From e85e6a21b2b5f31148cc3f2e785262b37c3e1ec7 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 10 Jan 2019 15:30:15 -0800 Subject: rcu: Unconditionally expedite during suspend/hibernate The rcu_pm_notify() function refuses to switch to/from expedited grace periods on systems with more than 256 CPUs due to the serialized initialization of expedited grace periods. However, expedited grace periods are now initialized in parallel, removing this concern. This commit therefore removes the checks from rcu_pm_notify(), so that expedited grace periods are used unconditionally during suspend/resume and hibernate/wake operations. As always, real-time workloads wishing to completely avoid expedited grace periods can use the rcupdate.rcu_normal= kernel parameter. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index acd6ccf56faf..95e3250b7b6e 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3559,13 +3559,11 @@ static int rcu_pm_notify(struct notifier_block *self, switch (action) { case PM_HIBERNATION_PREPARE: case PM_SUSPEND_PREPARE: - if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */ - rcu_expedite_gp(); + rcu_expedite_gp(); break; case PM_POST_HIBERNATION: case PM_POST_SUSPEND: - if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */ - rcu_unexpedite_gp(); + rcu_unexpedite_gp(); break; default: break; -- cgit From 671a63517cf983ad8eaa324167165cef245ab744 Mon Sep 17 00:00:00 2001 From: "Joel Fernandes (Google)" Date: Sat, 19 Jan 2019 11:14:18 -0500 Subject: rcu: Avoid unnecessary softirq when system is idle When there are no callbacks pending on an idle system, I noticed that RCU softirq is continuously firing. During this the cpu_no_qs is set to false, and core_needs_qs is set to true indefinitely. This causes rcu_process_callbacks to be repeatedly called, even though the node corresponding to the CPU has that CPU's mask bit cleared and the system is idle. I believe the race is when such mask clearing is done during idle CPU scan of the quiescent state forcing stage in the kthread instead of the softirq. Since the rnp mask is cleared, but the flags on the CPU's rdp are not cleared, the CPU thinks it still needs to report to core RCU. Cure this by clearing the core_needs_qs flag when the CPU detects that its node is already updated which will avoid the unwanted softirq raises to the benefit of real-time systems. Test: Ran rcutorture for various tree RCU configs. Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 95e3250b7b6e..2f78a115d34c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2296,6 +2296,7 @@ rcu_report_qs_rdp(int cpu, struct rcu_data *rdp) } mask = rdp->grpmask; if ((rnp->qsmask & mask) == 0) { + rdp->core_needs_qs = false; raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } else { rdp->core_needs_qs = false; -- cgit From 3ffe3d1adc0b6cfb9b24db9995a537bb0aa30a8b Mon Sep 17 00:00:00 2001 From: Liu Song Date: Thu, 21 Feb 2019 22:13:27 +0800 Subject: rcu: Set rcutree.kthread_prio sysfs access to read-only The rcutree.kthread_prio kernel-boot parameter is used to set the priority for boost (rcub), per-CPU (rcuc), and grace-period (rcu_preempt or rcu_sched) kthreads. It is also used by rcutorture to check whether it is possible to meaningfully test RCU priority boosting. However, all of these cases will either ignore or be confused by any post-boot changes to rcutree.kthread_prio. Note that the user really can change the priorities of all of these kthreads using chrt, given sufficient privileges. Therefore, the read-write nature of sysfs access to rcutree.kthread_prio is thus at best an attractive nuisance. This commit therefore changes sysfs access to rcutree.kthread_prio to be read-only. Signed-off-by: Liu Song Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 2f78a115d34c..296131450414 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -149,7 +149,7 @@ static void sync_sched_exp_online_cleanup(int cpu); /* rcuc/rcub kthread realtime priority */ static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0; -module_param(kthread_prio, int, 