * CONFIG_RCU_EQS_DEBUG=y. - */ -void rcu_idle_enter(void) -{ - lockdep_assert_irqs_disabled(); - rcu_eqs_enter(false); } -EXPORT_SYMBOL_GPL(rcu_idle_enter); -#ifdef CONFIG_NO_HZ_FULL -/** - * rcu_user_enter - inform RCU that we are resuming userspace. - * - * Enter RCU idle mode right before resuming userspace. No use of RCU - * is permitted between this call and rcu_user_exit(). This way the - * CPU doesn't need to maintain the tick for RCU maintenance purposes - * when the CPU runs in userspace. - * - * If you add or remove a call to rcu_user_enter(), be sure to test with - * CONFIG_RCU_EQS_DEBUG=y. - */ -noinstr void rcu_user_enter(void) -{ - lockdep_assert_irqs_disabled(); - rcu_eqs_enter(true); -} -#endif /* CONFIG_NO_HZ_FULL */ +static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) = + IRQ_WORK_INIT(late_wakeup_func); -/** - * rcu_nmi_exit - inform RCU of exit from NMI context +/* + * If either: * - * If we are returning from the outermost NMI handler that interrupted an - * RCU-idle period, update rdp->dynticks and rdp->dynticks_nmi_nesting - * to let the RCU grace-period handling know that the CPU is back to - * being RCU-idle. + * 1) the task is about to enter in guest mode and $ARCH doesn't support KVM generic work + * 2) the task is about to enter in user mode and $ARCH doesn't support generic entry. * - * If you add or remove a call to rcu_nmi_exit(), be sure to test - * with CONFIG_RCU_EQS_DEBUG=y. + * In these cases the late RCU wake ups aren't supported in the resched loops and our + * last resort is to fire a local irq_work that will trigger a reschedule once IRQs + * get re-enabled again. */ -noinstr void rcu_nmi_exit(void) +noinstr void rcu_irq_work_resched(void) { struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - instrumentation_begin(); - /* - * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks. - * (We are exiting an NMI handler, so RCU better be paying attention - * to us!) - */ - WARN_ON_ONCE(rdp->dynticks_nmi_nesting <= 0); - WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs()); - - /* - * If the nesting level is not 1, the CPU wasn't RCU-idle, so - * leave it in non-RCU-idle state. - */ - if (rdp->dynticks_nmi_nesting != 1) { - trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, - atomic_read(&rdp->dynticks)); - WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */ - rdp->dynticks_nmi_nesting - 2); - instrumentation_end(); + if (IS_ENABLED(CONFIG_GENERIC_ENTRY) && !(current->flags & PF_VCPU)) return; - } - - /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ - trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks)); - WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */ - if (!in_nmi()) - rcu_prepare_for_idle(); + if (IS_ENABLED(CONFIG_KVM_XFER_TO_GUEST_WORK) && (current->flags & PF_VCPU)) + return; - // instrumentation for the noinstr rcu_dynticks_eqs_enter() - instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks)); + instrumentation_begin(); + if (do_nocb_deferred_wakeup(rdp) && need_resched()) { + irq_work_queue(this_cpu_ptr(&late_wakeup_work)); + } instrumentation_end(); - - // RCU is watching here ... - rcu_dynticks_eqs_enter(); - // ... but is no longer watching here. - - if (!in_nmi()) - rcu_dynticks_task_enter(); -} - -/** - * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle - * - * Exit from an interrupt handler, which might possibly result in entering - * idle mode, in other words, leaving the mode in which read-side critical - * sections can occur. The caller must have disabled interrupts. - * - * This code assumes that the idle loop never does anything that might - * result in unbalanced calls to irq_enter() and irq_exit(). If your - * architecture's idle loop violates this assumption, RCU will give you what - * you deserve, good and hard. But very infrequently and irreproducibly. - * - * Use things like work queues to work around this limitation. - * - * You have been warned. - * - * If you add or remove a call to rcu_irq_exit(), be sure to test with - * CONFIG_RCU_EQS_DEBUG=y. - */ -void noinstr rcu_irq_exit(void) -{ - lockdep_assert_irqs_disabled(); - rcu_nmi_exit(); -} - -/** - * rcu_irq_exit_preempt - Inform RCU that current CPU is exiting irq - * towards in kernel preemption - * - * Same as rcu_irq_exit() but has a sanity check that scheduling is safe - * from RCU point of view. Invoked from return from interrupt before kernel - * preemption. - */ -void rcu_irq_exit_preempt(void) -{ - lockdep_assert_irqs_disabled(); - rcu_nmi_exit(); - - RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) <= 0, - "RCU dynticks_nesting counter underflow/zero!"); - RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) != - DYNTICK_IRQ_NONIDLE, - "Bad RCU dynticks_nmi_nesting counter\n"); - RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(), - "RCU in extended quiescent state!"); } +#endif /* #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK)) */ #ifdef CONFIG_PROVE_RCU /** @@ -807,9 +570,9 @@ void rcu_irq_exit_check_preempt(void) { lockdep_assert_irqs_disabled(); - RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) <= 0, + RCU_LOCKDEP_WARN(ct_dynticks_nesting() <= 0, "RCU dynticks_nesting counter underflow/zero!"); - RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) != + RCU_LOCKDEP_WARN(ct_dynticks_nmi_nesting() != DYNTICK_IRQ_NONIDLE, "Bad RCU dynticks_nmi_nesting counter\n"); RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(), @@ -817,96 +580,8 @@ void rcu_irq_exit_check_preempt(void) } #endif /* #ifdef CONFIG_PROVE_RCU */ -/* - * Wrapper for rcu_irq_exit() where interrupts are enabled. - * - * If you add or remove a call to rcu_irq_exit_irqson(), be sure to test - * with CONFIG_RCU_EQS_DEBUG=y. - */ -void rcu_irq_exit_irqson(void) -{ - unsigned long flags; - - local_irq_save(flags); - rcu_irq_exit(); - local_irq_restore(flags); -} - -/* - * Exit an RCU extended quiescent state, which can be either the - * idle loop or adaptive-tickless usermode execution. - * - * We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to - * allow for the possibility of usermode upcalls messing up our count of - * interrupt nesting level during the busy period that is just now starting. - */ -static void noinstr rcu_eqs_exit(bool user) -{ - struct rcu_data *rdp; - long oldval; - - lockdep_assert_irqs_disabled(); - rdp = this_cpu_ptr(&rcu_data); - oldval = rdp->dynticks_nesting; - WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0); - if (oldval) { - // RCU was already watching, so just do accounting and leave. - rdp->dynticks_nesting++; - return; - } - rcu_dynticks_task_exit(); - // RCU is not watching here ... - rcu_dynticks_eqs_exit(); - // ... but is watching here. - instrumentation_begin(); - - // instrumentation for the noinstr rcu_dynticks_eqs_exit() - instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks)); - - rcu_cleanup_after_idle(); - trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&rdp->dynticks)); - WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current)); - WRITE_ONCE(rdp->dynticks_nesting, 1); - WARN_ON_ONCE(rdp->dynticks_nmi_nesting); - WRITE_ONCE(rdp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE); - instrumentation_end(); -} - -/** - * rcu_idle_exit - inform RCU that current CPU is leaving idle - * - * Exit idle mode, in other words, -enter- the mode in which RCU - * read-side critical sections can occur. - * - * If you add or remove a call to rcu_idle_exit(), be sure to test with - * CONFIG_RCU_EQS_DEBUG=y. - */ -void rcu_idle_exit(void) -{ - unsigned long flags; - - local_irq_save(flags); - rcu_eqs_exit(false); - local_irq_restore(flags); -} -EXPORT_SYMBOL_GPL(rcu_idle_exit); - #ifdef CONFIG_NO_HZ_FULL /** - * rcu_user_exit - inform RCU that we are exiting userspace. - * - * Exit RCU idle mode while entering the kernel because it can - * run a RCU read side critical section anytime. - * - * If you add or remove a call to rcu_user_exit(), be sure to test with - * CONFIG_RCU_EQS_DEBUG=y. - */ -void noinstr rcu_user_exit(void) -{ - rcu_eqs_exit(1); -} - -/** * __rcu_irq_enter_check_tick - Enable scheduler tick on CPU if RCU needs it. * * The scheduler tick is not normally enabled when CPUs enter the kernel @@ -958,7 +633,7 @@ void __rcu_irq_enter_check_tick(void) // prevents self-deadlock. So we can safely recheck under the lock. // Note that the nohz_full state currently cannot change. raw_spin_lock_rcu_node(rdp->mynode); - if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) { + if (READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) { // A nohz_full CPU is in the kernel and RCU needs a // quiescent state. Turn on the tick! WRITE_ONCE(rdp->rcu_forced_tick, true); @@ -966,116 +641,24 @@ void __rcu_irq_enter_check_tick(void) } raw_spin_unlock_rcu_node(rdp->mynode); } +NOKPROBE_SYMBOL(__rcu_irq_enter_check_tick); #endif /* CONFIG_NO_HZ_FULL */ -/** - * rcu_nmi_enter - inform RCU of entry to NMI context - * - * If the CPU was idle from RCU's viewpoint, update rdp->dynticks and - * rdp->dynticks_nmi_nesting to let the RCU grace-period handling know - * that the CPU is active. This implementation permits nested NMIs, as - * long as the nesting level does not overflow an int. (You will probably - * run out of stack space first.) - * - * If you add or remove a call to rcu_nmi_enter(), be sure to test - * with CONFIG_RCU_EQS_DEBUG=y. - */ -noinstr void rcu_nmi_enter(void) -{ - long incby = 2; - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - - /* Complain about underflow. */ - WARN_ON_ONCE(rdp->dynticks_nmi_nesting < 0); - - /* - * If idle from RCU viewpoint, atomically increment ->dynticks - * to mark non-idle and increment ->dynticks_nmi_nesting by one. - * Otherwise, increment ->dynticks_nmi_nesting by two. This means - * if ->dynticks_nmi_nesting is equal to one, we are guaranteed - * to be in the outermost NMI handler that interrupted an RCU-idle - * period (observation due to Andy Lutomirski). - */ - if (rcu_dynticks_curr_cpu_in_eqs()) { - - if (!in_nmi()) - rcu_dynticks_task_exit(); - - // RCU is not watching here ... - rcu_dynticks_eqs_exit(); - // ... but is watching here. - - if (!in_nmi()) { - instrumentation_begin(); - rcu_cleanup_after_idle(); - instrumentation_end(); - } - - instrumentation_begin(); - // instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs() - instrument_atomic_read(&rdp->dynticks, sizeof(rdp->dynticks)); - // instrumentation for the noinstr rcu_dynticks_eqs_exit() - instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks)); - - incby = 1; - } else if (!in_nmi()) { - instrumentation_begin(); - rcu_irq_enter_check_tick(); - instrumentation_end(); - } else { - instrumentation_begin(); - } - - trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="), - rdp->dynticks_nmi_nesting, - rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks)); - instrumentation_end(); - WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */ - rdp->dynticks_nmi_nesting + incby); - barrier(); -} - -/** - * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle - * - * Enter an interrupt handler, which might possibly result in exiting - * idle mode, in other words, entering the mode in which read-side critical - * sections can occur. The caller must have disabled interrupts. - * - * Note that the Linux kernel is fully capable of entering an interrupt - * handler that it never exits, for example when doing upcalls to user mode! - * This code assumes that the idle loop never does upcalls to user mode. - * If your architecture's idle loop does do upcalls to user mode (or does - * anything else that results in unbalanced calls to the irq_enter() and - * irq_exit() functions), RCU will give you what you deserve, good and hard. - * But very infrequently and irreproducibly. - * - * Use things like work queues to work around this limitation. - * - * You have been warned. - * - * If you add or remove a call to rcu_irq_enter(), be sure to test with - * CONFIG_RCU_EQS_DEBUG=y. - */ -noinstr void rcu_irq_enter(void) -{ - lockdep_assert_irqs_disabled(); - rcu_nmi_enter(); -} - /* - * Wrapper for rcu_irq_enter() where interrupts are enabled. + * Check to see if any future non-offloaded RCU-related work will need + * to be done by the current CPU, even if none need be done immediately, + * returning 1 if so. This function is part of the RCU implementation; + * it is -not- an exported member of the RCU API. This is used by + * the idle-entry code to figure out whether it is safe to disable the + * scheduler-clock interrupt. * - * If you add or remove a call to rcu_irq_enter_irqson(), be sure to test - * with CONFIG_RCU_EQS_DEBUG=y. + * Just check whether or not this CPU has non-offloaded RCU callbacks + * queued. */ -void rcu_irq_enter_irqson(void) +int rcu_needs_cpu(void) { - unsigned long flags; - - local_irq_save(flags); - rcu_irq_enter(); - local_irq_restore(flags); + return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) && + !rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data)); } /* @@ -1095,12 +678,16 @@ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp) } /** - * rcu_is_watching - see if RCU thinks that the current CPU is not idle + * rcu_is_watching - RCU read-side critical sections permitted on current CPU? + * + * Return @true if RCU is watching the running CPU and @false otherwise. + * An @true return means that this CPU can safely enter RCU read-side + * critical sections. * - * Return true if RCU is watching the running CPU, which means that this - * CPU can safely enter RCU read-side critical sections. In other words, - * if the current CPU is not in its idle loop or is in an interrupt or - * NMI handler, return true. + * Although calls to rcu_is_watching() from most parts of the kernel + * will return @true, there are important exceptions. For example, if the + * current CPU is deep within its idle loop, in kernel entry/exit code, + * or offline, rcu_is_watching() will return @false. * * Make notrace because it can be called by the internal functions of * ftrace, and making this notrace removes unnecessary recursion calls. @@ -1134,43 +721,8 @@ void rcu_request_urgent_qs_task(struct task_struct *t) smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true); } -#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) - -/* - * Is the current CPU online as far as RCU is concerned? - * - * Disable preemption to avoid false positives that could otherwise - * happen due to the current CPU number being sampled, this task being - * preempted, its old CPU being taken offline, resuming on some other CPU, - * then determining that its old CPU is now offline. - * - * Disable checking if in an NMI handler because we cannot safely - * report errors from NMI handlers anyway. In addition, it is OK to use - * RCU on an offline processor during initial boot, hence the check for - * rcu_scheduler_fully_active. - */ -bool rcu_lockdep_current_cpu_online(void) -{ - struct rcu_data *rdp; - struct rcu_node *rnp; - bool ret = false; - - if (in_nmi() || !rcu_scheduler_fully_active) - return true; - preempt_disable_notrace(); - rdp = this_cpu_ptr(&rcu_data); - rnp = rdp->mynode; - if (rdp->grpmask & rcu_rnp_online_cpus(rnp) || READ_ONCE(rnp->ofl_seq) & 0x1) - ret = true; - preempt_enable_notrace(); - return ret; -} -EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); - -#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */ - /* - * We are reporting a quiescent state on behalf of some other CPU, so + * When trying to report a quiescent state on behalf of some other CPU, * it is our responsibility to check for and handle potential overflow * of the rcu_node ->gp_seq counter with respect to the rcu_data counters. * After all, the CPU might be in deep idle state, and thus executing no @@ -1193,7 +745,7 @@ static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp) */ static int dyntick_save_progress_counter(struct rcu_data *rdp) { - rdp->dynticks_snap = rcu_dynticks_snap(rdp); + rdp->dynticks_snap = rcu_dynticks_snap(rdp->cpu); if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) { trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti")); rcu_gpnum_ovf(rdp->mynode, rdp); @@ -1203,16 +755,19 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp) } /* - * Return true if the specified CPU has passed through a quiescent - * state by virtue of being in or having passed through an dynticks - * idle state since the last call to dyntick_save_progress_counter() - * for this same CPU, or by virtue of having been offline. + * Returns positive if the specified CPU has passed through a quiescent state + * by virtue of being in or having passed through an dynticks idle state since + * the last call to dyntick_save_progress_counter() for this same CPU, or by + * virtue of having been offline. + * + * Returns negative if the specified CPU needs a force resched. + * + * Returns zero otherwise. */ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) { unsigned long jtsq; - bool *rnhqp; - bool *ruqp; + int ret = 0; struct rcu_node *rnp = rdp->mynode; /* @@ -1247,8 +802,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) * For more detail, please refer to the "Hotplug CPU" section * of RCU's Requirements documentation. */ - if (WARN_ON_ONCE(!(rdp->grpmask & rcu_rnp_online_cpus(rnp)))) { - bool onl; + if (WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp))) { struct rcu_node *rnp1; pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n", @@ -1257,9 +811,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent) pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n", __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask); - onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp)); pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n", - __func__, rdp->cpu, ".o"[onl], + __func__, rdp->cpu, ".o"[rcu_rdp_cpu_online(rdp)], (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags, (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags); return 1; /* Break things loose after complaining. */ @@ -1277,17 +830,15 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) * is set way high. */ jtsq = READ_ONCE(jiffies_to_sched_qs); - ruqp = per_cpu_ptr(&rcu_data.rcu_urgent_qs, rdp->cpu); - rnhqp = &per_cpu(rcu_data.rcu_need_heavy_qs, rdp->cpu); - if (!READ_ONCE(*rnhqp) && + if (!READ_ONCE(rdp->rcu_need_heavy_qs) && (time_after(jiffies, rcu_state.gp_start + jtsq * 2) || time_after(jiffies, rcu_state.jiffies_resched) || rcu_state.cbovld)) { - WRITE_ONCE(*rnhqp, true); + WRITE_ONCE(rdp->rcu_need_heavy_qs, true); /* Store rcu_need_heavy_qs before rcu_urgent_qs. */ - smp_store_release(ruqp, true); + smp_store_release(&rdp->rcu_urgent_qs, true); } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) { - WRITE_ONCE(*ruqp, true); + WRITE_ONCE(rdp->rcu_urgent_qs, true); } /* @@ -1301,9 +852,9 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) if (tick_nohz_full_cpu(rdp->cpu) && (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) || rcu_state.cbovld)) { - WRITE_ONCE(*ruqp, true); - resched_cpu(rdp->cpu); + WRITE_ONCE(rdp->rcu_urgent_qs, true); WRITE_ONCE(rdp->last_fqs_resched, jiffies); + ret = -1; } /* @@ -1316,8 +867,8 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) if (time_after(jiffies, rcu_state.jiffies_resched)) { if (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq)) { - resched_cpu(rdp->cpu); WRITE_ONCE(rdp->last_fqs_resched, jiffies); + ret = -1; } if (IS_ENABLED(CONFIG_IRQ_WORK) && !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq && @@ -1326,9 +877,27 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) rdp->rcu_iw_gp_seq = rnp->gp_seq; irq_work_queue_on(&rdp->rcu_iw, rdp->cpu); } + + if (rcu_cpu_stall_cputime && rdp->snap_record.gp_seq != rdp->gp_seq) { + int cpu = rdp->cpu; + struct rcu_snap_record *rsrp; + struct kernel_cpustat *kcsp; + + kcsp = &kcpustat_cpu(cpu); + + rsrp = &rdp->snap_record; + rsrp->cputime_irq = kcpustat_field(kcsp, CPUTIME_IRQ, cpu); + rsrp->cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu); + rsrp->cputime_system = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu); + rsrp->nr_hardirqs = kstat_cpu_irqs_sum(rdp->cpu); + rsrp->nr_softirqs = kstat_cpu_softirqs_sum(rdp->cpu); + rsrp->nr_csw = nr_context_switches_cpu(rdp->cpu); + rsrp->jiffies = jiffies; + rsrp->gp_seq = rdp->gp_seq; + } } - return 0; + return ret; } /* Trace-event wrapper function for trace_rcu_future_grace_period. */ @@ -1444,6 +1013,38 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp) return needmore; } +static void swake_up_one_online_ipi(void *arg) +{ + struct swait_queue_head *wqh = arg; + + swake_up_one(wqh); +} + +static void swake_up_one_online(struct swait_queue_head *wqh) +{ + int cpu = get_cpu(); + + /* + * If called from rcutree_report_cpu_starting(), wake up + * is dangerous that late in the CPU-down hotplug process. The + * scheduler might queue an ignored hrtimer. Defer the wake up + * to an online CPU instead. + */ + if (unlikely(cpu_is_offline(cpu))) { + int target; + + target = cpumask_any_and(housekeeping_cpumask(HK_TYPE_RCU), + cpu_online_mask); + + smp_call_function_single(target, swake_up_one_online_ipi, + wqh, 0); + put_cpu(); + } else { + put_cpu(); + swake_up_one(wqh); + } +} + /* * Awaken the grace-period kthread. Don't do a self-awaken (unless in an * interrupt or softirq handler, in which case we just might immediately @@ -1463,12 +1064,12 @@ static void rcu_gp_kthread_wake(void) { struct task_struct *t = READ_ONCE(rcu_state.gp_kthread); - if ((current == t && !in_irq() && !in_serving_softirq()) || + if ((current == t && !in_hardirq() && !in_serving_softirq()) || !READ_ONCE(rcu_state.gp_flags) || !t) return; WRITE_ONCE(rcu_state.gp_wake_time, jiffies); WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq)); - swake_up_one(&rcu_state.gp_wq); + swake_up_one_online(&rcu_state.gp_wq); } /* @@ -1495,6 +1096,8 @@ static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp) if (!rcu_segcblist_pend_cbs(&rdp->cblist)) return false; + trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc")); + /* * Callbacks are often registered with incomplete grace-period * information. Something about the fact that getting exact @@ -1515,6 +1118,8 @@ static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp) else trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB")); + trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc")); + return ret; } @@ -1582,10 +1187,11 @@ static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp, struct rcu_data *rdp) { rcu_lockdep_assert_cblist_protected(rdp); - if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || - !raw_spin_trylock_rcu_node(rnp)) + if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp)) return; - WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp)); + // The grace period cannot end while we hold the rcu_node lock. + if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) + WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp)); raw_spin_unlock_rcu_node(rnp); } @@ -1612,7 +1218,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) { bool ret = false; bool need_qs; - const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); + const bool offloaded = rcu_rdp_is_offloaded(rdp); raw_lockdep_assert_held_rcu_node(rnp); @@ -1650,6 +1256,8 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */ if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap) WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed); + if (IS_ENABLED(CONFIG_PROVE_RCU) && READ_ONCE(rdp->gpwrap)) + WRITE_ONCE(rdp->last_sched_clock, jiffies); WRITE_ONCE(rdp->gpwrap, false); rcu_gpnum_ovf(rnp, rdp); return ret; @@ -1676,11 +1284,37 @@ static void note_gp_changes(struct rcu_data *rdp) rcu_gp_kthread_wake(); } +static atomic_t *rcu_gp_slow_suppress; + +/* Register a counter to suppress debugging grace-period delays. */ +void rcu_gp_slow_register(atomic_t *rgssp) +{ + WARN_ON_ONCE(rcu_gp_slow_suppress); + + WRITE_ONCE(rcu_gp_slow_suppress, rgssp); +} +EXPORT_SYMBOL_GPL(rcu_gp_slow_register); + +/* Unregister a counter, with NULL for not caring which. */ +void rcu_gp_slow_unregister(atomic_t *rgssp) +{ + WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress && rcu_gp_slow_suppress != NULL); + + WRITE_ONCE(rcu_gp_slow_suppress, NULL); +} +EXPORT_SYMBOL_GPL(rcu_gp_slow_unregister); + +static bool rcu_gp_slow_is_suppressed(void) +{ + atomic_t *rgssp = READ_ONCE(rcu_gp_slow_suppress); + + return rgssp && atomic_read(rgssp); +} + static void rcu_gp_slow(int delay) { - if (delay > 0 && - !(rcu_seq_ctr(rcu_state.gp_seq) % - (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay))) + if (!rcu_gp_slow_is_suppressed() && delay > 0 && + !(rcu_seq_ctr(rcu_state.gp_seq) % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay))) schedule_timeout_idle(delay); } @@ -1718,12 +1352,81 @@ static void rcu_strict_gp_boundary(void *unused) invoke_rcu_core(); } +// Make the polled API aware of the beginning of a grace period. +static void rcu_poll_gp_seq_start(unsigned long *snap) +{ + struct rcu_node *rnp = rcu_get_root(); + + if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) + raw_lockdep_assert_held_rcu_node(rnp); + + // If RCU was idle, note beginning of GP. + if (!rcu_seq_state(rcu_state.gp_seq_polled)) + rcu_seq_start(&rcu_state.gp_seq_polled); + + // Either way, record current state. + *snap = rcu_state.gp_seq_polled; +} + +// Make the polled API aware of the end of a grace period. +static void rcu_poll_gp_seq_end(unsigned long *snap) +{ + struct rcu_node *rnp = rcu_get_root(); + + if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) + raw_lockdep_assert_held_rcu_node(rnp); + + // If the previously noted GP is still in effect, record the + // end of that GP. Either way, zero counter to avoid counter-wrap + // problems. + if (*snap && *snap == rcu_state.gp_seq_polled) { + rcu_seq_end(&rcu_state.gp_seq_polled); + rcu_state.gp_seq_polled_snap = 0; + rcu_state.gp_seq_polled_exp_snap = 0; + } else { + *snap = 0; + } +} + +// Make the polled API aware of the beginning of a grace period, but +// where caller does not hold the root rcu_node structure's lock. +static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap) +{ + unsigned long flags; + struct rcu_node *rnp = rcu_get_root(); + + if (rcu_init_invoked()) { + if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) + lockdep_assert_irqs_enabled(); + raw_spin_lock_irqsave_rcu_node(rnp, flags); + } + rcu_poll_gp_seq_start(snap); + if (rcu_init_invoked()) + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); +} + +// Make the polled API aware of the end of a grace period, but where +// caller does not hold the root rcu_node structure's lock. +static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap) +{ + unsigned long flags; + struct rcu_node *rnp = rcu_get_root(); + + if (rcu_init_invoked()) { + if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) + lockdep_assert_irqs_enabled(); + raw_spin_lock_irqsave_rcu_node(rnp, flags); + } + rcu_poll_gp_seq_end(snap); + if (rcu_init_invoked()) + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); +} + /* * Initialize a new grace period. Return false if no grace period required. */ -static bool rcu_gp_init(void) +static noinline_for_stack bool rcu_gp_init(void) { - unsigned long firstseq; unsigned long flags; unsigned long oldmask; unsigned long mask; @@ -1754,6 +1457,7 @@ static bool rcu_gp_init(void) rcu_seq_start(&rcu_state.gp_seq); ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq); trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start")); + rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap); raw_spin_unlock_irq_rcu_node(rnp); /* @@ -1765,21 +1469,18 @@ static bool rcu_gp_init(void) * go offline later. Please also refer to "Hotplug CPU" section * of RCU's Requirements documentation. */ - rcu_state.gp_state = RCU_GP_ONOFF; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF); + /* Exclude CPU hotplug operations. */ rcu_for_each_leaf_node(rnp) { - smp_mb(); // Pair with barriers used when updating ->ofl_seq to odd values. - firstseq = READ_ONCE(rnp->ofl_seq); - if (firstseq & 0x1) - while (firstseq == READ_ONCE(rnp->ofl_seq)) - schedule_timeout_idle(1); // Can't wake unless RCU is watching. - smp_mb(); // Pair with barriers used when updating ->ofl_seq to even values. - raw_spin_lock(&rcu_state.ofl_lock); - raw_spin_lock_irq_rcu_node(rnp); + local_irq_save(flags); + arch_spin_lock(&rcu_state.ofl_lock); + raw_spin_lock_rcu_node(rnp); if (rnp->qsmaskinit == rnp->qsmaskinitnext && !rnp->wait_blkd_tasks) { /* Nothing to do on this leaf rcu_node structure. */ - raw_spin_unlock_irq_rcu_node(rnp); - raw_spin_unlock(&rcu_state.ofl_lock); + raw_spin_unlock_rcu_node(rnp); + arch_spin_unlock(&rcu_state.ofl_lock); + local_irq_restore(flags); continue; } @@ -1814,8 +1515,9 @@ static bool rcu_gp_init(void) rcu_cleanup_dead_rnp(rnp); } - raw_spin_unlock_irq_rcu_node(rnp); - raw_spin_unlock(&rcu_state.ofl_lock); + raw_spin_unlock_rcu_node(rnp); + arch_spin_unlock(&rcu_state.ofl_lock); + local_irq_restore(flags); } rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */ @@ -1831,7 +1533,7 @@ static bool rcu_gp_init(void) * The grace period cannot complete until the initialization * process finishes, because this kthread handles both. */ - rcu_state.gp_state = RCU_GP_INIT; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT); rcu_for_each_node_breadth_first(rnp) { rcu_gp_slow(gp_init_delay); raw_spin_lock_irqsave_rcu_node(rnp, flags); @@ -1892,10 +1594,22 @@ static bool rcu_gp_fqs_check_wake(int *gfp) */ static void rcu_gp_fqs(bool first_time) { + int nr_fqs = READ_ONCE(rcu_state.nr_fqs_jiffies_stall); struct rcu_node *rnp = rcu_get_root(); WRITE_ONCE(rcu_state.gp_activity, jiffies); - rcu_state.n_force_qs++; + WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1); + + WARN_ON_ONCE(nr_fqs > 3); + /* Only countdown nr_fqs for stall purposes if jiffies moves. */ + if (nr_fqs) { + if (nr_fqs == 1) { + WRITE_ONCE(rcu_state.jiffies_stall, + jiffies + rcu_jiffies_till_stall_check()); + } + WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, --nr_fqs); + } + if (first_time) { /* Collect dyntick-idle snapshots. */ force_qs_rnp(dyntick_save_progress_counter); @@ -1915,34 +1629,51 @@ static void rcu_gp_fqs(bool first_time) /* * Loop doing repeated quiescent-state forcing until the grace period ends. */ -static void rcu_gp_fqs_loop(void) +static noinline_for_stack void rcu_gp_fqs_loop(void) { - bool first_gp_fqs; + bool first_gp_fqs = true; int gf = 0; unsigned long j; int ret; struct rcu_node *rnp = rcu_get_root(); - first_gp_fqs = true; j = READ_ONCE(jiffies_till_first_fqs); if (rcu_state.cbovld) gf = RCU_GP_FLAG_OVLD; ret = 0; for (;;) { - if (!ret) { - rcu_state.jiffies_force_qs = jiffies + j; + if (rcu_state.cbovld) { + j = (j + 2) / 3; + if (j <= 0) + j = 1; + } + if (!ret || time_before(jiffies + j, rcu_state.jiffies_force_qs)) { + WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j); + /* + * jiffies_force_qs before RCU_GP_WAIT_FQS state + * update; required for stall checks. + */ + smp_wmb(); WRITE_ONCE(rcu_state.jiffies_kick_kthreads, jiffies + (j ? 3 * j : 2)); } trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("fqswait")); - rcu_state.gp_state = RCU_GP_WAIT_FQS; - ret = swait_event_idle_timeout_exclusive( - rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j); + WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS); + (void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq, + rcu_gp_fqs_check_wake(&gf), j); rcu_gp_torture_wait(); - rcu_state.gp_state = RCU_GP_DOING_FQS; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS); /* Locking provides needed memory barriers. */ - /* If grace period done, leave loop. */ + /* + * Exit the loop if the root rcu_node structure indicates that the grace period + * has ended, leave the loop. The rcu_preempt_blocked_readers_cgp(rnp) check + * is required only for single-node rcu_node trees because readers blocking + * the current grace period are queued only on leaf rcu_node structures. + * For multi-node trees, checking the root node's ->qsmask suffices, because a + * given root node's ->qsmask bit is cleared only when all CPUs and tasks from + * the corresponding leaf nodes have passed through their quiescent state. + */ if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)) break; @@ -1984,7 +1715,7 @@ static void rcu_gp_fqs_loop(void) /* * Clean up after the old grace period. */ -static void rcu_gp_cleanup(void) +static noinline void rcu_gp_cleanup(void) { int cpu; bool needgp = false; @@ -2010,6 +1741,7 @@ static void rcu_gp_cleanup(void) * safe for us to drop the lock in order to mark the grace * period as completed in all of the rcu_node structures. */ + rcu_poll_gp_seq_end(&rcu_state.gp_seq_polled_snap); raw_spin_unlock_irq_rcu_node(rnp); /* @@ -2029,6 +1761,8 @@ static void rcu_gp_cleanup(void) dump_blkd_tasks(rnp, 10); WARN_ON_ONCE(rnp->qsmask); WRITE_ONCE(rnp->gp_seq, new_gp_seq); + if (!rnp->parent) + smp_mb(); // Order against failing poll_state_synchronize_rcu_full(). rdp = this_cpu_ptr(&rcu_data); if (rnp == rdp->mynode) needgp = __note_gp_changes(rnp, rdp) || needgp; @@ -2054,7 +1788,7 @@ static void rcu_gp_cleanup(void) trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end")); rcu_seq_end(&rcu_state.gp_seq); ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq); - rcu_state.gp_state = RCU_GP_IDLE; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE); /* Check for GP requests since above loop. */ rdp = this_cpu_ptr(&rcu_data); if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) { @@ -2063,16 +1797,31 @@ static void rcu_gp_cleanup(void) needgp = true; } /* Advance CBs to reduce false positives below. */ - offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); + offloaded = rcu_rdp_is_offloaded(rdp); if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) { + + // We get here if a grace period was needed (“needgp”) + // and the above call to rcu_accelerate_cbs() did not set + // the RCU_GP_FLAG_INIT bit in ->gp_state (which records + // the need for another grace period). The purpose + // of the “offloaded” check is to avoid invoking + // rcu_accelerate_cbs() on an offloaded CPU because we do not + // hold the ->nocb_lock needed to safely access an offloaded + // ->cblist. We do not want to acquire that lock because + // it can be heavily contended during callback floods. + WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT); WRITE_ONCE(rcu_state.gp_req_activity, jiffies); - trace_rcu_grace_period(rcu_state.name, - rcu_state.gp_seq, - TPS("newreq")); + trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq")); } else { - WRITE_ONCE(rcu_state.gp_flags, - rcu_state.gp_flags & RCU_GP_FLAG_INIT); + + // We get here either if there is no need for an + // additional grace period or if rcu_accelerate_cbs() has + // already set the RCU_GP_FLAG_INIT bit in ->gp_flags. + // So all we need to do is to clear all of the other + // ->gp_flags bits. + + WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT); } raw_spin_unlock_irq_rcu_node(rnp); @@ -2093,12 +1842,12 @@ static int __noreturn rcu_gp_kthread(void *unused) for (;;) { trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("reqwait")); - rcu_state.gp_state = RCU_GP_WAIT_GPS; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS); swait_event_idle_exclusive(rcu_state.gp_wq, READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_INIT); rcu_gp_torture_wait(); - rcu_state.gp_state = RCU_GP_DONE_GPS; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS); /* Locking provides needed memory barrier. */ if (rcu_gp_init()) break; @@ -2113,9 +1862,9 @@ static int __noreturn rcu_gp_kthread(void *unused) rcu_gp_fqs_loop(); /* Handle grace-period end. */ - rcu_state.gp_state = RCU_GP_CLEANUP; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP); rcu_gp_cleanup(); - rcu_state.gp_state = RCU_GP_CLEANED; + WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED); } } @@ -2261,8 +2010,7 @@ rcu_report_qs_rdp(struct rcu_data *rdp) { unsigned long flags; unsigned long mask; - bool needwake = false; - const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); + bool needacc = false; struct rcu_node *rnp; WARN_ON_ONCE(rdp->cpu != smp_processor_id()); @@ -2289,15 +2037,33 @@ rcu_report_qs_rdp(struct rcu_data *rdp) /* * This GP can't end until cpu checks in, so all of our * callbacks can be processed during the next GP. + * + * NOCB kthreads have their own way to deal with that... */ - if (!offloaded) - needwake = rcu_accelerate_cbs(rnp, rdp); + if (!rcu_rdp_is_offloaded(rdp)) { + /* + * The current GP has not yet ended, so it + * should not be possible for rcu_accelerate_cbs() + * to return true. So complain, but don't awaken. + */ + WARN_ON_ONCE(rcu_accelerate_cbs(rnp, rdp)); + } else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) { + /* + * ...but NOCB kthreads may miss or delay callbacks acceleration + * if in the middle of a (de-)offloading process. + */ + needacc = true; + } rcu_disable_urgency_upon_qs(rdp); rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); /* ^^^ Released rnp->lock */ - if (needwake) - rcu_gp_kthread_wake(); + + if (needacc) { + rcu_nocb_lock_irqsave(rdp, flags); + rcu_accelerate_cbs_unlocked(rnp, rdp); + rcu_nocb_unlock_irqrestore(rdp, flags); + } } } @@ -2334,108 +2100,35 @@ rcu_check_quiescent_state(struct rcu_data *rdp) rcu_report_qs_rdp(rdp); } -/* - * Near the end of the offline process. Trace the fact that this CPU - * is going offline. - */ -int rcutree_dying_cpu(unsigned int cpu) -{ - bool blkd; - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - struct rcu_node *rnp = rdp->mynode; - - if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) - return 0; - - blkd = !!(rnp->qsmask & rdp->grpmask); - trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), - blkd ? TPS("cpuofl") : TPS("cpuofl-bgp")); - return 0; -} - -/* - * All CPUs for the specified rcu_node structure have gone offline, - * and all tasks that were preempted within an RCU read-side critical - * section while running on one of those CPUs have since exited their RCU - * read-side critical section. Some other CPU is reporting this fact with - * the specified rcu_node structure's ->lock held and interrupts disabled. - * This function therefore goes up the tree of rcu_node structures, - * clearing the corresponding bits in the ->qsmaskinit fields. Note that - * the leaf rcu_node structure's ->qsmaskinit field has already been - * updated. - * - * This function does check that the specified rcu_node structure has - * all CPUs offline and no blocked tasks, so it is OK to invoke it - * prematurely. That said, invoking it after the fact will cost you - * a needless lock acquisition. So once it has done its work, don't - * invoke it again. - */ -static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf) -{ - long mask; - struct rcu_node *rnp = rnp_leaf; - - raw_lockdep_assert_held_rcu_node(rnp_leaf); - if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || - WARN_ON_ONCE(rnp_leaf->qsmaskinit) || - WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf))) - return; - for (;;) { - mask = rnp->grpmask; - rnp = rnp->parent; - if (!rnp) - break; - raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ - rnp->qsmaskinit &= ~mask; - /* Between grace periods, so better already be zero! */ - WARN_ON_ONCE(rnp->qsmask); - if (rnp->qsmaskinit) { - raw_spin_unlock_rcu_node(rnp); - /* irqs remain disabled. */ - return; - } - raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ - } -} - -/* - * The CPU has been completely removed, and some other CPU is reporting - * this fact from process context. Do the remainder of the cleanup. - * There can only be one CPU hotplug operation at a time, so no need for - * explicit locking. - */ -int rcutree_dead_cpu(unsigned int cpu) +/* Return true if callback-invocation time limit exceeded. */ +static bool rcu_do_batch_check_time(long count, long tlimit, + bool jlimit_check, unsigned long jlimit) { - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); - struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ - - if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) - return 0; - - WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1); - /* Adjust any no-longer-needed kthreads. */ - rcu_boost_kthread_setaffinity(rnp, -1); - /* Do any needed no-CB deferred wakeups from this CPU. */ - do_nocb_deferred_wakeup(per_cpu_ptr(&rcu_data, cpu)); - - // Stop-machine done, so allow nohz_full to disable tick. - tick_dep_clear(TICK_DEP_BIT_RCU); - return 0; + // Invoke local_clock() only once per 32 consecutive callbacks. + return unlikely(tlimit) && + (!likely(count & 31) || + (IS_ENABLED(CONFIG_RCU_DOUBLE_CHECK_CB_TIME) && + jlimit_check && time_after(jiffies, jlimit))) && + local_clock() >= tlimit; } /* * Invoke any RCU callbacks that have made it to the end of their grace - * period. Thottle as specified by rdp->blimit. + * period. Throttle as specified by rdp->blimit. */ static void rcu_do_batch(struct rcu_data *rdp) { + long bl; + long count = 0; int div; + bool __maybe_unused empty; unsigned long flags; - const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); - struct rcu_head *rhp; + unsigned long jlimit; + bool jlimit_check = false; + long pending; struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); - long bl, count; - long pending, tlimit = 0; + struct rcu_head *rhp; + long tlimit = 0; /* If no callbacks are ready, just return. */ if (!rcu_segcblist_ready_cbs(&rdp->cblist)) { @@ -2444,47 +2137,55 @@ static void rcu_do_batch(struct rcu_data *rdp) trace_rcu_batch_end(rcu_state.name, 0, !rcu_segcblist_empty(&rdp->cblist), need_resched(), is_idle_task(current), - rcu_is_callbacks_kthread()); + rcu_is_callbacks_kthread(rdp)); return; } /* - * Extract the list of ready callbacks, disabling to prevent + * Extract the list of ready callbacks, disabling IRQs to prevent * races with call_rcu() from interrupt handlers. Leave the * callback counts, as rcu_barrier() needs to be conservative. */ - local_irq_save(flags); - rcu_nocb_lock(rdp); + rcu_nocb_lock_irqsave(rdp, flags); WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); - pending = rcu_segcblist_n_cbs(&rdp->cblist); + pending = rcu_segcblist_get_seglen(&rdp->cblist, RCU_DONE_TAIL); div = READ_ONCE(rcu_divisor); div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div; bl = max(rdp->blimit, pending >> div); - if (unlikely(bl > 100)) { + if ((in_serving_softirq() || rdp->rcu_cpu_kthread_status == RCU_KTHREAD_RUNNING) && + (IS_ENABLED(CONFIG_RCU_DOUBLE_CHECK_CB_TIME) || unlikely(bl > 100))) { + const long npj = NSEC_PER_SEC / HZ; long rrn = READ_ONCE(rcu_resched_ns); rrn = rrn < NSEC_PER_MSEC ? NSEC_PER_MSEC : rrn > NSEC_PER_SEC ? NSEC_PER_SEC : rrn; tlimit = local_clock() + rrn; + jlimit = jiffies + (rrn + npj + 1) / npj; + jlimit_check = true; } trace_rcu_batch_start(rcu_state.name, rcu_segcblist_n_cbs(&rdp->cblist), bl); rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl); - if (offloaded) + if (rcu_rdp_is_offloaded(rdp)) rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist); + + trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued")); rcu_nocb_unlock_irqrestore(rdp, flags); /* Invoke callbacks. */ tick_dep_set_task(current, TICK_DEP_BIT_RCU); rhp = rcu_cblist_dequeue(&rcl); + for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) { rcu_callback_t f; + count++; debug_rcu_head_unqueue(rhp); rcu_lock_acquire(&rcu_callback_map); trace_rcu_invoke_callback(rcu_state.name, rhp); f = rhp->func; + debug_rcu_head_callback(rhp); WRITE_ONCE(rhp->func, (rcu_callback_t)0L); f(rhp); @@ -2492,40 +2193,42 @@ static void rcu_do_batch(struct rcu_data *rdp) /* * Stop only if limit reached and CPU has something to do. - * Note: The rcl structure counts down from zero. */ - if (-rcl.len >= bl && !offloaded && - (need_resched() || - (!is_idle_task(current) && !rcu_is_callbacks_kthread()))) - break; - if (unlikely(tlimit)) { - /* only call local_clock() every 32 callbacks */ - if (likely((-rcl.len & 31) || local_clock() < tlimit)) - continue; - /* Exceeded the time limit, so leave. */ - break; - } - if (offloaded) { - WARN_ON_ONCE(in_serving_softirq()); + if (in_serving_softirq()) { + if (count >= bl && (need_resched() || !is_idle_task(current))) + break; + /* + * Make sure we don't spend too much time here and deprive other + * softirq vectors of CPU cycles. + */ + if (rcu_do_batch_check_time(count, tlimit, jlimit_check, jlimit)) + break; + } else { + // In rcuc/rcuoc context, so no worries about + // depriving other softirq vectors of CPU cycles. local_bh_enable(); lockdep_assert_irqs_enabled(); cond_resched_tasks_rcu_qs(); lockdep_assert_irqs_enabled(); local_bh_disable(); + // But rcuc kthreads can delay quiescent-state + // reporting, so check time limits for them. + if (rdp->rcu_cpu_kthread_status == RCU_KTHREAD_RUNNING && + rcu_do_batch_check_time(count, tlimit, jlimit_check, jlimit)) { + rdp->rcu_cpu_has_work = 1; + break; + } } } - local_irq_save(flags); - rcu_nocb_lock(rdp); - count = -rcl.len; + rcu_nocb_lock_irqsave(rdp, flags); rdp->n_cbs_invoked += count; trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(), - is_idle_task(current), rcu_is_callbacks_kthread()); + is_idle_task(current), rcu_is_callbacks_kthread(rdp)); /* Update counts and requeue any remaining callbacks. */ rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl); - smp_mb(); /* List handling before counting for rcu_barrier(). */ - rcu_segcblist_insert_count(&rdp->cblist, &rcl); + rcu_segcblist_add_len(&rdp->cblist, -count); /* Reinstate batch limit if we have worked down the excess. */ count = rcu_segcblist_n_cbs(&rdp->cblist); @@ -2535,7 +2238,7 @@ static void rcu_do_batch(struct rcu_data *rdp) /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */ if (count == 0 && rdp->qlen_last_fqs_check != 0) { rdp->qlen_last_fqs_check = 0; - rdp->n_force_qs_snap = rcu_state.n_force_qs; + rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs); } else if (count < rdp->qlen_last_fqs_check - qhimark) rdp->qlen_last_fqs_check = count; @@ -2543,15 +2246,15 @@ static void rcu_do_batch(struct rcu_data *rdp) * The following usually indicates a double call_rcu(). To track * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y. */ - WARN_ON_ONCE(count == 0 && !rcu_segcblist_empty(&rdp->cblist)); + empty = rcu_segcblist_empty(&rdp->cblist); + WARN_ON_ONCE(count == 0 && !empty); WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) && - count != 0 && rcu_segcblist_empty(&rdp->cblist)); + count != 0 && empty); + WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0); + WARN_ON_ONCE(!empty && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0); rcu_nocb_unlock_irqrestore(rdp, flags); - /* Re-invoke RCU core processing if there are callbacks remaining. */ - if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist)) - invoke_rcu_core(); tick_dep_clear_task(current, TICK_DEP_BIT_RCU); } @@ -2561,11 +2264,19 @@ static void rcu_do_batch(struct rcu_data *rdp) * state, for example, user mode or idle loop. It also schedules RCU * core processing. If the current grace period has gone on too long, * it will ask the scheduler to manufacture a context switch for the sole - * purpose of providing a providing the needed quiescent state. + * purpose of providing the needed quiescent state. */ void rcu_sched_clock_irq(int user) { + unsigned long j; + + if (IS_ENABLED(CONFIG_PROVE_RCU)) { + j = jiffies; + WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock))); + __this_cpu_write(rcu_data.last_sched_clock, j); + } trace_rcu_utilization(TPS("Start scheduler-tick")); + lockdep_assert_irqs_disabled(); raw_cpu_inc(rcu_data.ticks_this_gp); /* The load-acquire pairs with the store-release setting to true. */ if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) { @@ -2579,6 +2290,9 @@ void rcu_sched_clock_irq(int user) rcu_flavor_sched_clock_irq(user); if (rcu_pending(user)) invoke_rcu_core(); + if (user || rcu_is_cpu_rrupt_from_idle()) + rcu_note_voluntary_context_switch(current); + lockdep_assert_irqs_disabled(); trace_rcu_utilization(TPS("End scheduler-tick")); } @@ -2594,15 +2308,15 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) { int cpu; unsigned long flags; - unsigned long mask; - struct rcu_data *rdp; struct rcu_node *rnp; rcu_state.cbovld = rcu_state.cbovldnext; rcu_state.cbovldnext = false; rcu_for_each_leaf_node(rnp) { + unsigned long mask = 0; + unsigned long rsmask = 0; + cond_resched_tasks_rcu_qs(); - mask = 0; raw_spin_lock_irqsave_rcu_node(rnp, flags); rcu_state.cbovldnext |= !!rnp->cbovldmask; if (rnp->qsmask == 0) { @@ -2620,11 +2334,17 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) continue; } for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) { + struct rcu_data *rdp; + int ret; + rdp = per_cpu_ptr(&rcu_data, cpu); - if (f(rdp)) { + ret = f(rdp); + if (ret > 0) { mask |= rdp->grpmask; rcu_disable_urgency_upon_qs(rdp); } + if (ret < 0) + rsmask |= rdp->grpmask; } if (mask != 0) { /* Idle/offline CPUs, report (releases rnp->lock). */ @@ -2633,6 +2353,9 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) /* Nothing to do here, so just drop the lock. */ raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } + + for_each_leaf_node_cpu_mask(rnp, cpu, rsmask) + resched_cpu(cpu); } } @@ -2647,8 +2370,10 @@ void rcu_force_quiescent_state(void) struct rcu_node *rnp; struct rcu_node *rnp_old = NULL; + if (!rcu_gp_in_progress()) + return; /* Funnel through hierarchy to reduce memory contention. */ - rnp = __this_cpu_read(rcu_data.mynode); + rnp = raw_cpu_read(rcu_data.mynode); for (; rnp != NULL; rnp = rnp->parent) { ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) || !raw_spin_trylock(&rnp->fqslock); @@ -2688,7 +2413,24 @@ static __latent_entropy void rcu_core(void) unsigned long flags; struct rcu_data *rdp = raw_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; - const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); + /* + * On RT rcu_core() can be preempted when IRQs aren't disabled. + * Therefore this function can race with concurrent NOCB (de-)offloading + * on this CPU and the below condition must be considered volatile. + * However if we race with: + * + * _ Offloading: In the worst case we accelerate or process callbacks + * concurrently with NOCB kthreads. We are guaranteed to + * call rcu_nocb_lock() if that happens. + * + * _ Deoffloading: In the worst case we miss callbacks acceleration or + * processing. This is fine because the early stage + * of deoffloading invokes rcu_core() after setting + * SEGCBLIST_RCU_CORE. So we guarantee that we'll process + * what could have been dismissed without the need to wait + * for the next rcu_pending() check in the next jiffy. + */ + const bool do_batch = !rcu_segcblist_completely_offloaded(&rdp->cblist); if (cpu_is_offline(smp_processor_id())) return; @@ -2696,7 +2438,7 @@ static __latent_entropy void rcu_core(void) WARN_ON_ONCE(!rdp->beenonline); /* Report any deferred quiescent states if preemption enabled. */ - if (!(preempt_count() & PREEMPT_MASK)) { + if (IS_ENABLED(CONFIG_PREEMPT_COUNT) && (!(preempt_count() & PREEMPT_MASK))) { rcu_preempt_deferred_qs(current); } else if (rcu_preempt_need_deferred_qs(current)) { set_tsk_need_resched(current); @@ -2708,19 +2450,23 @@ static __latent_entropy void rcu_core(void) /* No grace period and unregistered callbacks? */ if (!rcu_gp_in_progress() && - rcu_segcblist_is_enabled(&rdp->cblist) && !offloaded) { - local_irq_save(flags); + rcu_segcblist_is_enabled(&rdp->cblist) && do_batch) { + rcu_nocb_lock_irqsave(rdp, flags); if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) rcu_accelerate_cbs_unlocked(rnp, rdp); - local_irq_restore(flags); + rcu_nocb_unlock_irqrestore(rdp, flags); } rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check()); /* If there are callbacks ready, invoke them. */ - if (!offloaded && rcu_segcblist_ready_cbs(&rdp->cblist) && - likely(READ_ONCE(rcu_scheduler_fully_active))) + if (do_batch && rcu_segcblist_ready_cbs(&rdp->cblist) && + likely(READ_ONCE(rcu_scheduler_fully_active))) { rcu_do_batch(rdp); + /* Re-invoke RCU core processing if there are callbacks remaining. */ + if (rcu_segcblist_ready_cbs(&rdp->cblist)) + invoke_rcu_core(); + } /* Do any needed deferred wakeups of rcuo kthreads. */ do_nocb_deferred_wakeup(rdp); @@ -2791,20 +2537,22 @@ static void rcu_cpu_kthread(unsigned int cpu) { unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status); char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work); + unsigned long *j = this_cpu_ptr(&rcu_data.rcuc_activity); int spincnt; trace_rcu_utilization(TPS("Start CPU kthread@rcu_run")); for (spincnt = 0; spincnt < 10; spincnt++) { + WRITE_ONCE(*j, jiffies); local_bh_disable(); *statusp = RCU_KTHREAD_RUNNING; local_irq_disable(); work = *workp; - *workp = 0; + WRITE_ONCE(*workp, 0); local_irq_enable(); if (work) rcu_core(); local_bh_enable(); - if (*workp == 0) { + if (!READ_ONCE(*workp)) { trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); *statusp = RCU_KTHREAD_WAITING; return; @@ -2815,6 +2563,7 @@ static void rcu_cpu_kthread(unsigned int cpu) schedule_timeout_idle(2); trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); *statusp = RCU_KTHREAD_WAITING; + WRITE_ONCE(*j, jiffies); } static struct smp_hotplug_thread rcu_cpu_thread_spec = { @@ -2835,13 +2584,12 @@ static int __init rcu_spawn_core_kthreads(void) for_each_possible_cpu(cpu) per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0; - if (!IS_ENABLED(CONFIG_RCU_BOOST) && use_softirq) + if (use_softirq) return 0; WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__); return 0; } -early_initcall(rcu_spawn_core_kthreads); /* * Handle any core-RCU processing required by a call_rcu() invocation. @@ -2879,10 +2627,10 @@ static void __call_rcu_core(struct rcu_data *rdp, struct rcu_head *head, } else { /* Give the grace period a kick. */ rdp->blimit = DEFAULT_MAX_RCU_BLIMIT; - if (rcu_state.n_force_qs == rdp->n_force_qs_snap && + if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap && rcu_segcblist_first_pend_cb(&rdp->cblist) != head) rcu_force_quiescent_state(); - rdp->n_force_qs_snap = rcu_state.n_force_qs; + rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs); rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist); } } @@ -2937,11 +2685,12 @@ static void check_cb_ovld(struct rcu_data *rdp) raw_spin_unlock_rcu_node(rnp); } -/* Helper function for call_rcu() and friends. */ static void -__call_rcu(struct rcu_head *head, rcu_callback_t func) +__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in) { + static atomic_t doublefrees; unsigned long flags; + bool lazy; struct rcu_data *rdp; bool was_alldone; @@ -2952,18 +2701,21 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func) /* * Probable double call_rcu(), so leak the callback. * Use rcu:rcu_callback trace event to find the previous - * time callback was passed to __call_rcu(). + * time callback was passed to call_rcu(). */ - WARN_ONCE(1, "__call_rcu(): Double-freed CB %p->%pS()!!!\n", - head, head->func); + if (atomic_inc_return(&doublefrees) < 4) { + pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func); + mem_dump_obj(head); + } WRITE_ONCE(head->func, rcu_leak_callback); return; } head->func = func; head->next = NULL; + kasan_record_aux_stack_noalloc(head); local_irq_save(flags); - kasan_record_aux_stack(head); rdp = this_cpu_ptr(&rcu_data); + lazy = lazy_in && !rcu_async_should_hurry(); /* Add the callback to our list. */ if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) { @@ -2977,7 +2729,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func) } check_cb_ovld(rdp); - if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags)) + if (rcu_nocb_try_bypass(rdp, head, &was_alldone, flags, lazy)) return; // Enqueued onto ->nocb_bypass, so just leave. // If no-CBs CPU gets here, rcu_nocb_try_bypass() acquired ->nocb_lock. rcu_segcblist_enqueue(&rdp->cblist, head); @@ -2989,8 +2741,10 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func) trace_rcu_callback(rcu_state.name, head, rcu_segcblist_n_cbs(&rdp->cblist)); + trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued")); + /* Go handle any RCU core processing required. */ - if (unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) { + if (unlikely(rcu_rdp_is_offloaded(rdp))) { __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */ } else { __call_rcu_core(rdp, head, flags); @@ -2998,8 +2752,40 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func) } } +#ifdef CONFIG_RCU_LAZY +/** + * call_rcu_hurry() - Queue RCU callback for invocation after grace period, and + * flush all lazy callbacks (including the new one) to the main ->cblist while + * doing so. + * + * @head: structure to be used for queueing the RCU updates. + * @func: actual callback function to be invoked after the grace period + * + * The callback function will be invoked some time after a full grace + * period elapses, in other words after all pre-existing RCU read-side + * critical sections have completed. + * + * Use this API instead of call_rcu() if you don't want the callback to be + * invoked after very long periods of time, which can happen on systems without + * memory pressure and on systems which are lightly loaded or mostly idle. + * This function will cause callbacks to be invoked sooner than later at the + * expense of extra power. Other than that, this function is identical to, and + * reuses call_rcu()'s logic. Refer to call_rcu() for more details about memory + * ordering and other functionality. + */ +void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func) +{ + __call_rcu_common(head, func, false); +} +EXPORT_SYMBOL_GPL(call_rcu_hurry); +#endif + /** * call_rcu() - Queue an RCU callback for invocation after a grace period. + * By default the callbacks are 'lazy' and are kept hidden from the main + * ->cblist to prevent starting of grace periods too soon. + * If you desire grace periods to start very soon, use call_rcu_hurry(). + * * @head: structure to be used for queueing the RCU updates. * @func: actual callback function to be invoked after the grace period * @@ -3007,12 +2793,14 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func) * period elapses, in other words after all pre-existing RCU read-side * critical sections have completed. However, the callback function * might well execute concurrently with RCU read-side critical sections - * that started after call_rcu() was invoked. RCU read-side critical - * sections are delimited by rcu_read_lock() and rcu_read_unlock(), and - * may be nested. In addition, regions of code across which interrupts, - * preemption, or softirqs have been disabled also serve as RCU read-side - * critical sections. This includes hardware interrupt handlers, softirq - * handlers, and NMI handlers. + * that started after call_rcu() was invoked. + * + * RCU read-side critical sections are delimited by rcu_read_lock() + * and rcu_read_unlock(), and may be nested. In addition, but only in + * v5.0 and later, regions of code across which interrupts, preemption, + * or softirqs have been disabled also serve as RCU read-side critical + * sections. This includes hardware interrupt handlers, softirq handlers, + * and NMI handlers. * * Note that all CPUs must agree that the grace period extended beyond * all pre-existing RCU read-side critical section. On systems with more @@ -3032,28 +2820,32 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func) * between the call to call_rcu() and the invocation of "func()" -- even * if CPU A and CPU B are the same CPU (but again only if the system has * more than one CPU). + * + * Implementation of these memory-ordering guarantees is described here: + * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst. */ void call_rcu(struct rcu_head *head, rcu_callback_t func) { - __call_rcu(head, func); + __call_rcu_common(head, func, IS_ENABLED(CONFIG_RCU_LAZY)); } EXPORT_SYMBOL_GPL(call_rcu); - /* Maximum number of jiffies to wait before draining a batch. */ -#define KFREE_DRAIN_JIFFIES (HZ / 50) +#define KFREE_DRAIN_JIFFIES (5 * HZ) #define KFREE_N_BATCHES 2 #define FREE_N_CHANNELS 2 /** * struct kvfree_rcu_bulk_data - single block to store kvfree_rcu() pointers + * @list: List node. All blocks are linked between each other + * @gp_snap: Snapshot of RCU state for objects placed to this bulk * @nr_records: Number of active pointers in the array - * @next: Next bulk object in the block chain * @records: Array of the kvfree_rcu() pointers */ struct kvfree_rcu_bulk_data { + struct list_head list; + struct rcu_gp_oldstate gp_snap; unsigned long nr_records; - struct kvfree_rcu_bulk_data *next; void *records[]; }; @@ -3069,33 +2861,37 @@ struct kvfree_rcu_bulk_data { * struct kfree_rcu_cpu_work - single batch of kfree_rcu() requests * @rcu_work: Let queue_rcu_work() invoke workqueue handler after grace period * @head_free: List of kfree_rcu() objects waiting for a grace period - * @bkvhead_free: Bulk-List of kvfree_rcu() objects waiting for a grace period + * @head_free_gp_snap: Grace-period snapshot to check for attempted premature frees. + * @bulk_head_free: Bulk-List of kvfree_rcu() objects waiting for a grace period * @krcp: Pointer to @kfree_rcu_cpu structure */ struct kfree_rcu_cpu_work { struct rcu_work rcu_work; struct rcu_head *head_free; - struct kvfree_rcu_bulk_data *bkvhead_free[FREE_N_CHANNELS]; + struct rcu_gp_oldstate head_free_gp_snap; + struct list_head bulk_head_free[FREE_N_CHANNELS]; struct kfree_rcu_cpu *krcp; }; /** * struct kfree_rcu_cpu - batch up kfree_rcu() requests for RCU grace period * @head: List of kfree_rcu() objects not yet waiting for a grace period - * @bkvhead: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period + * @head_gp_snap: Snapshot of RCU state for objects placed to "@head" + * @bulk_head: Bulk-List of kvfree_rcu() objects not yet waiting for a grace period * @krw_arr: Array of batches of kfree_rcu() objects waiting for a grace period * @lock: Synchronize access to this structure * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES - * @monitor_todo: Tracks whether a @monitor_work delayed work is pending * @initialized: The @rcu_work fields have been initialized - * @count: Number of objects for which GP not started + * @head_count: Number of objects in rcu_head singular list + * @bulk_count: Number of objects in bulk-list * @bkvcache: * A simple cache list that contains objects for reuse purpose. * In order to save some per-cpu space the list is singular. * Even though it is lockless an access has to be protected by the * per-cpu lock. * @page_cache_work: A work to refill the cache when it is empty + * @backoff_page_cache_fill: Delay cache refills * @work_in_progress: Indicates that page_cache_work is running * @hrtimer: A hrtimer for scheduling a page_cache_work * @nr_bkv_objs: number of allocated objects at @bkvcache. @@ -3106,16 +2902,23 @@ struct kfree_rcu_cpu_work { * the interactions with the slab allocators. */ struct kfree_rcu_cpu { + // Objects queued on a linked list + // through their rcu_head structures. struct rcu_head *head; - struct kvfree_rcu_bulk_data *bkvhead[FREE_N_CHANNELS]; + unsigned long head_gp_snap; + atomic_t head_count; + + // Objects queued on a bulk-list. + struct list_head bulk_head[FREE_N_CHANNELS]; + atomic_t bulk_count[FREE_N_CHANNELS]; + struct kfree_rcu_cpu_work krw_arr[KFREE_N_BATCHES]; raw_spinlock_t lock; struct delayed_work monitor_work; - bool monitor_todo; bool initialized; - int count; - struct work_struct page_cache_work; + struct delayed_work page_cache_work; + atomic_t backoff_page_cache_fill; atomic_t work_in_progress; struct hrtimer hrtimer; @@ -3153,8 +2956,7 @@ krc_this_cpu_lock(unsigned long *flags) static inline void krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags) { - raw_spin_unlock(&krcp->lock); - local_irq_restore(flags); + raw_spin_unlock_irqrestore(&krcp->lock, flags); } static inline struct kvfree_rcu_bulk_data * @@ -3163,7 +2965,7 @@ get_cached_bnode(struct kfree_rcu_cpu *krcp) if (!krcp->nr_bkv_objs) return NULL; - krcp->nr_bkv_objs--; + WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs - 1); return (struct kvfree_rcu_bulk_data *) llist_del_first(&krcp->bkvcache); } @@ -3177,85 +2979,79 @@ put_cached_bnode(struct kfree_rcu_cpu *krcp, return false; llist_add((struct llist_node *) bnode, &krcp->bkvcache); - krcp->nr_bkv_objs++; + WRITE_ONCE(krcp->nr_bkv_objs, krcp->nr_bkv_objs + 1); return true; - } -/* - * This function is invoked in workqueue context after a grace period. - * It frees all the objects queued on ->bhead_free or ->head_free. - */ -static void kfree_rcu_work(struct work_struct *work) +static int +drain_page_cache(struct kfree_rcu_cpu *krcp) { unsigned long flags; - struct kvfree_rcu_bulk_data *bkvhead[FREE_N_CHANNELS], *bnext; - struct rcu_head *head, *next; - struct kfree_rcu_cpu *krcp; - struct kfree_rcu_cpu_work *krwp; - int i, j; + struct llist_node *page_list, *pos, *n; + int freed = 0; - krwp = container_of(to_rcu_work(work), - struct kfree_rcu_cpu_work, rcu_work); - krcp = krwp->krcp; + if (!rcu_min_cached_objs) + return 0; raw_spin_lock_irqsave(&krcp->lock, flags); - // Channels 1 and 2. - for (i = 0; i < FREE_N_CHANNELS; i++) { - bkvhead[i] = krwp->bkvhead_free[i]; - krwp->bkvhead_free[i] = NULL; - } - - // Channel 3. - head = krwp->head_free; - krwp->head_free = NULL; + page_list = llist_del_all(&krcp->bkvcache); + WRITE_ONCE(krcp->nr_bkv_objs, 0); raw_spin_unlock_irqrestore(&krcp->lock, flags); - // Handle two first channels. - for (i = 0; i < FREE_N_CHANNELS; i++) { - for (; bkvhead[i]; bkvhead[i] = bnext) { - bnext = bkvhead[i]->next; - debug_rcu_bhead_unqueue(bkvhead[i]); - - rcu_lock_acquire(&rcu_callback_map); - if (i == 0) { // kmalloc() / kfree(). - trace_rcu_invoke_kfree_bulk_callback( - rcu_state.name, bkvhead[i]->nr_records, - bkvhead[i]->records); - - kfree_bulk(bkvhead[i]->nr_records, - bkvhead[i]->records); - } else { // vmalloc() / vfree(). - for (j = 0; j < bkvhead[i]->nr_records; j++) { - trace_rcu_invoke_kvfree_callback( - rcu_state.name, - bkvhead[i]->records[j], 0); - - vfree(bkvhead[i]->records[j]); - } - } - rcu_lock_release(&rcu_callback_map); + llist_for_each_safe(pos, n, page_list) { + free_page((unsigned long)pos); + freed++; + } - raw_spin_lock_irqsave(&krcp->lock, flags); - if (put_cached_bnode(krcp, bkvhead[i])) - bkvhead[i] = NULL; - raw_spin_unlock_irqrestore(&krcp->lock, flags); + return freed; +} - if (bkvhead[i]) - free_page((unsigned long) bkvhead[i]); +static void +kvfree_rcu_bulk(struct kfree_rcu_cpu *krcp, + struct kvfree_rcu_bulk_data *bnode, int idx) +{ + unsigned long flags; + int i; - cond_resched_tasks_rcu_qs(); + if (!WARN_ON_ONCE(!poll_state_synchronize_rcu_full(&bnode->gp_snap))) { + debug_rcu_bhead_unqueue(bnode); + rcu_lock_acquire(&rcu_callback_map); + if (idx == 0) { // kmalloc() / kfree(). + trace_rcu_invoke_kfree_bulk_callback( + rcu_state.name, bnode->nr_records, + bnode->records); + + kfree_bulk(bnode->nr_records, bnode->records); + } else { // vmalloc() / vfree(). + for (i = 0; i < bnode->nr_records; i++) { + trace_rcu_invoke_kvfree_callback( + rcu_state.name, bnode->records[i], 0); + + vfree(bnode->records[i]); + } } + rcu_lock_release(&rcu_callback_map); } - /* - * Emergency case only. It can happen under low memory - * condition when an allocation gets failed, so the "bulk" - * path can not be temporary maintained. - */ + raw_spin_lock_irqsave(&krcp->lock, flags); + if (put_cached_bnode(krcp, bnode)) + bnode = NULL; + raw_spin_unlock_irqrestore(&krcp->lock, flags); + + if (bnode) + free_page((unsigned long) bnode); + + cond_resched_tasks_rcu_qs(); +} + +static void +kvfree_rcu_list(struct rcu_head *head) +{ + struct rcu_head *next; + for (; head; head = next) { - unsigned long offset = (unsigned long)head->func; - void *ptr = (void *)head - offset; + void *ptr = (void *) head->func; + unsigned long offset = (void *) head - ptr; next = head->next; debug_rcu_head_unqueue((struct rcu_head *)ptr); @@ -3271,99 +3067,205 @@ static void kfree_rcu_work(struct work_struct *work) } /* - * Schedule the kfree batch RCU work to run in workqueue context after a GP. - * - * This function is invoked by kfree_rcu_monitor() when the KFREE_DRAIN_JIFFIES - * timeout has been reached. + * This function is invoked in workqueue context after a grace period. + * It frees all the objects queued on ->bulk_head_free or ->head_free. */ -static inline bool queue_kfree_rcu_work(struct kfree_rcu_cpu *krcp) +static void kfree_rcu_work(struct work_struct *work) { + unsigned long flags; + struct kvfree_rcu_bulk_data *bnode, *n; + struct list_head bulk_head[FREE_N_CHANNELS]; + struct rcu_head *head; + struct kfree_rcu_cpu *krcp; struct kfree_rcu_cpu_work *krwp; - bool repeat = false; - int i, j; + struct rcu_gp_oldstate head_gp_snap; + int i; - lockdep_assert_held(&krcp->lock); + krwp = container_of(to_rcu_work(work), + struct kfree_rcu_cpu_work, rcu_work); + krcp = krwp->krcp; - for (i = 0; i < KFREE_N_BATCHES; i++) { - krwp = &(krcp->krw_arr[i]); + raw_spin_lock_irqsave(&krcp->lock, flags); + // Channels 1 and 2. + for (i = 0; i < FREE_N_CHANNELS; i++) + list_replace_init(&krwp->bulk_head_free[i], &bulk_head[i]); - /* - * Try to detach bkvhead or head and attach it over any - * available corresponding free channel. It can be that - * a previous RCU batch is in progress, it means that - * immediately to queue another one is not possible so - * return false to tell caller to retry. - */ - if ((krcp->bkvhead[0] && !krwp->bkvhead_free[0]) || - (krcp->bkvhead[1] && !krwp->bkvhead_free[1]) || - (krcp->head && !krwp->head_free)) { - // Channel 1 corresponds to SLAB ptrs. - // Channel 2 corresponds to vmalloc ptrs. - for (j = 0; j < FREE_N_CHANNELS; j++) { - if (!krwp->bkvhead_free[j]) { - krwp->bkvhead_free[j] = krcp->bkvhead[j]; - krcp->bkvhead[j] = NULL; - } - } + // Channel 3. + head = krwp->head_free; + krwp->head_free = NULL; + head_gp_snap = krwp->head_free_gp_snap; + raw_spin_unlock_irqrestore(&krcp->lock, flags); - // Channel 3 corresponds to emergency path. - if (!krwp->head_free) { - krwp->head_free = krcp->head; - krcp->head = NULL; - } + // Handle the first two channels. + for (i = 0; i < FREE_N_CHANNELS; i++) { + // Start from the tail page, so a GP is likely passed for it. + list_for_each_entry_safe(bnode, n, &bulk_head[i], list) + kvfree_rcu_bulk(krcp, bnode, i); + } - WRITE_ONCE(krcp->count, 0); + /* + * This is used when the "bulk" path can not be used for the + * double-argument of kvfree_rcu(). This happens when the + * page-cache is empty, which means that objects are instead + * queued on a linked list through their rcu_head structures. + * This list is named "Channel 3". + */ + if (head && !WARN_ON_ONCE(!poll_state_synchronize_rcu_full(&head_gp_snap))) + kvfree_rcu_list(head); +} - /* - * One work is per one batch, so there are three - * "free channels", the batch can handle. It can - * be that the work is in the pending state when - * channels have been detached following by each - * other. - */ - queue_rcu_work(system_wq, &krwp->rcu_work); - } +static bool +need_offload_krc(struct kfree_rcu_cpu *krcp) +{ + int i; - // Repeat if any "free" corresponding channel is still busy. - if (krcp->bkvhead[0] || krcp->bkvhead[1] || krcp->head) - repeat = true; - } + for (i = 0; i < FREE_N_CHANNELS; i++) + if (!list_empty(&krcp->bulk_head[i])) + return true; - return !repeat; + return !!READ_ONCE(krcp->head); } -static inline void kfree_rcu_drain_unlock(struct kfree_rcu_cpu *krcp, - unsigned long flags) +static bool +need_wait_for_krwp_work(struct kfree_rcu_cpu_work *krwp) { - // Attempt to start a new batch. - krcp->monitor_todo = false; - if (queue_kfree_rcu_work(krcp)) { - // Success! Our job is done here. - raw_spin_unlock_irqrestore(&krcp->lock, flags); + int i; + + for (i = 0; i < FREE_N_CHANNELS; i++) + if (!list_empty(&krwp->bulk_head_free[i])) + return true; + + return !!krwp->head_free; +} + +static int krc_count(struct kfree_rcu_cpu *krcp) +{ + int sum = atomic_read(&krcp->head_count); + int i; + + for (i = 0; i < FREE_N_CHANNELS; i++) + sum += atomic_read(&krcp->bulk_count[i]); + + return sum; +} + +static void +schedule_delayed_monitor_work(struct kfree_rcu_cpu *krcp) +{ + long delay, delay_left; + + delay = krc_count(krcp) >= KVFREE_BULK_MAX_ENTR ? 1:KFREE_DRAIN_JIFFIES; + if (delayed_work_pending(&krcp->monitor_work)) { + delay_left = krcp->monitor_work.timer.expires - jiffies; + if (delay < delay_left) + mod_delayed_work(system_wq, &krcp->monitor_work, delay); return; } + queue_delayed_work(system_wq, &krcp->monitor_work, delay); +} - // Previous RCU batch still in progress, try again later. - krcp->monitor_todo = true; - schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES); +static void +kvfree_rcu_drain_ready(struct kfree_rcu_cpu *krcp) +{ + struct list_head bulk_ready[FREE_N_CHANNELS]; + struct kvfree_rcu_bulk_data *bnode, *n; + struct rcu_head *head_ready = NULL; + unsigned long flags; + int i; + + raw_spin_lock_irqsave(&krcp->lock, flags); + for (i = 0; i < FREE_N_CHANNELS; i++) { + INIT_LIST_HEAD(&bulk_ready[i]); + + list_for_each_entry_safe_reverse(bnode, n, &krcp->bulk_head[i], list) { + if (!poll_state_synchronize_rcu_full(&bnode->gp_snap)) + break; + + atomic_sub(bnode->nr_records, &krcp->bulk_count[i]); + list_move(&bnode->list, &bulk_ready[i]); + } + } + + if (krcp->head && poll_state_synchronize_rcu(krcp->head_gp_snap)) { + head_ready = krcp->head; + atomic_set(&krcp->head_count, 0); + WRITE_ONCE(krcp->head, NULL); + } raw_spin_unlock_irqrestore(&krcp->lock, flags); + + for (i = 0; i < FREE_N_CHANNELS; i++) { + list_for_each_entry_safe(bnode, n, &bulk_ready[i], list) + kvfree_rcu_bulk(krcp, bnode, i); + } + + if (head_ready) + kvfree_rcu_list(head_ready); } /* * This function is invoked after the KFREE_DRAIN_JIFFIES timeout. - * It invokes kfree_rcu_drain_unlock() to attempt to start another batch. */ static void kfree_rcu_monitor(struct work_struct *work) { + struct kfree_rcu_cpu *krcp = container_of(work, + struct kfree_rcu_cpu, monitor_work.work); unsigned long flags; - struct kfree_rcu_cpu *krcp = container_of(work, struct kfree_rcu_cpu, - monitor_work.work); + int i, j; + + // Drain ready for reclaim. + kvfree_rcu_drain_ready(krcp); raw_spin_lock_irqsave(&krcp->lock, flags); - if (krcp->monitor_todo) - kfree_rcu_drain_unlock(krcp, flags); - else - raw_spin_unlock_irqrestore(&krcp->lock, flags); + + // Attempt to start a new batch. + for (i = 0; i < KFREE_N_BATCHES; i++) { + struct kfree_rcu_cpu_work *krwp = &(krcp->krw_arr[i]); + + // Try to detach bulk_head or head and attach it, only when + // all channels are free. Any channel is not free means at krwp + // there is on-going rcu work to handle krwp's free business. + if (need_wait_for_krwp_work(krwp)) + continue; + + // kvfree_rcu_drain_ready() might handle this krcp, if so give up. + if (need_offload_krc(krcp)) { + // Channel 1 corresponds to the SLAB-pointer bulk path. + // Channel 2 corresponds to vmalloc-pointer bulk path. + for (j = 0; j < FREE_N_CHANNELS; j++) { + if (list_empty(&krwp->bulk_head_free[j])) { + atomic_set(&krcp->bulk_count[j], 0); + list_replace_init(&krcp->bulk_head[j], + &krwp->bulk_head_free[j]); + } + } + + // Channel 3 corresponds to both SLAB and vmalloc + // objects queued on the linked list. + if (!krwp->head_free) { + krwp->head_free = krcp->head; + get_state_synchronize_rcu_full(&krwp->head_free_gp_snap); + atomic_set(&krcp->head_count, 0); + WRITE_ONCE(krcp->head, NULL); + } + + // One work is per one batch, so there are three + // "free channels", the batch can handle. It can + // be that the work is in the pending state when + // channels have been detached following by each + // other. + queue_rcu_work(system_wq, &krwp->rcu_work); + } + } + + raw_spin_unlock_irqrestore(&krcp->lock, flags); + + // If there is nothing to detach, it means that our job is + // successfully done here. In case of having at least one + // of the channels that is still busy we should rearm the + // work to repeat an attempt. Because previous batches are + // still in progress. + if (need_offload_krc(krcp)) + schedule_delayed_monitor_work(krcp); } static enum hrtimer_restart @@ -3372,7 +3274,7 @@ schedule_page_work_fn(struct hrtimer *t) struct kfree_rcu_cpu *krcp = container_of(t, struct kfree_rcu_cpu, hrtimer); - queue_work(system_highpri_wq, &krcp->page_cache_work); + queue_delayed_work(system_highpri_wq, &krcp->page_cache_work, 0); return HRTIMER_NORESTART; } @@ -3381,111 +3283,143 @@ static void fill_page_cache_func(struct work_struct *work) struct kvfree_rcu_bulk_data *bnode; struct kfree_rcu_cpu *krcp = container_of(work, struct kfree_rcu_cpu, - page_cache_work); + page_cache_work.work); unsigned long flags; + int nr_pages; bool pushed; int i; - for (i = 0; i < rcu_min_cached_objs; i++) { + nr_pages = atomic_read(&krcp->backoff_page_cache_fill) ? + 1 : rcu_min_cached_objs; + + for (i = READ_ONCE(krcp->nr_bkv_objs); i < nr_pages; i++) { bnode = (struct kvfree_rcu_bulk_data *) - __get_free_page(GFP_KERNEL | __GFP_NOWARN); + __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN); - if (bnode) { - raw_spin_lock_irqsave(&krcp->lock, flags); - pushed = put_cached_bnode(krcp, bnode); - raw_spin_unlock_irqrestore(&krcp->lock, flags); + if (!bnode) + break; - if (!pushed) { - free_page((unsigned long) bnode); - break; - } + raw_spin_lock_irqsave(&krcp->lock, flags); + pushed = put_cached_bnode(krcp, bnode); + raw_spin_unlock_irqrestore(&krcp->lock, flags); + + if (!pushed) { + free_page((unsigned long) bnode); + break; } } atomic_set(&krcp->work_in_progress, 0); + atomic_set(&krcp->backoff_page_cache_fill, 0); } static void run_page_cache_worker(struct kfree_rcu_cpu *krcp) { + // If cache disabled, bail out. + if (!rcu_min_cached_objs) + return; + if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING && !atomic_xchg(&krcp->work_in_progress, 1)) { - hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, - HRTIMER_MODE_REL); - krcp->hrtimer.function = schedule_page_work_fn; - hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL); + if (atomic_read(&krcp->backoff_page_cache_fill)) { + queue_delayed_work(system_wq, + &krcp->page_cache_work, + msecs_to_jiffies(rcu_delay_page_cache_fill_msec)); + } else { + hrtimer_init(&krcp->hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); + krcp->hrtimer.function = schedule_page_work_fn; + hrtimer_start(&krcp->hrtimer, 0, HRTIMER_MODE_REL); + } } } +// Record ptr in a page managed by krcp, with the pre-krc_this_cpu_lock() +// state specified by flags. If can_alloc is true, the caller must +// be schedulable and not be holding any locks or mutexes that might be +// acquired by the memory allocator or anything that it might invoke. +// Returns true if ptr was successfully recorded, else the caller must +// use a fallback. static inline bool -kvfree_call_rcu_add_ptr_to_bulk(struct kfree_rcu_cpu *krcp, void *ptr) +add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp, + unsigned long *flags, void *ptr, bool can_alloc) { struct kvfree_rcu_bulk_data *bnode; int idx; - if (unlikely(!krcp->initialized)) + *krcp = krc_this_cpu_lock(flags); + if (unlikely(!(*krcp)->initialized)) return false; - lockdep_assert_held(&krcp->lock); idx = !!is_vmalloc_addr(ptr); + bnode = list_first_entry_or_null(&(*krcp)->bulk_head[idx], + struct kvfree_rcu_bulk_data, list); /* Check if a new block is required. */ - if (!krcp->bkvhead[idx] || - krcp->bkvhead[idx]->nr_records == KVFREE_BULK_MAX_ENTR) { - bnode = get_cached_bnode(krcp); - /* Switch to emergency path. */ + if (!bnode || bnode->nr_records == KVFREE_BULK_MAX_ENTR) { + bnode = get_cached_bnode(*krcp); + if (!bnode && can_alloc) { + krc_this_cpu_unlock(*krcp, *flags); + + // __GFP_NORETRY - allows a light-weight direct reclaim + // what is OK from minimizing of fallback hitting point of + // view. Apart of that it forbids any OOM invoking what is + // also beneficial since we are about to release memory soon. + // + // __GFP_NOMEMALLOC - prevents from consuming of all the + // memory reserves. Please note we have a fallback path. + // + // __GFP_NOWARN - it is supposed that an allocation can + // be failed under low memory or high memory pressure + // scenarios. + bnode = (struct kvfree_rcu_bulk_data *) + __get_free_page(GFP_KERNEL | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN); + raw_spin_lock_irqsave(&(*krcp)->lock, *flags); + } + if (!bnode) return false; - /* Initialize the new block. */ + // Initialize the new block and attach it. bnode->nr_records = 0; - bnode->next = krcp->bkvhead[idx]; - - /* Attach it to the head. */ - krcp->bkvhead[idx] = bnode; + list_add(&bnode->list, &(*krcp)->bulk_head[idx]); } - /* Finally insert. */ - krcp->bkvhead[idx]->records - [krcp->bkvhead[idx]->nr_records++] = ptr; + // Finally insert and update the GP for this page. + bnode->records[bnode->nr_records++] = ptr; + get_state_synchronize_rcu_full(&bnode->gp_snap); + atomic_inc(&(*krcp)->bulk_count[idx]); return true; } /* - * Queue a request for lazy invocation of appropriate free routine after a - * grace period. Please note there are three paths are maintained, two are the - * main ones that use array of pointers interface and third one is emergency - * one, that is used only when the main path can not be maintained temporary, - * due to memory pressure. + * Queue a request for lazy invocation of the appropriate free routine + * after a grace period. Please note that three paths are maintained, + * two for the common case using arrays of pointers and a third one that + * is used only when the main paths cannot be used, for example, due to + * memory pressure. * * Each kvfree_call_rcu() request is added to a batch. The batch will be drained * every KFREE_DRAIN_JIFFIES number of jiffies. All the objects in the batch will * be free'd in workqueue context. This allows us to: batch requests together to * reduce the number of grace periods during heavy kfree_rcu()/kvfree_rcu() load. */ -void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) +void kvfree_call_rcu(struct rcu_head *head, void *ptr) { unsigned long flags; struct kfree_rcu_cpu *krcp; bool success; - void *ptr; - if (head) { - ptr = (void *) head - (unsigned long) func; - } else { - /* - * Please note there is a limitation for the head-less - * variant, that is why there is a clear rule for such - * objects: it can be used from might_sleep() context - * only. For other places please embed an rcu_head to - * your data. - */ + /* + * Please note there is a limitation for the head-less + * variant, that is why there is a clear rule for such + * objects: it can be used from might_sleep() context + * only. For other places please embed an rcu_head to + * your data. + */ + if (!head) might_sleep(); - ptr = (unsigned long *) func; - } - - krcp = krc_this_cpu_lock(&flags); // Queue the object but don't yet schedule the batch. if (debug_rcu_head_queue(ptr)) { @@ -3494,11 +3428,11 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) __func__, head); // Mark as success and leave. - success = true; - goto unlock_return; + return; } - success = kvfree_call_rcu_add_ptr_to_bulk(krcp, ptr); + kasan_record_aux_stack_noalloc(ptr); + success = add_ptr_to_bulk_krc_lock(&krcp, &flags, ptr, !head); if (!success) { run_page_cache_worker(krcp); @@ -3506,20 +3440,27 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func) // Inline if kvfree_rcu(one_arg) call. goto unlock_return; - head->func = func; + head->func = ptr; head->next = krcp->head; - krcp->head = head; + WRITE_ONCE(krcp->head, head); + atomic_inc(&krcp->head_count); + + // Take a snapshot for this krcp. + krcp->head_gp_snap = get_state_synchronize_rcu(); success = true; } - WRITE_ONCE(krcp->count, krcp->count + 1); + /* + * The kvfree_rcu() caller considers the pointer freed at this point + * and likely removes any references to it. Since the actual slab + * freeing (and kmemleak_free()) is deferred, tell kmemleak to ignore + * this object (no scanning or false positives reporting). + */ + kmemleak_ignore(ptr); // Set timer to drain after KFREE_DRAIN_JIFFIES. - if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING && - !krcp->monitor_todo) { - krcp->monitor_todo = true; - schedule_delayed_work(&krcp->monitor_work, KFREE_DRAIN_JIFFIES); - } + if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING) + schedule_delayed_monitor_work(krcp); unlock_return: krc_this_cpu_unlock(krcp, flags); @@ -3547,28 +3488,26 @@ kfree_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) for_each_possible_cpu(cpu) { struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); - count += READ_ONCE(krcp->count); + count += krc_count(krcp); + count += READ_ONCE(krcp->nr_bkv_objs); + atomic_set(&krcp->backoff_page_cache_fill, 1); } - return count; + return count == 0 ? SHRINK_EMPTY : count; } static unsigned long kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) { int cpu, freed = 0; - unsigned long flags; for_each_possible_cpu(cpu) { int count; struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); - count = krcp->count; - raw_spin_lock_irqsave(&krcp->lock, flags); - if (krcp->monitor_todo) - kfree_rcu_drain_unlock(krcp, flags); - else - raw_spin_unlock_irqrestore(&krcp->lock, flags); + count = krc_count(krcp); + count += drain_page_cache(krcp); + kfree_rcu_monitor(&krcp->monitor_work.work); sc->nr_to_scan -= count; freed += count; @@ -3580,69 +3519,35 @@ kfree_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) return freed == 0 ? SHRINK_STOP : freed; } -static struct shrinker kfree_rcu_shrinker = { - .count_objects = kfree_rcu_shrink_count, - .scan_objects = kfree_rcu_shrink_scan, - .batch = 0, - .seeks = DEFAULT_SEEKS, -}; - void __init kfree_rcu_scheduler_running(void) { int cpu; - unsigned long flags; for_each_possible_cpu(cpu) { struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); - raw_spin_lock_irqsave(&krcp->lock, flags); - if (!krcp->head || krcp->monitor_todo) { - raw_spin_unlock_irqrestore(&krcp->lock, flags); - continue; - } - krcp->monitor_todo = true; - schedule_delayed_work_on(cpu, &krcp->monitor_work, - KFREE_DRAIN_JIFFIES); - raw_spin_unlock_irqrestore(&krcp->lock, flags); + if (need_offload_krc(krcp)) + schedule_delayed_monitor_work(krcp); } } /* * During early boot, any blocking grace-period wait automatically - * implies a grace period. Later on, this is never the case for PREEMPTION. + * implies a grace period. * - * However, because a context switch is a grace period for !PREEMPTION, any - * blocking grace-period wait automatically implies a grace period if - * there is only one CPU online at any point time during execution of - * either synchronize_rcu() or synchronize_rcu_expedited(). It is OK to - * occasionally incorrectly indicate that there are multiple CPUs online - * when there was in fact only one the whole time, as this just adds some - * overhead: RCU still operates correctly. + * Later on, this could in theory be the case for kernels built with + * CONFIG_SMP=y && CONFIG_PREEMPTION=y running on a single CPU, but this + * is not a common case. Furthermore, this optimization would cause + * the rcu_gp_oldstate structure to expand by 50%, so this potential + * grace-period optimization is ignored once the scheduler is running. */ static int rcu_blocking_is_gp(void) { - int ret; - - if (IS_ENABLED(CONFIG_PREEMPTION)) - return rcu_scheduler_active == RCU_SCHEDULER_INACTIVE; - might_sleep(); /* Check for RCU read-side critical section. */ - preempt_disable(); - /* - * If the rcu_state.n_online_cpus counter is equal to one, - * there is only one CPU, and that CPU sees all prior accesses - * made by any CPU that was online at the time of its access. - * Furthermore, if this counter is equal to one, its value cannot - * change until after the preempt_enable() below. - * - * Furthermore, if rcu_state.n_online_cpus is equal to one here, - * all later CPUs (both this one and any that come online later - * on) are guaranteed to see all accesses prior to this point - * in the code, without the need for additional memory barriers. - * Those memory barriers are provided by CPU-hotplug code. - */ - ret = READ_ONCE(rcu_state.n_online_cpus) <= 1; - preempt_enable(); - return ret; + if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) { + might_sleep(); + return false; + } + return true; } /** @@ -3653,10 +3558,12 @@ static int rcu_blocking_is_gp(void) * read-side critical sections have completed. Note, however, that * upon return from synchronize_rcu(), the caller might well be executing * concurrently with new RCU read-side critical sections that began while - * synchronize_rcu() was waiting. RCU read-side critical sections are - * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. - * In addition, regions of code across which interrupts, preemption, or - * softirqs have been disabled also serve as RCU read-side critical + * synchronize_rcu() was waiting. + * + * RCU read-side critical sections are delimited by rcu_read_lock() + * and rcu_read_unlock(), and may be nested. In addition, but only in + * v5.0 and later, regions of code across which interrupts, preemption, + * or softirqs have been disabled also serve as RCU read-side critical * sections. This includes hardware interrupt handlers, softirq handlers, * and NMI handlers. * @@ -3677,28 +3584,70 @@ static int rcu_blocking_is_gp(void) * to have executed a full memory barrier during the execution of * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but * again only if the system has more than one CPU). + * + * Implementation of these memory-ordering guarantees is described here: + * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst. */ void synchronize_rcu(void) { + unsigned long flags; + struct rcu_node *rnp; + RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map), "Illegal synchronize_rcu() in RCU read-side critical section"); - if (rcu_blocking_is_gp()) - return; // Context allows vacuous grace periods. - if (rcu_gp_is_expedited()) - synchronize_rcu_expedited(); - else - wait_rcu_gp(call_rcu); + if (!rcu_blocking_is_gp()) { + if (rcu_gp_is_expedited()) + synchronize_rcu_expedited(); + else + wait_rcu_gp(call_rcu_hurry); + return; + } + + // Context allows vacuous grace periods. + // Note well that this code runs with !PREEMPT && !SMP. + // In addition, all code that advances grace periods runs at + // process level. Therefore, this normal GP overlaps with other + // normal GPs only by being fully nested within them, which allows + // reuse of ->gp_seq_polled_snap. + rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap); + rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap); + + // Update the normal grace-period counters to record + // this grace period, but only those used by the boot CPU. + // The rcu_scheduler_starting() will take care of the rest of + // these counters. + local_irq_save(flags); + WARN_ON_ONCE(num_online_cpus() > 1); + rcu_state.gp_seq += (1 << RCU_SEQ_CTR_SHIFT); + for (rnp = this_cpu_ptr(&rcu_data)->mynode; rnp; rnp = rnp->parent) + rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq; + local_irq_restore(flags); } EXPORT_SYMBOL_GPL(synchronize_rcu); /** + * get_completed_synchronize_rcu_full - Return a full pre-completed polled state cookie + * @rgosp: Place to put state cookie + * + * Stores into @rgosp a value that will always be treated by functions + * like poll_state_synchronize_rcu_full() as a cookie whose grace period + * has already completed. + */ +void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) +{ + rgosp->rgos_norm = RCU_GET_STATE_COMPLETED; + rgosp->rgos_exp = RCU_GET_STATE_COMPLETED; +} +EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full); + +/** * get_state_synchronize_rcu - Snapshot current RCU state * * Returns a cookie that is used by a later call to cond_synchronize_rcu() - * to determine whether or not a full grace period has elapsed in the - * meantime. + * or poll_state_synchronize_rcu() to determine whether or not a full + * grace period has elapsed in the meantime. */ unsigned long get_state_synchronize_rcu(void) { @@ -3707,33 +3656,256 @@ unsigned long get_state_synchronize_rcu(void) * before the load from ->gp_seq. */ smp_mb(); /* ^^^ */ - return rcu_seq_snap(&rcu_state.gp_seq); + return rcu_seq_snap(&rcu_state.gp_seq_polled); } EXPORT_SYMBOL_GPL(get_state_synchronize_rcu); /** - * cond_synchronize_rcu - Conditionally wait for an RCU grace period + * get_state_synchronize_rcu_full - Snapshot RCU state, both normal and expedited + * @rgosp: location to place combined normal/expedited grace-period state * - * @oldstate: return value from earlier call to get_state_synchronize_rcu() + * Places the normal and expedited grace-period states in @rgosp. This + * state value can be passed to a later call to cond_synchronize_rcu_full() + * or poll_state_synchronize_rcu_full() to determine whether or not a + * grace period (whether normal or expedited) has elapsed in the meantime. + * The rcu_gp_oldstate structure takes up twice the memory of an unsigned + * long, but is guaranteed to see all grace periods. In contrast, the + * combined state occupies less memory, but can sometimes fail to take + * grace periods into account. + * + * This does not guarantee that the needed grace period will actually + * start. + */ +void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) +{ + struct rcu_node *rnp = rcu_get_root(); + + /* + * Any prior manipulation of RCU-protected data must happen + * before the loads from ->gp_seq and ->expedited_sequence. + */ + smp_mb(); /* ^^^ */ + rgosp->rgos_norm = rcu_seq_snap(&rnp->gp_seq); + rgosp->rgos_exp = rcu_seq_snap(&rcu_state.expedited_sequence); +} +EXPORT_SYMBOL_GPL(get_state_synchronize_rcu_full); + +/* + * Helper function for start_poll_synchronize_rcu() and + * start_poll_synchronize_rcu_full(). + */ +static void start_poll_synchronize_rcu_common(void) +{ + unsigned long flags; + bool needwake; + struct rcu_data *rdp; + struct rcu_node *rnp; + + lockdep_assert_irqs_enabled(); + local_irq_save(flags); + rdp = this_cpu_ptr(&rcu_data); + rnp = rdp->mynode; + raw_spin_lock_rcu_node(rnp); // irqs already disabled. + // Note it is possible for a grace period to have elapsed between + // the above call to get_state_synchronize_rcu() and the below call + // to rcu_seq_snap. This is OK, the worst that happens is that we + // get a grace period that no one needed. These accesses are ordered + // by smp_mb(), and we are accessing them in the opposite order + // from which they are updated at grace-period start, as required. + needwake = rcu_start_this_gp(rnp, rdp, rcu_seq_snap(&rcu_state.gp_seq)); + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + if (needwake) + rcu_gp_kthread_wake(); +} + +/** + * start_poll_synchronize_rcu - Snapshot and start RCU grace period + * + * Returns a cookie that is used by a later call to cond_synchronize_rcu() + * or poll_state_synchronize_rcu() to determine whether or not a full + * grace period has elapsed in the meantime. If the needed grace period + * is not already slated to start, notifies RCU core of the need for that + * grace period. + * + * Interrupts must be enabled for the case where it is necessary to awaken + * the grace-period kthread. + */ +unsigned long start_poll_synchronize_rcu(void) +{ + unsigned long gp_seq = get_state_synchronize_rcu(); + + start_poll_synchronize_rcu_common(); + return gp_seq; +} +EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu); + +/** + * start_poll_synchronize_rcu_full - Take a full snapshot and start RCU grace period + * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full() + * + * Places the normal and expedited grace-period states in *@rgos. This + * state value can be passed to a later call to cond_synchronize_rcu_full() + * or poll_state_synchronize_rcu_full() to determine whether or not a + * grace period (whether normal or expedited) has elapsed in the meantime. + * If the needed grace period is not already slated to start, notifies + * RCU core of the need for that grace period. + * + * Interrupts must be enabled for the case where it is necessary to awaken + * the grace-period kthread. + */ +void start_poll_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) +{ + get_state_synchronize_rcu_full(rgosp); + + start_poll_synchronize_rcu_common(); +} +EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_full); + +/** + * poll_state_synchronize_rcu - Has the specified RCU grace period completed? + * @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu() + * + * If a full RCU grace period has elapsed since the earlier call from + * which @oldstate was obtained, return @true, otherwise return @false. + * If @false is returned, it is the caller's responsibility to invoke this + * function later on until it does return @true. Alternatively, the caller + * can explicitly wait for a grace period, for example, by passing @oldstate + * to either cond_synchronize_rcu() or cond_synchronize_rcu_expedited() + * on the one hand or by directly invoking either synchronize_rcu() or + * synchronize_rcu_expedited() on the other. + * + * Yes, this function does not take counter wrap into account. + * But counter wrap is harmless. If the counter wraps, we have waited for + * more than a billion grace periods (and way more on a 64-bit system!). + * Those needing to keep old state values for very long time periods + * (many hours even on 32-bit systems) should check them occasionally and + * either refresh them or set a flag indicating that the grace period has + * completed. Alternatively, they can use get_completed_synchronize_rcu() + * to get a guaranteed-completed grace-period state. + * + * In addition, because oldstate compresses the grace-period state for + * both normal and expedited grace periods into a single unsigned long, + * it can miss a grace period when synchronize_rcu() runs concurrently + * with synchronize_rcu_expedited(). If this is unacceptable, please + * instead use the _full() variant of these polling APIs. + * + * This function provides the same memory-ordering guarantees that + * would be provided by a synchronize_rcu() that was invoked at the call + * to the function that provided @oldstate, and that returned at the end + * of this function. + */ +bool poll_state_synchronize_rcu(unsigned long oldstate) +{ + if (oldstate == RCU_GET_STATE_COMPLETED || + rcu_seq_done_exact(&rcu_state.gp_seq_polled, oldstate)) { + smp_mb(); /* Ensure GP ends before subsequent accesses. */ + return true; + } + return false; +} +EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu); + +/** + * poll_state_synchronize_rcu_full - Has the specified RCU grace period completed? + * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full() + * + * If a full RCU grace period has elapsed since the earlier call from + * which *rgosp was obtained, return @true, otherwise return @false. + * If @false is returned, it is the caller's responsibility to invoke this + * function later on until it does return @true. Alternatively, the caller + * can explicitly wait for a grace period, for example, by passing @rgosp + * to cond_synchronize_rcu() or by directly invoking synchronize_rcu(). + * + * Yes, this function does not take counter wrap into account. + * But counter wrap is harmless. If the counter wraps, we have waited + * for more than a billion grace periods (and way more on a 64-bit + * system!). Those needing to keep rcu_gp_oldstate values for very + * long time periods (many hours even on 32-bit systems) should check + * them occasionally and either refresh them or set a flag indicating + * that the grace period has completed. Alternatively, they can use + * get_completed_synchronize_rcu_full() to get a guaranteed-completed + * grace-period state. + * + * This function provides the same memory-ordering guarantees that would + * be provided by a synchronize_rcu() that was invoked at the call to + * the function that provided @rgosp, and that returned at the end of this + * function. And this guarantee requires that the root rcu_node structure's + * ->gp_seq field be checked instead of that of the rcu_state structure. + * The problem is that the just-ending grace-period's callbacks can be + * invoked between the time that the root rcu_node structure's ->gp_seq + * field is updated and the time that the rcu_state structure's ->gp_seq + * field is updated. Therefore, if a single synchronize_rcu() is to + * cause a subsequent poll_state_synchronize_rcu_full() to return @true, + * then the root rcu_node structure is the one that needs to be polled. + */ +bool poll_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) +{ + struct rcu_node *rnp = rcu_get_root(); + + smp_mb(); // Order against root rcu_node structure grace-period cleanup. + if (rgosp->rgos_norm == RCU_GET_STATE_COMPLETED || + rcu_seq_done_exact(&rnp->gp_seq, rgosp->rgos_norm) || + rgosp->rgos_exp == RCU_GET_STATE_COMPLETED || + rcu_seq_done_exact(&rcu_state.expedited_sequence, rgosp->rgos_exp)) { + smp_mb(); /* Ensure GP ends before subsequent accesses. */ + return true; + } + return false; +} +EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu_full); + +/** + * cond_synchronize_rcu - Conditionally wait for an RCU grace period + * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited() * * If a full RCU grace period has elapsed since the earlier call to - * get_state_synchronize_rcu(), just return. Otherwise, invoke - * synchronize_rcu() to wait for a full grace period. + * get_state_synchronize_rcu() or start_poll_synchronize_rcu(), just return. + * Otherwise, invoke synchronize_rcu() to wait for a full grace period. * - * Yes, this function does not take counter wrap into account. But - * counter wrap is harmless. If the counter wraps, we have waited for + * Yes, this function does not take counter wrap into account. + * But counter wrap is harmless. If the counter wraps, we have waited for * more than 2 billion grace periods (and way more on a 64-bit system!), - * so waiting for one additional grace period should be just fine. + * so waiting for a couple of additional grace periods should be just fine. + * + * This function provides the same memory-ordering guarantees that + * would be provided by a synchronize_rcu() that was invoked at the call + * to the function that provided @oldstate and that returned at the end + * of this function. */ void cond_synchronize_rcu(unsigned long oldstate) { - if (!rcu_seq_done(&rcu_state.gp_seq, oldstate)) + if (!poll_state_synchronize_rcu(oldstate)) synchronize_rcu(); - else - smp_mb(); /* Ensure GP ends before subsequent accesses. */ } EXPORT_SYMBOL_GPL(cond_synchronize_rcu); +/** + * cond_synchronize_rcu_full - Conditionally wait for an RCU grace period + * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full() + * + * If a full RCU grace period has elapsed since the call to + * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), + * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was + * obtained, just return. Otherwise, invoke synchronize_rcu() to wait + * for a full grace period. + * + * Yes, this function does not take counter wrap into account. + * But counter wrap is harmless. If the counter wraps, we have waited for + * more than 2 billion grace periods (and way more on a 64-bit system!), + * so waiting for a couple of additional grace periods should be just fine. + * + * This function provides the same memory-ordering guarantees that + * would be provided by a synchronize_rcu() that was invoked at the call + * to the function that provided @rgosp and that returned at the end of + * this function. + */ +void cond_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp) +{ + if (!poll_state_synchronize_rcu_full(rgosp)) + synchronize_rcu(); +} +EXPORT_SYMBOL_GPL(cond_synchronize_rcu_full); + /* * Check to see if there is any immediate RCU-related work to be done by * the current CPU, returning 1 if so and zero otherwise. The checks are @@ -3747,11 +3919,13 @@ static int rcu_pending(int user) struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; + lockdep_assert_irqs_disabled(); + /* Check for CPU stalls, if enabled. */ check_cpu_stall(rdp); /* Does this CPU need a deferred NOCB wakeup? */ - if (rcu_nocb_need_deferred_wakeup(rdp)) + if (rcu_nocb_need_deferred_wakeup(rdp, RCU_NOCB_WAKE)) return 1; /* Is this a nohz_full CPU in userspace or idle? (Ignore RCU if so.) */ @@ -3764,13 +3938,13 @@ static int rcu_pending(int user) return 1; /* Does this CPU have callbacks ready to invoke? */ - if (!rcu_segcblist_is_offloaded(&rdp->cblist) && + if (!rcu_rdp_is_offloaded(rdp) && rcu_segcblist_ready_cbs(&rdp->cblist)) return 1; /* Has RCU gone idle with this CPU needing another grace period? */ if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) && - !rcu_segcblist_is_offloaded(&rdp->cblist) && + !rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) return 1; @@ -3816,26 +3990,56 @@ static void rcu_barrier_callback(struct rcu_head *rhp) } /* - * Called with preemption disabled, and from cross-cpu IRQ context. + * If needed, entrain an rcu_barrier() callback on rdp->cblist. */ -static void rcu_barrier_func(void *cpu_in) +static void rcu_barrier_entrain(struct rcu_data *rdp) { - uintptr_t cpu = (uintptr_t)cpu_in; - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + unsigned long gseq = READ_ONCE(rcu_state.barrier_sequence); + unsigned long lseq = READ_ONCE(rdp->barrier_seq_snap); + bool wake_nocb = false; + bool was_alldone = false; + lockdep_assert_held(&rcu_state.barrier_lock); + if (rcu_seq_state(lseq) || !rcu_seq_state(gseq) || rcu_seq_ctr(lseq) != rcu_seq_ctr(gseq)) + return; rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence); rdp->barrier_head.func = rcu_barrier_callback; debug_rcu_head_queue(&rdp->barrier_head); rcu_nocb_lock(rdp); - WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies)); + /* + * Flush bypass and wakeup rcuog if we add callbacks to an empty regular + * queue. This way we don't wait for bypass timer that can reach seconds + * if it's fully lazy. + */ + was_alldone = rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_pend_cbs(&rdp->cblist); + WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false)); + wake_nocb = was_alldone && rcu_segcblist_pend_cbs(&rdp->cblist); if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) { atomic_inc(&rcu_state.barrier_cpu_count); } else { debug_rcu_head_unqueue(&rdp->barrier_head); - rcu_barrier_trace(TPS("IRQNQ"), -1, - rcu_state.barrier_sequence); + rcu_barrier_trace(TPS("IRQNQ"), -1, rcu_state.barrier_sequence); } rcu_nocb_unlock(rdp); + if (wake_nocb) + wake_nocb_gp(rdp, false); + smp_store_release(&rdp->barrier_seq_snap, gseq); +} + +/* + * Called with preemption disabled, and from cross-cpu IRQ context. + */ +static void rcu_barrier_handler(void *cpu_in) +{ + uintptr_t cpu = (uintptr_t)cpu_in; + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + + lockdep_assert_irqs_disabled(); + WARN_ON_ONCE(cpu != rdp->cpu); + WARN_ON_ONCE(cpu != smp_processor_id()); + raw_spin_lock(&rcu_state.barrier_lock); + rcu_barrier_entrain(rdp); + raw_spin_unlock(&rcu_state.barrier_lock); } /** @@ -3849,6 +4053,8 @@ static void rcu_barrier_func(void *cpu_in) void rcu_barrier(void) { uintptr_t cpu; + unsigned long flags; + unsigned long gseq; struct rcu_data *rdp; unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence); @@ -3859,15 +4065,16 @@ void rcu_barrier(void) /* Did someone else do our work for us? */ if (rcu_seq_done(&rcu_state.barrier_sequence, s)) { - rcu_barrier_trace(TPS("EarlyExit"), -1, - rcu_state.barrier_sequence); + rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_state.barrier_sequence); smp_mb(); /* caller's subsequent code after above check. */ mutex_unlock(&rcu_state.barrier_mutex); return; } /* Mark the start of the barrier operation. */ + raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags); rcu_seq_start(&rcu_state.barrier_sequence); + gseq = rcu_state.barrier_sequence; rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence); /* @@ -3879,7 +4086,7 @@ void rcu_barrier(void) */ init_completion(&rcu_state.barrier_completion); atomic_set(&rcu_state.barrier_cpu_count, 2); - get_online_cpus(); + raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags); /* * Force each CPU with callbacks to register a new callback. @@ -3888,29 +4095,31 @@ void rcu_barrier(void) */ for_each_possible_cpu(cpu) { rdp = per_cpu_ptr(&rcu_data, cpu); - if (cpu_is_offline(cpu) && - !rcu_segcblist_is_offloaded(&rdp->cblist)) +retry: + if (smp_load_acquire(&rdp->barrier_seq_snap) == gseq) continue; - if (rcu_segcblist_n_cbs(&rdp->cblist) && cpu_online(cpu)) { - rcu_barrier_trace(TPS("OnlineQ"), cpu, - rcu_state.barrier_sequence); - smp_call_function_single(cpu, rcu_barrier_func, (void *)cpu, 1); - } else if (rcu_segcblist_n_cbs(&rdp->cblist) && - cpu_is_offline(cpu)) { - rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, - rcu_state.barrier_sequence); - local_irq_disable(); - rcu_barrier_func((void *)cpu); - local_irq_enable(); - } else if (cpu_is_offline(cpu)) { - rcu_barrier_trace(TPS("OfflineNoCBNoQ"), cpu, - rcu_state.barrier_sequence); - } else { - rcu_barrier_trace(TPS("OnlineNQ"), cpu, - rcu_state.barrier_sequence); + raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags); + if (!rcu_segcblist_n_cbs(&rdp->cblist)) { + WRITE_ONCE(rdp->barrier_seq_snap, gseq); + raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags); + rcu_barrier_trace(TPS("NQ"), cpu, rcu_state.barrier_sequence); + continue; + } + if (!rcu_rdp_cpu_online(rdp)) { + rcu_barrier_entrain(rdp); + WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq); + raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags); + rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, rcu_state.barrier_sequence); + continue; + } + raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags); + if (smp_call_function_single(cpu, rcu_barrier_handler, (void *)cpu, 1)) { + schedule_timeout_uninterruptible(1); + goto retry; } + WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq); + rcu_barrier_trace(TPS("OnlineQ"), cpu, rcu_state.barrier_sequence); } - put_online_cpus(); /* * Now that we have an rcu_barrier_callback() callback on each @@ -3925,16 +4134,218 @@ void rcu_barrier(void) /* Mark the end of the barrier operation. */ rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence); rcu_seq_end(&rcu_state.barrier_sequence); + gseq = rcu_state.barrier_sequence; + for_each_possible_cpu(cpu) { + rdp = per_cpu_ptr(&rcu_data, cpu); + + WRITE_ONCE(rdp->barrier_seq_snap, gseq); + } /* Other rcu_barrier() invocations can now safely proceed. */ mutex_unlock(&rcu_state.barrier_mutex); } EXPORT_SYMBOL_GPL(rcu_barrier); +static unsigned long rcu_barrier_last_throttle; + +/** + * rcu_barrier_throttled - Do rcu_barrier(), but limit to one per second + * + * This can be thought of as guard rails around rcu_barrier() that + * permits unrestricted userspace use, at least assuming the hardware's + * try_cmpxchg() is robust. There will be at most one call per second to + * rcu_barrier() system-wide from use of this function, which means that + * callers might needlessly wait a second or three. + * + * This is intended for use by test suites to avoid OOM by flushing RCU + * callbacks from the previous test before starting the next. See the + * rcutree.do_rcu_barrier module parameter for more information. + * + * Why not simply make rcu_barrier() more scalable? That might be + * the eventual endpoint, but let's keep it simple for the time being. + * Note that the module parameter infrastructure serializes calls to a + * given .set() function, but should concurrent .set() invocation ever be + * possible, we are ready! + */ +static void rcu_barrier_throttled(void) +{ + unsigned long j = jiffies; + unsigned long old = READ_ONCE(rcu_barrier_last_throttle); + unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence); + + while (time_in_range(j, old, old + HZ / 16) || + !try_cmpxchg(&rcu_barrier_last_throttle, &old, j)) { + schedule_timeout_idle(HZ / 16); + if (rcu_seq_done(&rcu_state.barrier_sequence, s)) { + smp_mb(); /* caller's subsequent code after above check. */ + return; + } + j = jiffies; + old = READ_ONCE(rcu_barrier_last_throttle); + } + rcu_barrier(); +} + +/* + * Invoke rcu_barrier_throttled() when a rcutree.do_rcu_barrier + * request arrives. We insist on a true value to allow for possible + * future expansion. + */ +static int param_set_do_rcu_barrier(const char *val, const struct kernel_param *kp) +{ + bool b; + int ret; + + if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) + return -EAGAIN; + ret = kstrtobool(val, &b); + if (!ret && b) { + atomic_inc((atomic_t *)kp->arg); + rcu_barrier_throttled(); + atomic_dec((atomic_t *)kp->arg); + } + return ret; +} + +/* + * Output the number of outstanding rcutree.do_rcu_barrier requests. + */ +static int param_get_do_rcu_barrier(char *buffer, const struct kernel_param *kp) +{ + return sprintf(buffer, "%d\n", atomic_read((atomic_t *)kp->arg)); +} + +static const struct kernel_param_ops do_rcu_barrier_ops = { + .set = param_set_do_rcu_barrier, + .get = param_get_do_rcu_barrier, +}; +static atomic_t do_rcu_barrier; +module_param_cb(do_rcu_barrier, &do_rcu_barrier_ops, &do_rcu_barrier, 0644); + +/* + * Compute the mask of online CPUs for the specified rcu_node structure. + * This will not be stable unless the rcu_node structure's ->lock is + * held, but the bit corresponding to the current CPU will be stable + * in most contexts. + */ +static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp) +{ + return READ_ONCE(rnp->qsmaskinitnext); +} + +/* + * Is the CPU corresponding to the specified rcu_data structure online + * from RCU's perspective? This perspective is given by that structure's + * ->qsmaskinitnext field rather than by the global cpu_online_mask. + */ +static bool rcu_rdp_cpu_online(struct rcu_data *rdp) +{ + return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode)); +} + +bool rcu_cpu_online(int cpu) +{ + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + + return rcu_rdp_cpu_online(rdp); +} + +#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) + +/* + * Is the current CPU online as far as RCU is concerned? + * + * Disable preemption to avoid false positives that could otherwise + * happen due to the current CPU number being sampled, this task being + * preempted, its old CPU being taken offline, resuming on some other CPU, + * then determining that its old CPU is now offline. + * + * Disable checking if in an NMI handler because we cannot safely + * report errors from NMI handlers anyway. In addition, it is OK to use + * RCU on an offline processor during initial boot, hence the check for + * rcu_scheduler_fully_active. + */ +bool rcu_lockdep_current_cpu_online(void) +{ + struct rcu_data *rdp; + bool ret = false; + + if (in_nmi() || !rcu_scheduler_fully_active) + return true; + preempt_disable_notrace(); + rdp = this_cpu_ptr(&rcu_data); + /* + * Strictly, we care here about the case where the current CPU is + * in rcutree_report_cpu_starting() and thus has an excuse for rdp->grpmask + * not being up to date. So arch_spin_is_locked() might have a + * false positive if it's held by some *other* CPU, but that's + * OK because that just means a false *negative* on the warning. + */ + if (rcu_rdp_cpu_online(rdp) || arch_spin_is_locked(&rcu_state.ofl_lock)) + ret = true; + preempt_enable_notrace(); + return ret; +} +EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); + +#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */ + +// Has rcu_init() been invoked? This is used (for example) to determine +// whether spinlocks may be acquired safely. +static bool rcu_init_invoked(void) +{ + return !!rcu_state.n_online_cpus; +} + +/* + * All CPUs for the specified rcu_node structure have gone offline, + * and all tasks that were preempted within an RCU read-side critical + * section while running on one of those CPUs have since exited their RCU + * read-side critical section. Some other CPU is reporting this fact with + * the specified rcu_node structure's ->lock held and interrupts disabled. + * This function therefore goes up the tree of rcu_node structures, + * clearing the corresponding bits in the ->qsmaskinit fields. Note that + * the leaf rcu_node structure's ->qsmaskinit field has already been + * updated. + * + * This function does check that the specified rcu_node structure has + * all CPUs offline and no blocked tasks, so it is OK to invoke it + * prematurely. That said, invoking it after the fact will cost you + * a needless lock acquisition. So once it has done its work, don't + * invoke it again. + */ +static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf) +{ + long mask; + struct rcu_node *rnp = rnp_leaf; + + raw_lockdep_assert_held_rcu_node(rnp_leaf); + if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || + WARN_ON_ONCE(rnp_leaf->qsmaskinit) || + WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf))) + return; + for (;;) { + mask = rnp->grpmask; + rnp = rnp->parent; + if (!rnp) + break; + raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ + rnp->qsmaskinit &= ~mask; + /* Between grace periods, so better already be zero! */ + WARN_ON_ONCE(rnp->qsmask); + if (rnp->qsmaskinit) { + raw_spin_unlock_rcu_node(rnp); + /* irqs remain disabled. */ + return; + } + raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ + } +} + /* * Propagate ->qsinitmask bits up the rcu_node tree to account for the * first CPU in a given leaf rcu_node structure coming online. The caller - * must hold the corresponding leaf rcu_node ->lock with interrrupts + * must hold the corresponding leaf rcu_node ->lock with interrupts * disabled. */ static void rcu_init_new_rnp(struct rcu_node *rnp_leaf) @@ -3965,17 +4376,20 @@ static void rcu_init_new_rnp(struct rcu_node *rnp_leaf) static void __init rcu_boot_init_percpu_data(int cpu) { + struct context_tracking *ct = this_cpu_ptr(&context_tracking); struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); /* Set up local state, ensuring consistent view of global state. */ rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu); INIT_WORK(&rdp->strict_work, strict_work_handler); - WARN_ON_ONCE(rdp->dynticks_nesting != 1); - WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp))); + WARN_ON_ONCE(ct->dynticks_nesting != 1); + WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu))); + rdp->barrier_seq_snap = rcu_state.barrier_sequence; rdp->rcu_ofl_gp_seq = rcu_state.gp_seq; rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED; rdp->rcu_onl_gp_seq = rcu_state.gp_seq; rdp->rcu_onl_gp_flags = RCU_GP_CLEANED; + rdp->last_sched_clock = jiffies; rdp->cpu = cpu; rcu_boot_init_nocb_percpu_data(rdp); } @@ -3993,29 +4407,32 @@ rcu_boot_init_percpu_data(int cpu) int rcutree_prepare_cpu(unsigned int cpu) { unsigned long flags; + struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu); struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); struct rcu_node *rnp = rcu_get_root(); /* Set up local state, ensuring consistent view of global state. */ raw_spin_lock_irqsave_rcu_node(rnp, flags); rdp->qlen_last_fqs_check = 0; - rdp->n_force_qs_snap = rcu_state.n_force_qs; + rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs); rdp->blimit = blimit; - if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */ - !rcu_segcblist_is_offloaded(&rdp->cblist)) - rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */ - rdp->dynticks_nesting = 1; /* CPU not up, no tearing. */ - rcu_dynticks_eqs_online(); + ct->dynticks_nesting = 1; /* CPU not up, no tearing. */ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ /* + * Only non-NOCB CPUs that didn't have early-boot callbacks need to be + * (re-)initialized. + */ + if (!rcu_segcblist_is_enabled(&rdp->cblist)) + rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */ + + /* * Add CPU to leaf rcu_node pending-online bitmask. Any needed * propagation up the rcu_node tree will happen at the beginning * of the next grace period. */ rnp = rdp->mynode; raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ - rdp->beenonline = true; /* We have now been online. */ rdp->gp_seq = READ_ONCE(rnp->gp_seq); rdp->gp_seq_needed = rdp->gp_seq; rdp->cpu_no_qs.b.norm = true; @@ -4025,7 +4442,7 @@ int rcutree_prepare_cpu(unsigned int cpu) rdp->rcu_iw_gp_seq = rdp->gp_seq - 1; trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl")); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - rcu_prepare_kthreads(cpu); + rcu_spawn_one_boost_kthread(rnp); rcu_spawn_cpu_nocb_kthread(cpu); WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1); @@ -4043,6 +4460,16 @@ static void rcutree_affinity_setting(unsigned int cpu, int outgoing) } /* + * Has the specified (known valid) CPU ever been fully online? + */ +bool rcu_cpu_beenfullyonline(int cpu) +{ + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + + return smp_load_acquire(&rdp->beenonline); +} + +/* * Near the end of the CPU-online process. Pretty much all services * enabled, and the CPU is now very much alive. */ @@ -4068,29 +4495,6 @@ int rcutree_online_cpu(unsigned int cpu) } /* - * Near the beginning of the process. The CPU is still very much alive - * with pretty much all services enabled. - */ -int rcutree_offline_cpu(unsigned int cpu) -{ - unsigned long flags; - struct rcu_data *rdp; - struct rcu_node *rnp; - - rdp = per_cpu_ptr(&rcu_data, cpu); - rnp = rdp->mynode; - raw_spin_lock_irqsave_rcu_node(rnp, flags); - rnp->ffmask &= ~rdp->grpmask; - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - - rcutree_affinity_setting(cpu, cpu); - - // nohz_full CPUs need the tick for stop-machine to work quickly - tick_dep_set(TICK_DEP_BIT_RCU); - return 0; -} - -/* * Mark the specified CPU as being online so that subsequent grace periods * (both expedited and normal) will wait on it. Note that this means that * incoming CPUs are not allowed to use RCU read-side critical sections @@ -4100,15 +4504,18 @@ int rcutree_offline_cpu(unsigned int cpu) * Note that this function is special in that it is invoked directly * from the incoming CPU rather than from the cpuhp_step mechanism. * This is because this function must be invoked at a precise location. + * This incoming CPU must not have enabled interrupts yet. + * + * This mirrors the effects of rcutree_report_cpu_dead(). */ -void rcu_cpu_starting(unsigned int cpu) +void rcutree_report_cpu_starting(unsigned int cpu) { - unsigned long flags; unsigned long mask; struct rcu_data *rdp; struct rcu_node *rnp; bool newcpu; + lockdep_assert_irqs_disabled(); rdp = per_cpu_ptr(&rcu_data, cpu); if (rdp->cpu_started) return; @@ -4116,11 +4523,12 @@ void rcu_cpu_starting(unsigned int cpu) rnp = rdp->mynode; mask = rdp->grpmask; - WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1); - WARN_ON_ONCE(!(rnp->ofl_seq & 0x1)); - smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier(). - raw_spin_lock_irqsave_rcu_node(rnp, flags); + arch_spin_lock(&rcu_state.ofl_lock); + rcu_dynticks_eqs_online(); + raw_spin_lock(&rcu_state.barrier_lock); + raw_spin_lock_rcu_node(rnp); WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask); + raw_spin_unlock(&rcu_state.barrier_lock); newcpu = !(rnp->expmaskinitnext & mask); rnp->expmaskinitnext |= mask; /* Allow lockless access for expedited grace periods. */ @@ -4132,15 +4540,18 @@ void rcu_cpu_starting(unsigned int cpu) /* An incoming CPU should never be blocking a grace period. */ if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */ + /* rcu_report_qs_rnp() *really* wants some flags to restore */ + unsigned long flags; + + local_irq_save(flags); rcu_disable_urgency_upon_qs(rdp); /* Report QS -after- changing ->qsmaskinitnext! */ rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); } else { - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + raw_spin_unlock_rcu_node(rnp); } - smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier(). - WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1); - WARN_ON_ONCE(rnp->ofl_seq & 0x1); + arch_spin_unlock(&rcu_state.ofl_lock); + smp_store_release(&rdp->beenonline, true); smp_mb(); /* Ensure RCU read-side usage follows above initialization. */ } @@ -4151,41 +4562,41 @@ void rcu_cpu_starting(unsigned int cpu) * Note that this function is special in that it is invoked directly * from the outgoing CPU rather than from the cpuhp_step mechanism. * This is because this function must be invoked at a precise location. + * + * This mirrors the effect of rcutree_report_cpu_starting(). */ -void rcu_report_dead(unsigned int cpu) +void rcutree_report_cpu_dead(void) { unsigned long flags; unsigned long mask; - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ - /* QS for any half-done expedited grace period. */ - preempt_disable(); - rcu_report_exp_rdp(this_cpu_ptr(&rcu_data)); - preempt_enable(); + /* + * IRQS must be disabled from now on and until the CPU dies, or an interrupt + * may introduce a new READ-side while it is actually off the QS masks. + */ + lockdep_assert_irqs_disabled(); + // Do any dangling deferred wakeups. + do_nocb_deferred_wakeup(rdp); + rcu_preempt_deferred_qs(current); /* Remove outgoing CPU from mask in the leaf rcu_node structure. */ mask = rdp->grpmask; - WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1); - WARN_ON_ONCE(!(rnp->ofl_seq & 0x1)); - smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier(). - raw_spin_lock(&rcu_state.ofl_lock); + arch_spin_lock(&rcu_state.ofl_lock); raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */ rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq); rdp->rcu_ofl_gp_flags = READ_ONCE(rcu_state.gp_flags); if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */ /* Report quiescent state -before- changing ->qsmaskinitnext! */ + rcu_disable_urgency_upon_qs(rdp); rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); raw_spin_lock_irqsave_rcu_node(rnp, flags); } WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - raw_spin_unlock(&rcu_state.ofl_lock); - smp_mb(); // Pair with rcu_gp_cleanup()'s ->ofl_seq barrier(). - WRITE_ONCE(rnp->ofl_seq, rnp->ofl_seq + 1); - WARN_ON_ONCE(rnp->ofl_seq & 0x1); - + arch_spin_unlock(&rcu_state.ofl_lock); rdp->cpu_started = false; } @@ -4203,25 +4614,28 @@ void rcutree_migrate_callbacks(int cpu) struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); bool needwake; - if (rcu_segcblist_is_offloaded(&rdp->cblist) || + if (rcu_rdp_is_offloaded(rdp) || rcu_segcblist_empty(&rdp->cblist)) return; /* No callbacks to migrate. */ - local_irq_save(flags); + raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags); + WARN_ON_ONCE(rcu_rdp_cpu_online(rdp)); + rcu_barrier_entrain(rdp); my_rdp = this_cpu_ptr(&rcu_data); my_rnp = my_rdp->mynode; rcu_nocb_lock(my_rdp); /* irqs already disabled. */ - WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies)); + WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies, false)); raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */ /* Leverage recent GPs and set GP for new callbacks. */ needwake = rcu_advance_cbs(my_rnp, rdp) || rcu_advance_cbs(my_rnp, my_rdp); rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist); + raw_spin_unlock(&rcu_state.barrier_lock); /* irqs remain disabled. */ needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp); rcu_segcblist_disable(&rdp->cblist); - WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != - !rcu_segcblist_n_cbs(&my_rdp->cblist)); - if (rcu_segcblist_is_offloaded(&my_rdp->cblist)) { + WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist)); + check_cb_ovld_locked(my_rdp, my_rnp); + if (rcu_rdp_is_offloaded(my_rdp)) { raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */ __call_rcu_nocb_wake(my_rdp, true, flags); } else { @@ -4237,7 +4651,60 @@ void rcutree_migrate_callbacks(int cpu) cpu, rcu_segcblist_n_cbs(&rdp->cblist), rcu_segcblist_first_cb(&rdp->cblist)); } -#endif + +/* + * The CPU has been completely removed, and some other CPU is reporting + * this fact from process context. Do the remainder of the cleanup. + * There can only be one CPU hotplug operation at a time, so no need for + * explicit locking. + */ +int rcutree_dead_cpu(unsigned int cpu) +{ + WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1); + // Stop-machine done, so allow nohz_full to disable tick. + tick_dep_clear(TICK_DEP_BIT_RCU); + return 0; +} + +/* + * Near the end of the offline process. Trace the fact that this CPU + * is going offline. + */ +int rcutree_dying_cpu(unsigned int cpu) +{ + bool blkd; + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + struct rcu_node *rnp = rdp->mynode; + + blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask); + trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), + blkd ? TPS("cpuofl-bgp") : TPS("cpuofl")); + return 0; +} + +/* + * Near the beginning of the process. The CPU is still very much alive + * with pretty much all services enabled. + */ +int rcutree_offline_cpu(unsigned int cpu) +{ + unsigned long flags; + struct rcu_data *rdp; + struct rcu_node *rnp; + + rdp = per_cpu_ptr(&rcu_data, cpu); + rnp = rdp->mynode; + raw_spin_lock_irqsave_rcu_node(rnp, flags); + rnp->ffmask &= ~rdp->grpmask; + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + + rcutree_affinity_setting(cpu, cpu); + + // nohz_full CPUs need the tick for stop-machine to work quickly + tick_dep_set(TICK_DEP_BIT_RCU); + return 0; +} +#endif /* #ifdef CONFIG_HOTPLUG_CPU */ /* * On non-huge systems, use expedited RCU grace periods to make suspend @@ -4249,11 +4716,13 @@ static int rcu_pm_notify(struct notifier_block *self, switch (action) { case PM_HIBERNATION_PREPARE: case PM_SUSPEND_PREPARE: + rcu_async_hurry(); rcu_expedite_gp(); break; case PM_POST_HIBERNATION: case PM_POST_SUSPEND: rcu_unexpedite_gp(); + rcu_async_relax(); break; default: break; @@ -4261,31 +4730,61 @@ static int rcu_pm_notify(struct notifier_block *self, return NOTIFY_OK; } +#ifdef CONFIG_RCU_EXP_KTHREAD +struct kthread_worker *rcu_exp_gp_kworker; +struct kthread_worker *rcu_exp_par_gp_kworker; + +static void __init rcu_start_exp_gp_kworkers(void) +{ + const char *par_gp_kworker_name = "rcu_exp_par_gp_kthread_worker"; + const char *gp_kworker_name = "rcu_exp_gp_kthread_worker"; + struct sched_param param = { .sched_priority = kthread_prio }; + + rcu_exp_gp_kworker = kthread_create_worker(0, gp_kworker_name); + if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) { + pr_err("Failed to create %s!\n", gp_kworker_name); + return; + } + + rcu_exp_par_gp_kworker = kthread_create_worker(0, par_gp_kworker_name); + if (IS_ERR_OR_NULL(rcu_exp_par_gp_kworker)) { + pr_err("Failed to create %s!\n", par_gp_kworker_name); + kthread_destroy_worker(rcu_exp_gp_kworker); + return; + } + + sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, ¶m); + sched_setscheduler_nocheck(rcu_exp_par_gp_kworker->task, SCHED_FIFO, + ¶m); +} + +static inline void rcu_alloc_par_gp_wq(void) +{ +} +#else /* !CONFIG_RCU_EXP_KTHREAD */ +struct workqueue_struct *rcu_par_gp_wq; + +static void __init rcu_start_exp_gp_kworkers(void) +{ +} + +static inline void rcu_alloc_par_gp_wq(void) +{ + rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0); + WARN_ON(!rcu_par_gp_wq); +} +#endif /* CONFIG_RCU_EXP_KTHREAD */ + /* * Spawn the kthreads that handle RCU's grace periods. */ static int __init rcu_spawn_gp_kthread(void) { unsigned long flags; - int kthread_prio_in = kthread_prio; struct rcu_node *rnp; struct sched_param sp; struct task_struct *t; - - /* Force priority into range. */ - if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2 - && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)) - kthread_prio = 2; - else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1) - kthread_prio = 1; - else if (kthread_prio < 0) - kthread_prio = 0; - else if (kthread_prio > 99) - kthread_prio = 99; - - if (kthread_prio != kthread_prio_in) - pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n", - kthread_prio, kthread_prio_in); + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); rcu_scheduler_fully_active = 1; t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name); @@ -4303,8 +4802,17 @@ static int __init rcu_spawn_gp_kthread(void) smp_store_release(&rcu_state.gp_kthread, t); /* ^^^ */ raw_spin_unlock_irqrestore_rcu_node(rnp, flags); wake_up_process(t); - rcu_spawn_nocb_kthreads(); - rcu_spawn_boost_kthreads(); + /* This is a pre-SMP initcall, we expect a single CPU */ + WARN_ON(num_online_cpus() > 1); + /* + * Those kthreads couldn't be created on rcu_init() -> rcutree_prepare_cpu() + * due to rcu_scheduler_fully_active. + */ + rcu_spawn_cpu_nocb_kthread(smp_processor_id()); + rcu_spawn_one_boost_kthread(rdp->mynode); + rcu_spawn_core_kthreads(); + /* Create kthread worker for expedited GPs */ + rcu_start_exp_gp_kworkers(); return 0; } early_initcall(rcu_spawn_gp_kthread); @@ -4321,9 +4829,20 @@ early_initcall(rcu_spawn_gp_kthread); */ void rcu_scheduler_starting(void) { + unsigned long flags; + struct rcu_node *rnp; + WARN_ON(num_online_cpus() != 1); WARN_ON(nr_context_switches() > 0); rcu_test_sync_prims(); + + // Fix up the ->gp_seq counters. + local_irq_save(flags); + rcu_for_each_node_breadth_first(rnp) + rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq; + local_irq_restore(flags); + + // Switch out of early boot mode. rcu_scheduler_active = RCU_SCHEDULER_INIT; rcu_test_sync_prims(); } @@ -4396,6 +4915,10 @@ static void __init rcu_init_one(void) init_waitqueue_head(&rnp->exp_wq[2]); init_waitqueue_head(&rnp->exp_wq[3]); spin_lock_init(&rnp->exp_lock); + mutex_init(&rnp->boost_kthread_mutex); + raw_spin_lock_init(&rnp->exp_poll_lock); + rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED; + INIT_WORK(&rnp->exp_poll_wq, sync_rcu_do_polled_gp); } } @@ -4411,15 +4934,51 @@ static void __init rcu_init_one(void) } /* + * Force priority from the kernel command-line into range. + */ +static void __init sanitize_kthread_prio(void) +{ + int kthread_prio_in = kthread_prio; + + if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2 + && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)) + kthread_prio = 2; + else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1) + kthread_prio = 1; + else if (kthread_prio < 0) + kthread_prio = 0; + else if (kthread_prio > 99) + kthread_prio = 99; + + if (kthread_prio != kthread_prio_in) + pr_alert("%s: Limited prio to %d from %d\n", + __func__, kthread_prio, kthread_prio_in); +} + +/* * Compute the rcu_node tree geometry from kernel parameters. This cannot * replace the definitions in tree.h because those are needed to size * the ->node array in the rcu_state structure. */ -static void __init rcu_init_geometry(void) +void rcu_init_geometry(void) { ulong d; int i; + static unsigned long old_nr_cpu_ids; int rcu_capacity[RCU_NUM_LVLS]; + static bool initialized; + + if (initialized) { + /* + * Warn if setup_nr_cpu_ids() had not yet been invoked, + * unless nr_cpus_ids == NR_CPUS, in which case who cares? + */ + WARN_ON_ONCE(old_nr_cpu_ids != nr_cpu_ids); + return; + } + + old_nr_cpu_ids = nr_cpu_ids; + initialized = true; /* * Initialize any unspecified boot parameters. @@ -4513,12 +5072,24 @@ static void __init rcu_dump_rcu_node_tree(void) } struct workqueue_struct *rcu_gp_wq; -struct workqueue_struct *rcu_par_gp_wq; static void __init kfree_rcu_batch_init(void) { int cpu; - int i; + int i, j; + struct shrinker *kfree_rcu_shrinker; + + /* Clamp it to [0:100] seconds interval. */ + if (rcu_delay_page_cache_fill_msec < 0 || + rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) { + + rcu_delay_page_cache_fill_msec = + clamp(rcu_delay_page_cache_fill_msec, 0, + (int) (100 * MSEC_PER_SEC)); + + pr_info("Adjusting rcutree.rcu_delay_page_cache_fill_msec to %d ms.\n", + rcu_delay_page_cache_fill_msec); + } for_each_possible_cpu(cpu) { struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); @@ -4526,24 +5097,40 @@ static void __init kfree_rcu_batch_init(void) for (i = 0; i < KFREE_N_BATCHES; i++) { INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work); krcp->krw_arr[i].krcp = krcp; + + for (j = 0; j < FREE_N_CHANNELS; j++) + INIT_LIST_HEAD(&krcp->krw_arr[i].bulk_head_free[j]); } + for (i = 0; i < FREE_N_CHANNELS; i++) + INIT_LIST_HEAD(&krcp->bulk_head[i]); + INIT_DELAYED_WORK(&krcp->monitor_work, kfree_rcu_monitor); - INIT_WORK(&krcp->page_cache_work, fill_page_cache_func); + INIT_DELAYED_WORK(&krcp->page_cache_work, fill_page_cache_func); krcp->initialized = true; } - if (register_shrinker(&kfree_rcu_shrinker)) - pr_err("Failed to register kfree_rcu() shrinker!\n"); + + kfree_rcu_shrinker = shrinker_alloc(0, "rcu-kfree"); + if (!kfree_rcu_shrinker) { + pr_err("Failed to allocate kfree_rcu() shrinker!\n"); + return; + } + + kfree_rcu_shrinker->count_objects = kfree_rcu_shrink_count; + kfree_rcu_shrinker->scan_objects = kfree_rcu_shrink_scan; + + shrinker_register(kfree_rcu_shrinker); } void __init rcu_init(void) { - int cpu; + int cpu = smp_processor_id(); rcu_early_boot_tests(); kfree_rcu_batch_init(); rcu_bootup_announce(); + sanitize_kthread_prio(); rcu_init_geometry(); rcu_init_one(); if (dump_tree) @@ -4557,18 +5144,15 @@ void __init rcu_init(void) * or the scheduler are operational. */ pm_notifier(rcu_pm_notify, 0); - for_each_online_cpu(cpu) { - rcutree_prepare_cpu(cpu); - rcu_cpu_starting(cpu); - rcutree_online_cpu(cpu); - } + WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot. + rcutree_prepare_cpu(cpu); + rcutree_report_cpu_starting(cpu); + rcutree_online_cpu(cpu); - /* Create workqueue for expedited GPs and for Tree SRCU. */ + /* Create workqueue for Tree SRCU and for expedited GPs. */ rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0); WARN_ON(!rcu_gp_wq); - rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0); - WARN_ON(!rcu_par_gp_wq); - srcu_init(); + rcu_alloc_par_gp_wq(); /* Fill in default value for rcutree.qovld boot parameter. */ /* -After- the rcu_node ->lock fields are initialized! */ @@ -4576,8 +5160,14 @@ void __init rcu_init(void) qovld_calc = DEFAULT_RCU_QOVLD_MULT * qhimark; else qovld_calc = qovld; + + // Kick-start in case any polled grace periods started early. + (void)start_poll_synchronize_rcu_expedited(); + + rcu_test_sync_prims(); } #include "tree_stall.h" #include "tree_exp.h" +#include "tree_nocb.h" #include "tree_plugin.h" diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index 7708ed161f4a..e9821a8422db 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -10,6 +10,7 @@ */ #include <linux/cache.h> +#include <linux/kthread.h> #include <linux/spinlock.h> #include <linux/rtmutex.h> #include <linux/threads.h> @@ -23,7 +24,11 @@ /* Communicate arguments to a workqueue handler. */ struct rcu_exp_work { unsigned long rew_s; +#ifdef CONFIG_RCU_EXP_KTHREAD + struct kthread_work rew_work; +#else struct work_struct rew_work; +#endif /* CONFIG_RCU_EXP_KTHREAD */ }; /* RCU's kthread states for tracing. */ @@ -56,8 +61,6 @@ struct rcu_node { /* Initialized from ->qsmaskinitnext at the */ /* beginning of each grace period. */ unsigned long qsmaskinitnext; - unsigned long ofl_seq; /* CPU-hotplug operation sequence count. */ - /* Online CPUs for next grace period. */ unsigned long expmask; /* CPUs or groups that need to check in */ /* to allow the current expedited GP */ /* to complete. */ @@ -110,11 +113,15 @@ struct rcu_node { /* side effect, not as a lock. */ unsigned long boost_time; /* When to start boosting (jiffies). */ + struct mutex boost_kthread_mutex; + /* Exclusion for thread spawning and affinity */ + /* manipulation. */ struct task_struct *boost_kthread_task; /* kthread that takes care of priority */ /* boosting for this rcu_node structure. */ unsigned int boost_kthread_status; /* State of boost_kthread_task for tracing. */ + unsigned long n_boosts; /* Number of boosts for this rcu_node structure. */ #ifdef CONFIG_RCU_NOCB_CPU struct swait_queue_head nocb_gp_wq[2]; /* Place for rcu_nocb_kthread() to wait GP. */ @@ -126,6 +133,10 @@ struct rcu_node { wait_queue_head_t exp_wq[4]; struct rcu_exp_work rew; bool exp_need_flush; /* Need to flush workitem? */ + raw_spinlock_t exp_poll_lock; + /* Lock and data for polled expedited grace periods. */ + unsigned long exp_seq_poll_rq; + struct work_struct exp_poll_wq; } ____cacheline_internodealigned_in_smp; /* @@ -147,16 +158,32 @@ union rcu_noqs { u16 s; /* Set of bits, aggregate OR here. */ }; +/* + * Record the snapshot of the core stats at half of the first RCU stall timeout. + * The member gp_seq is used to ensure that all members are updated only once + * during the sampling period. The snapshot is taken only if this gp_seq is not + * equal to rdp->gp_seq. + */ +struct rcu_snap_record { + unsigned long gp_seq; /* Track rdp->gp_seq counter */ + u64 cputime_irq; /* Accumulated cputime of hard irqs */ + u64 cputime_softirq;/* Accumulated cputime of soft irqs */ + u64 cputime_system; /* Accumulated cputime of kernel tasks */ + unsigned long nr_hardirqs; /* Accumulated number of hard irqs */ + unsigned int nr_softirqs; /* Accumulated number of soft irqs */ + unsigned long long nr_csw; /* Accumulated number of task switches */ + unsigned long jiffies; /* Track jiffies value */ +}; + /* Per-CPU data for read-copy update. */ struct rcu_data { /* 1) quiescent-state and grace-period handling : */ unsigned long gp_seq; /* Track rsp->gp_seq counter. */ unsigned long gp_seq_needed; /* Track furthest future GP request. */ union rcu_noqs cpu_no_qs; /* No QSes yet for this CPU. */ - bool core_needs_qs; /* Core waits for quiesc state. */ + bool core_needs_qs; /* Core waits for quiescent state. */ bool beenonline; /* CPU online at least once. */ bool gpwrap; /* Possible ->gp_seq wrap. */ - bool exp_deferred_qs; /* This CPU awaiting a deferred QS? */ bool cpu_started; /* RCU watching this onlining CPU. */ struct rcu_node *mynode; /* This CPU's leaf of hierarchy */ unsigned long grpmask; /* Mask to apply to leaf qsmask. */ @@ -181,32 +208,28 @@ struct rcu_data { /* 3) dynticks interface. */ int dynticks_snap; /* Per-GP tracking for dynticks. */ - long dynticks_nesting; /* Track process nesting level. */ - long dynticks_nmi_nesting; /* Track irq/NMI nesting level. */ - atomic_t dynticks; /* Even value for idle, else odd. */ bool rcu_need_heavy_qs; /* GP old, so heavy quiescent state! */ bool rcu_urgent_qs; /* GP old need light quiescent state. */ bool rcu_forced_tick; /* Forced tick to provide QS. */ bool rcu_forced_tick_exp; /* ... provide QS to expedited GP. */ -#ifdef CONFIG_RCU_FAST_NO_HZ - unsigned long last_accelerate; /* Last jiffy CBs were accelerated. */ - unsigned long last_advance_all; /* Last jiffy CBs were all advanced. */ - int tick_nohz_enabled_snap; /* Previously seen value from sysfs. */ -#endif /* #ifdef CONFIG_RCU_FAST_NO_HZ */ /* 4) rcu_barrier(), OOM callbacks, and expediting. */ + unsigned long barrier_seq_snap; /* Snap of rcu_state.barrier_sequence. */ struct rcu_head barrier_head; int exp_dynticks_snap; /* Double-check need for IPI. */ /* 5) Callback offloading. */ #ifdef CONFIG_RCU_NOCB_CPU struct swait_queue_head nocb_cb_wq; /* For nocb kthreads to sleep on. */ + struct swait_queue_head nocb_state_wq; /* For offloading state changes */ struct task_struct *nocb_gp_kthread; raw_spinlock_t nocb_lock; /* Guard following pair of fields. */ atomic_t nocb_lock_contended; /* Contention experienced. */ int nocb_defer_wakeup; /* Defer wakeup of nocb_kthread. */ struct timer_list nocb_timer; /* Enforce finite deferral. */ unsigned long nocb_gp_adv_time; /* Last call_rcu() CB adv (jiffies). */ + struct mutex nocb_gp_kthread_mutex; /* Exclusion for nocb gp kthread */ + /* spawning */ /* The following fields are used by call_rcu, hence own cacheline. */ raw_spinlock_t nocb_bypass_lock ____cacheline_internodealigned_in_smp; @@ -217,7 +240,6 @@ struct rcu_data { /* The following fields are used by GP kthread, hence own cacheline. */ raw_spinlock_t nocb_gp_lock ____cacheline_internodealigned_in_smp; - struct timer_list nocb_bypass_timer; /* Force nocb_bypass flush. */ u8 nocb_gp_sleep; /* Is the nocb GP thread asleep? */ u8 nocb_gp_bypass; /* Found a bypass on last scan? */ u8 nocb_gp_gp; /* GP to wait for on last scan? */ @@ -226,8 +248,12 @@ struct rcu_data { struct swait_queue_head nocb_gp_wq; /* For nocb kthreads to sleep on. */ bool nocb_cb_sleep; /* Is the nocb CB thread asleep? */ struct task_struct *nocb_cb_kthread; - struct rcu_data *nocb_next_cb_rdp; - /* Next rcu_data in wakeup chain. */ + struct list_head nocb_head_rdp; /* + * Head of rcu_data list in wakeup chain, + * if rdp_gp. + */ + struct list_head nocb_entry_rdp; /* rcu_data node in wakeup chain. */ + struct rcu_data *nocb_toggling_rdp; /* rdp queued for (de-)offloading */ /* The following fields are used by CB kthread, hence new cacheline. */ struct rcu_data *nocb_gp_rdp ____cacheline_internodealigned_in_smp; @@ -239,6 +265,7 @@ struct rcu_data { /* rcuc per-CPU kthread or NULL. */ unsigned int rcu_cpu_kthread_status; char rcu_cpu_has_work; + unsigned long rcuc_activity; /* 7) Diagnostic data, including RCU CPU stall warnings. */ unsigned int softirq_snap; /* Snapshot of softirq activity. */ @@ -251,14 +278,20 @@ struct rcu_data { unsigned long rcu_onl_gp_seq; /* ->gp_seq at last online. */ short rcu_onl_gp_flags; /* ->gp_flags at last online. */ unsigned long last_fqs_resched; /* Time of last rcu_resched(). */ + unsigned long last_sched_clock; /* Jiffies of last rcu_sched_clock_irq(). */ + struct rcu_snap_record snap_record; /* Snapshot of core stats at half of */ + /* the first RCU stall timeout */ + long lazy_len; /* Length of buffered lazy callbacks. */ int cpu; }; /* Values for nocb_defer_wakeup field in struct rcu_data. */ #define RCU_NOCB_WAKE_NOT 0 -#define RCU_NOCB_WAKE 1 -#define RCU_NOCB_WAKE_FORCE 2 +#define RCU_NOCB_WAKE_BYPASS 1 +#define RCU_NOCB_WAKE_LAZY 2 +#define RCU_NOCB_WAKE 3 +#define RCU_NOCB_WAKE_FORCE 4 #define RCU_JIFFIES_TILL_FORCE_QS (1 + (HZ > 250) + (HZ > 500)) /* For jiffies_till_first_fqs and */ @@ -303,9 +336,8 @@ struct rcu_state { /* The following fields are guarded by the root rcu_node's lock. */ - u8 boost ____cacheline_internodealigned_in_smp; - /* Subject to priority boost. */ - unsigned long gp_seq; /* Grace-period sequence #. */ + unsigned long gp_seq ____cacheline_internodealigned_in_smp; + /* Grace-period sequence #. */ unsigned long gp_max; /* Maximum GP duration in */ /* jiffies. */ struct task_struct *gp_kthread; /* Task for grace periods. */ @@ -314,6 +346,9 @@ struct rcu_state { short gp_state; /* GP kthread sleep state. */ unsigned long gp_wake_time; /* Last GP kthread wake. */ unsigned long gp_wake_seq; /* ->gp_seq at ^^^. */ + unsigned long gp_seq_polled; /* GP seq for polled API. */ + unsigned long gp_seq_polled_snap; /* ->gp_seq_polled at normal GP start. */ + unsigned long gp_seq_polled_exp_snap; /* ->gp_seq_polled at expedited GP start. */ /* End of fields guarded by root rcu_node's lock. */ @@ -324,6 +359,8 @@ struct rcu_state { /* rcu_barrier(). */ /* End of fields guarded by barrier_mutex. */ + raw_spinlock_t barrier_lock; /* Protects ->barrier_seq_snap. */ + struct mutex exp_mutex; /* Serialize expedited GP. */ struct mutex exp_wake_mutex; /* Serialize wakeup. */ unsigned long expedited_sequence; /* Take a ticket. */ @@ -349,6 +386,10 @@ struct rcu_state { /* in jiffies. */ unsigned long jiffies_stall; /* Time at which to check */ /* for CPU stalls. */ + int nr_fqs_jiffies_stall; /* Number of fqs loops after + * which read jiffies and set + * jiffies_stall. Stall + * warnings disabled if !0. */ unsigned long jiffies_resched; /* Time at which to resched */ /* a reluctant CPU. */ unsigned long n_force_qs_gpstart; /* Snapshot of n_force_qs at */ @@ -356,9 +397,10 @@ struct rcu_state { const char *name; /* Name of structure. */ char abbr; /* Abbreviated name. */ - raw_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp; + arch_spinlock_t ofl_lock ____cacheline_internodealigned_in_smp; /* Synchronize offline with */ /* GP pre-initialization. */ + int nocb_is_setup; /* nocb is setup from boot */ }; /* Values for rcu_state structure's gp_flags field. */ @@ -413,30 +455,27 @@ static void rcu_flavor_sched_clock_irq(int user); static void dump_blkd_tasks(struct rcu_node *rnp, int ncheck); static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags); static void rcu_preempt_boost_start_gp(struct rcu_node *rnp); -static bool rcu_is_callbacks_kthread(void); +static bool rcu_is_callbacks_kthread(struct rcu_data *rdp); static void rcu_cpu_kthread_setup(unsigned int cpu); -static void __init rcu_spawn_boost_kthreads(void); -static void rcu_prepare_kthreads(int cpu); -static void rcu_cleanup_after_idle(void); -static void rcu_prepare_for_idle(void); +static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp); static bool rcu_preempt_has_tasks(struct rcu_node *rnp); static bool rcu_preempt_need_deferred_qs(struct task_struct *t); -static void rcu_preempt_deferred_qs(struct task_struct *t); static void zero_cpu_stall_ticks(struct rcu_data *rdp); static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp); static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq); static void rcu_init_one_nocb(struct rcu_node *rnp); +static bool wake_nocb_gp(struct rcu_data *rdp, bool force); static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - unsigned long j); + unsigned long j, bool lazy); static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - bool *was_alldone, unsigned long flags); + bool *was_alldone, unsigned long flags, + bool lazy); static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty, unsigned long flags); -static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp); -static void do_nocb_deferred_wakeup(struct rcu_data *rdp); +static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level); +static bool do_nocb_deferred_wakeup(struct rcu_data *rdp); static void rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp); static void rcu_spawn_cpu_nocb_kthread(int cpu); -static void __init rcu_spawn_nocb_kthreads(void); static void show_rcu_nocb_state(struct rcu_data *rdp); static void rcu_nocb_lock(struct rcu_data *rdp); static void rcu_nocb_unlock(struct rcu_data *rdp); @@ -445,12 +484,16 @@ static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp); #ifdef CONFIG_RCU_NOCB_CPU static void __init rcu_organize_nocb_kthreads(void); -#define rcu_nocb_lock_irqsave(rdp, flags) \ -do { \ - if (!rcu_segcblist_is_offloaded(&(rdp)->cblist)) \ - local_irq_save(flags); \ - else \ - raw_spin_lock_irqsave(&(rdp)->nocb_lock, (flags)); \ + +/* + * Disable IRQs before checking offloaded state so that local + * locking is safe against concurrent de-offloading. + */ +#define rcu_nocb_lock_irqsave(rdp, flags) \ +do { \ + local_irq_save(flags); \ + if (rcu_segcblist_is_offloaded(&(rdp)->cblist)) \ + raw_spin_lock(&(rdp)->nocb_lock); \ } while (0) #else /* #ifdef CONFIG_RCU_NOCB_CPU */ #define rcu_nocb_lock_irqsave(rdp, flags) local_irq_save(flags) @@ -458,10 +501,6 @@ do { \ static void rcu_bind_gp_kthread(void); static bool rcu_nohz_full_cpu(void); -static void rcu_dynticks_task_enter(void); -static void rcu_dynticks_task_exit(void); -static void rcu_dynticks_task_trace_enter(void); -static void rcu_dynticks_task_trace_exit(void); /* Forward declarations for tree_stall.h */ static void record_gp_stall_check_time(void); @@ -469,3 +508,6 @@ static void rcu_iw_handler(struct irq_work *iwp); static void check_cpu_stall(struct rcu_data *rdp); static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, const unsigned long gpssdelay); + +/* Forward declarations for tree_exp.h. */ +static void sync_rcu_do_polled_gp(struct work_struct *wp); diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 8760b6ead770..2ac440bc7e10 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -11,6 +11,7 @@ static void rcu_exp_handler(void *unused); static int rcu_print_task_exp_stall(struct rcu_node *rnp); +static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp); /* * Record the start of an expedited grace period. @@ -18,6 +19,7 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp); static void rcu_exp_gp_seq_start(void) { rcu_seq_start(&rcu_state.expedited_sequence); + rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap); } /* @@ -34,6 +36,7 @@ static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void) */ static void rcu_exp_gp_seq_end(void) { + rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap); rcu_seq_end(&rcu_state.expedited_sequence); smp_mb(); /* Ensure that consecutive grace periods serialize. */ } @@ -170,7 +173,6 @@ static bool sync_rcu_exp_done_unlocked(struct rcu_node *rnp) return ret; } - /* * Report the exit from RCU read-side critical section for the last task * that queued itself during or before the current expedited preemptible-RCU @@ -198,7 +200,7 @@ static void __rcu_report_exp_rnp(struct rcu_node *rnp, raw_spin_unlock_irqrestore_rcu_node(rnp, flags); if (wake) { smp_mb(); /* EGP done before wake_up(). */ - swake_up_one(&rcu_state.expedited_wq); + swake_up_one_online(&rcu_state.expedited_wq); } break; } @@ -255,7 +257,7 @@ static void rcu_report_exp_cpu_mult(struct rcu_node *rnp, */ static void rcu_report_exp_rdp(struct rcu_data *rdp) { - WRITE_ONCE(rdp->exp_deferred_qs, false); + WRITE_ONCE(rdp->cpu_no_qs.b.exp, false); rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true); } @@ -334,15 +336,13 @@ fastpath: * Select the CPUs within the specified rcu_node that the upcoming * expedited grace period needs to wait for. */ -static void sync_rcu_exp_select_node_cpus(struct work_struct *wp) +static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp) { int cpu; unsigned long flags; unsigned long mask_ofl_test; unsigned long mask_ofl_ipi; int ret; - struct rcu_exp_work *rewp = - container_of(wp, struct rcu_exp_work, rew_work); struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew); raw_spin_lock_irqsave_rcu_node(rnp, flags); @@ -358,7 +358,7 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp) !(rnp->qsmaskinitnext & mask)) { mask_ofl_test |= mask; } else { - snap = rcu_dynticks_snap(rdp); + snap = rcu_dynticks_snap(cpu); if (rcu_dynticks_in_eqs(snap)) mask_ofl_test |= mask; else @@ -387,6 +387,7 @@ retry_ipi: continue; } if (get_cpu() == cpu) { + mask_ofl_test |= mask; put_cpu(); continue; } @@ -416,13 +417,119 @@ retry_ipi: rcu_report_exp_cpu_mult(rnp, mask_ofl_test, false); } +static void rcu_exp_sel_wait_wake(unsigned long s); + +#ifdef CONFIG_RCU_EXP_KTHREAD +static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp) +{ + struct rcu_exp_work *rewp = + container_of(wp, struct rcu_exp_work, rew_work); + + __sync_rcu_exp_select_node_cpus(rewp); +} + +static inline bool rcu_gp_par_worker_started(void) +{ + return !!READ_ONCE(rcu_exp_par_gp_kworker); +} + +static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp) +{ + kthread_init_work(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus); + /* + * Use rcu_exp_par_gp_kworker, because flushing a work item from + * another work item on the same kthread worker can result in + * deadlock. + */ + kthread_queue_work(rcu_exp_par_gp_kworker, &rnp->rew.rew_work); +} + +static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp) +{ + kthread_flush_work(&rnp->rew.rew_work); +} + +/* + * Work-queue handler to drive an expedited grace period forward. + */ +static void wait_rcu_exp_gp(struct kthread_work *wp) +{ + struct rcu_exp_work *rewp; + + rewp = container_of(wp, struct rcu_exp_work, rew_work); + rcu_exp_sel_wait_wake(rewp->rew_s); +} + +static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew) +{ + kthread_init_work(&rew->rew_work, wait_rcu_exp_gp); + kthread_queue_work(rcu_exp_gp_kworker, &rew->rew_work); +} + +static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew) +{ +} +#else /* !CONFIG_RCU_EXP_KTHREAD */ +static void sync_rcu_exp_select_node_cpus(struct work_struct *wp) +{ + struct rcu_exp_work *rewp = + container_of(wp, struct rcu_exp_work, rew_work); + + __sync_rcu_exp_select_node_cpus(rewp); +} + +static inline bool rcu_gp_par_worker_started(void) +{ + return !!READ_ONCE(rcu_par_gp_wq); +} + +static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp) +{ + int cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1); + + INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus); + /* If all offline, queue the work on an unbound CPU. */ + if (unlikely(cpu > rnp->grphi - rnp->grplo)) + cpu = WORK_CPU_UNBOUND; + else + cpu += rnp->grplo; + queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work); +} + +static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp) +{ + flush_work(&rnp->rew.rew_work); +} + +/* + * Work-queue handler to drive an expedited grace period forward. + */ +static void wait_rcu_exp_gp(struct work_struct *wp) +{ + struct rcu_exp_work *rewp; + + rewp = container_of(wp, struct rcu_exp_work, rew_work); + rcu_exp_sel_wait_wake(rewp->rew_s); +} + +static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew) +{ + INIT_WORK_ONSTACK(&rew->rew_work, wait_rcu_exp_gp); + queue_work(rcu_gp_wq, &rew->rew_work); +} + +static inline void synchronize_rcu_expedited_destroy_work(struct rcu_exp_work *rew) +{ + destroy_work_on_stack(&rew->rew_work); +} +#endif /* CONFIG_RCU_EXP_KTHREAD */ + /* * Select the nodes that the upcoming expedited grace period needs * to wait for. */ static void sync_rcu_exp_select_cpus(void) { - int cpu; struct rcu_node *rnp; trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset")); @@ -434,28 +541,21 @@ static void sync_rcu_exp_select_cpus(void) rnp->exp_need_flush = false; if (!READ_ONCE(rnp->expmask)) continue; /* Avoid early boot non-existent wq. */ - if (!READ_ONCE(rcu_par_gp_wq) || + if (!rcu_gp_par_worker_started() || rcu_scheduler_active != RCU_SCHEDULER_RUNNING || rcu_is_last_leaf_node(rnp)) { - /* No workqueues yet or last leaf, do direct call. */ + /* No worker started yet or last leaf, do direct call. */ sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work); continue; } - INIT_WORK(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus); - cpu = find_next_bit(&rnp->ffmask, BITS_PER_LONG, -1); - /* If all offline, queue the work on an unbound CPU. */ - if (unlikely(cpu > rnp->grphi - rnp->grplo)) - cpu = WORK_CPU_UNBOUND; - else - cpu += rnp->grplo; - queue_work_on(cpu, rcu_par_gp_wq, &rnp->rew.rew_work); + sync_rcu_exp_select_cpus_queue_work(rnp); rnp->exp_need_flush = true; } - /* Wait for workqueue jobs (if any) to complete. */ + /* Wait for jobs (if any) to complete. */ rcu_for_each_leaf_node(rnp) if (rnp->exp_need_flush) - flush_work(&rnp->rew.rew_work); + sync_rcu_exp_select_cpus_flush_work(rnp); } /* @@ -493,34 +593,42 @@ static void synchronize_rcu_expedited_wait(void) struct rcu_data *rdp; struct rcu_node *rnp; struct rcu_node *rnp_root = rcu_get_root(); + unsigned long flags; trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait")); - jiffies_stall = rcu_jiffies_till_stall_check(); + jiffies_stall = rcu_exp_jiffies_till_stall_check(); jiffies_start = jiffies; if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) { if (synchronize_rcu_expedited_wait_once(1)) return; rcu_for_each_leaf_node(rnp) { - for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) { + raw_spin_lock_irqsave_rcu_node(rnp, flags); + mask = READ_ONCE(rnp->expmask); + for_each_leaf_node_cpu_mask(rnp, cpu, mask) { rdp = per_cpu_ptr(&rcu_data, cpu); if (rdp->rcu_forced_tick_exp) continue; rdp->rcu_forced_tick_exp = true; - tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP); + if (cpu_online(cpu)) + tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP); } + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } j = READ_ONCE(jiffies_till_first_fqs); if (synchronize_rcu_expedited_wait_once(j + HZ)) return; - WARN_ON_ONCE(IS_ENABLED(CONFIG_PREEMPT_RT)); } for (;;) { + unsigned long j; + if (synchronize_rcu_expedited_wait_once(jiffies_stall)) return; if (rcu_stall_is_suppressed()) continue; - panic_on_rcu_stall(); + j = jiffies; + rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_EXP, (void *)(j - jiffies_start)); + trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall")); pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {", rcu_state.name); ndetected = 0; @@ -534,18 +642,19 @@ static void synchronize_rcu_expedited_wait(void) continue; ndetected++; rdp = per_cpu_ptr(&rcu_data, cpu); - pr_cont(" %d-%c%c%c", cpu, + pr_cont(" %d-%c%c%c%c", cpu, "O."[!!cpu_online(cpu)], "o."[!!(rdp->grpmask & rnp->expmaskinit)], - "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]); + "N."[!!(rdp->grpmask & rnp->expmaskinitnext)], + "D."[!!data_race(rdp->cpu_no_qs.b.exp)]); } } pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n", - jiffies - jiffies_start, rcu_state.expedited_sequence, + j - jiffies_start, rcu_state.expedited_sequence, data_race(rnp_root->expmask), ".T"[!!data_race(rnp_root->exp_tasks)]); if (ndetected) { - pr_err("blocking rcu_node structures:"); + pr_err("blocking rcu_node structures (internal RCU debug):"); rcu_for_each_node_breadth_first(rnp) { if (rnp == rnp_root) continue; /* printed unconditionally */ @@ -563,10 +672,14 @@ static void synchronize_rcu_expedited_wait(void) mask = leaf_node_cpu_bit(rnp, cpu); if (!(READ_ONCE(rnp->expmask) & mask)) continue; + preempt_disable(); // For smp_processor_id() in dump_cpu_task(). dump_cpu_task(cpu); + preempt_enable(); } + rcu_exp_print_detail_task_stall_rnp(rnp); } - jiffies_stall = 3 * rcu_jiffies_till_stall_check() + 3; + jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3; + panic_on_rcu_stall(); } } @@ -617,17 +730,6 @@ static void rcu_exp_sel_wait_wake(unsigned long s) rcu_exp_wait_wake(s); } -/* - * Work-queue handler to drive an expedited grace period forward. - */ -static void wait_rcu_exp_gp(struct work_struct *wp) -{ - struct rcu_exp_work *rewp; - - rewp = container_of(wp, struct rcu_exp_work, rew_work); - rcu_exp_sel_wait_wake(rewp->rew_s); -} - #ifdef CONFIG_PREEMPT_RCU /* @@ -652,10 +754,10 @@ static void rcu_exp_handler(void *unused) */ if (!depth) { if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || - rcu_dynticks_curr_cpu_in_eqs()) { + rcu_is_cpu_rrupt_from_idle()) { rcu_report_exp_rdp(rdp); } else { - rdp->exp_deferred_qs = true; + WRITE_ONCE(rdp->cpu_no_qs.b.exp, true); set_tsk_need_resched(t); set_preempt_need_resched(); } @@ -677,7 +779,7 @@ static void rcu_exp_handler(void *unused) if (depth > 0) { raw_spin_lock_irqsave_rcu_node(rnp, flags); if (rnp->expmask & rdp->grpmask) { - rdp->exp_deferred_qs = true; + WRITE_ONCE(rdp->cpu_no_qs.b.exp, true); t->rcu_read_unlock_special.b.exp_hint = true; } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); @@ -704,9 +806,11 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp) int ndetected = 0; struct task_struct *t; - if (!READ_ONCE(rnp->exp_tasks)) - return 0; raw_spin_lock_irqsave_rcu_node(rnp, flags); + if (!rnp->exp_tasks) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + return 0; + } t = list_entry(rnp->exp_tasks->prev, struct task_struct, rcu_node_entry); list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { @@ -717,6 +821,36 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp) return ndetected; } +/* + * Scan the current list of tasks blocked within RCU read-side critical + * sections, dumping the stack of each that is blocking the current + * expedited grace period. + */ +static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp) +{ + unsigned long flags; + struct task_struct *t; + + if (!rcu_exp_stall_task_details) + return; + raw_spin_lock_irqsave_rcu_node(rnp, flags); + if (!READ_ONCE(rnp->exp_tasks)) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + return; + } + t = list_entry(rnp->exp_tasks->prev, + struct task_struct, rcu_node_entry); + list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { + /* + * We could be printing a lot while holding a spinlock. + * Avoid triggering hard lockup. + */ + touch_nmi_watchdog(); + sched_show_task(t); + } + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); +} + #else /* #ifdef CONFIG_PREEMPT_RCU */ /* Request an expedited quiescent state. */ @@ -734,11 +868,13 @@ static void rcu_exp_handler(void *unused) { struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; + bool preempt_bh_enabled = !(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)); if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) || __this_cpu_read(rcu_data.cpu_no_qs.b.exp)) return; - if (rcu_is_cpu_rrupt_from_idle()) { + if (rcu_is_cpu_rrupt_from_idle() || + (IS_ENABLED(CONFIG_PREEMPT_COUNT) && preempt_bh_enabled)) { rcu_report_exp_rdp(this_cpu_ptr(&rcu_data)); return; } @@ -759,7 +895,7 @@ static void sync_sched_exp_online_cleanup(int cpu) my_cpu = get_cpu(); /* Quiescent state either not needed or already requested, leave. */ if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) || - __this_cpu_read(rcu_data.cpu_no_qs.b.exp)) { + READ_ONCE(rdp->cpu_no_qs.b.exp)) { put_cpu(); return; } @@ -787,6 +923,15 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp) return 0; } +/* + * Because preemptible RCU does not exist, we never have to print out + * tasks blocked within RCU read-side critical sections that are blocking + * the current expedited grace period. + */ +static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp) +{ +} + #endif /* #else #ifdef CONFIG_PREEMPT_RCU */ /** @@ -812,6 +957,7 @@ static int rcu_print_task_exp_stall(struct rcu_node *rnp) void synchronize_rcu_expedited(void) { bool boottime = (rcu_scheduler_active == RCU_SCHEDULER_INIT); + unsigned long flags; struct rcu_exp_work rew; struct rcu_node *rnp; unsigned long s; @@ -822,12 +968,25 @@ void synchronize_rcu_expedited(void) "Illegal synchronize_rcu_expedited() in RCU read-side critical section"); /* Is the state is such that the call is a grace period? */ - if (rcu_blocking_is_gp()) - return; + if (rcu_blocking_is_gp()) { + // Note well that this code runs with !PREEMPT && !SMP. + // In addition, all code that advances grace periods runs + // at process level. Therefore, this expedited GP overlaps + // with other expedited GPs only by being fully nested within + // them, which allows reuse of ->gp_seq_polled_exp_snap. + rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap); + rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap); + + local_irq_save(flags); + WARN_ON_ONCE(num_online_cpus() > 1); + rcu_state.expedited_sequence += (1 << RCU_SEQ_CTR_SHIFT); + local_irq_restore(flags); + return; // Context allows vacuous grace periods. + } /* If expedited grace periods are prohibited, fall back to normal. */ if (rcu_gp_is_normal()) { - wait_rcu_gp(call_rcu); + wait_rcu_gp(call_rcu_hurry); return; } @@ -843,20 +1002,155 @@ void synchronize_rcu_expedited(void) } else { /* Marshall arguments & schedule the expedited grace period. */ rew.rew_s = s; - INIT_WORK_ONSTACK(&rew.rew_work, wait_rcu_exp_gp); - queue_work(rcu_gp_wq, &rew.rew_work); + synchronize_rcu_expedited_queue_work(&rew); } /* Wait for expedited grace period to complete. */ rnp = rcu_get_root(); wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3], sync_exp_work_done(s)); - smp_mb(); /* Workqueue actions happen before return. */ + smp_mb(); /* Work actions happen before return. */ /* Let the next expedited grace period start. */ mutex_unlock(&rcu_state.exp_mutex); if (likely(!boottime)) - destroy_work_on_stack(&rew.rew_work); + synchronize_rcu_expedited_destroy_work(&rew); } EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); + +/* + * Ensure that start_poll_synchronize_rcu_expedited() has the expedited + * RCU grace periods that it needs. + */ +static void sync_rcu_do_polled_gp(struct work_struct *wp) +{ + unsigned long flags; + int i = 0; + struct rcu_node *rnp = container_of(wp, struct rcu_node, exp_poll_wq); + unsigned long s; + + raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags); + s = rnp->exp_seq_poll_rq; + rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED; + raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags); + if (s == RCU_GET_STATE_COMPLETED) + return; + while (!poll_state_synchronize_rcu(s)) { + synchronize_rcu_expedited(); + if (i == 10 || i == 20) + pr_info("%s: i = %d s = %lx gp_seq_polled = %lx\n", __func__, i, s, READ_ONCE(rcu_state.gp_seq_polled)); + i++; + } + raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags); + s = rnp->exp_seq_poll_rq; + if (poll_state_synchronize_rcu(s)) + rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED; + raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags); +} + +/** + * start_poll_synchronize_rcu_expedited - Snapshot current RCU state and start expedited grace period + * + * Returns a cookie to pass to a call to cond_synchronize_rcu(), + * cond_synchronize_rcu_expedited(), or poll_state_synchronize_rcu(), + * allowing them to determine whether or not any sort of grace period has + * elapsed in the meantime. If the needed expedited grace period is not + * already slated to start, initiates that grace period. + */ +unsigned long start_poll_synchronize_rcu_expedited(void) +{ + unsigned long flags; + struct rcu_data *rdp; + struct rcu_node *rnp; + unsigned long s; + + s = get_state_synchronize_rcu(); + rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id()); + rnp = rdp->mynode; + if (rcu_init_invoked()) + raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags); + if (!poll_state_synchronize_rcu(s)) { + if (rcu_init_invoked()) { + rnp->exp_seq_poll_rq = s; + queue_work(rcu_gp_wq, &rnp->exp_poll_wq); + } + } + if (rcu_init_invoked()) + raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags); + + return s; +} +EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited); + +/** + * start_poll_synchronize_rcu_expedited_full - Take a full snapshot and start expedited grace period + * @rgosp: Place to put snapshot of grace-period state + * + * Places the normal and expedited grace-period states in rgosp. This + * state value can be passed to a later call to cond_synchronize_rcu_full() + * or poll_state_synchronize_rcu_full() to determine whether or not a + * grace period (whether normal or expedited) has elapsed in the meantime. + * If the needed expedited grace period is not already slated to start, + * initiates that grace period. + */ +void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp) +{ + get_state_synchronize_rcu_full(rgosp); + (void)start_poll_synchronize_rcu_expedited(); +} +EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited_full); + +/** + * cond_synchronize_rcu_expedited - Conditionally wait for an expedited RCU grace period + * + * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited() + * + * If any type of full RCU grace period has elapsed since the earlier + * call to get_state_synchronize_rcu(), start_poll_synchronize_rcu(), + * or start_poll_synchronize_rcu_expedited(), just return. Otherwise, + * invoke synchronize_rcu_expedited() to wait for a full grace period. + * + * Yes, this function does not take counter wrap into account. + * But counter wrap is harmless. If the counter wraps, we have waited for + * more than 2 billion grace periods (and way more on a 64-bit system!), + * so waiting for a couple of additional grace periods should be just fine. + * + * This function provides the same memory-ordering guarantees that + * would be provided by a synchronize_rcu() that was invoked at the call + * to the function that provided @oldstate and that returned at the end + * of this function. + */ +void cond_synchronize_rcu_expedited(unsigned long oldstate) +{ + if (!poll_state_synchronize_rcu(oldstate)) + synchronize_rcu_expedited(); +} +EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited); + +/** + * cond_synchronize_rcu_expedited_full - Conditionally wait for an expedited RCU grace period + * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full() + * + * If a full RCU grace period has elapsed since the call to + * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), + * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was + * obtained, just return. Otherwise, invoke synchronize_rcu_expedited() + * to wait for a full grace period. + * + * Yes, this function does not take counter wrap into account. + * But counter wrap is harmless. If the counter wraps, we have waited for + * more than 2 billion grace periods (and way more on a 64-bit system!), + * so waiting for a couple of additional grace periods should be just fine. + * + * This function provides the same memory-ordering guarantees that + * would be provided by a synchronize_rcu() that was invoked at the call + * to the function that provided @rgosp and that returned at the end of + * this function. + */ +void cond_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp) +{ + if (!poll_state_synchronize_rcu_full(rgosp)) + synchronize_rcu_expedited(); +} +EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited_full); diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h new file mode 100644 index 000000000000..4efbf7333d4e --- /dev/null +++ b/kernel/rcu/tree_nocb.h @@ -0,0 +1,1805 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * Read-Copy Update mechanism for mutual exclusion (tree-based version) + * Internal non-public definitions that provide either classic + * or preemptible semantics. + * + * Copyright Red Hat, 2009 + * Copyright IBM Corporation, 2009 + * Copyright SUSE, 2021 + * + * Author: Ingo Molnar <mingo@elte.hu> + * Paul E. McKenney <paulmck@linux.ibm.com> + * Frederic Weisbecker <frederic@kernel.org> + */ + +#ifdef CONFIG_RCU_NOCB_CPU +static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ +static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ +static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp) +{ + return lockdep_is_held(&rdp->nocb_lock); +} + +static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp) +{ + /* Race on early boot between thread creation and assignment */ + if (!rdp->nocb_cb_kthread || !rdp->nocb_gp_kthread) + return true; + + if (current == rdp->nocb_cb_kthread || current == rdp->nocb_gp_kthread) + if (in_task()) + return true; + return false; +} + +/* + * Offload callback processing from the boot-time-specified set of CPUs + * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads + * created that pull the callbacks from the corresponding CPU, wait for + * a grace period to elapse, and invoke the callbacks. These kthreads + * are organized into GP kthreads, which manage incoming callbacks, wait for + * grace periods, and awaken CB kthreads, and the CB kthreads, which only + * invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs + * do a wake_up() on their GP kthread when they insert a callback into any + * empty list, unless the rcu_nocb_poll boot parameter has been specified, + * in which case each kthread actively polls its CPU. (Which isn't so great + * for energy efficiency, but which does reduce RCU's overhead on that CPU.) + * + * This is intended to be used in conjunction with Frederic Weisbecker's + * adaptive-idle work, which would seriously reduce OS jitter on CPUs + * running CPU-bound user-mode computations. + * + * Offloading of callbacks can also be used as an energy-efficiency + * measure because CPUs with no RCU callbacks queued are more aggressive + * about entering dyntick-idle mode. + */ + + +/* + * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. + * If the list is invalid, a warning is emitted and all CPUs are offloaded. + */ +static int __init rcu_nocb_setup(char *str) +{ + alloc_bootmem_cpumask_var(&rcu_nocb_mask); + if (*str == '=') { + if (cpulist_parse(++str, rcu_nocb_mask)) { + pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n"); + cpumask_setall(rcu_nocb_mask); + } + } + rcu_state.nocb_is_setup = true; + return 1; +} +__setup("rcu_nocbs", rcu_nocb_setup); + +static int __init parse_rcu_nocb_poll(char *arg) +{ + rcu_nocb_poll = true; + return 1; +} +__setup("rcu_nocb_poll", parse_rcu_nocb_poll); + +/* + * Don't bother bypassing ->cblist if the call_rcu() rate is low. + * After all, the main point of bypassing is to avoid lock contention + * on ->nocb_lock, which only can happen at high call_rcu() rates. + */ +static int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ; +module_param(nocb_nobypass_lim_per_jiffy, int, 0); + +/* + * Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the + * lock isn't immediately available, increment ->nocb_lock_contended to + * flag the contention. + */ +static void rcu_nocb_bypass_lock(struct rcu_data *rdp) + __acquires(&rdp->nocb_bypass_lock) +{ + lockdep_assert_irqs_disabled(); + if (raw_spin_trylock(&rdp->nocb_bypass_lock)) + return; + atomic_inc(&rdp->nocb_lock_contended); + WARN_ON_ONCE(smp_processor_id() != rdp->cpu); + smp_mb__after_atomic(); /* atomic_inc() before lock. */ + raw_spin_lock(&rdp->nocb_bypass_lock); + smp_mb__before_atomic(); /* atomic_dec() after lock. */ + atomic_dec(&rdp->nocb_lock_contended); +} + +/* + * Spinwait until the specified rcu_data structure's ->nocb_lock is + * not contended. Please note that this is extremely special-purpose, + * relying on the fact that at most two kthreads and one CPU contend for + * this lock, and also that the two kthreads are guaranteed to have frequent + * grace-period-duration time intervals between successive acquisitions + * of the lock. This allows us to use an extremely simple throttling + * mechanism, and further to apply it only to the CPU doing floods of + * call_rcu() invocations. Don't try this at home! + */ +static void rcu_nocb_wait_contended(struct rcu_data *rdp) +{ + WARN_ON_ONCE(smp_processor_id() != rdp->cpu); + while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended))) + cpu_relax(); +} + +/* + * Conditionally acquire the specified rcu_data structure's + * ->nocb_bypass_lock. + */ +static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp) +{ + lockdep_assert_irqs_disabled(); + return raw_spin_trylock(&rdp->nocb_bypass_lock); +} + +/* + * Release the specified rcu_data structure's ->nocb_bypass_lock. + */ +static void rcu_nocb_bypass_unlock(struct rcu_data *rdp) + __releases(&rdp->nocb_bypass_lock) +{ + lockdep_assert_irqs_disabled(); + raw_spin_unlock(&rdp->nocb_bypass_lock); +} + +/* + * Acquire the specified rcu_data structure's ->nocb_lock, but only + * if it corresponds to a no-CBs CPU. + */ +static void rcu_nocb_lock(struct rcu_data *rdp) +{ + lockdep_assert_irqs_disabled(); + if (!rcu_rdp_is_offloaded(rdp)) + return; + raw_spin_lock(&rdp->nocb_lock); +} + +/* + * Release the specified rcu_data structure's ->nocb_lock, but only + * if it corresponds to a no-CBs CPU. + */ +static void rcu_nocb_unlock(struct rcu_data *rdp) +{ + if (rcu_rdp_is_offloaded(rdp)) { + lockdep_assert_irqs_disabled(); + raw_spin_unlock(&rdp->nocb_lock); + } +} + +/* + * Release the specified rcu_data structure's ->nocb_lock and restore + * interrupts, but only if it corresponds to a no-CBs CPU. + */ +static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, + unsigned long flags) +{ + if (rcu_rdp_is_offloaded(rdp)) { + lockdep_assert_irqs_disabled(); + raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); + } else { + local_irq_restore(flags); + } +} + +/* Lockdep check that ->cblist may be safely accessed. */ +static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp) +{ + lockdep_assert_irqs_disabled(); + if (rcu_rdp_is_offloaded(rdp)) + lockdep_assert_held(&rdp->nocb_lock); +} + +/* + * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended + * grace period. + */ +static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) +{ + swake_up_all(sq); +} + +static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) +{ + return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1]; +} + +static void rcu_init_one_nocb(struct rcu_node *rnp) +{ + init_swait_queue_head(&rnp->nocb_gp_wq[0]); + init_swait_queue_head(&rnp->nocb_gp_wq[1]); +} + +static bool __wake_nocb_gp(struct rcu_data *rdp_gp, + struct rcu_data *rdp, + bool force, unsigned long flags) + __releases(rdp_gp->nocb_gp_lock) +{ + bool needwake = false; + + if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) { + raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags); + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, + TPS("AlreadyAwake")); + return false; + } + + if (rdp_gp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) { + WRITE_ONCE(rdp_gp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT); + del_timer(&rdp_gp->nocb_timer); + } + + if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) { + WRITE_ONCE(rdp_gp->nocb_gp_sleep, false); + needwake = true; + } + raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags); + if (needwake) { + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake")); + wake_up_process(rdp_gp->nocb_gp_kthread); + } + + return needwake; +} + +/* + * Kick the GP kthread for this NOCB group. + */ +static bool wake_nocb_gp(struct rcu_data *rdp, bool force) +{ + unsigned long flags; + struct rcu_data *rdp_gp = rdp->nocb_gp_rdp; + + raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags); + return __wake_nocb_gp(rdp_gp, rdp, force, flags); +} + +/* + * LAZY_FLUSH_JIFFIES decides the maximum amount of time that + * can elapse before lazy callbacks are flushed. Lazy callbacks + * could be flushed much earlier for a number of other reasons + * however, LAZY_FLUSH_JIFFIES will ensure no lazy callbacks are + * left unsubmitted to RCU after those many jiffies. + */ +#define LAZY_FLUSH_JIFFIES (10 * HZ) +static unsigned long jiffies_till_flush = LAZY_FLUSH_JIFFIES; + +#ifdef CONFIG_RCU_LAZY +// To be called only from test code. +void rcu_lazy_set_jiffies_till_flush(unsigned long jif) +{ + jiffies_till_flush = jif; +} +EXPORT_SYMBOL(rcu_lazy_set_jiffies_till_flush); + +unsigned long rcu_lazy_get_jiffies_till_flush(void) +{ + return jiffies_till_flush; +} +EXPORT_SYMBOL(rcu_lazy_get_jiffies_till_flush); +#endif + +/* + * Arrange to wake the GP kthread for this NOCB group at some future + * time when it is safe to do so. + */ +static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype, + const char *reason) +{ + unsigned long flags; + struct rcu_data *rdp_gp = rdp->nocb_gp_rdp; + + raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags); + + /* + * Bypass wakeup overrides previous deferments. In case of + * callback storms, no need to wake up too early. + */ + if (waketype == RCU_NOCB_WAKE_LAZY && + rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) { + mod_timer(&rdp_gp->nocb_timer, jiffies + jiffies_till_flush); + WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); + } else if (waketype == RCU_NOCB_WAKE_BYPASS) { + mod_timer(&rdp_gp->nocb_timer, jiffies + 2); + WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); + } else { + if (rdp_gp->nocb_defer_wakeup < RCU_NOCB_WAKE) + mod_timer(&rdp_gp->nocb_timer, jiffies + 1); + if (rdp_gp->nocb_defer_wakeup < waketype) + WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); + } + + raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags); + + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason); +} + +/* + * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL. + * However, if there is a callback to be enqueued and if ->nocb_bypass + * proves to be initially empty, just return false because the no-CB GP + * kthread may need to be awakened in this case. + * + * Return true if there was something to be flushed and it succeeded, otherwise + * false. + * + * Note that this function always returns true if rhp is NULL. + */ +static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp_in, + unsigned long j, bool lazy) +{ + struct rcu_cblist rcl; + struct rcu_head *rhp = rhp_in; + + WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp)); + rcu_lockdep_assert_cblist_protected(rdp); + lockdep_assert_held(&rdp->nocb_bypass_lock); + if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) { + raw_spin_unlock(&rdp->nocb_bypass_lock); + return false; + } + /* Note: ->cblist.len already accounts for ->nocb_bypass contents. */ + if (rhp) + rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */ + + /* + * If the new CB requested was a lazy one, queue it onto the main + * ->cblist so that we can take advantage of the grace-period that will + * happen regardless. But queue it onto the bypass list first so that + * the lazy CB is ordered with the existing CBs in the bypass list. + */ + if (lazy && rhp) { + rcu_cblist_enqueue(&rdp->nocb_bypass, rhp); + rhp = NULL; + } + rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp); + WRITE_ONCE(rdp->lazy_len, 0); + + rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl); + WRITE_ONCE(rdp->nocb_bypass_first, j); + rcu_nocb_bypass_unlock(rdp); + return true; +} + +/* + * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL. + * However, if there is a callback to be enqueued and if ->nocb_bypass + * proves to be initially empty, just return false because the no-CB GP + * kthread may need to be awakened in this case. + * + * Note that this function always returns true if rhp is NULL. + */ +static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, + unsigned long j, bool lazy) +{ + if (!rcu_rdp_is_offloaded(rdp)) + return true; + rcu_lockdep_assert_cblist_protected(rdp); + rcu_nocb_bypass_lock(rdp); + return rcu_nocb_do_flush_bypass(rdp, rhp, j, lazy); +} + +/* + * If the ->nocb_bypass_lock is immediately available, flush the + * ->nocb_bypass queue into ->cblist. + */ +static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j) +{ + rcu_lockdep_assert_cblist_protected(rdp); + if (!rcu_rdp_is_offloaded(rdp) || + !rcu_nocb_bypass_trylock(rdp)) + return; + WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j, false)); +} + +/* + * See whether it is appropriate to use the ->nocb_bypass list in order + * to control contention on ->nocb_lock. A limited number of direct + * enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass + * is non-empty, further callbacks must be placed into ->nocb_bypass, + * otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch + * back to direct use of ->cblist. However, ->nocb_bypass should not be + * used if ->cblist is empty, because otherwise callbacks can be stranded + * on ->nocb_bypass because we cannot count on the current CPU ever again + * invoking call_rcu(). The general rule is that if ->nocb_bypass is + * non-empty, the corresponding no-CBs grace-period kthread must not be + * in an indefinite sleep state. + * + * Finally, it is not permitted to use the bypass during early boot, + * as doing so would confuse the auto-initialization code. Besides + * which, there is no point in worrying about lock contention while + * there is only one CPU in operation. + */ +static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, + bool *was_alldone, unsigned long flags, + bool lazy) +{ + unsigned long c; + unsigned long cur_gp_seq; + unsigned long j = jiffies; + long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); + bool bypass_is_lazy = (ncbs == READ_ONCE(rdp->lazy_len)); + + lockdep_assert_irqs_disabled(); + + // Pure softirq/rcuc based processing: no bypassing, no + // locking. + if (!rcu_rdp_is_offloaded(rdp)) { + *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); + return false; + } + + // In the process of (de-)offloading: no bypassing, but + // locking. + if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) { + rcu_nocb_lock(rdp); + *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); + return false; /* Not offloaded, no bypassing. */ + } + + // Don't use ->nocb_bypass during early boot. + if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) { + rcu_nocb_lock(rdp); + WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass)); + *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); + return false; + } + + // If we have advanced to a new jiffy, reset counts to allow + // moving back from ->nocb_bypass to ->cblist. + if (j == rdp->nocb_nobypass_last) { + c = rdp->nocb_nobypass_count + 1; + } else { + WRITE_ONCE(rdp->nocb_nobypass_last, j); + c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy; + if (ULONG_CMP_LT(rdp->nocb_nobypass_count, + nocb_nobypass_lim_per_jiffy)) + c = 0; + else if (c > nocb_nobypass_lim_per_jiffy) + c = nocb_nobypass_lim_per_jiffy; + } + WRITE_ONCE(rdp->nocb_nobypass_count, c); + + // If there hasn't yet been all that many ->cblist enqueues + // this jiffy, tell the caller to enqueue onto ->cblist. But flush + // ->nocb_bypass first. + // Lazy CBs throttle this back and do immediate bypass queuing. + if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy && !lazy) { + rcu_nocb_lock(rdp); + *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); + if (*was_alldone) + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, + TPS("FirstQ")); + + WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j, false)); + WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass)); + return false; // Caller must enqueue the callback. + } + + // If ->nocb_bypass has been used too long or is too full, + // flush ->nocb_bypass to ->cblist. + if ((ncbs && !bypass_is_lazy && j != READ_ONCE(rdp->nocb_bypass_first)) || + (ncbs && bypass_is_lazy && + (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush))) || + ncbs >= qhimark) { + rcu_nocb_lock(rdp); + *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); + + if (!rcu_nocb_flush_bypass(rdp, rhp, j, lazy)) { + if (*was_alldone) + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, + TPS("FirstQ")); + WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass)); + return false; // Caller must enqueue the callback. + } + if (j != rdp->nocb_gp_adv_time && + rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) && + rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) { + rcu_advance_cbs_nowake(rdp->mynode, rdp); + rdp->nocb_gp_adv_time = j; + } + + // The flush succeeded and we moved CBs into the regular list. + // Don't wait for the wake up timer as it may be too far ahead. + // Wake up the GP thread now instead, if the cblist was empty. + __call_rcu_nocb_wake(rdp, *was_alldone, flags); + + return true; // Callback already enqueued. + } + + // We need to use the bypass. + rcu_nocb_wait_contended(rdp); + rcu_nocb_bypass_lock(rdp); + ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); + rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */ + rcu_cblist_enqueue(&rdp->nocb_bypass, rhp); + + if (lazy) + WRITE_ONCE(rdp->lazy_len, rdp->lazy_len + 1); + + if (!ncbs) { + WRITE_ONCE(rdp->nocb_bypass_first, j); + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ")); + } + rcu_nocb_bypass_unlock(rdp); + smp_mb(); /* Order enqueue before wake. */ + // A wake up of the grace period kthread or timer adjustment + // needs to be done only if: + // 1. Bypass list was fully empty before (this is the first + // bypass list entry), or: + // 2. Both of these conditions are met: + // a. The bypass list previously had only lazy CBs, and: + // b. The new CB is non-lazy. + if (ncbs && (!bypass_is_lazy || lazy)) { + local_irq_restore(flags); + } else { + // No-CBs GP kthread might be indefinitely asleep, if so, wake. + rcu_nocb_lock(rdp); // Rare during call_rcu() flood. + if (!rcu_segcblist_pend_cbs(&rdp->cblist)) { + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, + TPS("FirstBQwake")); + __call_rcu_nocb_wake(rdp, true, flags); + } else { + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, + TPS("FirstBQnoWake")); + rcu_nocb_unlock_irqrestore(rdp, flags); + } + } + return true; // Callback already enqueued. +} + +/* + * Awaken the no-CBs grace-period kthread if needed, either due to it + * legitimately being asleep or due to overload conditions. + * + * If warranted, also wake up the kthread servicing this CPUs queues. + */ +static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, + unsigned long flags) + __releases(rdp->nocb_lock) +{ + long bypass_len; + unsigned long cur_gp_seq; + unsigned long j; + long lazy_len; + long len; + struct task_struct *t; + + // If we are being polled or there is no kthread, just leave. + t = READ_ONCE(rdp->nocb_gp_kthread); + if (rcu_nocb_poll || !t) { + rcu_nocb_unlock_irqrestore(rdp, flags); + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, + TPS("WakeNotPoll")); + return; + } + // Need to actually to a wakeup. + len = rcu_segcblist_n_cbs(&rdp->cblist); + bypass_len = rcu_cblist_n_cbs(&rdp->nocb_bypass); + lazy_len = READ_ONCE(rdp->lazy_len); + if (was_alldone) { + rdp->qlen_last_fqs_check = len; + // Only lazy CBs in bypass list + if (lazy_len && bypass_len == lazy_len) { + rcu_nocb_unlock_irqrestore(rdp, flags); + wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_LAZY, + TPS("WakeLazy")); + } else if (!irqs_disabled_flags(flags)) { + /* ... if queue was empty ... */ + rcu_nocb_unlock_irqrestore(rdp, flags); + wake_nocb_gp(rdp, false); + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, + TPS("WakeEmpty")); + } else { + rcu_nocb_unlock_irqrestore(rdp, flags); + wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE, + TPS("WakeEmptyIsDeferred")); + } + } else if (len > rdp->qlen_last_fqs_check + qhimark) { + /* ... or if many callbacks queued. */ + rdp->qlen_last_fqs_check = len; + j = jiffies; + if (j != rdp->nocb_gp_adv_time && + rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) && + rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) { + rcu_advance_cbs_nowake(rdp->mynode, rdp); + rdp->nocb_gp_adv_time = j; + } + smp_mb(); /* Enqueue before timer_pending(). */ + if ((rdp->nocb_cb_sleep || + !rcu_segcblist_ready_cbs(&rdp->cblist)) && + !timer_pending(&rdp->nocb_timer)) { + rcu_nocb_unlock_irqrestore(rdp, flags); + wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE, + TPS("WakeOvfIsDeferred")); + } else { + rcu_nocb_unlock_irqrestore(rdp, flags); + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot")); + } + } else { + rcu_nocb_unlock_irqrestore(rdp, flags); + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot")); + } +} + +static int nocb_gp_toggle_rdp(struct rcu_data *rdp, + bool *wake_state) +{ + struct rcu_segcblist *cblist = &rdp->cblist; + unsigned long flags; + int ret; + + rcu_nocb_lock_irqsave(rdp, flags); + if (rcu_segcblist_test_flags(cblist, SEGCBLIST_OFFLOADED) && + !rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP)) { + /* + * Offloading. Set our flag and notify the offload worker. + * We will handle this rdp until it ever gets de-offloaded. + */ + rcu_segcblist_set_flags(cblist, SEGCBLIST_KTHREAD_GP); + if (rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB)) + *wake_state = true; + ret = 1; + } else if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_OFFLOADED) && + rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP)) { + /* + * De-offloading. Clear our flag and notify the de-offload worker. + * We will ignore this rdp until it ever gets re-offloaded. + */ + rcu_segcblist_clear_flags(cblist, SEGCBLIST_KTHREAD_GP); + if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB)) + *wake_state = true; + ret = 0; + } else { + WARN_ON_ONCE(1); + ret = -1; + } + + rcu_nocb_unlock_irqrestore(rdp, flags); + + return ret; +} + +static void nocb_gp_sleep(struct rcu_data *my_rdp, int cpu) +{ + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep")); + swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq, + !READ_ONCE(my_rdp->nocb_gp_sleep)); + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep")); +} + +/* + * No-CBs GP kthreads come here to wait for additional callbacks to show up + * or for grace periods to end. + */ +static void nocb_gp_wait(struct rcu_data *my_rdp) +{ + bool bypass = false; + int __maybe_unused cpu = my_rdp->cpu; + unsigned long cur_gp_seq; + unsigned long flags; + bool gotcbs = false; + unsigned long j = jiffies; + bool lazy = false; + bool needwait_gp = false; // This prevents actual uninitialized use. + bool needwake; + bool needwake_gp; + struct rcu_data *rdp, *rdp_toggling = NULL; + struct rcu_node *rnp; + unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning. + bool wasempty = false; + + /* + * Each pass through the following loop checks for CBs and for the + * nearest grace period (if any) to wait for next. The CB kthreads + * and the global grace-period kthread are awakened if needed. + */ + WARN_ON_ONCE(my_rdp->nocb_gp_rdp != my_rdp); + /* + * An rcu_data structure is removed from the list after its + * CPU is de-offloaded and added to the list before that CPU is + * (re-)offloaded. If the following loop happens to be referencing + * that rcu_data structure during the time that the corresponding + * CPU is de-offloaded and then immediately re-offloaded, this + * loop's rdp pointer will be carried to the end of the list by + * the resulting pair of list operations. This can cause the loop + * to skip over some of the rcu_data structures that were supposed + * to have been scanned. Fortunately a new iteration through the + * entire loop is forced after a given CPU's rcu_data structure + * is added to the list, so the skipped-over rcu_data structures + * won't be ignored for long. + */ + list_for_each_entry(rdp, &my_rdp->nocb_head_rdp, nocb_entry_rdp) { + long bypass_ncbs; + bool flush_bypass = false; + long lazy_ncbs; + + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check")); + rcu_nocb_lock_irqsave(rdp, flags); + lockdep_assert_held(&rdp->nocb_lock); + bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); + lazy_ncbs = READ_ONCE(rdp->lazy_len); + + if (bypass_ncbs && (lazy_ncbs == bypass_ncbs) && + (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + jiffies_till_flush) || + bypass_ncbs > 2 * qhimark)) { + flush_bypass = true; + } else if (bypass_ncbs && (lazy_ncbs != bypass_ncbs) && + (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) || + bypass_ncbs > 2 * qhimark)) { + flush_bypass = true; + } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) { + rcu_nocb_unlock_irqrestore(rdp, flags); + continue; /* No callbacks here, try next. */ + } + + if (flush_bypass) { + // Bypass full or old, so flush it. + (void)rcu_nocb_try_flush_bypass(rdp, j); + bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); + lazy_ncbs = READ_ONCE(rdp->lazy_len); + } + + if (bypass_ncbs) { + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, + bypass_ncbs == lazy_ncbs ? TPS("Lazy") : TPS("Bypass")); + if (bypass_ncbs == lazy_ncbs) + lazy = true; + else + bypass = true; + } + rnp = rdp->mynode; + + // Advance callbacks if helpful and low contention. + needwake_gp = false; + if (!rcu_segcblist_restempty(&rdp->cblist, + RCU_NEXT_READY_TAIL) || + (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) && + rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) { + raw_spin_lock_rcu_node(rnp); /* irqs disabled. */ + needwake_gp = rcu_advance_cbs(rnp, rdp); + wasempty = rcu_segcblist_restempty(&rdp->cblist, + RCU_NEXT_READY_TAIL); + raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */ + } + // Need to wait on some grace period? + WARN_ON_ONCE(wasempty && + !rcu_segcblist_restempty(&rdp->cblist, + RCU_NEXT_READY_TAIL)); + if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) { + if (!needwait_gp || + ULONG_CMP_LT(cur_gp_seq, wait_gp_seq)) + wait_gp_seq = cur_gp_seq; + needwait_gp = true; + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, + TPS("NeedWaitGP")); + } + if (rcu_segcblist_ready_cbs(&rdp->cblist)) { + needwake = rdp->nocb_cb_sleep; + WRITE_ONCE(rdp->nocb_cb_sleep, false); + smp_mb(); /* CB invocation -after- GP end. */ + } else { + needwake = false; + } + rcu_nocb_unlock_irqrestore(rdp, flags); + if (needwake) { + swake_up_one(&rdp->nocb_cb_wq); + gotcbs = true; + } + if (needwake_gp) + rcu_gp_kthread_wake(); + } + + my_rdp->nocb_gp_bypass = bypass; + my_rdp->nocb_gp_gp = needwait_gp; + my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0; + + // At least one child with non-empty ->nocb_bypass, so set + // timer in order to avoid stranding its callbacks. + if (!rcu_nocb_poll) { + // If bypass list only has lazy CBs. Add a deferred lazy wake up. + if (lazy && !bypass) { + wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_LAZY, + TPS("WakeLazyIsDeferred")); + // Otherwise add a deferred bypass wake up. + } else if (bypass) { + wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS, + TPS("WakeBypassIsDeferred")); + } + } + + if (rcu_nocb_poll) { + /* Polling, so trace if first poll in the series. */ + if (gotcbs) + trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll")); + if (list_empty(&my_rdp->nocb_head_rdp)) { + raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags); + if (!my_rdp->nocb_toggling_rdp) + WRITE_ONCE(my_rdp->nocb_gp_sleep, true); + raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags); + /* Wait for any offloading rdp */ + nocb_gp_sleep(my_rdp, cpu); + } else { + schedule_timeout_idle(1); + } + } else if (!needwait_gp) { + /* Wait for callbacks to appear. */ + nocb_gp_sleep(my_rdp, cpu); + } else { + rnp = my_rdp->mynode; + trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait")); + swait_event_interruptible_exclusive( + rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1], + rcu_seq_done(&rnp->gp_seq, wait_gp_seq) || + !READ_ONCE(my_rdp->nocb_gp_sleep)); + trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait")); + } + + if (!rcu_nocb_poll) { + raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags); + // (De-)queue an rdp to/from the group if its nocb state is changing + rdp_toggling = my_rdp->nocb_toggling_rdp; + if (rdp_toggling) + my_rdp->nocb_toggling_rdp = NULL; + + if (my_rdp->nocb_defer_wakeup > RCU_NOCB_WAKE_NOT) { + WRITE_ONCE(my_rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT); + del_timer(&my_rdp->nocb_timer); + } + WRITE_ONCE(my_rdp->nocb_gp_sleep, true); + raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags); + } else { + rdp_toggling = READ_ONCE(my_rdp->nocb_toggling_rdp); + if (rdp_toggling) { + /* + * Paranoid locking to make sure nocb_toggling_rdp is well + * reset *before* we (re)set SEGCBLIST_KTHREAD_GP or we could + * race with another round of nocb toggling for this rdp. + * Nocb locking should prevent from that already but we stick + * to paranoia, especially in rare path. + */ + raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags); + my_rdp->nocb_toggling_rdp = NULL; + raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags); + } + } + + if (rdp_toggling) { + bool wake_state = false; + int ret; + + ret = nocb_gp_toggle_rdp(rdp_toggling, &wake_state); + if (ret == 1) + list_add_tail(&rdp_toggling->nocb_entry_rdp, &my_rdp->nocb_head_rdp); + else if (ret == 0) + list_del(&rdp_toggling->nocb_entry_rdp); + if (wake_state) + swake_up_one(&rdp_toggling->nocb_state_wq); + } + + my_rdp->nocb_gp_seq = -1; + WARN_ON(signal_pending(current)); +} + +/* + * No-CBs grace-period-wait kthread. There is one of these per group + * of CPUs, but only once at least one CPU in that group has come online + * at least once since boot. This kthread checks for newly posted + * callbacks from any of the CPUs it is responsible for, waits for a + * grace period, then awakens all of the rcu_nocb_cb_kthread() instances + * that then have callback-invocation work to do. + */ +static int rcu_nocb_gp_kthread(void *arg) +{ + struct rcu_data *rdp = arg; + + for (;;) { + WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1); + nocb_gp_wait(rdp); + cond_resched_tasks_rcu_qs(); + } + return 0; +} + +static inline bool nocb_cb_can_run(struct rcu_data *rdp) +{ + u8 flags = SEGCBLIST_OFFLOADED | SEGCBLIST_KTHREAD_CB; + + return rcu_segcblist_test_flags(&rdp->cblist, flags); +} + +static inline bool nocb_cb_wait_cond(struct rcu_data *rdp) +{ + return nocb_cb_can_run(rdp) && !READ_ONCE(rdp->nocb_cb_sleep); +} + +/* + * Invoke any ready callbacks from the corresponding no-CBs CPU, + * then, if there are no more, wait for more to appear. + */ +static void nocb_cb_wait(struct rcu_data *rdp) +{ + struct rcu_segcblist *cblist = &rdp->cblist; + unsigned long cur_gp_seq; + unsigned long flags; + bool needwake_state = false; + bool needwake_gp = false; + bool can_sleep = true; + struct rcu_node *rnp = rdp->mynode; + + do { + swait_event_interruptible_exclusive(rdp->nocb_cb_wq, + nocb_cb_wait_cond(rdp)); + + // VVV Ensure CB invocation follows _sleep test. + if (smp_load_acquire(&rdp->nocb_cb_sleep)) { // ^^^ + WARN_ON(signal_pending(current)); + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty")); + } + } while (!nocb_cb_can_run(rdp)); + + + local_irq_save(flags); + rcu_momentary_dyntick_idle(); + local_irq_restore(flags); + /* + * Disable BH to provide the expected environment. Also, when + * transitioning to/from NOCB mode, a self-requeuing callback might + * be invoked from softirq. A short grace period could cause both + * instances of this callback would execute concurrently. + */ + local_bh_disable(); + rcu_do_batch(rdp); + local_bh_enable(); + lockdep_assert_irqs_enabled(); + rcu_nocb_lock_irqsave(rdp, flags); + if (rcu_segcblist_nextgp(cblist, &cur_gp_seq) && + rcu_seq_done(&rnp->gp_seq, cur_gp_seq) && + raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */ + needwake_gp = rcu_advance_cbs(rdp->mynode, rdp); + raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ + } + + if (rcu_segcblist_test_flags(cblist, SEGCBLIST_OFFLOADED)) { + if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB)) { + rcu_segcblist_set_flags(cblist, SEGCBLIST_KTHREAD_CB); + if (rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP)) + needwake_state = true; + } + if (rcu_segcblist_ready_cbs(cblist)) + can_sleep = false; + } else { + /* + * De-offloading. Clear our flag and notify the de-offload worker. + * We won't touch the callbacks and keep sleeping until we ever + * get re-offloaded. + */ + WARN_ON_ONCE(!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB)); + rcu_segcblist_clear_flags(cblist, SEGCBLIST_KTHREAD_CB); + if (!rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP)) + needwake_state = true; + } + + WRITE_ONCE(rdp->nocb_cb_sleep, can_sleep); + + if (rdp->nocb_cb_sleep) + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep")); + + rcu_nocb_unlock_irqrestore(rdp, flags); + if (needwake_gp) + rcu_gp_kthread_wake(); + + if (needwake_state) + swake_up_one(&rdp->nocb_state_wq); +} + +/* + * Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke + * nocb_cb_wait() to do the dirty work. + */ +static int rcu_nocb_cb_kthread(void *arg) +{ + struct rcu_data *rdp = arg; + + // Each pass through this loop does one callback batch, and, + // if there are no more ready callbacks, waits for them. + for (;;) { + nocb_cb_wait(rdp); + cond_resched_tasks_rcu_qs(); + } + return 0; +} + +/* Is a deferred wakeup of rcu_nocb_kthread() required? */ +static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level) +{ + return READ_ONCE(rdp->nocb_defer_wakeup) >= level; +} + +/* Do a deferred wakeup of rcu_nocb_kthread(). */ +static bool do_nocb_deferred_wakeup_common(struct rcu_data *rdp_gp, + struct rcu_data *rdp, int level, + unsigned long flags) + __releases(rdp_gp->nocb_gp_lock) +{ + int ndw; + int ret; + + if (!rcu_nocb_need_deferred_wakeup(rdp_gp, level)) { + raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags); + return false; + } + + ndw = rdp_gp->nocb_defer_wakeup; + ret = __wake_nocb_gp(rdp_gp, rdp, ndw == RCU_NOCB_WAKE_FORCE, flags); + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake")); + + return ret; +} + +/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */ +static void do_nocb_deferred_wakeup_timer(struct timer_list *t) +{ + unsigned long flags; + struct rcu_data *rdp = from_timer(rdp, t, nocb_timer); + + WARN_ON_ONCE(rdp->nocb_gp_rdp != rdp); + trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer")); + + raw_spin_lock_irqsave(&rdp->nocb_gp_lock, flags); + smp_mb__after_spinlock(); /* Timer expire before wakeup. */ + do_nocb_deferred_wakeup_common(rdp, rdp, RCU_NOCB_WAKE_BYPASS, flags); +} + +/* + * Do a deferred wakeup of rcu_nocb_kthread() from fastpath. + * This means we do an inexact common-case check. Note that if + * we miss, ->nocb_timer will eventually clean things up. + */ +static bool do_nocb_deferred_wakeup(struct rcu_data *rdp) +{ + unsigned long flags; + struct rcu_data *rdp_gp = rdp->nocb_gp_rdp; + + if (!rdp_gp || !rcu_nocb_need_deferred_wakeup(rdp_gp, RCU_NOCB_WAKE)) + return false; + + raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags); + return do_nocb_deferred_wakeup_common(rdp_gp, rdp, RCU_NOCB_WAKE, flags); +} + +void rcu_nocb_flush_deferred_wakeup(void) +{ + do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data)); +} +EXPORT_SYMBOL_GPL(rcu_nocb_flush_deferred_wakeup); + +static int rdp_offload_toggle(struct rcu_data *rdp, + bool offload, unsigned long flags) + __releases(rdp->nocb_lock) +{ + struct rcu_segcblist *cblist = &rdp->cblist; + struct rcu_data *rdp_gp = rdp->nocb_gp_rdp; + bool wake_gp = false; + + rcu_segcblist_offload(cblist, offload); + + if (rdp->nocb_cb_sleep) + rdp->nocb_cb_sleep = false; + rcu_nocb_unlock_irqrestore(rdp, flags); + + /* + * Ignore former value of nocb_cb_sleep and force wake up as it could + * have been spuriously set to false already. + */ + swake_up_one(&rdp->nocb_cb_wq); + + raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags); + // Queue this rdp for add/del to/from the list to iterate on rcuog + WRITE_ONCE(rdp_gp->nocb_toggling_rdp, rdp); + if (rdp_gp->nocb_gp_sleep) { + rdp_gp->nocb_gp_sleep = false; + wake_gp = true; + } + raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags); + + return wake_gp; +} + +static long rcu_nocb_rdp_deoffload(void *arg) +{ + struct rcu_data *rdp = arg; + struct rcu_segcblist *cblist = &rdp->cblist; + unsigned long flags; + int wake_gp; + struct rcu_data *rdp_gp = rdp->nocb_gp_rdp; + + /* + * rcu_nocb_rdp_deoffload() may be called directly if + * rcuog/o[p] spawn failed, because at this time the rdp->cpu + * is not online yet. + */ + WARN_ON_ONCE((rdp->cpu != raw_smp_processor_id()) && cpu_online(rdp->cpu)); + + pr_info("De-offloading %d\n", rdp->cpu); + + rcu_nocb_lock_irqsave(rdp, flags); + /* + * Flush once and for all now. This suffices because we are + * running on the target CPU holding ->nocb_lock (thus having + * interrupts disabled), and because rdp_offload_toggle() + * invokes rcu_segcblist_offload(), which clears SEGCBLIST_OFFLOADED. + * Thus future calls to rcu_segcblist_completely_offloaded() will + * return false, which means that future calls to rcu_nocb_try_bypass() + * will refuse to put anything into the bypass. + */ + WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false)); + /* + * Start with invoking rcu_core() early. This way if the current thread + * happens to preempt an ongoing call to rcu_core() in the middle, + * leaving some work dismissed because rcu_core() still thinks the rdp is + * completely offloaded, we are guaranteed a nearby future instance of + * rcu_core() to catch up. + */ + rcu_segcblist_set_flags(cblist, SEGCBLIST_RCU_CORE); + invoke_rcu_core(); + wake_gp = rdp_offload_toggle(rdp, false, flags); + + mutex_lock(&rdp_gp->nocb_gp_kthread_mutex); + if (rdp_gp->nocb_gp_kthread) { + if (wake_gp) + wake_up_process(rdp_gp->nocb_gp_kthread); + + /* + * If rcuo[p] kthread spawn failed, directly remove SEGCBLIST_KTHREAD_CB. + * Just wait SEGCBLIST_KTHREAD_GP to be cleared by rcuog. + */ + if (!rdp->nocb_cb_kthread) { + rcu_nocb_lock_irqsave(rdp, flags); + rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_KTHREAD_CB); + rcu_nocb_unlock_irqrestore(rdp, flags); + } + + swait_event_exclusive(rdp->nocb_state_wq, + !rcu_segcblist_test_flags(cblist, + SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP)); + } else { + /* + * No kthread to clear the flags for us or remove the rdp from the nocb list + * to iterate. Do it here instead. Locking doesn't look stricly necessary + * but we stick to paranoia in this rare path. + */ + rcu_nocb_lock_irqsave(rdp, flags); + rcu_segcblist_clear_flags(&rdp->cblist, + SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP); + rcu_nocb_unlock_irqrestore(rdp, flags); + + list_del(&rdp->nocb_entry_rdp); + } + mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); + + /* + * Lock one last time to acquire latest callback updates from kthreads + * so we can later handle callbacks locally without locking. + */ + rcu_nocb_lock_irqsave(rdp, flags); + /* + * Theoretically we could clear SEGCBLIST_LOCKING after the nocb + * lock is released but how about being paranoid for once? + */ + rcu_segcblist_clear_flags(cblist, SEGCBLIST_LOCKING); + /* + * Without SEGCBLIST_LOCKING, we can't use + * rcu_nocb_unlock_irqrestore() anymore. + */ + raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); + + /* Sanity check */ + WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass)); + + + return 0; +} + +int rcu_nocb_cpu_deoffload(int cpu) +{ + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + int ret = 0; + + cpus_read_lock(); + mutex_lock(&rcu_state.barrier_mutex); + if (rcu_rdp_is_offloaded(rdp)) { + if (cpu_online(cpu)) { + ret = work_on_cpu(cpu, rcu_nocb_rdp_deoffload, rdp); + if (!ret) + cpumask_clear_cpu(cpu, rcu_nocb_mask); + } else { + pr_info("NOCB: Cannot CB-deoffload offline CPU %d\n", rdp->cpu); + ret = -EINVAL; + } + } + mutex_unlock(&rcu_state.barrier_mutex); + cpus_read_unlock(); + + return ret; +} +EXPORT_SYMBOL_GPL(rcu_nocb_cpu_deoffload); + +static long rcu_nocb_rdp_offload(void *arg) +{ + struct rcu_data *rdp = arg; + struct rcu_segcblist *cblist = &rdp->cblist; + unsigned long flags; + int wake_gp; + struct rcu_data *rdp_gp = rdp->nocb_gp_rdp; + + WARN_ON_ONCE(rdp->cpu != raw_smp_processor_id()); + /* + * For now we only support re-offload, ie: the rdp must have been + * offloaded on boot first. + */ + if (!rdp->nocb_gp_rdp) + return -EINVAL; + + if (WARN_ON_ONCE(!rdp_gp->nocb_gp_kthread)) + return -EINVAL; + + pr_info("Offloading %d\n", rdp->cpu); + + /* + * Can't use rcu_nocb_lock_irqsave() before SEGCBLIST_LOCKING + * is set. + */ + raw_spin_lock_irqsave(&rdp->nocb_lock, flags); + + /* + * We didn't take the nocb lock while working on the + * rdp->cblist with SEGCBLIST_LOCKING cleared (pure softirq/rcuc mode). + * Every modifications that have been done previously on + * rdp->cblist must be visible remotely by the nocb kthreads + * upon wake up after reading the cblist flags. + * + * The layout against nocb_lock enforces that ordering: + * + * __rcu_nocb_rdp_offload() nocb_cb_wait()/nocb_gp_wait() + * ------------------------- ---------------------------- + * WRITE callbacks rcu_nocb_lock() + * rcu_nocb_lock() READ flags + * WRITE flags READ callbacks + * rcu_nocb_unlock() rcu_nocb_unlock() + */ + wake_gp = rdp_offload_toggle(rdp, true, flags); + if (wake_gp) + wake_up_process(rdp_gp->nocb_gp_kthread); + swait_event_exclusive(rdp->nocb_state_wq, + rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_CB) && + rcu_segcblist_test_flags(cblist, SEGCBLIST_KTHREAD_GP)); + + /* + * All kthreads are ready to work, we can finally relieve rcu_core() and + * enable nocb bypass. + */ + rcu_nocb_lock_irqsave(rdp, flags); + rcu_segcblist_clear_flags(cblist, SEGCBLIST_RCU_CORE); + rcu_nocb_unlock_irqrestore(rdp, flags); + + return 0; +} + +int rcu_nocb_cpu_offload(int cpu) +{ + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + int ret = 0; + + cpus_read_lock(); + mutex_lock(&rcu_state.barrier_mutex); + if (!rcu_rdp_is_offloaded(rdp)) { + if (cpu_online(cpu)) { + ret = work_on_cpu(cpu, rcu_nocb_rdp_offload, rdp); + if (!ret) + cpumask_set_cpu(cpu, rcu_nocb_mask); + } else { + pr_info("NOCB: Cannot CB-offload offline CPU %d\n", rdp->cpu); + ret = -EINVAL; + } + } + mutex_unlock(&rcu_state.barrier_mutex); + cpus_read_unlock(); + + return ret; +} +EXPORT_SYMBOL_GPL(rcu_nocb_cpu_offload); + +#ifdef CONFIG_RCU_LAZY +static unsigned long +lazy_rcu_shrink_count(struct shrinker *shrink, struct shrink_control *sc) +{ + int cpu; + unsigned long count = 0; + + if (WARN_ON_ONCE(!cpumask_available(rcu_nocb_mask))) + return 0; + + /* Protect rcu_nocb_mask against concurrent (de-)offloading. */ + if (!mutex_trylock(&rcu_state.barrier_mutex)) + return 0; + + /* Snapshot count of all CPUs */ + for_each_cpu(cpu, rcu_nocb_mask) { + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + + count += READ_ONCE(rdp->lazy_len); + } + + mutex_unlock(&rcu_state.barrier_mutex); + + return count ? count : SHRINK_EMPTY; +} + +static unsigned long +lazy_rcu_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) +{ + int cpu; + unsigned long flags; + unsigned long count = 0; + + if (WARN_ON_ONCE(!cpumask_available(rcu_nocb_mask))) + return 0; + /* + * Protect against concurrent (de-)offloading. Otherwise nocb locking + * may be ignored or imbalanced. + */ + if (!mutex_trylock(&rcu_state.barrier_mutex)) { + /* + * But really don't insist if barrier_mutex is contended since we + * can't guarantee that it will never engage in a dependency + * chain involving memory allocation. The lock is seldom contended + * anyway. + */ + return 0; + } + + /* Snapshot count of all CPUs */ + for_each_cpu(cpu, rcu_nocb_mask) { + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + int _count; + + if (WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp))) + continue; + + if (!READ_ONCE(rdp->lazy_len)) + continue; + + rcu_nocb_lock_irqsave(rdp, flags); + /* + * Recheck under the nocb lock. Since we are not holding the bypass + * lock we may still race with increments from the enqueuer but still + * we know for sure if there is at least one lazy callback. + */ + _count = READ_ONCE(rdp->lazy_len); + if (!_count) { + rcu_nocb_unlock_irqrestore(rdp, flags); + continue; + } + WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false)); + rcu_nocb_unlock_irqrestore(rdp, flags); + wake_nocb_gp(rdp, false); + sc->nr_to_scan -= _count; + count += _count; + if (sc->nr_to_scan <= 0) + break; + } + + mutex_unlock(&rcu_state.barrier_mutex); + + return count ? count : SHRINK_STOP; +} +#endif // #ifdef CONFIG_RCU_LAZY + +void __init rcu_init_nohz(void) +{ + int cpu; + struct rcu_data *rdp; + const struct cpumask *cpumask = NULL; + struct shrinker * __maybe_unused lazy_rcu_shrinker; + +#if defined(CONFIG_NO_HZ_FULL) + if (tick_nohz_full_running && !cpumask_empty(tick_nohz_full_mask)) + cpumask = tick_nohz_full_mask; +#endif + + if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_DEFAULT_ALL) && + !rcu_state.nocb_is_setup && !cpumask) + cpumask = cpu_possible_mask; + + if (cpumask) { + if (!cpumask_available(rcu_nocb_mask)) { + if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { + pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); + return; + } + } + + cpumask_or(rcu_nocb_mask, rcu_nocb_mask, cpumask); + rcu_state.nocb_is_setup = true; + } + + if (!rcu_state.nocb_is_setup) + return; + +#ifdef CONFIG_RCU_LAZY + lazy_rcu_shrinker = shrinker_alloc(0, "rcu-lazy"); + if (!lazy_rcu_shrinker) { + pr_err("Failed to allocate lazy_rcu shrinker!\n"); + } else { + lazy_rcu_shrinker->count_objects = lazy_rcu_shrink_count; + lazy_rcu_shrinker->scan_objects = lazy_rcu_shrink_scan; + + shrinker_register(lazy_rcu_shrinker); + } +#endif // #ifdef CONFIG_RCU_LAZY + + if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { + pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n"); + cpumask_and(rcu_nocb_mask, cpu_possible_mask, + rcu_nocb_mask); + } + if (cpumask_empty(rcu_nocb_mask)) + pr_info("\tOffload RCU callbacks from CPUs: (none).\n"); + else + pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n", + cpumask_pr_args(rcu_nocb_mask)); + if (rcu_nocb_poll) + pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); + + for_each_cpu(cpu, rcu_nocb_mask) { + rdp = per_cpu_ptr(&rcu_data, cpu); + if (rcu_segcblist_empty(&rdp->cblist)) + rcu_segcblist_init(&rdp->cblist); + rcu_segcblist_offload(&rdp->cblist, true); + rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP); + rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_RCU_CORE); + } + rcu_organize_nocb_kthreads(); +} + +/* Initialize per-rcu_data variables for no-CBs CPUs. */ +static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) +{ + init_swait_queue_head(&rdp->nocb_cb_wq); + init_swait_queue_head(&rdp->nocb_gp_wq); + init_swait_queue_head(&rdp->nocb_state_wq); + raw_spin_lock_init(&rdp->nocb_lock); + raw_spin_lock_init(&rdp->nocb_bypass_lock); + raw_spin_lock_init(&rdp->nocb_gp_lock); + timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0); + rcu_cblist_init(&rdp->nocb_bypass); + WRITE_ONCE(rdp->lazy_len, 0); + mutex_init(&rdp->nocb_gp_kthread_mutex); +} + +/* + * If the specified CPU is a no-CBs CPU that does not already have its + * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread + * for this CPU's group has not yet been created, spawn it as well. + */ +static void rcu_spawn_cpu_nocb_kthread(int cpu) +{ + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + struct rcu_data *rdp_gp; + struct task_struct *t; + struct sched_param sp; + + if (!rcu_scheduler_fully_active || !rcu_state.nocb_is_setup) + return; + + /* If there already is an rcuo kthread, then nothing to do. */ + if (rdp->nocb_cb_kthread) + return; + + /* If we didn't spawn the GP kthread first, reorganize! */ + sp.sched_priority = kthread_prio; + rdp_gp = rdp->nocb_gp_rdp; + mutex_lock(&rdp_gp->nocb_gp_kthread_mutex); + if (!rdp_gp->nocb_gp_kthread) { + t = kthread_run(rcu_nocb_gp_kthread, rdp_gp, + "rcuog/%d", rdp_gp->cpu); + if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) { + mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); + goto end; + } + WRITE_ONCE(rdp_gp->nocb_gp_kthread, t); + if (kthread_prio) + sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); + } + mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex); + + /* Spawn the kthread for this CPU. */ + t = kthread_run(rcu_nocb_cb_kthread, rdp, + "rcuo%c/%d", rcu_state.abbr, cpu); + if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__)) + goto end; + + if (IS_ENABLED(CONFIG_RCU_NOCB_CPU_CB_BOOST) && kthread_prio) + sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); + + WRITE_ONCE(rdp->nocb_cb_kthread, t); + WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread); + return; +end: + mutex_lock(&rcu_state.barrier_mutex); + if (rcu_rdp_is_offloaded(rdp)) { + rcu_nocb_rdp_deoffload(rdp); + cpumask_clear_cpu(cpu, rcu_nocb_mask); + } + mutex_unlock(&rcu_state.barrier_mutex); +} + +/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */ +static int rcu_nocb_gp_stride = -1; +module_param(rcu_nocb_gp_stride, int, 0444); + +/* + * Initialize GP-CB relationships for all no-CBs CPU. + */ +static void __init rcu_organize_nocb_kthreads(void) +{ + int cpu; + bool firsttime = true; + bool gotnocbs = false; + bool gotnocbscbs = true; + int ls = rcu_nocb_gp_stride; + int nl = 0; /* Next GP kthread. */ + struct rcu_data *rdp; + struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */ + + if (!cpumask_available(rcu_nocb_mask)) + return; + if (ls == -1) { + ls = nr_cpu_ids / int_sqrt(nr_cpu_ids); + rcu_nocb_gp_stride = ls; + } + + /* + * Each pass through this loop sets up one rcu_data structure. + * Should the corresponding CPU come online in the future, then + * we will spawn the needed set of rcu_nocb_kthread() kthreads. + */ + for_each_possible_cpu(cpu) { + rdp = per_cpu_ptr(&rcu_data, cpu); + if (rdp->cpu >= nl) { + /* New GP kthread, set up for CBs & next GP. */ + gotnocbs = true; + nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls; + rdp_gp = rdp; + INIT_LIST_HEAD(&rdp->nocb_head_rdp); + if (dump_tree) { + if (!firsttime) + pr_cont("%s\n", gotnocbscbs + ? "" : " (self only)"); + gotnocbscbs = false; + firsttime = false; + pr_alert("%s: No-CB GP kthread CPU %d:", + __func__, cpu); + } + } else { + /* Another CB kthread, link to previous GP kthread. */ + gotnocbscbs = true; + if (dump_tree) + pr_cont(" %d", cpu); + } + rdp->nocb_gp_rdp = rdp_gp; + if (cpumask_test_cpu(cpu, rcu_nocb_mask)) + list_add_tail(&rdp->nocb_entry_rdp, &rdp_gp->nocb_head_rdp); + } + if (gotnocbs && dump_tree) + pr_cont("%s\n", gotnocbscbs ? "" : " (self only)"); +} + +/* + * Bind the current task to the offloaded CPUs. If there are no offloaded + * CPUs, leave the task unbound. Splat if the bind attempt fails. + */ +void rcu_bind_current_to_nocb(void) +{ + if (cpumask_available(rcu_nocb_mask) && !cpumask_empty(rcu_nocb_mask)) + WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask)); +} +EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb); + +// The ->on_cpu field is available only in CONFIG_SMP=y, so... +#ifdef CONFIG_SMP +static char *show_rcu_should_be_on_cpu(struct task_struct *tsp) +{ + return tsp && task_is_running(tsp) && !tsp->on_cpu ? "!" : ""; +} +#else // #ifdef CONFIG_SMP +static char *show_rcu_should_be_on_cpu(struct task_struct *tsp) +{ + return ""; +} +#endif // #else #ifdef CONFIG_SMP + +/* + * Dump out nocb grace-period kthread state for the specified rcu_data + * structure. + */ +static void show_rcu_nocb_gp_state(struct rcu_data *rdp) +{ + struct rcu_node *rnp = rdp->mynode; + + pr_info("nocb GP %d %c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu %c CPU %d%s\n", + rdp->cpu, + "kK"[!!rdp->nocb_gp_kthread], + "lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)], + "dD"[!!rdp->nocb_defer_wakeup], + "tT"[timer_pending(&rdp->nocb_timer)], + "sS"[!!rdp->nocb_gp_sleep], + ".W"[swait_active(&rdp->nocb_gp_wq)], + ".W"[swait_active(&rnp->nocb_gp_wq[0])], + ".W"[swait_active(&rnp->nocb_gp_wq[1])], + ".B"[!!rdp->nocb_gp_bypass], + ".G"[!!rdp->nocb_gp_gp], + (long)rdp->nocb_gp_seq, + rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops), + rdp->nocb_gp_kthread ? task_state_to_char(rdp->nocb_gp_kthread) : '.', + rdp->nocb_gp_kthread ? (int)task_cpu(rdp->nocb_gp_kthread) : -1, + show_rcu_should_be_on_cpu(rdp->nocb_gp_kthread)); +} + +/* Dump out nocb kthread state for the specified rcu_data structure. */ +static void show_rcu_nocb_state(struct rcu_data *rdp) +{ + char bufw[20]; + char bufr[20]; + struct rcu_data *nocb_next_rdp; + struct rcu_segcblist *rsclp = &rdp->cblist; + bool waslocked; + bool wassleep; + + if (rdp->nocb_gp_rdp == rdp) + show_rcu_nocb_gp_state(rdp); + + nocb_next_rdp = list_next_or_null_rcu(&rdp->nocb_gp_rdp->nocb_head_rdp, + &rdp->nocb_entry_rdp, + typeof(*rdp), + nocb_entry_rdp); + + sprintf(bufw, "%ld", rsclp->gp_seq[RCU_WAIT_TAIL]); + sprintf(bufr, "%ld", rsclp->gp_seq[RCU_NEXT_READY_TAIL]); + pr_info(" CB %d^%d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%s%c%s%c%c q%ld %c CPU %d%s\n", + rdp->cpu, rdp->nocb_gp_rdp->cpu, + nocb_next_rdp ? nocb_next_rdp->cpu : -1, + "kK"[!!rdp->nocb_cb_kthread], + "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)], + "cC"[!!atomic_read(&rdp->nocb_lock_contended)], + "lL"[raw_spin_is_locked(&rdp->nocb_lock)], + "sS"[!!rdp->nocb_cb_sleep], + ".W"[swait_active(&rdp->nocb_cb_wq)], + jiffies - rdp->nocb_bypass_first, + jiffies - rdp->nocb_nobypass_last, + rdp->nocb_nobypass_count, + ".D"[rcu_segcblist_ready_cbs(rsclp)], + ".W"[!rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL)], + rcu_segcblist_segempty(rsclp, RCU_WAIT_TAIL) ? "" : bufw, + ".R"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL)], + rcu_segcblist_segempty(rsclp, RCU_NEXT_READY_TAIL) ? "" : bufr, + ".N"[!rcu_segcblist_segempty(rsclp, RCU_NEXT_TAIL)], + ".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)], + rcu_segcblist_n_cbs(&rdp->cblist), + rdp->nocb_cb_kthread ? task_state_to_char(rdp->nocb_cb_kthread) : '.', + rdp->nocb_cb_kthread ? (int)task_cpu(rdp->nocb_cb_kthread) : -1, + show_rcu_should_be_on_cpu(rdp->nocb_cb_kthread)); + + /* It is OK for GP kthreads to have GP state. */ + if (rdp->nocb_gp_rdp == rdp) + return; + + waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock); + wassleep = swait_active(&rdp->nocb_gp_wq); + if (!rdp->nocb_gp_sleep && !waslocked && !wassleep) + return; /* Nothing untoward. */ + + pr_info(" nocb GP activity on CB-only CPU!!! %c%c%c %c\n", + "lL"[waslocked], + "dD"[!!rdp->nocb_defer_wakeup], + "sS"[!!rdp->nocb_gp_sleep], + ".W"[wassleep]); +} + +#else /* #ifdef CONFIG_RCU_NOCB_CPU */ + +static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp) +{ + return 0; +} + +static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp) +{ + return false; +} + +/* No ->nocb_lock to acquire. */ +static void rcu_nocb_lock(struct rcu_data *rdp) +{ +} + +/* No ->nocb_lock to release. */ +static void rcu_nocb_unlock(struct rcu_data *rdp) +{ +} + +/* No ->nocb_lock to release. */ +static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, + unsigned long flags) +{ + local_irq_restore(flags); +} + +/* Lockdep check that ->cblist may be safely accessed. */ +static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp) +{ + lockdep_assert_irqs_disabled(); +} + +static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) +{ +} + +static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) +{ + return NULL; +} + +static void rcu_init_one_nocb(struct rcu_node *rnp) +{ +} + +static bool wake_nocb_gp(struct rcu_data *rdp, bool force) +{ + return false; +} + +static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, + unsigned long j, bool lazy) +{ + return true; +} + +static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, + bool *was_alldone, unsigned long flags, bool lazy) +{ + return false; +} + +static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty, + unsigned long flags) +{ + WARN_ON_ONCE(1); /* Should be dead code! */ +} + +static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) +{ +} + +static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp, int level) +{ + return false; +} + +static bool do_nocb_deferred_wakeup(struct rcu_data *rdp) +{ + return false; +} + +static void rcu_spawn_cpu_nocb_kthread(int cpu) +{ +} + +static void show_rcu_nocb_state(struct rcu_data *rdp) +{ +} + +#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 7e291ce0a1d6..41021080ad25 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -13,10 +13,29 @@ #include "../locking/rtmutex_common.h" -#ifdef CONFIG_RCU_NOCB_CPU -static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ -static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ -#endif /* #ifdef CONFIG_RCU_NOCB_CPU */ +static bool rcu_rdp_is_offloaded(struct rcu_data *rdp) +{ + /* + * In order to read the offloaded state of an rdp in a safe + * and stable way and prevent from its value to be changed + * under us, we must either hold the barrier mutex, the cpu + * hotplug lock (read or write) or the nocb lock. Local + * non-preemptible reads are also safe. NOCB kthreads and + * timers have their own means of synchronization against the + * offloaded state updaters. + */ + RCU_LOCKDEP_WARN( + !(lockdep_is_held(&rcu_state.barrier_mutex) || + (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) || + rcu_lockdep_is_held_nocb(rdp) || + (rdp == this_cpu_ptr(&rcu_data) && + !(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())) || + rcu_current_is_nocb_kthread(rdp)), + "Unsafe read of RCU_NOCB offloaded state" + ); + + return rcu_segcblist_is_offloaded(&rdp->cblist); +} /* * Check the RCU kernel configuration parameters and print informative @@ -32,12 +51,10 @@ static void __init rcu_bootup_announce_oddness(void) RCU_FANOUT); if (rcu_fanout_exact) pr_info("\tHierarchical RCU autobalancing is disabled.\n"); - if (IS_ENABLED(CONFIG_RCU_FAST_NO_HZ)) - pr_info("\tRCU dyntick-idle grace-period acceleration is enabled.\n"); if (IS_ENABLED(CONFIG_PROVE_RCU)) pr_info("\tRCU lockdep checking is enabled.\n"); if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) - pr_info("\tRCU strict (and thus non-scalable) grace periods enabled.\n"); + pr_info("\tRCU strict (and thus non-scalable) grace periods are enabled.\n"); if (RCU_NUM_LVLS >= 4) pr_info("\tFour(or more)-level hierarchy is enabled.\n"); if (RCU_FANOUT_LEAF != 16) @@ -69,13 +86,13 @@ static void __init rcu_bootup_announce_oddness(void) if (rcu_kick_kthreads) pr_info("\tKick kthreads if too-long grace period.\n"); if (IS_ENABLED(CONFIG_DEBUG_OBJECTS_RCU_HEAD)) - pr_info("\tRCU callback double-/use-after-free debug enabled.\n"); + pr_info("\tRCU callback double-/use-after-free debug is enabled.\n"); if (gp_preinit_delay) pr_info("\tRCU debug GP pre-init slowdown %d jiffies.\n", gp_preinit_delay); if (gp_init_delay) pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_init_delay); if (gp_cleanup_delay) - pr_info("\tRCU debug GP init slowdown %d jiffies.\n", gp_cleanup_delay); + pr_info("\tRCU debug GP cleanup slowdown %d jiffies.\n", gp_cleanup_delay); if (!use_softirq) pr_info("\tRCU_SOFTIRQ processing moved to rcuc kthreads.\n"); if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG)) @@ -240,11 +257,13 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) * GP should not be able to end until we report, so there should be * no need to check for a subsequent expedited GP. (Though we are * still in a quiescent state in any case.) + * + * Interrupts are disabled, so ->cpu_no_qs.b.exp cannot change. */ - if (blkd_state & RCU_EXP_BLKD && rdp->exp_deferred_qs) + if (blkd_state & RCU_EXP_BLKD && rdp->cpu_no_qs.b.exp) rcu_report_exp_rdp(rdp); else - WARN_ON_ONCE(rdp->exp_deferred_qs); + WARN_ON_ONCE(rdp->cpu_no_qs.b.exp); } /* @@ -258,12 +277,16 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp) * current task, there might be any number of other tasks blocked while * in an RCU read-side critical section. * + * Unlike non-preemptible-RCU, quiescent state reports for expedited + * grace periods are handled separately via deferred quiescent states + * and context switch events. + * * Callers to this function must disable preemption. */ static void rcu_qs(void) { RCU_LOCKDEP_WARN(preemptible(), "rcu_qs() invoked with preemption enabled!!!\n"); - if (__this_cpu_read(rcu_data.cpu_no_qs.s)) { + if (__this_cpu_read(rcu_data.cpu_no_qs.b.norm)) { trace_rcu_grace_period(TPS("rcu_preempt"), __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs")); @@ -294,7 +317,7 @@ void rcu_note_context_switch(bool preempt) trace_rcu_utilization(TPS("Start context switch")); lockdep_assert_irqs_disabled(); - WARN_ON_ONCE(!preempt && rcu_preempt_depth() > 0); + WARN_ONCE(!preempt && rcu_preempt_depth() > 0, "Voluntary context switch within RCU read-side critical section!"); if (rcu_preempt_depth() > 0 && !t->rcu_read_unlock_special.b.blocked) { @@ -309,7 +332,7 @@ void rcu_note_context_switch(bool preempt) * then queue the task as required based on the states * of any ongoing and expedited grace periods. */ - WARN_ON_ONCE((rdp->grpmask & rcu_rnp_online_cpus(rnp)) == 0); + WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp)); WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); trace_rcu_preempt_task(rcu_state.name, t->pid, @@ -331,7 +354,7 @@ void rcu_note_context_switch(bool preempt) * means that we continue to block the current grace period. */ rcu_qs(); - if (rdp->exp_deferred_qs) + if (rdp->cpu_no_qs.b.exp) rcu_report_exp_rdp(rdp); rcu_tasks_qs(current, preempt); trace_rcu_utilization(TPS("End context switch")); @@ -353,17 +376,20 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) static void rcu_preempt_read_enter(void) { - current->rcu_read_lock_nesting++; + WRITE_ONCE(current->rcu_read_lock_nesting, READ_ONCE(current->rcu_read_lock_nesting) + 1); } static int rcu_preempt_read_exit(void) { - return --current->rcu_read_lock_nesting; + int ret = READ_ONCE(current->rcu_read_lock_nesting) - 1; + + WRITE_ONCE(current->rcu_read_lock_nesting, ret); + return ret; } static void rcu_preempt_depth_set(int val) { - current->rcu_read_lock_nesting = val; + WRITE_ONCE(current->rcu_read_lock_nesting, val); } /* @@ -393,8 +419,9 @@ void __rcu_read_unlock(void) { struct task_struct *t = current; + barrier(); // critical section before exit code. if (rcu_preempt_read_exit() == 0) { - barrier(); /* critical section before exit code. */ + barrier(); // critical-section exit before .s check. if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s))) rcu_read_unlock_special(t); } @@ -435,7 +462,7 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp) * be quite short, for example, in the case of the call from * rcu_read_unlock_special(). */ -static void +static notrace void rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) { bool empty_exp; @@ -454,13 +481,14 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) */ special = t->rcu_read_unlock_special; rdp = this_cpu_ptr(&rcu_data); - if (!special.s && !rdp->exp_deferred_qs) { + if (!special.s && !rdp->cpu_no_qs.b.exp) { local_irq_restore(flags); return; } t->rcu_read_unlock_special.s = 0; if (special.b.need_qs) { if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) { + rdp->cpu_no_qs.b.norm = false; rcu_report_qs_rdp(rdp); udelay(rcu_unlock_delay); } else { @@ -474,7 +502,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) * tasks are handled when removing the task from the * blocked-tasks list below. */ - if (rdp->exp_deferred_qs) + if (rdp->cpu_no_qs.b.exp) rcu_report_exp_rdp(rdp); /* Clean up if blocked during RCU read-side critical section. */ @@ -506,7 +534,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) WRITE_ONCE(rnp->exp_tasks, np); if (IS_ENABLED(CONFIG_RCU_BOOST)) { /* Snapshot ->boost_mtx ownership w/rnp->lock held. */ - drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t; + drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx.rtmutex) == t; if (&t->rcu_node_entry == rnp->boost_tasks) WRITE_ONCE(rnp->boost_tasks, np); } @@ -531,16 +559,16 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } - /* Unboost if we were boosted. */ - if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) - rt_mutex_futex_unlock(&rnp->boost_mtx); - /* * If this was the last task on the expedited lists, * then we need to report up the rcu_node hierarchy. */ if (!empty_exp && empty_exp_now) rcu_report_exp_rnp(rnp, true); + + /* Unboost if we were boosted. */ + if (IS_ENABLED(CONFIG_RCU_BOOST) && drop_boost_mutex) + rt_mutex_futex_unlock(&rnp->boost_mtx.rtmutex); } else { local_irq_restore(flags); } @@ -555,9 +583,9 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags) * is disabled. This function cannot be expected to understand these * nuances, so the caller must handle them. */ -static bool rcu_preempt_need_deferred_qs(struct task_struct *t) +static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t) { - return (__this_cpu_read(rcu_data.exp_deferred_qs) || + return (__this_cpu_read(rcu_data.cpu_no_qs.b.exp) || READ_ONCE(t->rcu_read_unlock_special.s)) && rcu_preempt_depth() == 0; } @@ -569,7 +597,7 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) * evaluate safety in terms of interrupt, softirq, and preemption * disabling. */ -static void rcu_preempt_deferred_qs(struct task_struct *t) +notrace void rcu_preempt_deferred_qs(struct task_struct *t) { unsigned long flags; @@ -598,9 +626,9 @@ static void rcu_preempt_deferred_qs_handler(struct irq_work *iwp) static void rcu_read_unlock_special(struct task_struct *t) { unsigned long flags; + bool irqs_were_disabled; bool preempt_bh_were_disabled = !!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)); - bool irqs_were_disabled; /* NMI handlers cannot block and cannot safely manipulate state. */ if (in_nmi()) @@ -609,30 +637,40 @@ static void rcu_read_unlock_special(struct task_struct *t) local_irq_save(flags); irqs_were_disabled = irqs_disabled_flags(flags); if (preempt_bh_were_disabled || irqs_were_disabled) { - bool exp; + bool expboost; // Expedited GP in flight or possible boosting. struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; - exp = (t->rcu_blocked_node && - READ_ONCE(t->rcu_blocked_node->exp_tasks)) || - (rdp->grpmask & READ_ONCE(rnp->expmask)); + expboost = (t->rcu_blocked_node && READ_ONCE(t->rcu_blocked_node->exp_tasks)) || + (rdp->grpmask & READ_ONCE(rnp->expmask)) || + (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && + ((rdp->grpmask & READ_ONCE(rnp->qsmask)) || t->rcu_blocked_node)) || + (IS_ENABLED(CONFIG_RCU_BOOST) && irqs_were_disabled && + t->rcu_blocked_node); // Need to defer quiescent state until everything is enabled. - if (use_softirq && (in_irq() || (exp && !irqs_were_disabled))) { + if (use_softirq && (in_hardirq() || (expboost && !irqs_were_disabled))) { // Using softirq, safe to awaken, and either the - // wakeup is free or there is an expedited GP. + // wakeup is free or there is either an expedited + // GP in flight or a potential need to deboost. raise_softirq_irqoff(RCU_SOFTIRQ); } else { // Enabling BH or preempt does reschedule, so... - // Also if no expediting, slow is OK. - // Plus nohz_full CPUs eventually get tick enabled. + // Also if no expediting and no possible deboosting, + // slow is OK. Plus nohz_full CPUs eventually get + // tick enabled. set_tsk_need_resched(current); set_preempt_need_resched(); if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled && - !rdp->defer_qs_iw_pending && exp && cpu_online(rdp->cpu)) { + expboost && !rdp->defer_qs_iw_pending && cpu_online(rdp->cpu)) { // Get scheduler to re-evaluate and call hooks. // If !IRQ_WORK, FQS scan will eventually IPI. - init_irq_work(&rdp->defer_qs_iw, - rcu_preempt_deferred_qs_handler); + if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) && + IS_ENABLED(CONFIG_PREEMPT_RT)) + rdp->defer_qs_iw = IRQ_WORK_INIT_HARD( + rcu_preempt_deferred_qs_handler); + else + init_irq_work(&rdp->defer_qs_iw, + rcu_preempt_deferred_qs_handler); rdp->defer_qs_iw_pending = true; irq_work_queue_on(&rdp->defer_qs_iw, rdp->cpu); } @@ -682,9 +720,7 @@ static void rcu_flavor_sched_clock_irq(int user) { struct task_struct *t = current; - if (user || rcu_is_cpu_rrupt_from_idle()) { - rcu_note_voluntary_context_switch(current); - } + lockdep_assert_irqs_disabled(); if (rcu_preempt_depth() > 0 || (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) { /* No QS, force context switch if deferred. */ @@ -744,7 +780,6 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck) int cpu; int i; struct list_head *lhp; - bool onl; struct rcu_data *rdp; struct rcu_node *rnp1; @@ -768,9 +803,8 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck) pr_cont("\n"); for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) { rdp = per_cpu_ptr(&rcu_data, cpu); - onl = !!(rdp->grpmask & rcu_rnp_online_cpus(rnp)); pr_info("\t%d: %c online: %ld(%d) offline: %ld(%d)\n", - cpu, ".o"[onl], + cpu, ".o"[rcu_rdp_cpu_online(rdp)], (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_flags, (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_flags); } @@ -787,10 +821,10 @@ void rcu_read_unlock_strict(void) { struct rcu_data *rdp; - if (!IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) || - irqs_disabled() || preempt_count() || !rcu_state.gp_kthread) + if (irqs_disabled() || preempt_count() || !rcu_state.gp_kthread) return; rdp = this_cpu_ptr(&rcu_data); + rdp->cpu_no_qs.b.norm = false; rcu_report_qs_rdp(rdp); udelay(rcu_unlock_delay); } @@ -819,10 +853,8 @@ static void rcu_qs(void) trace_rcu_grace_period(TPS("rcu_sched"), __this_cpu_read(rcu_data.gp_seq), TPS("cpuqs")); __this_cpu_write(rcu_data.cpu_no_qs.b.norm, false); - if (!__this_cpu_read(rcu_data.cpu_no_qs.b.exp)) - return; - __this_cpu_write(rcu_data.cpu_no_qs.b.exp, false); - rcu_report_exp_rdp(this_cpu_ptr(&rcu_data)); + if (__this_cpu_read(rcu_data.cpu_no_qs.b.exp)) + rcu_report_exp_rdp(this_cpu_ptr(&rcu_data)); } /* @@ -838,7 +870,7 @@ void rcu_all_qs(void) if (!raw_cpu_read(rcu_data.rcu_urgent_qs)) return; - preempt_disable(); + preempt_disable(); // For CONFIG_PREEMPT_COUNT=y kernels /* Load rcu_urgent_qs before other flags. */ if (!smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) { preempt_enable(); @@ -868,8 +900,8 @@ void rcu_note_context_switch(bool preempt) this_cpu_write(rcu_data.rcu_urgent_qs, false); if (unlikely(raw_cpu_read(rcu_data.rcu_need_heavy_qs))) rcu_momentary_dyntick_idle(); - rcu_tasks_qs(current, preempt); out: + rcu_tasks_qs(current, preempt); trace_rcu_utilization(TPS("End context switch")); } EXPORT_SYMBOL_GPL(rcu_note_context_switch); @@ -895,11 +927,25 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp) * Because there is no preemptible RCU, there can be no deferred quiescent * states. */ -static bool rcu_preempt_need_deferred_qs(struct task_struct *t) +static notrace bool rcu_preempt_need_deferred_qs(struct task_struct *t) { return false; } -static void rcu_preempt_deferred_qs(struct task_struct *t) { } + +// Except that we do need to respond to a request by an expedited +// grace period for a quiescent state from this CPU. Note that in +// non-preemptible kernels, there can be no context switches within RCU +// read-side critical sections, which in turn means that the leaf rcu_node +// structure's blocked-tasks list is always empty. is therefore no need to +// actually check it. Instead, a quiescent state from this CPU suffices, +// and this function is only called from such a quiescent state. +notrace void rcu_preempt_deferred_qs(struct task_struct *t) +{ + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); + + if (READ_ONCE(rdp->cpu_no_qs.b.exp)) + rcu_report_exp_rdp(rdp); +} /* * Because there is no preemptible RCU, there can be no readers blocked, @@ -930,7 +976,6 @@ static void rcu_flavor_sched_clock_irq(int user) * neither access nor modify, at least not while the * corresponding CPU is online. */ - rcu_qs(); } } @@ -959,12 +1004,34 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck) */ static void rcu_cpu_kthread_setup(unsigned int cpu) { + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); #ifdef CONFIG_RCU_BOOST struct sched_param sp; sp.sched_priority = kthread_prio; sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); #endif /* #ifdef CONFIG_RCU_BOOST */ + + WRITE_ONCE(rdp->rcuc_activity, jiffies); +} + +static bool rcu_is_callbacks_nocb_kthread(struct rcu_data *rdp) +{ +#ifdef CONFIG_RCU_NOCB_CPU + return rdp->nocb_cb_kthread == current; +#else + return false; +#endif +} + +/* + * Is the current CPU running the RCU-callbacks kthread? + * Caller must have preemption disabled. + */ +static bool rcu_is_callbacks_kthread(struct rcu_data *rdp) +{ + return rdp->rcu_cpu_kthread_task == current || + rcu_is_callbacks_nocb_kthread(rdp); } #ifdef CONFIG_RCU_BOOST @@ -1026,11 +1093,12 @@ static int rcu_boost(struct rcu_node *rnp) * section. */ t = container_of(tb, struct task_struct, rcu_node_entry); - rt_mutex_init_proxy_locked(&rnp->boost_mtx, t); + rt_mutex_init_proxy_locked(&rnp->boost_mtx.rtmutex, t); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); /* Lock only for side effect: boosts task t's priority. */ rt_mutex_lock(&rnp->boost_mtx); rt_mutex_unlock(&rnp->boost_mtx); /* Then keep lockdep happy. */ + rnp->n_boosts++; return READ_ONCE(rnp->exp_tasks) != NULL || READ_ONCE(rnp->boost_tasks) != NULL; @@ -1085,7 +1153,8 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) __releases(rnp->lock) { raw_lockdep_assert_held_rcu_node(rnp); - if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { + if (!rnp->boost_kthread_task || + (!rcu_preempt_blocked_readers_cgp(rnp) && !rnp->exp_tasks)) { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; } @@ -1093,7 +1162,8 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) (rnp->gp_tasks != NULL && rnp->boost_tasks == NULL && rnp->qsmask == 0 && - (!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld))) { + (!time_after(rnp->boost_time, jiffies) || rcu_state.cbovld || + IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)))) { if (rnp->exp_tasks == NULL) WRITE_ONCE(rnp->boost_tasks, rnp->gp_tasks); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); @@ -1104,15 +1174,6 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) } } -/* - * Is the current CPU running the RCU-callbacks kthread? - * Caller must have preemption disabled. - */ -static bool rcu_is_callbacks_kthread(void) -{ - return __this_cpu_read(rcu_data.rcu_cpu_kthread_task) == current; -} - #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) /* @@ -1126,30 +1187,22 @@ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) /* * Create an RCU-boost kthread for the specified node if one does not * already exist. We only create this kthread for preemptible RCU. - * Returns zero if all is well, a negated errno otherwise. */ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp) { - int rnp_index = rnp - rcu_get_root(); unsigned long flags; + int rnp_index = rnp - rcu_get_root(); struct sched_param sp; struct task_struct *t; - if (!IS_ENABLED(CONFIG_PREEMPT_RCU)) - return; - - if (!rcu_scheduler_fully_active || rcu_rnp_online_cpus(rnp) == 0) - return; - - rcu_state.boost = 1; - - if (rnp->boost_kthread_task != NULL) - return; + mutex_lock(&rnp->boost_kthread_mutex); + if (rnp->boost_kthread_task || !rcu_scheduler_fully_active) + goto out; t = kthread_create(rcu_boost_kthread, (void *)rnp, "rcub/%d", rnp_index); if (WARN_ON_ONCE(IS_ERR(t))) - return; + goto out; raw_spin_lock_irqsave_rcu_node(rnp, flags); rnp->boost_kthread_task = t; @@ -1157,6 +1210,9 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp) sp.sched_priority = kthread_prio; sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ + + out: + mutex_unlock(&rnp->boost_kthread_mutex); } /* @@ -1167,11 +1223,13 @@ static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp) * We don't include outgoingcpu in the affinity set, use -1 if there is * no outgoing CPU. If there are no CPUs left in the affinity set, * this function allows the kthread to execute on any CPU. + * + * Any future concurrent calls are serialized via ->boost_kthread_mutex. */ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) { struct task_struct *t = rnp->boost_kthread_task; - unsigned long mask = rcu_rnp_online_cpus(rnp); + unsigned long mask; cpumask_var_t cm; int cpu; @@ -1179,37 +1237,23 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) return; if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) return; + mutex_lock(&rnp->boost_kthread_mutex); + mask = rcu_rnp_online_cpus(rnp); for_each_leaf_node_possible_cpu(rnp, cpu) if ((mask & leaf_node_cpu_bit(rnp, cpu)) && cpu != outgoingcpu) cpumask_set_cpu(cpu, cm); - if (cpumask_weight(cm) == 0) - cpumask_setall(cm); + cpumask_and(cm, cm, housekeeping_cpumask(HK_TYPE_RCU)); + if (cpumask_empty(cm)) { + cpumask_copy(cm, housekeeping_cpumask(HK_TYPE_RCU)); + if (outgoingcpu >= 0) + cpumask_clear_cpu(outgoingcpu, cm); + } set_cpus_allowed_ptr(t, cm); + mutex_unlock(&rnp->boost_kthread_mutex); free_cpumask_var(cm); } -/* - * Spawn boost kthreads -- called as soon as the scheduler is running. - */ -static void __init rcu_spawn_boost_kthreads(void) -{ - struct rcu_node *rnp; - - rcu_for_each_leaf_node(rnp) - rcu_spawn_one_boost_kthread(rnp); -} - -static void rcu_prepare_kthreads(int cpu) -{ - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); - struct rcu_node *rnp = rdp->mynode; - - /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ - if (rcu_scheduler_fully_active) - rcu_spawn_one_boost_kthread(rnp); -} - #else /* #ifdef CONFIG_RCU_BOOST */ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) @@ -1218,1324 +1262,20 @@ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } -static bool rcu_is_callbacks_kthread(void) -{ - return false; -} - static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) { } -static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) -{ -} - -static void __init rcu_spawn_boost_kthreads(void) +static void rcu_spawn_one_boost_kthread(struct rcu_node *rnp) { } -static void rcu_prepare_kthreads(int cpu) +static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) { } #endif /* #else #ifdef CONFIG_RCU_BOOST */ -#if !defined(CONFIG_RCU_FAST_NO_HZ) - -/* - * Check to see if any future non-offloaded RCU-related work will need - * to be done by the current CPU, even if none need be done immediately, - * returning 1 if so. This function is part of the RCU implementation; - * it is -not- an exported member of the RCU API. - * - * Because we not have RCU_FAST_NO_HZ, just check whether or not this - * CPU has RCU callbacks queued. - */ -int rcu_needs_cpu(u64 basemono, u64 *nextevt) -{ - *nextevt = KTIME_MAX; - return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) && - !rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist); -} - -/* - * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up - * after it. - */ -static void rcu_cleanup_after_idle(void) -{ -} - -/* - * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, - * is nothing. - */ -static void rcu_prepare_for_idle(void) -{ -} - -#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ - -/* - * This code is invoked when a CPU goes idle, at which point we want - * to have the CPU do everything required for RCU so that it can enter - * the energy-efficient dyntick-idle mode. - * - * The following preprocessor symbol controls this: - * - * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted - * to sleep in dyntick-idle mode with RCU callbacks pending. This - * is sized to be roughly one RCU grace period. Those energy-efficiency - * benchmarkers who might otherwise be tempted to set this to a large - * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your - * system. And if you are -that- concerned about energy efficiency, - * just power the system down and be done with it! - * - * The value below works well in practice. If future workloads require - * adjustment, they can be converted into kernel config parameters, though - * making the state machine smarter might be a better option. - */ -#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ - -static int rcu_idle_gp_delay = RCU_IDLE_GP_DELAY; -module_param(rcu_idle_gp_delay, int, 0644); - -/* - * Try to advance callbacks on the current CPU, but only if it has been - * awhile since the last time we did so. Afterwards, if there are any - * callbacks ready for immediate invocation, return true. - */ -static bool __maybe_unused rcu_try_advance_all_cbs(void) -{ - bool cbs_ready = false; - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - struct rcu_node *rnp; - - /* Exit early if we advanced recently. */ - if (jiffies == rdp->last_advance_all) - return false; - rdp->last_advance_all = jiffies; - - rnp = rdp->mynode; - - /* - * Don't bother checking unless a grace period has - * completed since we last checked and there are - * callbacks not yet ready to invoke. - */ - if ((rcu_seq_completed_gp(rdp->gp_seq, - rcu_seq_current(&rnp->gp_seq)) || - unlikely(READ_ONCE(rdp->gpwrap))) && - rcu_segcblist_pend_cbs(&rdp->cblist)) - note_gp_changes(rdp); - - if (rcu_segcblist_ready_cbs(&rdp->cblist)) - cbs_ready = true; - return cbs_ready; -} - -/* - * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready - * to invoke. If the CPU has callbacks, try to advance them. Tell the - * caller about what to set the timeout. - * - * The caller must have disabled interrupts. - */ -int rcu_needs_cpu(u64 basemono, u64 *nextevt) -{ - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - unsigned long dj; - - lockdep_assert_irqs_disabled(); - - /* If no non-offloaded callbacks, RCU doesn't need the CPU. */ - if (rcu_segcblist_empty(&rdp->cblist) || - rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist)) { - *nextevt = KTIME_MAX; - return 0; - } - - /* Attempt to advance callbacks. */ - if (rcu_try_advance_all_cbs()) { - /* Some ready to invoke, so initiate later invocation. */ - invoke_rcu_core(); - return 1; - } - rdp->last_accelerate = jiffies; - - /* Request timer and round. */ - dj = round_up(rcu_idle_gp_delay + jiffies, rcu_idle_gp_delay) - jiffies; - - *nextevt = basemono + dj * TICK_NSEC; - return 0; -} - -/* - * Prepare a CPU for idle from an RCU perspective. The first major task is to - * sense whether nohz mode has been enabled or disabled via sysfs. The second - * major task is to accelerate (that is, assign grace-period numbers to) any - * recently arrived callbacks. - * - * The caller must have disabled interrupts. - */ -static void rcu_prepare_for_idle(void) -{ - bool needwake; - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - struct rcu_node *rnp; - int tne; - - lockdep_assert_irqs_disabled(); - if (rcu_segcblist_is_offloaded(&rdp->cblist)) - return; - - /* Handle nohz enablement switches conservatively. */ - tne = READ_ONCE(tick_nohz_active); - if (tne != rdp->tick_nohz_enabled_snap) { - if (!rcu_segcblist_empty(&rdp->cblist)) - invoke_rcu_core(); /* force nohz to see update. */ - rdp->tick_nohz_enabled_snap = tne; - return; - } - if (!tne) - return; - - /* - * If we have not yet accelerated this jiffy, accelerate all - * callbacks on this CPU. - */ - if (rdp->last_accelerate == jiffies) - return; - rdp->last_accelerate = jiffies; - if (rcu_segcblist_pend_cbs(&rdp->cblist)) { - rnp = rdp->mynode; - raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ - needwake = rcu_accelerate_cbs(rnp, rdp); - raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ - if (needwake) - rcu_gp_kthread_wake(); - } -} - -/* - * Clean up for exit from idle. Attempt to advance callbacks based on - * any grace periods that elapsed while the CPU was idle, and if any - * callbacks are now ready to invoke, initiate invocation. - */ -static void rcu_cleanup_after_idle(void) -{ - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - - lockdep_assert_irqs_disabled(); - if (rcu_segcblist_is_offloaded(&rdp->cblist)) - return; - if (rcu_try_advance_all_cbs()) - invoke_rcu_core(); -} - -#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ - -#ifdef CONFIG_RCU_NOCB_CPU - -/* - * Offload callback processing from the boot-time-specified set of CPUs - * specified by rcu_nocb_mask. For the CPUs in the set, there are kthreads - * created that pull the callbacks from the corresponding CPU, wait for - * a grace period to elapse, and invoke the callbacks. These kthreads - * are organized into GP kthreads, which manage incoming callbacks, wait for - * grace periods, and awaken CB kthreads, and the CB kthreads, which only - * invoke callbacks. Each GP kthread invokes its own CBs. The no-CBs CPUs - * do a wake_up() on their GP kthread when they insert a callback into any - * empty list, unless the rcu_nocb_poll boot parameter has been specified, - * in which case each kthread actively polls its CPU. (Which isn't so great - * for energy efficiency, but which does reduce RCU's overhead on that CPU.) - * - * This is intended to be used in conjunction with Frederic Weisbecker's - * adaptive-idle work, which would seriously reduce OS jitter on CPUs - * running CPU-bound user-mode computations. - * - * Offloading of callbacks can also be used as an energy-efficiency - * measure because CPUs with no RCU callbacks queued are more aggressive - * about entering dyntick-idle mode. - */ - - -/* - * Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. - * The string after the "rcu_nocbs=" is either "all" for all CPUs, or a - * comma-separated list of CPUs and/or CPU ranges. If an invalid list is - * given, a warning is emitted and all CPUs are offloaded. - */ -static int __init rcu_nocb_setup(char *str) -{ - alloc_bootmem_cpumask_var(&rcu_nocb_mask); - if (!strcasecmp(str, "all")) - cpumask_setall(rcu_nocb_mask); - else - if (cpulist_parse(str, rcu_nocb_mask)) { - pr_warn("rcu_nocbs= bad CPU range, all CPUs set\n"); - cpumask_setall(rcu_nocb_mask); - } - return 1; -} -__setup("rcu_nocbs=", rcu_nocb_setup); - -static int __init parse_rcu_nocb_poll(char *arg) -{ - rcu_nocb_poll = true; - return 0; -} -early_param("rcu_nocb_poll", parse_rcu_nocb_poll); - -/* - * Don't bother bypassing ->cblist if the call_rcu() rate is low. - * After all, the main point of bypassing is to avoid lock contention - * on ->nocb_lock, which only can happen at high call_rcu() rates. - */ -int nocb_nobypass_lim_per_jiffy = 16 * 1000 / HZ; -module_param(nocb_nobypass_lim_per_jiffy, int, 0); - -/* - * Acquire the specified rcu_data structure's ->nocb_bypass_lock. If the - * lock isn't immediately available, increment ->nocb_lock_contended to - * flag the contention. - */ -static void rcu_nocb_bypass_lock(struct rcu_data *rdp) - __acquires(&rdp->nocb_bypass_lock) -{ - lockdep_assert_irqs_disabled(); - if (raw_spin_trylock(&rdp->nocb_bypass_lock)) - return; - atomic_inc(&rdp->nocb_lock_contended); - WARN_ON_ONCE(smp_processor_id() != rdp->cpu); - smp_mb__after_atomic(); /* atomic_inc() before lock. */ - raw_spin_lock(&rdp->nocb_bypass_lock); - smp_mb__before_atomic(); /* atomic_dec() after lock. */ - atomic_dec(&rdp->nocb_lock_contended); -} - -/* - * Spinwait until the specified rcu_data structure's ->nocb_lock is - * not contended. Please note that this is extremely special-purpose, - * relying on the fact that at most two kthreads and one CPU contend for - * this lock, and also that the two kthreads are guaranteed to have frequent - * grace-period-duration time intervals between successive acquisitions - * of the lock. This allows us to use an extremely simple throttling - * mechanism, and further to apply it only to the CPU doing floods of - * call_rcu() invocations. Don't try this at home! - */ -static void rcu_nocb_wait_contended(struct rcu_data *rdp) -{ - WARN_ON_ONCE(smp_processor_id() != rdp->cpu); - while (WARN_ON_ONCE(atomic_read(&rdp->nocb_lock_contended))) - cpu_relax(); -} - -/* - * Conditionally acquire the specified rcu_data structure's - * ->nocb_bypass_lock. - */ -static bool rcu_nocb_bypass_trylock(struct rcu_data *rdp) -{ - lockdep_assert_irqs_disabled(); - return raw_spin_trylock(&rdp->nocb_bypass_lock); -} - -/* - * Release the specified rcu_data structure's ->nocb_bypass_lock. - */ -static void rcu_nocb_bypass_unlock(struct rcu_data *rdp) - __releases(&rdp->nocb_bypass_lock) -{ - lockdep_assert_irqs_disabled(); - raw_spin_unlock(&rdp->nocb_bypass_lock); -} - -/* - * Acquire the specified rcu_data structure's ->nocb_lock, but only - * if it corresponds to a no-CBs CPU. - */ -static void rcu_nocb_lock(struct rcu_data *rdp) -{ - lockdep_assert_irqs_disabled(); - if (!rcu_segcblist_is_offloaded(&rdp->cblist)) - return; - raw_spin_lock(&rdp->nocb_lock); -} - -/* - * Release the specified rcu_data structure's ->nocb_lock, but only - * if it corresponds to a no-CBs CPU. - */ -static void rcu_nocb_unlock(struct rcu_data *rdp) -{ - if (rcu_segcblist_is_offloaded(&rdp->cblist)) { - lockdep_assert_irqs_disabled(); - raw_spin_unlock(&rdp->nocb_lock); - } -} - -/* - * Release the specified rcu_data structure's ->nocb_lock and restore - * interrupts, but only if it corresponds to a no-CBs CPU. - */ -static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, - unsigned long flags) -{ - if (rcu_segcblist_is_offloaded(&rdp->cblist)) { - lockdep_assert_irqs_disabled(); - raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); - } else { - local_irq_restore(flags); - } -} - -/* Lockdep check that ->cblist may be safely accessed. */ -static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp) -{ - lockdep_assert_irqs_disabled(); - if (rcu_segcblist_is_offloaded(&rdp->cblist)) - lockdep_assert_held(&rdp->nocb_lock); -} - -/* - * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended - * grace period. - */ -static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) -{ - swake_up_all(sq); -} - -static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) -{ - return &rnp->nocb_gp_wq[rcu_seq_ctr(rnp->gp_seq) & 0x1]; -} - -static void rcu_init_one_nocb(struct rcu_node *rnp) -{ - init_swait_queue_head(&rnp->nocb_gp_wq[0]); - init_swait_queue_head(&rnp->nocb_gp_wq[1]); -} - -/* Is the specified CPU a no-CBs CPU? */ -bool rcu_is_nocb_cpu(int cpu) -{ - if (cpumask_available(rcu_nocb_mask)) - return cpumask_test_cpu(cpu, rcu_nocb_mask); - return false; -} - -/* - * Kick the GP kthread for this NOCB group. Caller holds ->nocb_lock - * and this function releases it. - */ -static void wake_nocb_gp(struct rcu_data *rdp, bool force, - unsigned long flags) - __releases(rdp->nocb_lock) -{ - bool needwake = false; - struct rcu_data *rdp_gp = rdp->nocb_gp_rdp; - - lockdep_assert_held(&rdp->nocb_lock); - if (!READ_ONCE(rdp_gp->nocb_gp_kthread)) { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("AlreadyAwake")); - rcu_nocb_unlock_irqrestore(rdp, flags); - return; - } - del_timer(&rdp->nocb_timer); - rcu_nocb_unlock_irqrestore(rdp, flags); - raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags); - if (force || READ_ONCE(rdp_gp->nocb_gp_sleep)) { - WRITE_ONCE(rdp_gp->nocb_gp_sleep, false); - needwake = true; - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DoWake")); - } - raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags); - if (needwake) - wake_up_process(rdp_gp->nocb_gp_kthread); -} - -/* - * Arrange to wake the GP kthread for this NOCB group at some future - * time when it is safe to do so. - */ -static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype, - const char *reason) -{ - if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) - mod_timer(&rdp->nocb_timer, jiffies + 1); - if (rdp->nocb_defer_wakeup < waketype) - WRITE_ONCE(rdp->nocb_defer_wakeup, waketype); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, reason); -} - -/* - * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL. - * However, if there is a callback to be enqueued and if ->nocb_bypass - * proves to be initially empty, just return false because the no-CB GP - * kthread may need to be awakened in this case. - * - * Note that this function always returns true if rhp is NULL. - */ -static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - unsigned long j) -{ - struct rcu_cblist rcl; - - WARN_ON_ONCE(!rcu_segcblist_is_offloaded(&rdp->cblist)); - rcu_lockdep_assert_cblist_protected(rdp); - lockdep_assert_held(&rdp->nocb_bypass_lock); - if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) { - raw_spin_unlock(&rdp->nocb_bypass_lock); - return false; - } - /* Note: ->cblist.len already accounts for ->nocb_bypass contents. */ - if (rhp) - rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */ - rcu_cblist_flush_enqueue(&rcl, &rdp->nocb_bypass, rhp); - rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl); - WRITE_ONCE(rdp->nocb_bypass_first, j); - rcu_nocb_bypass_unlock(rdp); - return true; -} - -/* - * Flush the ->nocb_bypass queue into ->cblist, enqueuing rhp if non-NULL. - * However, if there is a callback to be enqueued and if ->nocb_bypass - * proves to be initially empty, just return false because the no-CB GP - * kthread may need to be awakened in this case. - * - * Note that this function always returns true if rhp is NULL. - */ -static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - unsigned long j) -{ - if (!rcu_segcblist_is_offloaded(&rdp->cblist)) - return true; - rcu_lockdep_assert_cblist_protected(rdp); - rcu_nocb_bypass_lock(rdp); - return rcu_nocb_do_flush_bypass(rdp, rhp, j); -} - -/* - * If the ->nocb_bypass_lock is immediately available, flush the - * ->nocb_bypass queue into ->cblist. - */ -static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j) -{ - rcu_lockdep_assert_cblist_protected(rdp); - if (!rcu_segcblist_is_offloaded(&rdp->cblist) || - !rcu_nocb_bypass_trylock(rdp)) - return; - WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j)); -} - -/* - * See whether it is appropriate to use the ->nocb_bypass list in order - * to control contention on ->nocb_lock. A limited number of direct - * enqueues are permitted into ->cblist per jiffy. If ->nocb_bypass - * is non-empty, further callbacks must be placed into ->nocb_bypass, - * otherwise rcu_barrier() breaks. Use rcu_nocb_flush_bypass() to switch - * back to direct use of ->cblist. However, ->nocb_bypass should not be - * used if ->cblist is empty, because otherwise callbacks can be stranded - * on ->nocb_bypass because we cannot count on the current CPU ever again - * invoking call_rcu(). The general rule is that if ->nocb_bypass is - * non-empty, the corresponding no-CBs grace-period kthread must not be - * in an indefinite sleep state. - * - * Finally, it is not permitted to use the bypass during early boot, - * as doing so would confuse the auto-initialization code. Besides - * which, there is no point in worrying about lock contention while - * there is only one CPU in operation. - */ -static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - bool *was_alldone, unsigned long flags) -{ - unsigned long c; - unsigned long cur_gp_seq; - unsigned long j = jiffies; - long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); - - if (!rcu_segcblist_is_offloaded(&rdp->cblist)) { - *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); - return false; /* Not offloaded, no bypassing. */ - } - lockdep_assert_irqs_disabled(); - - // Don't use ->nocb_bypass during early boot. - if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) { - rcu_nocb_lock(rdp); - WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass)); - *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); - return false; - } - - // If we have advanced to a new jiffy, reset counts to allow - // moving back from ->nocb_bypass to ->cblist. - if (j == rdp->nocb_nobypass_last) { - c = rdp->nocb_nobypass_count + 1; - } else { - WRITE_ONCE(rdp->nocb_nobypass_last, j); - c = rdp->nocb_nobypass_count - nocb_nobypass_lim_per_jiffy; - if (ULONG_CMP_LT(rdp->nocb_nobypass_count, - nocb_nobypass_lim_per_jiffy)) - c = 0; - else if (c > nocb_nobypass_lim_per_jiffy) - c = nocb_nobypass_lim_per_jiffy; - } - WRITE_ONCE(rdp->nocb_nobypass_count, c); - - // If there hasn't yet been all that many ->cblist enqueues - // this jiffy, tell the caller to enqueue onto ->cblist. But flush - // ->nocb_bypass first. - if (rdp->nocb_nobypass_count < nocb_nobypass_lim_per_jiffy) { - rcu_nocb_lock(rdp); - *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); - if (*was_alldone) - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("FirstQ")); - WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, j)); - WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass)); - return false; // Caller must enqueue the callback. - } - - // If ->nocb_bypass has been used too long or is too full, - // flush ->nocb_bypass to ->cblist. - if ((ncbs && j != READ_ONCE(rdp->nocb_bypass_first)) || - ncbs >= qhimark) { - rcu_nocb_lock(rdp); - if (!rcu_nocb_flush_bypass(rdp, rhp, j)) { - *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); - if (*was_alldone) - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("FirstQ")); - WARN_ON_ONCE(rcu_cblist_n_cbs(&rdp->nocb_bypass)); - return false; // Caller must enqueue the callback. - } - if (j != rdp->nocb_gp_adv_time && - rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) && - rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) { - rcu_advance_cbs_nowake(rdp->mynode, rdp); - rdp->nocb_gp_adv_time = j; - } - rcu_nocb_unlock_irqrestore(rdp, flags); - return true; // Callback already enqueued. - } - - // We need to use the bypass. - rcu_nocb_wait_contended(rdp); - rcu_nocb_bypass_lock(rdp); - ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); - rcu_segcblist_inc_len(&rdp->cblist); /* Must precede enqueue. */ - rcu_cblist_enqueue(&rdp->nocb_bypass, rhp); - if (!ncbs) { - WRITE_ONCE(rdp->nocb_bypass_first, j); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("FirstBQ")); - } - rcu_nocb_bypass_unlock(rdp); - smp_mb(); /* Order enqueue before wake. */ - if (ncbs) { - local_irq_restore(flags); - } else { - // No-CBs GP kthread might be indefinitely asleep, if so, wake. - rcu_nocb_lock(rdp); // Rare during call_rcu() flood. - if (!rcu_segcblist_pend_cbs(&rdp->cblist)) { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("FirstBQwake")); - __call_rcu_nocb_wake(rdp, true, flags); - } else { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("FirstBQnoWake")); - rcu_nocb_unlock_irqrestore(rdp, flags); - } - } - return true; // Callback already enqueued. -} - -/* - * Awaken the no-CBs grace-period kthead if needed, either due to it - * legitimately being asleep or due to overload conditions. - * - * If warranted, also wake up the kthread servicing this CPUs queues. - */ -static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_alldone, - unsigned long flags) - __releases(rdp->nocb_lock) -{ - unsigned long cur_gp_seq; - unsigned long j; - long len; - struct task_struct *t; - - // If we are being polled or there is no kthread, just leave. - t = READ_ONCE(rdp->nocb_gp_kthread); - if (rcu_nocb_poll || !t) { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("WakeNotPoll")); - rcu_nocb_unlock_irqrestore(rdp, flags); - return; - } - // Need to actually to a wakeup. - len = rcu_segcblist_n_cbs(&rdp->cblist); - if (was_alldone) { - rdp->qlen_last_fqs_check = len; - if (!irqs_disabled_flags(flags)) { - /* ... if queue was empty ... */ - wake_nocb_gp(rdp, false, flags); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("WakeEmpty")); - } else { - wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE, - TPS("WakeEmptyIsDeferred")); - rcu_nocb_unlock_irqrestore(rdp, flags); - } - } else if (len > rdp->qlen_last_fqs_check + qhimark) { - /* ... or if many callbacks queued. */ - rdp->qlen_last_fqs_check = len; - j = jiffies; - if (j != rdp->nocb_gp_adv_time && - rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) && - rcu_seq_done(&rdp->mynode->gp_seq, cur_gp_seq)) { - rcu_advance_cbs_nowake(rdp->mynode, rdp); - rdp->nocb_gp_adv_time = j; - } - smp_mb(); /* Enqueue before timer_pending(). */ - if ((rdp->nocb_cb_sleep || - !rcu_segcblist_ready_cbs(&rdp->cblist)) && - !timer_pending(&rdp->nocb_bypass_timer)) - wake_nocb_gp_defer(rdp, RCU_NOCB_WAKE_FORCE, - TPS("WakeOvfIsDeferred")); - rcu_nocb_unlock_irqrestore(rdp, flags); - } else { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WakeNot")); - rcu_nocb_unlock_irqrestore(rdp, flags); - } - return; -} - -/* Wake up the no-CBs GP kthread to flush ->nocb_bypass. */ -static void do_nocb_bypass_wakeup_timer(struct timer_list *t) -{ - unsigned long flags; - struct rcu_data *rdp = from_timer(rdp, t, nocb_bypass_timer); - - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Timer")); - rcu_nocb_lock_irqsave(rdp, flags); - smp_mb__after_spinlock(); /* Timer expire before wakeup. */ - __call_rcu_nocb_wake(rdp, true, flags); -} - -/* - * No-CBs GP kthreads come here to wait for additional callbacks to show up - * or for grace periods to end. - */ -static void nocb_gp_wait(struct rcu_data *my_rdp) -{ - bool bypass = false; - long bypass_ncbs; - int __maybe_unused cpu = my_rdp->cpu; - unsigned long cur_gp_seq; - unsigned long flags; - bool gotcbs = false; - unsigned long j = jiffies; - bool needwait_gp = false; // This prevents actual uninitialized use. - bool needwake; - bool needwake_gp; - struct rcu_data *rdp; - struct rcu_node *rnp; - unsigned long wait_gp_seq = 0; // Suppress "use uninitialized" warning. - bool wasempty = false; - - /* - * Each pass through the following loop checks for CBs and for the - * nearest grace period (if any) to wait for next. The CB kthreads - * and the global grace-period kthread are awakened if needed. - */ - WARN_ON_ONCE(my_rdp->nocb_gp_rdp != my_rdp); - for (rdp = my_rdp; rdp; rdp = rdp->nocb_next_cb_rdp) { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("Check")); - rcu_nocb_lock_irqsave(rdp, flags); - bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); - if (bypass_ncbs && - (time_after(j, READ_ONCE(rdp->nocb_bypass_first) + 1) || - bypass_ncbs > 2 * qhimark)) { - // Bypass full or old, so flush it. - (void)rcu_nocb_try_flush_bypass(rdp, j); - bypass_ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); - } else if (!bypass_ncbs && rcu_segcblist_empty(&rdp->cblist)) { - rcu_nocb_unlock_irqrestore(rdp, flags); - continue; /* No callbacks here, try next. */ - } - if (bypass_ncbs) { - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("Bypass")); - bypass = true; - } - rnp = rdp->mynode; - if (bypass) { // Avoid race with first bypass CB. - WRITE_ONCE(my_rdp->nocb_defer_wakeup, - RCU_NOCB_WAKE_NOT); - del_timer(&my_rdp->nocb_timer); - } - // Advance callbacks if helpful and low contention. - needwake_gp = false; - if (!rcu_segcblist_restempty(&rdp->cblist, - RCU_NEXT_READY_TAIL) || - (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) && - rcu_seq_done(&rnp->gp_seq, cur_gp_seq))) { - raw_spin_lock_rcu_node(rnp); /* irqs disabled. */ - needwake_gp = rcu_advance_cbs(rnp, rdp); - wasempty = rcu_segcblist_restempty(&rdp->cblist, - RCU_NEXT_READY_TAIL); - raw_spin_unlock_rcu_node(rnp); /* irqs disabled. */ - } - // Need to wait on some grace period? - WARN_ON_ONCE(wasempty && - !rcu_segcblist_restempty(&rdp->cblist, - RCU_NEXT_READY_TAIL)); - if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq)) { - if (!needwait_gp || - ULONG_CMP_LT(cur_gp_seq, wait_gp_seq)) - wait_gp_seq = cur_gp_seq; - needwait_gp = true; - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, - TPS("NeedWaitGP")); - } - if (rcu_segcblist_ready_cbs(&rdp->cblist)) { - needwake = rdp->nocb_cb_sleep; - WRITE_ONCE(rdp->nocb_cb_sleep, false); - smp_mb(); /* CB invocation -after- GP end. */ - } else { - needwake = false; - } - rcu_nocb_unlock_irqrestore(rdp, flags); - if (needwake) { - swake_up_one(&rdp->nocb_cb_wq); - gotcbs = true; - } - if (needwake_gp) - rcu_gp_kthread_wake(); - } - - my_rdp->nocb_gp_bypass = bypass; - my_rdp->nocb_gp_gp = needwait_gp; - my_rdp->nocb_gp_seq = needwait_gp ? wait_gp_seq : 0; - if (bypass && !rcu_nocb_poll) { - // At least one child with non-empty ->nocb_bypass, so set - // timer in order to avoid stranding its callbacks. - raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags); - mod_timer(&my_rdp->nocb_bypass_timer, j + 2); - raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags); - } - if (rcu_nocb_poll) { - /* Polling, so trace if first poll in the series. */ - if (gotcbs) - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Poll")); - schedule_timeout_idle(1); - } else if (!needwait_gp) { - /* Wait for callbacks to appear. */ - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("Sleep")); - swait_event_interruptible_exclusive(my_rdp->nocb_gp_wq, - !READ_ONCE(my_rdp->nocb_gp_sleep)); - trace_rcu_nocb_wake(rcu_state.name, cpu, TPS("EndSleep")); - } else { - rnp = my_rdp->mynode; - trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("StartWait")); - swait_event_interruptible_exclusive( - rnp->nocb_gp_wq[rcu_seq_ctr(wait_gp_seq) & 0x1], - rcu_seq_done(&rnp->gp_seq, wait_gp_seq) || - !READ_ONCE(my_rdp->nocb_gp_sleep)); - trace_rcu_this_gp(rnp, my_rdp, wait_gp_seq, TPS("EndWait")); - } - if (!rcu_nocb_poll) { - raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags); - if (bypass) - del_timer(&my_rdp->nocb_bypass_timer); - WRITE_ONCE(my_rdp->nocb_gp_sleep, true); - raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags); - } - my_rdp->nocb_gp_seq = -1; - WARN_ON(signal_pending(current)); -} - -/* - * No-CBs grace-period-wait kthread. There is one of these per group - * of CPUs, but only once at least one CPU in that group has come online - * at least once since boot. This kthread checks for newly posted - * callbacks from any of the CPUs it is responsible for, waits for a - * grace period, then awakens all of the rcu_nocb_cb_kthread() instances - * that then have callback-invocation work to do. - */ -static int rcu_nocb_gp_kthread(void *arg) -{ - struct rcu_data *rdp = arg; - - for (;;) { - WRITE_ONCE(rdp->nocb_gp_loops, rdp->nocb_gp_loops + 1); - nocb_gp_wait(rdp); - cond_resched_tasks_rcu_qs(); - } - return 0; -} - -/* - * Invoke any ready callbacks from the corresponding no-CBs CPU, - * then, if there are no more, wait for more to appear. - */ -static void nocb_cb_wait(struct rcu_data *rdp) -{ - unsigned long cur_gp_seq; - unsigned long flags; - bool needwake_gp = false; - struct rcu_node *rnp = rdp->mynode; - - local_irq_save(flags); - rcu_momentary_dyntick_idle(); - local_irq_restore(flags); - local_bh_disable(); - rcu_do_batch(rdp); - local_bh_enable(); - lockdep_assert_irqs_enabled(); - rcu_nocb_lock_irqsave(rdp, flags); - if (rcu_segcblist_nextgp(&rdp->cblist, &cur_gp_seq) && - rcu_seq_done(&rnp->gp_seq, cur_gp_seq) && - raw_spin_trylock_rcu_node(rnp)) { /* irqs already disabled. */ - needwake_gp = rcu_advance_cbs(rdp->mynode, rdp); - raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ - } - if (rcu_segcblist_ready_cbs(&rdp->cblist)) { - rcu_nocb_unlock_irqrestore(rdp, flags); - if (needwake_gp) - rcu_gp_kthread_wake(); - return; - } - - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("CBSleep")); - WRITE_ONCE(rdp->nocb_cb_sleep, true); - rcu_nocb_unlock_irqrestore(rdp, flags); - if (needwake_gp) - rcu_gp_kthread_wake(); - swait_event_interruptible_exclusive(rdp->nocb_cb_wq, - !READ_ONCE(rdp->nocb_cb_sleep)); - if (!smp_load_acquire(&rdp->nocb_cb_sleep)) { /* VVV */ - /* ^^^ Ensure CB invocation follows _sleep test. */ - return; - } - WARN_ON(signal_pending(current)); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("WokeEmpty")); -} - -/* - * Per-rcu_data kthread, but only for no-CBs CPUs. Repeatedly invoke - * nocb_cb_wait() to do the dirty work. - */ -static int rcu_nocb_cb_kthread(void *arg) -{ - struct rcu_data *rdp = arg; - - // Each pass through this loop does one callback batch, and, - // if there are no more ready callbacks, waits for them. - for (;;) { - nocb_cb_wait(rdp); - cond_resched_tasks_rcu_qs(); - } - return 0; -} - -/* Is a deferred wakeup of rcu_nocb_kthread() required? */ -static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) -{ - return READ_ONCE(rdp->nocb_defer_wakeup); -} - -/* Do a deferred wakeup of rcu_nocb_kthread(). */ -static void do_nocb_deferred_wakeup_common(struct rcu_data *rdp) -{ - unsigned long flags; - int ndw; - - rcu_nocb_lock_irqsave(rdp, flags); - if (!rcu_nocb_need_deferred_wakeup(rdp)) { - rcu_nocb_unlock_irqrestore(rdp, flags); - return; - } - ndw = READ_ONCE(rdp->nocb_defer_wakeup); - WRITE_ONCE(rdp->nocb_defer_wakeup, RCU_NOCB_WAKE_NOT); - wake_nocb_gp(rdp, ndw == RCU_NOCB_WAKE_FORCE, flags); - trace_rcu_nocb_wake(rcu_state.name, rdp->cpu, TPS("DeferredWake")); -} - -/* Do a deferred wakeup of rcu_nocb_kthread() from a timer handler. */ -static void do_nocb_deferred_wakeup_timer(struct timer_list *t) -{ - struct rcu_data *rdp = from_timer(rdp, t, nocb_timer); - - do_nocb_deferred_wakeup_common(rdp); -} - -/* - * Do a deferred wakeup of rcu_nocb_kthread() from fastpath. - * This means we do an inexact common-case check. Note that if - * we miss, ->nocb_timer will eventually clean things up. - */ -static void do_nocb_deferred_wakeup(struct rcu_data *rdp) -{ - if (rcu_nocb_need_deferred_wakeup(rdp)) - do_nocb_deferred_wakeup_common(rdp); -} - -void __init rcu_init_nohz(void) -{ - int cpu; - bool need_rcu_nocb_mask = false; - struct rcu_data *rdp; - -#if defined(CONFIG_NO_HZ_FULL) - if (tick_nohz_full_running && cpumask_weight(tick_nohz_full_mask)) - need_rcu_nocb_mask = true; -#endif /* #if defined(CONFIG_NO_HZ_FULL) */ - - if (!cpumask_available(rcu_nocb_mask) && need_rcu_nocb_mask) { - if (!zalloc_cpumask_var(&rcu_nocb_mask, GFP_KERNEL)) { - pr_info("rcu_nocb_mask allocation failed, callback offloading disabled.\n"); - return; - } - } - if (!cpumask_available(rcu_nocb_mask)) - return; - -#if defined(CONFIG_NO_HZ_FULL) - if (tick_nohz_full_running) - cpumask_or(rcu_nocb_mask, rcu_nocb_mask, tick_nohz_full_mask); -#endif /* #if defined(CONFIG_NO_HZ_FULL) */ - - if (!cpumask_subset(rcu_nocb_mask, cpu_possible_mask)) { - pr_info("\tNote: kernel parameter 'rcu_nocbs=', 'nohz_full', or 'isolcpus=' contains nonexistent CPUs.\n"); - cpumask_and(rcu_nocb_mask, cpu_possible_mask, - rcu_nocb_mask); - } - if (cpumask_empty(rcu_nocb_mask)) - pr_info("\tOffload RCU callbacks from CPUs: (none).\n"); - else - pr_info("\tOffload RCU callbacks from CPUs: %*pbl.\n", - cpumask_pr_args(rcu_nocb_mask)); - if (rcu_nocb_poll) - pr_info("\tPoll for callbacks from no-CBs CPUs.\n"); - - for_each_cpu(cpu, rcu_nocb_mask) { - rdp = per_cpu_ptr(&rcu_data, cpu); - if (rcu_segcblist_empty(&rdp->cblist)) - rcu_segcblist_init(&rdp->cblist); - rcu_segcblist_offload(&rdp->cblist); - } - rcu_organize_nocb_kthreads(); -} - -/* Initialize per-rcu_data variables for no-CBs CPUs. */ -static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) -{ - init_swait_queue_head(&rdp->nocb_cb_wq); - init_swait_queue_head(&rdp->nocb_gp_wq); - raw_spin_lock_init(&rdp->nocb_lock); - raw_spin_lock_init(&rdp->nocb_bypass_lock); - raw_spin_lock_init(&rdp->nocb_gp_lock); - timer_setup(&rdp->nocb_timer, do_nocb_deferred_wakeup_timer, 0); - timer_setup(&rdp->nocb_bypass_timer, do_nocb_bypass_wakeup_timer, 0); - rcu_cblist_init(&rdp->nocb_bypass); -} - -/* - * If the specified CPU is a no-CBs CPU that does not already have its - * rcuo CB kthread, spawn it. Additionally, if the rcuo GP kthread - * for this CPU's group has not yet been created, spawn it as well. - */ -static void rcu_spawn_one_nocb_kthread(int cpu) -{ - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); - struct rcu_data *rdp_gp; - struct task_struct *t; - - /* - * If this isn't a no-CBs CPU or if it already has an rcuo kthread, - * then nothing to do. - */ - if (!rcu_is_nocb_cpu(cpu) || rdp->nocb_cb_kthread) - return; - - /* If we didn't spawn the GP kthread first, reorganize! */ - rdp_gp = rdp->nocb_gp_rdp; - if (!rdp_gp->nocb_gp_kthread) { - t = kthread_run(rcu_nocb_gp_kthread, rdp_gp, - "rcuog/%d", rdp_gp->cpu); - if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) - return; - WRITE_ONCE(rdp_gp->nocb_gp_kthread, t); - } - - /* Spawn the kthread for this CPU. */ - t = kthread_run(rcu_nocb_cb_kthread, rdp, - "rcuo%c/%d", rcu_state.abbr, cpu); - if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__)) - return; - WRITE_ONCE(rdp->nocb_cb_kthread, t); - WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread); -} - -/* - * If the specified CPU is a no-CBs CPU that does not already have its - * rcuo kthread, spawn it. - */ -static void rcu_spawn_cpu_nocb_kthread(int cpu) -{ - if (rcu_scheduler_fully_active) - rcu_spawn_one_nocb_kthread(cpu); -} - -/* - * Once the scheduler is running, spawn rcuo kthreads for all online - * no-CBs CPUs. This assumes that the early_initcall()s happen before - * non-boot CPUs come online -- if this changes, we will need to add - * some mutual exclusion. - */ -static void __init rcu_spawn_nocb_kthreads(void) -{ - int cpu; - - for_each_online_cpu(cpu) - rcu_spawn_cpu_nocb_kthread(cpu); -} - -/* How many CB CPU IDs per GP kthread? Default of -1 for sqrt(nr_cpu_ids). */ -static int rcu_nocb_gp_stride = -1; -module_param(rcu_nocb_gp_stride, int, 0444); - -/* - * Initialize GP-CB relationships for all no-CBs CPU. - */ -static void __init rcu_organize_nocb_kthreads(void) -{ - int cpu; - bool firsttime = true; - bool gotnocbs = false; - bool gotnocbscbs = true; - int ls = rcu_nocb_gp_stride; - int nl = 0; /* Next GP kthread. */ - struct rcu_data *rdp; - struct rcu_data *rdp_gp = NULL; /* Suppress misguided gcc warn. */ - struct rcu_data *rdp_prev = NULL; - - if (!cpumask_available(rcu_nocb_mask)) - return; - if (ls == -1) { - ls = nr_cpu_ids / int_sqrt(nr_cpu_ids); - rcu_nocb_gp_stride = ls; - } - - /* - * Each pass through this loop sets up one rcu_data structure. - * Should the corresponding CPU come online in the future, then - * we will spawn the needed set of rcu_nocb_kthread() kthreads. - */ - for_each_cpu(cpu, rcu_nocb_mask) { - rdp = per_cpu_ptr(&rcu_data, cpu); - if (rdp->cpu >= nl) { - /* New GP kthread, set up for CBs & next GP. */ - gotnocbs = true; - nl = DIV_ROUND_UP(rdp->cpu + 1, ls) * ls; - rdp->nocb_gp_rdp = rdp; - rdp_gp = rdp; - if (dump_tree) { - if (!firsttime) - pr_cont("%s\n", gotnocbscbs - ? "" : " (self only)"); - gotnocbscbs = false; - firsttime = false; - pr_alert("%s: No-CB GP kthread CPU %d:", - __func__, cpu); - } - } else { - /* Another CB kthread, link to previous GP kthread. */ - gotnocbscbs = true; - rdp->nocb_gp_rdp = rdp_gp; - rdp_prev->nocb_next_cb_rdp = rdp; - if (dump_tree) - pr_cont(" %d", cpu); - } - rdp_prev = rdp; - } - if (gotnocbs && dump_tree) - pr_cont("%s\n", gotnocbscbs ? "" : " (self only)"); -} - -/* - * Bind the current task to the offloaded CPUs. If there are no offloaded - * CPUs, leave the task unbound. Splat if the bind attempt fails. - */ -void rcu_bind_current_to_nocb(void) -{ - if (cpumask_available(rcu_nocb_mask) && cpumask_weight(rcu_nocb_mask)) - WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask)); -} -EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb); - -/* - * Dump out nocb grace-period kthread state for the specified rcu_data - * structure. - */ -static void show_rcu_nocb_gp_state(struct rcu_data *rdp) -{ - struct rcu_node *rnp = rdp->mynode; - - pr_info("nocb GP %d %c%c%c%c%c%c %c[%c%c] %c%c:%ld rnp %d:%d %lu\n", - rdp->cpu, - "kK"[!!rdp->nocb_gp_kthread], - "lL"[raw_spin_is_locked(&rdp->nocb_gp_lock)], - "dD"[!!rdp->nocb_defer_wakeup], - "tT"[timer_pending(&rdp->nocb_timer)], - "bB"[timer_pending(&rdp->nocb_bypass_timer)], - "sS"[!!rdp->nocb_gp_sleep], - ".W"[swait_active(&rdp->nocb_gp_wq)], - ".W"[swait_active(&rnp->nocb_gp_wq[0])], - ".W"[swait_active(&rnp->nocb_gp_wq[1])], - ".B"[!!rdp->nocb_gp_bypass], - ".G"[!!rdp->nocb_gp_gp], - (long)rdp->nocb_gp_seq, - rnp->grplo, rnp->grphi, READ_ONCE(rdp->nocb_gp_loops)); -} - -/* Dump out nocb kthread state for the specified rcu_data structure. */ -static void show_rcu_nocb_state(struct rcu_data *rdp) -{ - struct rcu_segcblist *rsclp = &rdp->cblist; - bool waslocked; - bool wastimer; - bool wassleep; - - if (rdp->nocb_gp_rdp == rdp) - show_rcu_nocb_gp_state(rdp); - - pr_info(" CB %d->%d %c%c%c%c%c%c F%ld L%ld C%d %c%c%c%c%c q%ld\n", - rdp->cpu, rdp->nocb_gp_rdp->cpu, - "kK"[!!rdp->nocb_cb_kthread], - "bB"[raw_spin_is_locked(&rdp->nocb_bypass_lock)], - "cC"[!!atomic_read(&rdp->nocb_lock_contended)], - "lL"[raw_spin_is_locked(&rdp->nocb_lock)], - "sS"[!!rdp->nocb_cb_sleep], - ".W"[swait_active(&rdp->nocb_cb_wq)], - jiffies - rdp->nocb_bypass_first, - jiffies - rdp->nocb_nobypass_last, - rdp->nocb_nobypass_count, - ".D"[rcu_segcblist_ready_cbs(rsclp)], - ".W"[!rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)], - ".R"[!rcu_segcblist_restempty(rsclp, RCU_WAIT_TAIL)], - ".N"[!rcu_segcblist_restempty(rsclp, RCU_NEXT_READY_TAIL)], - ".B"[!!rcu_cblist_n_cbs(&rdp->nocb_bypass)], - rcu_segcblist_n_cbs(&rdp->cblist)); - - /* It is OK for GP kthreads to have GP state. */ - if (rdp->nocb_gp_rdp == rdp) - return; - - waslocked = raw_spin_is_locked(&rdp->nocb_gp_lock); - wastimer = timer_pending(&rdp->nocb_bypass_timer); - wassleep = swait_active(&rdp->nocb_gp_wq); - if (!rdp->nocb_gp_sleep && !waslocked && !wastimer && !wassleep) - return; /* Nothing untowards. */ - - pr_info(" nocb GP activity on CB-only CPU!!! %c%c%c%c %c\n", - "lL"[waslocked], - "dD"[!!rdp->nocb_defer_wakeup], - "tT"[wastimer], - "sS"[!!rdp->nocb_gp_sleep], - ".W"[wassleep]); -} - -#else /* #ifdef CONFIG_RCU_NOCB_CPU */ - -/* No ->nocb_lock to acquire. */ -static void rcu_nocb_lock(struct rcu_data *rdp) -{ -} - -/* No ->nocb_lock to release. */ -static void rcu_nocb_unlock(struct rcu_data *rdp) -{ -} - -/* No ->nocb_lock to release. */ -static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, - unsigned long flags) -{ - local_irq_restore(flags); -} - -/* Lockdep check that ->cblist may be safely accessed. */ -static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp) -{ - lockdep_assert_irqs_disabled(); -} - -static void rcu_nocb_gp_cleanup(struct swait_queue_head *sq) -{ -} - -static struct swait_queue_head *rcu_nocb_gp_get(struct rcu_node *rnp) -{ - return NULL; -} - -static void rcu_init_one_nocb(struct rcu_node *rnp) -{ -} - -static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - unsigned long j) -{ - return true; -} - -static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, - bool *was_alldone, unsigned long flags) -{ - return false; -} - -static void __call_rcu_nocb_wake(struct rcu_data *rdp, bool was_empty, - unsigned long flags) -{ - WARN_ON_ONCE(1); /* Should be dead code! */ -} - -static void __init rcu_boot_init_nocb_percpu_data(struct rcu_data *rdp) -{ -} - -static int rcu_nocb_need_deferred_wakeup(struct rcu_data *rdp) -{ - return false; -} - -static void do_nocb_deferred_wakeup(struct rcu_data *rdp) -{ -} - -static void rcu_spawn_cpu_nocb_kthread(int cpu) -{ -} - -static void __init rcu_spawn_nocb_kthreads(void) -{ -} - -static void show_rcu_nocb_state(struct rcu_data *rdp) -{ -} - -#endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */ - /* * Is this CPU a NO_HZ_FULL CPU that should ignore RCU so that the * grace-period kthread will do force_quiescent_state() processing? @@ -2543,7 +1283,7 @@ static void show_rcu_nocb_state(struct rcu_data *rdp) * CPU unless the grace period has extended for too long. * * This code relies on the fact that all NO_HZ_FULL CPUs are also - * CONFIG_RCU_NOCB_CPU CPUs. + * RCU_NOCB_CPU CPUs. */ static bool rcu_nohz_full_cpu(void) { @@ -2563,39 +1303,5 @@ static void rcu_bind_gp_kthread(void) { if (!tick_nohz_full_enabled()) return; - housekeeping_affine(current, HK_FLAG_RCU); -} - -/* Record the current task on dyntick-idle entry. */ -static void noinstr rcu_dynticks_task_enter(void) -{ -#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) - WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id()); -#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ -} - -/* Record no current task on dyntick-idle exit. */ -static void noinstr rcu_dynticks_task_exit(void) -{ -#if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) - WRITE_ONCE(current->rcu_tasks_idle_cpu, -1); -#endif /* #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL) */ -} - -/* Turn on heavyweight RCU tasks trace readers on idle/user entry. */ -static void rcu_dynticks_task_trace_enter(void) -{ -#ifdef CONFIG_TASKS_RCU_TRACE - if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) - current->trc_reader_special.b.need_mb = true; -#endif /* #ifdef CONFIG_TASKS_RCU_TRACE */ -} - -/* Turn off heavyweight RCU tasks trace readers on idle/user exit. */ -static void rcu_dynticks_task_trace_exit(void) -{ -#ifdef CONFIG_TASKS_RCU_TRACE - if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB)) - current->trc_reader_special.b.need_mb = false; -#endif /* #ifdef CONFIG_TASKS_RCU_TRACE */ + housekeeping_affine(current, HK_TYPE_RCU); } diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 70d48c52fabc..5d666428546b 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -7,6 +7,9 @@ * Author: Paul E. McKenney <paulmck@linux.ibm.com> */ +#include <linux/kvm_para.h> +#include <linux/rcu_notifier.h> + ////////////////////////////////////////////////////////////////////////////// // // Controlling CPU stall warnings, including delay calculation. @@ -23,6 +26,34 @@ int sysctl_max_rcu_stall_to_panic __read_mostly; #define RCU_STALL_MIGHT_DIV 8 #define RCU_STALL_MIGHT_MIN (2 * HZ) +int rcu_exp_jiffies_till_stall_check(void) +{ + int cpu_stall_timeout = READ_ONCE(rcu_exp_cpu_stall_timeout); + int exp_stall_delay_delta = 0; + int till_stall_check; + + // Zero says to use rcu_cpu_stall_timeout, but in milliseconds. + if (!cpu_stall_timeout) + cpu_stall_timeout = jiffies_to_msecs(rcu_jiffies_till_stall_check()); + + // Limit check must be consistent with the Kconfig limits for + // CONFIG_RCU_EXP_CPU_STALL_TIMEOUT, so check the allowed range. + // The minimum clamped value is "2UL", because at least one full + // tick has to be guaranteed. + till_stall_check = clamp(msecs_to_jiffies(cpu_stall_timeout), 2UL, 300UL * HZ); + + if (cpu_stall_timeout && jiffies_to_msecs(till_stall_check) != cpu_stall_timeout) + WRITE_ONCE(rcu_exp_cpu_stall_timeout, jiffies_to_msecs(till_stall_check)); + +#ifdef CONFIG_PROVE_RCU + /* Add extra ~25% out of till_stall_check. */ + exp_stall_delay_delta = ((till_stall_check * 25) / 100) + 1; +#endif + + return till_stall_check + exp_stall_delay_delta; +} +EXPORT_SYMBOL_GPL(rcu_exp_jiffies_till_stall_check); + /* Limit-check stall timeouts specified at boottime and runtime. */ int rcu_jiffies_till_stall_check(void) { @@ -117,17 +148,19 @@ static void panic_on_rcu_stall(void) } /** - * rcu_cpu_stall_reset - prevent further stall warnings in current grace period + * rcu_cpu_stall_reset - restart stall-warning timeout for current grace period * - * Set the stall-warning timeout way off into the future, thus preventing - * any RCU CPU stall-warning messages from appearing in the current set of - * RCU grace periods. + * To perform the reset request from the caller, disable stall detection until + * 3 fqs loops have passed. This is required to ensure a fresh jiffies is + * loaded. It should be safe to do from the fqs loop as enough timer + * interrupts and context switches should have passed. * * The caller must disable hard irqs. */ void rcu_cpu_stall_reset(void) { - WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2); + WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, 3); + WRITE_ONCE(rcu_state.jiffies_stall, ULONG_MAX); } ////////////////////////////////////////////////////////////////////////////// @@ -143,6 +176,7 @@ static void record_gp_stall_check_time(void) WRITE_ONCE(rcu_state.gp_start, j); j1 = rcu_jiffies_till_stall_check(); smp_mb(); // ->gp_start before ->jiffies_stall and caller's ->gp_seq. + WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, 0); WRITE_ONCE(rcu_state.jiffies_stall, j + j1); rcu_state.jiffies_resched = j + j1 / 2; rcu_state.n_force_qs_gpstart = READ_ONCE(rcu_state.n_force_qs); @@ -241,16 +275,16 @@ struct rcu_stall_chk_rdr { * Report out the state of a not-running task that is stalling the * current RCU grace period. */ -static bool check_slow_task(struct task_struct *t, void *arg) +static int check_slow_task(struct task_struct *t, void *arg) { struct rcu_stall_chk_rdr *rscrp = arg; if (task_curr(t)) - return false; // It is running, so decline to inspect it. + return -EBUSY; // It is running, so decline to inspect it. rscrp->nesting = t->rcu_read_lock_nesting; rscrp->rs = t->rcu_read_unlock_special; rscrp->on_blkd_list = !list_empty(&t->rcu_node_entry); - return true; + return 0; } /* @@ -266,8 +300,11 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) struct task_struct *t; struct task_struct *ts[8]; - if (!rcu_preempt_blocked_readers_cgp(rnp)) + lockdep_assert_irqs_disabled(); + if (!rcu_preempt_blocked_readers_cgp(rnp)) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return 0; + } pr_err("\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", rnp->level, rnp->grplo, rnp->grphi); t = list_entry(rnp->gp_tasks->prev, @@ -279,9 +316,9 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) break; } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - for (i--; i; i--) { - t = ts[i]; - if (!try_invoke_on_locked_down_task(t, check_slow_task, &rscr)) + while (i) { + t = ts[--i]; + if (task_call_func(t, check_slow_task, &rscr)) pr_cont(" P%d", t->pid); else pr_cont(" P%d/%d:%c%c%c%c", @@ -290,6 +327,7 @@ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) ".q"[rscr.rs.b.need_qs], ".e"[rscr.rs.b.exp_hint], ".l"[rscr.on_blkd_list]); + lockdep_assert_irqs_disabled(); put_task_struct(t); ndetected++; } @@ -312,6 +350,7 @@ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) * tasks blocked within RCU read-side critical sections. */ static int rcu_print_task_stall(struct rcu_node *rnp, unsigned long flags) + __releases(rnp->lock) { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return 0; @@ -333,33 +372,16 @@ static void rcu_dump_cpu_stacks(void) rcu_for_each_leaf_node(rnp) { raw_spin_lock_irqsave_rcu_node(rnp, flags); for_each_leaf_node_possible_cpu(rnp, cpu) - if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) - if (!trigger_single_cpu_backtrace(cpu)) + if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { + if (cpu_is_offline(cpu)) + pr_err("Offline CPU %d blocking current GP.\n", cpu); + else dump_cpu_task(cpu); + } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } } -#ifdef CONFIG_RCU_FAST_NO_HZ - -static void print_cpu_stall_fast_no_hz(char *cp, int cpu) -{ - struct rcu_data *rdp = &per_cpu(rcu_data, cpu); - - sprintf(cp, "last_accelerate: %04lx/%04lx dyntick_enabled: %d", - rdp->last_accelerate & 0xffff, jiffies & 0xffff, - !!rdp->tick_nohz_enabled_snap); -} - -#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ - -static void print_cpu_stall_fast_no_hz(char *cp, int cpu) -{ - *cp = '\0'; -} - -#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ - static const char * const gp_state_names[] = { [RCU_GP_IDLE] = "RCU_GP_IDLE", [RCU_GP_WAIT_GPS] = "RCU_GP_WAIT_GPS", @@ -392,6 +414,56 @@ static bool rcu_is_gp_kthread_starving(unsigned long *jp) return j > 2 * HZ; } +static bool rcu_is_rcuc_kthread_starving(struct rcu_data *rdp, unsigned long *jp) +{ + int cpu; + struct task_struct *rcuc; + unsigned long j; + + rcuc = rdp->rcu_cpu_kthread_task; + if (!rcuc) + return false; + + cpu = task_cpu(rcuc); + if (cpu_is_offline(cpu) || idle_cpu(cpu)) + return false; + + j = jiffies - READ_ONCE(rdp->rcuc_activity); + + if (jp) + *jp = j; + return j > 2 * HZ; +} + +static void print_cpu_stat_info(int cpu) +{ + struct rcu_snap_record rsr, *rsrp; + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + struct kernel_cpustat *kcsp = &kcpustat_cpu(cpu); + + if (!rcu_cpu_stall_cputime) + return; + + rsrp = &rdp->snap_record; + if (rsrp->gp_seq != rdp->gp_seq) + return; + + rsr.cputime_irq = kcpustat_field(kcsp, CPUTIME_IRQ, cpu); + rsr.cputime_softirq = kcpustat_field(kcsp, CPUTIME_SOFTIRQ, cpu); + rsr.cputime_system = kcpustat_field(kcsp, CPUTIME_SYSTEM, cpu); + + pr_err("\t hardirqs softirqs csw/system\n"); + pr_err("\t number: %8ld %10d %12lld\n", + kstat_cpu_irqs_sum(cpu) - rsrp->nr_hardirqs, + kstat_cpu_softirqs_sum(cpu) - rsrp->nr_softirqs, + nr_context_switches_cpu(cpu) - rsrp->nr_csw); + pr_err("\tcputime: %8lld %10lld %12lld ==> %d(ms)\n", + div_u64(rsr.cputime_irq - rsrp->cputime_irq, NSEC_PER_MSEC), + div_u64(rsr.cputime_softirq - rsrp->cputime_softirq, NSEC_PER_MSEC), + div_u64(rsr.cputime_system - rsrp->cputime_system, NSEC_PER_MSEC), + jiffies_to_msecs(jiffies - rsrp->jiffies)); +} + /* * Print out diagnostic information for the specified stalled CPU. * @@ -401,16 +473,18 @@ static bool rcu_is_gp_kthread_starving(unsigned long *jp) * of RCU grace periods that this CPU is ignorant of, for example, "1" * if the CPU was aware of the previous grace period. * - * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. + * Also print out idle info. */ static void print_cpu_stall_info(int cpu) { unsigned long delta; bool falsepositive; - char fast_no_hz[72]; struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); char *ticks_title; unsigned long ticks_value; + bool rcuc_starved; + unsigned long j; + char buf[32]; /* * We could be printing a lot while holding a spinlock. Avoid @@ -425,11 +499,13 @@ static void print_cpu_stall_info(int cpu) ticks_title = "ticks this GP"; ticks_value = rdp->ticks_this_gp; } - print_cpu_stall_fast_no_hz(fast_no_hz, cpu); delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq); falsepositive = rcu_is_gp_kthread_starving(NULL) && - rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)); - pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s%s\n", + rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu)); + rcuc_starved = rcu_is_rcuc_kthread_starving(rdp, &j); + if (rcuc_starved) + sprintf(buf, " rcuc=%ld jiffies(starved)", j); + pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%04x/%ld/%#lx softirq=%u/%u fqs=%ld%s%s\n", cpu, "O."[!!cpu_online(cpu)], "o."[!!(rdp->grpmask & rdp->mynode->qsmaskinit)], @@ -438,36 +514,79 @@ static void print_cpu_stall_info(int cpu) rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' : "!."[!delta], ticks_value, ticks_title, - rcu_dynticks_snap(rdp) & 0xfff, - rdp->dynticks_nesting, rdp->dynticks_nmi_nesting, + rcu_dynticks_snap(cpu) & 0xffff, + ct_dynticks_nesting_cpu(cpu), ct_dynticks_nmi_nesting_cpu(cpu), rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu), data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart, - fast_no_hz, + rcuc_starved ? buf : "", falsepositive ? " (false positive?)" : ""); + + print_cpu_stat_info(cpu); } /* Complain about starvation of grace-period kthread. */ static void rcu_check_gp_kthread_starvation(void) { + int cpu; struct task_struct *gpk = rcu_state.gp_kthread; unsigned long j; if (rcu_is_gp_kthread_starving(&j)) { - pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n", + cpu = gpk ? task_cpu(gpk) : -1; + pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#x ->cpu=%d\n", rcu_state.name, j, (long)rcu_seq_current(&rcu_state.gp_seq), - data_race(rcu_state.gp_flags), - gp_state_getname(rcu_state.gp_state), rcu_state.gp_state, - gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1); + data_race(READ_ONCE(rcu_state.gp_flags)), + gp_state_getname(rcu_state.gp_state), + data_race(READ_ONCE(rcu_state.gp_state)), + gpk ? data_race(READ_ONCE(gpk->__state)) : ~0, cpu); if (gpk) { + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name); pr_err("RCU grace-period kthread stack dump:\n"); sched_show_task(gpk); + if (cpu_is_offline(cpu)) { + pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); + } else if (!(data_race(READ_ONCE(rdp->mynode->qsmask)) & rdp->grpmask)) { + pr_err("Stack dump where RCU GP kthread last ran:\n"); + dump_cpu_task(cpu); + } wake_up_process(gpk); } } } +/* Complain about missing wakeups from expired fqs wait timer */ +static void rcu_check_gp_kthread_expired_fqs_timer(void) +{ + struct task_struct *gpk = rcu_state.gp_kthread; + short gp_state; + unsigned long jiffies_fqs; + int cpu; + + /* + * Order reads of .gp_state and .jiffies_force_qs. + * Matching smp_wmb() is present in rcu_gp_fqs_loop(). + */ + gp_state = smp_load_acquire(&rcu_state.gp_state); + jiffies_fqs = READ_ONCE(rcu_state.jiffies_force_qs); + + if (gp_state == RCU_GP_WAIT_FQS && + time_after(jiffies, jiffies_fqs + RCU_STALL_MIGHT_MIN) && + gpk && !READ_ONCE(gpk->on_rq)) { + cpu = task_cpu(gpk); + pr_err("%s kthread timer wakeup didn't happen for %ld jiffies! g%ld f%#x %s(%d) ->state=%#x\n", + rcu_state.name, (jiffies - jiffies_fqs), + (long)rcu_seq_current(&rcu_state.gp_seq), + data_race(rcu_state.gp_flags), + gp_state_getname(RCU_GP_WAIT_FQS), RCU_GP_WAIT_FQS, + data_race(READ_ONCE(gpk->__state))); + pr_err("\tPossible timer handling issue on cpu=%d timer-softirq=%u\n", + cpu, kstat_softirqs_cpu(TIMER_SOFTIRQ, cpu)); + } +} + static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) { int cpu; @@ -478,6 +597,8 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) struct rcu_node *rnp; long totqlen = 0; + lockdep_assert_irqs_disabled(); + /* Kick and suppress, if so configured. */ rcu_stall_kick_kthreads(); if (rcu_stall_is_suppressed()) @@ -488,6 +609,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) * See Documentation/RCU/stallwarn.rst for info on how to debug * RCU CPU stall warnings. */ + trace_rcu_stall_warning(rcu_state.name, TPS("StallDetected")); pr_err("INFO: %s detected stalls on CPUs/tasks:\n", rcu_state.name); rcu_for_each_leaf_node(rnp) { raw_spin_lock_irqsave_rcu_node(rnp, flags); @@ -499,13 +621,14 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) } } ndetected += rcu_print_task_stall(rnp, flags); // Releases rnp->lock. + lockdep_assert_irqs_disabled(); } for_each_possible_cpu(cpu) totqlen += rcu_get_n_cbs_cpu(cpu); - pr_cont("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n", + pr_err("\t(detected by %d, t=%ld jiffies, g=%ld, q=%lu ncpus=%d)\n", smp_processor_id(), (long)(jiffies - gps), - (long)rcu_seq_current(&rcu_state.gp_seq), totqlen); + (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus); if (ndetected) { rcu_dump_cpu_stacks(); @@ -517,11 +640,11 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) pr_err("INFO: Stall ended before state dump start\n"); } else { j = jiffies; - gpa = data_race(rcu_state.gp_activity); + gpa = data_race(READ_ONCE(rcu_state.gp_activity)); pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n", rcu_state.name, j - gpa, j, gpa, - data_race(jiffies_till_next_fqs), - rcu_get_root()->qsmask); + data_race(READ_ONCE(jiffies_till_next_fqs)), + data_race(READ_ONCE(rcu_get_root()->qsmask))); } } /* Rewrite if needed in case of slow consoles. */ @@ -529,6 +652,7 @@ static void print_other_cpu_stall(unsigned long gp_seq, unsigned long gps) WRITE_ONCE(rcu_state.jiffies_stall, jiffies + 3 * rcu_jiffies_till_stall_check() + 3); + rcu_check_gp_kthread_expired_fqs_timer(); rcu_check_gp_kthread_starvation(); panic_on_rcu_stall(); @@ -544,6 +668,8 @@ static void print_cpu_stall(unsigned long gps) struct rcu_node *rnp = rcu_get_root(); long totqlen = 0; + lockdep_assert_irqs_disabled(); + /* Kick and suppress, if so configured. */ rcu_stall_kick_kthreads(); if (rcu_stall_is_suppressed()) @@ -554,16 +680,18 @@ static void print_cpu_stall(unsigned long gps) * See Documentation/RCU/stallwarn.rst for info on how to debug * RCU CPU stall warnings. */ + trace_rcu_stall_warning(rcu_state.name, TPS("SelfDetected")); pr_err("INFO: %s self-detected stall on CPU\n", rcu_state.name); raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags); print_cpu_stall_info(smp_processor_id()); raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags); for_each_possible_cpu(cpu) totqlen += rcu_get_n_cbs_cpu(cpu); - pr_cont("\t(t=%lu jiffies g=%ld q=%lu)\n", + pr_err("\t(t=%lu jiffies g=%ld q=%lu ncpus=%d)\n", jiffies - gps, - (long)rcu_seq_current(&rcu_state.gp_seq), totqlen); + (long)rcu_seq_current(&rcu_state.gp_seq), totqlen, rcu_state.n_online_cpus); + rcu_check_gp_kthread_expired_fqs_timer(); rcu_check_gp_kthread_starvation(); rcu_dump_cpu_stacks(); @@ -590,6 +718,7 @@ static void print_cpu_stall(unsigned long gps) static void check_cpu_stall(struct rcu_data *rdp) { + bool self_detected; unsigned long gs1; unsigned long gs2; unsigned long gps; @@ -598,10 +727,21 @@ static void check_cpu_stall(struct rcu_data *rdp) unsigned long js; struct rcu_node *rnp; + lockdep_assert_irqs_disabled(); if ((rcu_stall_is_suppressed() && !READ_ONCE(rcu_kick_kthreads)) || !rcu_gp_in_progress()) return; rcu_stall_kick_kthreads(); + + /* + * Check if it was requested (via rcu_cpu_stall_reset()) that the FQS + * loop has to set jiffies to ensure a non-stale jiffies value. This + * is required to have good jiffies value after coming out of long + * breaks of jiffies updates. Not doing so can cause false positives. + */ + if (READ_ONCE(rcu_state.nr_fqs_jiffies_stall) > 0) + return; + j = jiffies; /* @@ -634,33 +774,101 @@ static void check_cpu_stall(struct rcu_data *rdp) ULONG_CMP_GE(gps, js)) return; /* No stall or GP completed since entering function. */ rnp = rdp->mynode; - jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3; + jn = jiffies + ULONG_MAX / 2; + self_detected = READ_ONCE(rnp->qsmask) & rdp->grpmask; if (rcu_gp_in_progress() && - (READ_ONCE(rnp->qsmask) & rdp->grpmask) && + (self_detected || ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) && cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) { + /* + * If a virtual machine is stopped by the host it can look to + * the watchdog like an RCU stall. Check to see if the host + * stopped the vm. + */ + if (kvm_check_and_clear_guest_paused()) + return; - /* We haven't checked in, so go dump stack. */ - print_cpu_stall(gps); - if (READ_ONCE(rcu_cpu_stall_ftrace_dump)) - rcu_ftrace_dump(DUMP_ALL); - - } else if (rcu_gp_in_progress() && - ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) && - cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) { + rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_NORM, (void *)j - gps); + if (self_detected) { + /* We haven't checked in, so go dump stack. */ + print_cpu_stall(gps); + } else { + /* They had a few time units to dump stack, so complain. */ + print_other_cpu_stall(gs2, gps); + } - /* They had a few time units to dump stack, so complain. */ - print_other_cpu_stall(gs2, gps); if (READ_ONCE(rcu_cpu_stall_ftrace_dump)) rcu_ftrace_dump(DUMP_ALL); + + if (READ_ONCE(rcu_state.jiffies_stall) == jn) { + jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3; + WRITE_ONCE(rcu_state.jiffies_stall, jn); + } } } ////////////////////////////////////////////////////////////////////////////// // -// RCU forward-progress mechanisms, including of callback invocation. +// RCU forward-progress mechanisms, including for callback invocation. /* + * Check to see if a failure to end RCU priority inversion was due to + * a CPU not passing through a quiescent state. When this happens, there + * is nothing that RCU priority boosting can do to help, so we shouldn't + * count this as an RCU priority boosting failure. A return of true says + * RCU priority boosting is to blame, and false says otherwise. If false + * is returned, the first of the CPUs to blame is stored through cpup. + * If there was no CPU blocking the current grace period, but also nothing + * in need of being boosted, *cpup is set to -1. This can happen in case + * of vCPU preemption while the last CPU is reporting its quiscent state, + * for example. + * + * If cpup is NULL, then a lockless quick check is carried out, suitable + * for high-rate usage. On the other hand, if cpup is non-NULL, each + * rcu_node structure's ->lock is acquired, ruling out high-rate usage. + */ +bool rcu_check_boost_fail(unsigned long gp_state, int *cpup) +{ + bool atb = false; + int cpu; + unsigned long flags; + struct rcu_node *rnp; + + rcu_for_each_leaf_node(rnp) { + if (!cpup) { + if (data_race(READ_ONCE(rnp->qsmask))) { + return false; + } else { + if (READ_ONCE(rnp->gp_tasks)) + atb = true; + continue; + } + } + *cpup = -1; + raw_spin_lock_irqsave_rcu_node(rnp, flags); + if (rnp->gp_tasks) + atb = true; + if (!rnp->qsmask) { + // No CPUs without quiescent states for this rnp. + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + continue; + } + // Find the first holdout CPU. + for_each_leaf_node_possible_cpu(rnp, cpu) { + if (rnp->qsmask & (1UL << (cpu - rnp->grplo))) { + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + *cpup = cpu; + return false; + } + } + raw_spin_unlock_irqrestore_rcu_node(rnp, flags); + } + // Can't blame CPUs, so must blame RCU priority boosting. + return atb; +} +EXPORT_SYMBOL_GPL(rcu_check_boost_fail); + +/* * Show the state of the grace-period kthreads. */ void show_rcu_gp_kthreads(void) @@ -670,29 +878,41 @@ void show_rcu_gp_kthreads(void) unsigned long j; unsigned long ja; unsigned long jr; + unsigned long js; unsigned long jw; struct rcu_data *rdp; struct rcu_node *rnp; struct task_struct *t = READ_ONCE(rcu_state.gp_kthread); j = jiffies; - ja = j - data_race(rcu_state.gp_activity); - jr = j - data_race(rcu_state.gp_req_activity); - jw = j - data_race(rcu_state.gp_wake_time); - pr_info("%s: wait state: %s(%d) ->state: %#lx delta ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_flags %#x\n", + ja = j - data_race(READ_ONCE(rcu_state.gp_activity)); + jr = j - data_race(READ_ONCE(rcu_state.gp_req_activity)); + js = j - data_race(READ_ONCE(rcu_state.gp_start)); + jw = j - data_race(READ_ONCE(rcu_state.gp_wake_time)); + pr_info("%s: wait state: %s(%d) ->state: %#x ->rt_priority %u delta ->gp_start %lu ->gp_activity %lu ->gp_req_activity %lu ->gp_wake_time %lu ->gp_wake_seq %ld ->gp_seq %ld ->gp_seq_needed %ld ->gp_max %lu ->gp_flags %#x\n", rcu_state.name, gp_state_getname(rcu_state.gp_state), - rcu_state.gp_state, t ? t->state : 0x1ffffL, - ja, jr, jw, (long)data_race(rcu_state.gp_wake_seq), - (long)data_race(rcu_state.gp_seq), - (long)data_race(rcu_get_root()->gp_seq_needed), - data_race(rcu_state.gp_flags)); + data_race(READ_ONCE(rcu_state.gp_state)), + t ? data_race(READ_ONCE(t->__state)) : 0x1ffff, t ? t->rt_priority : 0xffU, + js, ja, jr, jw, (long)data_race(READ_ONCE(rcu_state.gp_wake_seq)), + (long)data_race(READ_ONCE(rcu_state.gp_seq)), + (long)data_race(READ_ONCE(rcu_get_root()->gp_seq_needed)), + data_race(READ_ONCE(rcu_state.gp_max)), + data_race(READ_ONCE(rcu_state.gp_flags))); rcu_for_each_node_breadth_first(rnp) { - if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), - READ_ONCE(rnp->gp_seq_needed))) + if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), READ_ONCE(rnp->gp_seq_needed)) && + !data_race(READ_ONCE(rnp->qsmask)) && !data_race(READ_ONCE(rnp->boost_tasks)) && + !data_race(READ_ONCE(rnp->exp_tasks)) && !data_race(READ_ONCE(rnp->gp_tasks))) continue; - pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n", - rnp->grplo, rnp->grphi, (long)data_race(rnp->gp_seq), - (long)data_race(rnp->gp_seq_needed)); + pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld ->qsmask %#lx %c%c%c%c ->n_boosts %ld\n", + rnp->grplo, rnp->grphi, + (long)data_race(READ_ONCE(rnp->gp_seq)), + (long)data_race(READ_ONCE(rnp->gp_seq_needed)), + data_race(READ_ONCE(rnp->qsmask)), + ".b"[!!data_race(READ_ONCE(rnp->boost_kthread_task))], + ".B"[!!data_race(READ_ONCE(rnp->boost_tasks))], + ".E"[!!data_race(READ_ONCE(rnp->exp_tasks))], + ".G"[!!data_race(READ_ONCE(rnp->gp_tasks))], + data_race(READ_ONCE(rnp->n_boosts))); if (!rcu_is_leaf_node(rnp)) continue; for_each_leaf_node_possible_cpu(rnp, cpu) { @@ -702,12 +922,12 @@ void show_rcu_gp_kthreads(void) READ_ONCE(rdp->gp_seq_needed))) continue; pr_info("\tcpu %d ->gp_seq_needed %ld\n", - cpu, (long)data_race(rdp->gp_seq_needed)); + cpu, (long)data_race(READ_ONCE(rdp->gp_seq_needed))); } } for_each_possible_cpu(cpu) { rdp = per_cpu_ptr(&rcu_data, cpu); - cbs += data_race(rdp->n_cbs_invoked); + cbs += data_race(READ_ONCE(rdp->n_cbs_invoked)); if (rcu_segcblist_is_offloaded(&rdp->cblist)) show_rcu_nocb_state(rdp); } @@ -789,11 +1009,11 @@ void rcu_fwd_progress_check(unsigned long j) if (rcu_gp_in_progress()) { pr_info("%s: GP age %lu jiffies\n", - __func__, jiffies - rcu_state.gp_start); + __func__, jiffies - data_race(READ_ONCE(rcu_state.gp_start))); show_rcu_gp_kthreads(); } else { pr_info("%s: Last GP end %lu jiffies ago\n", - __func__, jiffies - rcu_state.gp_end); + __func__, jiffies - data_race(READ_ONCE(rcu_state.gp_end))); preempt_disable(); rdp = this_cpu_ptr(&rcu_data); rcu_check_gp_start_stall(rdp->mynode, rdp, j); @@ -821,7 +1041,7 @@ static bool sysrq_rcu; module_param(sysrq_rcu, bool, 0444); /* Dump grace-period-request information due to commandeered sysrq. */ -static void sysrq_show_rcu(int key) +static void sysrq_show_rcu(u8 key) { show_rcu_gp_kthreads(); } @@ -840,3 +1060,67 @@ static int __init rcu_sysrq_init(void) return 0; } early_initcall(rcu_sysrq_init); + +#ifdef CONFIG_RCU_CPU_STALL_NOTIFIER + +////////////////////////////////////////////////////////////////////////////// +// +// RCU CPU stall-warning notifiers + +static ATOMIC_NOTIFIER_HEAD(rcu_cpu_stall_notifier_list); + +/** + * rcu_stall_chain_notifier_register - Add an RCU CPU stall notifier + * @n: Entry to add. + * + * Adds an RCU CPU stall notifier to an atomic notifier chain. + * The @action passed to a notifier will be @RCU_STALL_NOTIFY_NORM or + * friends. The @data will be the duration of the stalled grace period, + * in jiffies, coerced to a void* pointer. + * + * Returns 0 on success, %-EEXIST on error. + */ +int rcu_stall_chain_notifier_register(struct notifier_block *n) +{ + int rcsn = rcu_cpu_stall_notifiers; + + WARN(1, "Adding %pS() to RCU stall notifier list (%s).\n", n->notifier_call, + rcsn ? "possibly suppressing RCU CPU stall warnings" : "failed, so all is well"); + if (rcsn) + return atomic_notifier_chain_register(&rcu_cpu_stall_notifier_list, n); + return -EEXIST; +} +EXPORT_SYMBOL_GPL(rcu_stall_chain_notifier_register); + +/** + * rcu_stall_chain_notifier_unregister - Remove an RCU CPU stall notifier + * @n: Entry to add. + * + * Removes an RCU CPU stall notifier from an atomic notifier chain. + * + * Returns zero on success, %-ENOENT on failure. + */ +int rcu_stall_chain_notifier_unregister(struct notifier_block *n) +{ + return atomic_notifier_chain_unregister(&rcu_cpu_stall_notifier_list, n); +} +EXPORT_SYMBOL_GPL(rcu_stall_chain_notifier_unregister); + +/* + * rcu_stall_notifier_call_chain - Call functions in an RCU CPU stall notifier chain + * @val: Value passed unmodified to notifier function + * @v: Pointer passed unmodified to notifier function + * + * Calls each function in the RCU CPU stall notifier chain in turn, which + * is an atomic call chain. See atomic_notifier_call_chain() for more + * information. + * + * This is for use within RCU, hence the omission of the extra asterisk + * to indicate a non-kerneldoc format header comment. + */ +int rcu_stall_notifier_call_chain(unsigned long val, void *v) +{ + return atomic_notifier_call_chain(&rcu_cpu_stall_notifier_list, val, v); +} + +#endif // #ifdef CONFIG_RCU_CPU_STALL_NOTIFIER diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 39334d2d2b37..46aaaa9fe339 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -25,6 +25,7 @@ #include <linux/interrupt.h> #include <linux/sched/signal.h> #include <linux/sched/debug.h> +#include <linux/torture.h> #include <linux/atomic.h> #include <linux/bitops.h> #include <linux/percpu.h> @@ -54,10 +55,12 @@ #define MODULE_PARAM_PREFIX "rcupdate." #ifndef CONFIG_TINY_RCU -module_param(rcu_expedited, int, 0); -module_param(rcu_normal, int, 0); -static int rcu_normal_after_boot; -module_param(rcu_normal_after_boot, int, 0); +module_param(rcu_expedited, int, 0444); +module_param(rcu_normal, int, 0444); +static int rcu_normal_after_boot = IS_ENABLED(CONFIG_PREEMPT_RT); +#if !defined(CONFIG_PREEMPT_RT) || defined(CONFIG_NO_HZ_FULL) +module_param(rcu_normal_after_boot, int, 0444); +#endif #endif /* #ifndef CONFIG_TINY_RCU */ #ifdef CONFIG_DEBUG_LOCK_ALLOC @@ -83,7 +86,7 @@ module_param(rcu_normal_after_boot, int, 0); * and while lockdep is disabled. * * Note that if the CPU is in the idle loop from an RCU point of view (ie: - * that we are in the section between rcu_idle_enter() and rcu_idle_exit()) + * that we are in the section between ct_idle_enter() and ct_idle_exit()) * then rcu_read_lock_held() sets ``*ret`` to false even if the CPU did an * rcu_read_lock(). The reason for this is that RCU ignores CPUs that are * in such a section, considering these as in extended quiescent state, @@ -142,8 +145,45 @@ bool rcu_gp_is_normal(void) } EXPORT_SYMBOL_GPL(rcu_gp_is_normal); -static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1); +static atomic_t rcu_async_hurry_nesting = ATOMIC_INIT(1); +/* + * Should call_rcu() callbacks be processed with urgency or are + * they OK being executed with arbitrary delays? + */ +bool rcu_async_should_hurry(void) +{ + return !IS_ENABLED(CONFIG_RCU_LAZY) || + atomic_read(&rcu_async_hurry_nesting); +} +EXPORT_SYMBOL_GPL(rcu_async_should_hurry); + +/** + * rcu_async_hurry - Make future async RCU callbacks not lazy. + * + * After a call to this function, future calls to call_rcu() + * will be processed in a timely fashion. + */ +void rcu_async_hurry(void) +{ + if (IS_ENABLED(CONFIG_RCU_LAZY)) + atomic_inc(&rcu_async_hurry_nesting); +} +EXPORT_SYMBOL_GPL(rcu_async_hurry); +/** + * rcu_async_relax - Make future async RCU callbacks lazy. + * + * After a call to this function, future calls to call_rcu() + * will be processed in a lazy fashion. + */ +void rcu_async_relax(void) +{ + if (IS_ENABLED(CONFIG_RCU_LAZY)) + atomic_dec(&rcu_async_hurry_nesting); +} +EXPORT_SYMBOL_GPL(rcu_async_relax); + +static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1); /* * Should normal grace-period primitives be expedited? Intended for * use within RCU. Note that this function takes the rcu_expedited @@ -193,6 +233,7 @@ static bool rcu_boot_ended __read_mostly; void rcu_end_inkernel_boot(void) { rcu_unexpedite_gp(); + rcu_async_relax(); if (rcu_normal_after_boot) WRITE_ONCE(rcu_normal, 1); rcu_boot_ended = true; @@ -218,11 +259,12 @@ void rcu_test_sync_prims(void) { if (!IS_ENABLED(CONFIG_PROVE_RCU)) return; + pr_info("Running RCU synchronous self tests\n"); synchronize_rcu(); synchronize_rcu_expedited(); } -#if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) +#if !defined(CONFIG_TINY_RCU) /* * Switch to run-time mode once RCU has fully initialized. @@ -237,7 +279,7 @@ static int __init rcu_set_runtime_mode(void) } core_initcall(rcu_set_runtime_mode); -#endif /* #if !defined(CONFIG_TINY_RCU) || defined(CONFIG_SRCU) */ +#endif /* #if !defined(CONFIG_TINY_RCU) */ #ifdef CONFIG_DEBUG_LOCK_ALLOC static struct lock_class_key rcu_lock_key; @@ -245,7 +287,7 @@ struct lockdep_map rcu_lock_map = { .name = "rcu_read_lock", .key = &rcu_lock_key, .wait_type_outer = LD_WAIT_FREE, - .wait_type_inner = LD_WAIT_CONFIG, /* XXX PREEMPT_RCU ? */ + .wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_RT implies PREEMPT_RCU */ }; EXPORT_SYMBOL_GPL(rcu_lock_map); @@ -254,7 +296,7 @@ struct lockdep_map rcu_bh_lock_map = { .name = "rcu_read_lock_bh", .key = &rcu_bh_lock_key, .wait_type_outer = LD_WAIT_FREE, - .wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_LOCK also makes BH preemptible */ + .wait_type_inner = LD_WAIT_CONFIG, /* PREEMPT_RT makes BH preemptible. */ }; EXPORT_SYMBOL_GPL(rcu_bh_lock_map); @@ -275,7 +317,7 @@ EXPORT_SYMBOL_GPL(rcu_callback_map); noinstr int notrace debug_lockdep_rcu_enabled(void) { - return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && debug_locks && + return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && READ_ONCE(debug_locks) && current->lockdep_recursion == 0; } EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled); @@ -405,6 +447,13 @@ void __wait_rcu_gp(bool checktiny, int n, call_rcu_func_t *crcu_array, } EXPORT_SYMBOL_GPL(__wait_rcu_gp); +void finish_rcuwait(struct rcuwait *w) +{ + rcu_assign_pointer(w->task, NULL); + __set_current_state(TASK_RUNNING); +} +EXPORT_SYMBOL_GPL(finish_rcuwait); + #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD void init_rcu_head(struct rcu_head *head) { @@ -476,27 +525,39 @@ EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read); do { } while (0) #endif -#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST) +#if IS_ENABLED(CONFIG_RCU_TORTURE_TEST) || IS_MODULE(CONFIG_RCU_TORTURE_TEST) || IS_ENABLED(CONFIG_LOCK_TORTURE_TEST) || IS_MODULE(CONFIG_LOCK_TORTURE_TEST) /* Get rcutorture access to sched_setaffinity(). */ -long rcutorture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask) +long torture_sched_setaffinity(pid_t pid, const struct cpumask *in_mask) { int ret; ret = sched_setaffinity(pid, in_mask); - WARN_ONCE(ret, "%s: sched_setaffinity() returned %d\n", __func__, ret); + WARN_ONCE(ret, "%s: sched_setaffinity(%d) returned %d\n", __func__, pid, ret); return ret; } -EXPORT_SYMBOL_GPL(rcutorture_sched_setaffinity); +EXPORT_SYMBOL_GPL(torture_sched_setaffinity); #endif +int rcu_cpu_stall_notifiers __read_mostly; // !0 = provide stall notifiers (rarely useful) +EXPORT_SYMBOL_GPL(rcu_cpu_stall_notifiers); + #ifdef CONFIG_RCU_STALL_COMMON int rcu_cpu_stall_ftrace_dump __read_mostly; module_param(rcu_cpu_stall_ftrace_dump, int, 0644); +#ifdef CONFIG_RCU_CPU_STALL_NOTIFIER +module_param(rcu_cpu_stall_notifiers, int, 0444); +#endif // #ifdef CONFIG_RCU_CPU_STALL_NOTIFIER int rcu_cpu_stall_suppress __read_mostly; // !0 = suppress stall warnings. EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress); module_param(rcu_cpu_stall_suppress, int, 0644); int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT; module_param(rcu_cpu_stall_timeout, int, 0644); +int rcu_exp_cpu_stall_timeout __read_mostly = CONFIG_RCU_EXP_CPU_STALL_TIMEOUT; +module_param(rcu_exp_cpu_stall_timeout, int, 0644); +int rcu_cpu_stall_cputime __read_mostly = IS_ENABLED(CONFIG_RCU_CPU_STALL_CPUTIME); +module_param(rcu_cpu_stall_cputime, int, 0644); +bool rcu_exp_stall_task_details __read_mostly; +module_param(rcu_exp_stall_task_details, bool, 0644); #endif /* #ifdef CONFIG_RCU_STALL_COMMON */ // Suppress boot-time RCU CPU stall warnings and rcutorture writer stall @@ -505,6 +566,19 @@ int rcu_cpu_stall_suppress_at_boot __read_mostly; // !0 = suppress boot stalls. EXPORT_SYMBOL_GPL(rcu_cpu_stall_suppress_at_boot); module_param(rcu_cpu_stall_suppress_at_boot, int, 0444); +/** + * get_completed_synchronize_rcu - Return a pre-completed polled state cookie + * + * Returns a value that will always be treated by functions like + * poll_state_synchronize_rcu() as a cookie whose grace period has already + * completed. + */ +unsigned long get_completed_synchronize_rcu(void) +{ + return RCU_GET_STATE_COMPLETED; +} +EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu); + #ifdef CONFIG_PROVE_RCU /* @@ -522,6 +596,7 @@ static void test_callback(struct rcu_head *r) } DEFINE_STATIC_SRCU(early_srcu); +static unsigned long early_srcu_cookie; struct early_boot_kfree_rcu { struct rcu_head rh; @@ -530,12 +605,15 @@ struct early_boot_kfree_rcu { static void early_boot_test_call_rcu(void) { static struct rcu_head head; + int idx; static struct rcu_head shead; struct early_boot_kfree_rcu *rhp; + idx = srcu_down_read(&early_srcu); + srcu_up_read(&early_srcu, idx); call_rcu(&head, test_callback); - if (IS_ENABLED(CONFIG_SRCU)) - call_srcu(&early_srcu, &shead, test_callback); + early_srcu_cookie = start_poll_synchronize_srcu(&early_srcu); + call_srcu(&early_srcu, &shead, test_callback); rhp = kmalloc(sizeof(*rhp), GFP_KERNEL); if (!WARN_ON_ONCE(!rhp)) kfree_rcu(rhp, rh); @@ -558,10 +636,10 @@ static int rcu_verify_early_boot_tests(void) if (rcu_self_test) { early_boot_test_counter++; rcu_barrier(); - if (IS_ENABLED(CONFIG_SRCU)) { - early_boot_test_counter++; - srcu_barrier(&early_srcu); - } + early_boot_test_counter++; + srcu_barrier(&early_srcu); + WARN_ON_ONCE(!poll_state_synchronize_srcu(&early_srcu, early_srcu_cookie)); + cleanup_srcu_struct(&early_srcu); } if (rcu_self_test_counter != early_boot_test_counter) { WARN_ON(1); |