0644); +module_param(kthread_prio, int, 0444); /* Delay in jiffies for grace-period initialization delays, debug only. */ -- cgit From b2eb85b49a576515fb845cb12568b173c2bedffc Mon Sep 17 00:00:00 2001 From: Akira Yokosawa Date: Sat, 2 Mar 2019 17:25:19 +0900 Subject: rcu: Move common code out of if-else block As the result of recent addition of "rdp->core_needs_qs = false;" in the "if" block, now both branches of the if-else have the same assignment. Factor it out and reduce line count. Signed-off-by: Akira Yokosawa Cc: Joel Fernandes Signed-off-by: Paul E. McKenney Acked-by: Joel Fernandes (Google) --- kernel/rcu/tree.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 296131450414..5aefd36ac648 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2295,12 +2295,10 @@ rcu_report_qs_rdp(int cpu, struct rcu_data *rdp) return; } mask = rdp->grpmask; + rdp->core_needs_qs = false; if ((rnp->qsmask & mask) == 0) { - rdp->core_needs_qs = false; raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } else { - rdp->core_needs_qs = false; - /* * This GP can't end until cpu checks in, so all of our * callbacks can be processed during the next GP. -- cgit From 0f58d2ac2c87d27006c2b610668ebc4ff1f7c3ba Mon Sep 17 00:00:00 2001 From: Neeraj Upadhyay Date: Fri, 8 Mar 2019 15:16:18 +0530 Subject: rcu: Fix self-wakeups for grace-period kthread The current rcu_gp_kthread_wake() function uses in_interrupt() and thus does a self-wakeup from all interrupt contexts, including the pointless case where the GP kthread happens to be running with bottom halves disabled, along with the impossible case where the GP kthread is running within an NMI handler (you are not supposed to invoke rcu_gp_kthread_wake() from within an NMI handler. This commit therefore replaces the in_interrupt() with in_irq(), so that the self-wakeups happen only from handlers for hardware interrupts and softirqs. This also makes the code match the comment. Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney Acked-by: Steven Rostedt (VMware) --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 5aefd36ac648..139fa1f5c537 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1585,7 +1585,7 @@ static bool rcu_future_gp_cleanup(struct rcu_node *rnp) static void rcu_gp_kthread_wake(void) { if ((current == rcu_state.gp_kthread && - !in_interrupt() && !in_serving_softirq()) || + !in_irq() && !in_serving_softirq()) || !READ_ONCE(rcu_state.gp_flags) || !rcu_state.gp_kthread) return; -- cgit From 6973032a602ee678c98644a30d57ebf9c72dd6d3 Mon Sep 17 00:00:00 2001 From: Neeraj Upadhyay Date: Mon, 11 Mar 2019 15:16:11 +0530 Subject: rcu: Default jiffies_to_sched_qs to jiffies_till_sched_qs The current code only calls adjust_jiffies_till_sched_qs() if jiffies_till_sched_qs is left at its default value, so when the jiffies_till_sched_qs kernel-boot parameter actually is specified, jiffies_to_sched_qs will be left with the value zero, which will result in useless slowdowns of cond_resched(). This commit therefore changes rcu_init_geometry() to unconditionally invoke adjust_jiffies_till_sched_qs(), which ensures that jiffies_to_sched_qs will be initialized in all cases, thus maintaining good cond_resched() performance. Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 139fa1f5c537..466299c3d2da 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3739,8 +3739,7 @@ static void __init rcu_init_geometry(void) jiffies_till_first_fqs = d; if (jiffies_till_next_fqs == ULONG_MAX) jiffies_till_next_fqs = d; - if (jiffies_till_sched_qs == ULONG_MAX) - adjust_jiffies_till_sched_qs(); + adjust_jiffies_till_sched_qs(); /* If the compile-time values are accurate, just leave. */ if (rcu_fanout_leaf == RCU_FANOUT_LEAF && -- cgit From 85f2b60c4321b088ba08ec9a05b8a7b68e4ada2a Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 11 Mar 2019 15:45:13 -0700 Subject: rcu: Update jiffies_to_sched_qs and adjust_jiffies_till_sched_qs() comments This commit better documents the jiffies_to_sched_qs default-value strategy used by adjust_jiffies_till_sched_qs() Reported-by: Joel Fernandes Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 466299c3d2da..e117732bcd5d 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -406,7 +406,7 @@ static bool rcu_kick_kthreads; */ static ulong jiffies_till_sched_qs = ULONG_MAX; module_param(jiffies_till_sched_qs, ulong, 0444); -static ulong jiffies_to_sched_qs; /* Adjusted version of above if not default */ +static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */ module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */ /* @@ -424,6 +424,7 @@ static void adjust_jiffies_till_sched_qs(void) WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs); return; } + /* Otherwise, set to third fqs scan, but bound below on large system. */ j = READ_ONCE(jiffies_till_first_fqs) + 2 * READ_ONCE(jiffies_till_next_fqs); if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV) -- cgit From 5d8a752e31aaa4c9703f201956a40b45ed791217 Mon Sep 17 00:00:00 2001 From: Zhouyi Zhou Date: Wed, 20 Mar 2019 03:33:00 +0000 Subject: rcu: Fix force_qs_rnp() header comment Previously, threads blocked on offlining CPUS were migrated to the root rcu_node structure, thus requiring RCU priority boosting on this structure. However, since commit d19fb8d1f3f6 ("rcu: Don't migrate blocked tasks even if all corresponding CPUs offline"), RCU does not migrate blocked tasks. Consequently, RCU no longer does RCU priority boosting on the root rcu_node structure as of commit 1be0085b515e ("rcu: Don't initiate RCU priority boosting on root rcu_node"). This commit therefore brings comments for the force_qs_rnp() function's header comment in line with this new no-root-boosting reality. Signed-off-by: Zhouyi Zhou [ paulmck: Also remove obsolete comment on suppressing new grace periods. ] Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e117732bcd5d..abc8512ceb5f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2548,11 +2548,11 @@ void rcu_sched_clock_irq(int user) } /* - * Scan the leaf rcu_node structures, processing dyntick state for any that - * have not yet encountered a quiescent state, using the function specified. - * Also initiate boosting for any threads blocked on the root rcu_node. - * - * The caller must have suppressed start of new grace periods. + * Scan the leaf rcu_node structures. For each structure on which all + * CPUs have reported a quiescent state and on which there are tasks + * blocking the current grace period, initiate RCU priority boosting. + * Otherwise, invoke the specified function to check dyntick state for + * each CPU that has not yet reported a quiescent state. */ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) { -- cgit From 10462d6f58fb6dbde7563e9343505d98d5bfba3d Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 11 Jan 2019 16:10:57 -0800 Subject: rcu: Move RCU CPU stall-warning code out of update.c The RCU CPU stall-warning code for normal grace periods is currently scattered across three files, due to earlier Tiny RCU support for RCU CPU stall warnings and for old Kconfig options that have long since been retired. Given that it is hard for the lead RCU maintainer to find relevant stall-warning code, it would be good to consolidate it. This commit starts this process by moving stall-warning code from kernel/rcu/update.c to a new kernel/rcu/tree_stall.h file. Note that the definitions of rcu_cpu_stall_suppress and rcu_cpu_stall_timeout must remain in kernel/rcu/update.h to provide compatibility for kernel boot parameter lists. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 1 + 1 file changed, 1 insertion(+) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index acd6ccf56faf..424d50ccf9e6 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3858,5 +3858,6 @@ void __init rcu_init(void) srcu_init(); } +#include "tree_stall.h" #include "tree_exp.h" #include "tree_plugin.h" -- cgit From 32255d51b6ed00de2b88970ceea8db0ec3bae6f8 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 11 Jan 2019 16:57:41 -0800 Subject: rcu: Move RCU CPU stall-warning code out of tree.c This commit completes the process of consolidating the code for RCU CPU stall warnings for normal grace periods by moving the remaining such code from kernel/rcu/tree.c to kernel/rcu/tree_stall.h. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 291 ------------------------------------------------------ 1 file changed, 291 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 424d50ccf9e6..001dd05f6e38 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -102,8 +102,6 @@ int rcu_num_lvls __read_mostly = RCU_NUM_LVLS; /* Number of rcu_nodes at specified level. */ int num_rcu_lvl[] = NUM_RCU_LVL_INIT; int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */ -/* panic() on RCU Stall sysctl. */ -int sysctl_panic_on_rcu_stall __read_mostly; /* Commandeer a sysrq key to dump RCU's tree. */ static bool sysrq_rcu; module_param(sysrq_rcu, bool, 0444); @@ -1167,295 +1165,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) return 0; } -static void record_gp_stall_check_time(void) -{ - unsigned long j = jiffies; - unsigned long j1; - - rcu_state.gp_start = j; - j1 = rcu_jiffies_till_stall_check(); - /* Record ->gp_start before ->jiffies_stall. */ - smp_store_release(&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); -} - -/* - * Complain about starvation of grace-period kthread. - */ -static void rcu_check_gp_kthread_starvation(void) -{ - struct task_struct *gpk = rcu_state.gp_kthread; - unsigned long j; - - j = jiffies - READ_ONCE(rcu_state.gp_activity); - if (j > 2 * HZ) { - pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n", - rcu_state.name, j, - (long)rcu_seq_current(&rcu_state.gp_seq), - READ_ONCE(rcu_state.gp_flags), - gp_state_getname(rcu_state.gp_state), rcu_state.gp_state, - gpk ? gpk->state : ~0, gpk ? task_cpu(gpk) : -1); - if (gpk) { - pr_err("RCU grace-period kthread stack dump:\n"); - sched_show_task(gpk); - wake_up_process(gpk); - } - } -} - -/* - * Dump stacks of all tasks running on stalled CPUs. First try using - * NMIs, but fall back to manual remote stack tracing on architectures - * that don't support NMI-based stack dumps. The NMI-triggered stack - * traces are more accurate because they are printed by the target CPU. - */ -static void rcu_dump_cpu_stacks(void) -{ - int cpu; - unsigned long flags; - struct rcu_node *rnp; - - 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)) - dump_cpu_task(cpu); - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - } -} - -/* - * If too much time has passed in the current grace period, and if - * so configured, go kick the relevant kthreads. - */ -static void rcu_stall_kick_kthreads(void) -{ - unsigned long j; - - if (!rcu_kick_kthreads) - return; - j = READ_ONCE(rcu_state.jiffies_kick_kthreads); - if (time_after(jiffies, j) && rcu_state.gp_kthread && - (rcu_gp_in_progress() || READ_ONCE(rcu_state.gp_flags))) { - WARN_ONCE(1, "Kicking %s grace-period kthread\n", - rcu_state.name); - rcu_ftrace_dump(DUMP_ALL); - wake_up_process(rcu_state.gp_kthread); - WRITE_ONCE(rcu_state.jiffies_kick_kthreads, j + HZ); - } -} - -static void panic_on_rcu_stall(void) -{ - if (sysctl_panic_on_rcu_stall) - panic("RCU Stall\n"); -} - -static void print_other_cpu_stall(unsigned long gp_seq) -{ - int cpu; - unsigned long flags; - unsigned long gpa; - unsigned long j; - int ndetected = 0; - struct rcu_node *rnp = rcu_get_root(); - long totqlen = 0; - - /* Kick and suppress, if so configured. */ - rcu_stall_kick_kthreads(); - if (rcu_cpu_stall_suppress) - return; - - /* - * OK, time to rat on our buddy... - * See Documentation/RCU/stallwarn.txt for info on how to debug - * RCU CPU stall warnings. - */ - pr_err("INFO: %s detected stalls on CPUs/tasks:", rcu_state.name); - print_cpu_stall_info_begin(); - rcu_for_each_leaf_node(rnp) { - raw_spin_lock_irqsave_rcu_node(rnp, flags); - ndetected += rcu_print_task_stall(rnp); - if (rnp->qsmask != 0) { - for_each_leaf_node_possible_cpu(rnp, cpu) - if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) { - print_cpu_stall_info(cpu); - ndetected++; - } - } - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - } - - print_cpu_stall_info_end(); - for_each_possible_cpu(cpu) - totqlen += rcu_get_n_cbs_cpu(cpu); - pr_cont("(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n", - smp_processor_id(), (long)(jiffies - rcu_state.gp_start), - (long)rcu_seq_current(&rcu_state.gp_seq), totqlen); - if (ndetected) { - rcu_dump_cpu_stacks(); - - /* Complain about tasks blocking the grace period. */ - rcu_print_detail_task_stall(); - } else { - if (rcu_seq_current(&rcu_state.gp_seq) != gp_seq) { - pr_err("INFO: Stall ended before state dump start\n"); - } else { - j = jiffies; - gpa = 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, - READ_ONCE(jiffies_till_next_fqs), - rcu_get_root()->qsmask); - /* In this case, the current CPU might be at fault. */ - sched_show_task(current); - } - } - /* Rewrite if needed in case of slow consoles. */ - if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall))) - WRITE_ONCE(rcu_state.jiffies_stall, - jiffies + 3 * rcu_jiffies_till_stall_check() + 3); - - rcu_check_gp_kthread_starvation(); - - panic_on_rcu_stall(); - - rcu_force_quiescent_state(); /* Kick them all. */ -} - -static void print_cpu_stall(void) -{ - int cpu; - unsigned long flags; - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); - struct rcu_node *rnp = rcu_get_root(); - long totqlen = 0; - - /* Kick and suppress, if so configured. */ - rcu_stall_kick_kthreads(); - if (rcu_cpu_stall_suppress) - return; - - /* - * OK, time to rat on ourselves... - * See Documentation/RCU/stallwarn.txt for info on how to debug - * RCU CPU stall warnings. - */ - pr_err("INFO: %s self-detected stall on CPU", rcu_state.name); - print_cpu_stall_info_begin(); - 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); - print_cpu_stall_info_end(); - for_each_possible_cpu(cpu) - totqlen += rcu_get_n_cbs_cpu(cpu); - pr_cont(" (t=%lu jiffies g=%ld q=%lu)\n", - jiffies - rcu_state.gp_start, - (long)rcu_seq_current(&rcu_state.gp_seq), totqlen); - - rcu_check_gp_kthread_starvation(); - - rcu_dump_cpu_stacks(); - - raw_spin_lock_irqsave_rcu_node(rnp, flags); - /* Rewrite if needed in case of slow consoles. */ - if (ULONG_CMP_GE(jiffies, READ_ONCE(rcu_state.jiffies_stall))) - WRITE_ONCE(rcu_state.jiffies_stall, - jiffies + 3 * rcu_jiffies_till_stall_check() + 3); - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - - panic_on_rcu_stall(); - - /* - * Attempt to revive the RCU machinery by forcing a context switch. - * - * A context switch would normally allow the RCU state machine to make - * progress and it could be we're stuck in kernel space without context - * switches for an entirely unreasonable amount of time. - */ - set_tsk_need_resched(current); - set_preempt_need_resched(); -} - -static void check_cpu_stall(struct rcu_data *rdp) -{ - unsigned long gs1; - unsigned long gs2; - unsigned long gps; - unsigned long j; - unsigned long jn; - unsigned long js; - struct rcu_node *rnp; - - if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) || - !rcu_gp_in_progress()) - return; - rcu_stall_kick_kthreads(); - j = jiffies; - - /* - * Lots of memory barriers to reject false positives. - * - * The idea is to pick up rcu_state.gp_seq, then - * rcu_state.jiffies_stall, then rcu_state.gp_start, and finally - * another copy of rcu_state.gp_seq. These values are updated in - * the opposite order with memory barriers (or equivalent) during - * grace-period initialization and cleanup. Now, a false positive - * can occur if we get an new value of rcu_state.gp_start and a old - * value of rcu_state.jiffies_stall. But given the memory barriers, - * the only way that this can happen is if one grace period ends - * and another starts between these two fetches. This is detected - * by comparing the second fetch of rcu_state.gp_seq with the - * previous fetch from rcu_state.gp_seq. - * - * Given this check, comparisons of jiffies, rcu_state.jiffies_stall, - * and rcu_state.gp_start suffice to forestall false positives. - */ - gs1 = READ_ONCE(rcu_state.gp_seq); - smp_rmb(); /* Pick up ->gp_seq first... */ - js = READ_ONCE(rcu_state.jiffies_stall); - smp_rmb(); /* ...then ->jiffies_stall before the rest... */ - gps = READ_ONCE(rcu_state.gp_start); - smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */ - gs2 = READ_ONCE(rcu_state.gp_seq); - if (gs1 != gs2 || - ULONG_CMP_LT(j, js) || - 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; - if (rcu_gp_in_progress() && - (READ_ONCE(rnp->qsmask) & rdp->grpmask) && - cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) { - - /* We haven't checked in, so go dump stack. */ - print_cpu_stall(); - - } else if (rcu_gp_in_progress() && - ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) && - cmpxchg(&rcu_state.jiffies_stall, js, jn) == js) { - - /* They had a few time units to dump stack, so complain. */ - print_other_cpu_stall(gs2); - } -} - -/** - * rcu_cpu_stall_reset - prevent further stall warnings in 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. - * - * The caller must disable hard irqs. - */ -void rcu_cpu_stall_reset(void) -{ - WRITE_ONCE(rcu_state.jiffies_stall, jiffies + ULONG_MAX / 2); -} - /* Trace-event wrapper function for trace_rcu_future_grace_period. */ static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, unsigned long gp_seq_req, const char *s) -- cgit From 7ac1907c9e7ba5f80d3c298fe9d2dbf620566a49 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 14 Jan 2019 10:19:20 -0800 Subject: rcu: Move irq-disabled stall-warning checking to tree_stall.h The rcu_iw_handler() function's sole purpose in life is to indicate whether a stalled CPU had interrupts disabled, so it belongs in kernel/rcu/tree_stall.h. This commit therefore makes that move, clarifying its header comment while in the area. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 21 --------------------- 1 file changed, 21 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 001dd05f6e38..929531ed168c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1031,27 +1031,6 @@ static int dyntick_save_progress_counter(struct rcu_data *rdp) return 0; } -/* - * Handler for the irq_work request posted when a grace period has - * gone on for too long, but not yet long enough for an RCU CPU - * stall warning. Set state appropriately, but just complain if - * there is unexpected state on entry. - */ -static void rcu_iw_handler(struct irq_work *iwp) -{ - struct rcu_data *rdp; - struct rcu_node *rnp; - - rdp = container_of(iwp, struct rcu_data, rcu_iw); - rnp = rdp->mynode; - raw_spin_lock_rcu_node(rnp); - if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) { - rdp->rcu_iw_gp_seq = rnp->gp_seq; - rdp->rcu_iw_pending = false; - } - raw_spin_unlock_rcu_node(rnp); -} - /* * Return true if the specified CPU has passed through a quiescent * state by virtue of being in or having passed through an dynticks -- cgit From b51bcbbf16ef0ea352e8b924dd8638112e4037a5 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 15 Jan 2019 07:01:33 -0800 Subject: rcu: Move forward-progress checkers into tree_stall.h This commit further consolidates stall-warning functionality by moving forward-progress checkers into kernel/rcu/tree_stall.h, updating a comment or two while in the area. More specifically, this commit moves show_rcu_gp_kthreads(), rcu_check_gp_start_stall(), rcu_fwd_progress_check(), sysrq_rcu, sysrq_show_rcu(), sysrq_rcudump_op, and rcu_sysrq_init() from kernel/rcu/tree.c to kernel/rcu/tree_stall.h. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 166 ------------------------------------------------------ 1 file changed, 166 deletions(-) (limited to 'kernel/rcu/tree.c') diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 929531ed168c..4cb1ebd93b0c 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -102,9 +102,6 @@ int rcu_num_lvls __read_mostly = RCU_NUM_LVLS; /* Number of rcu_nodes at specified level. */ int num_rcu_lvl[] = NUM_RCU_LVL_INIT; int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */ -/* Commandeer a sysrq key to dump RCU's tree. */ -static bool sysrq_rcu; -module_param(sysrq_rcu, bool, 0444); /* * The rcu_scheduler_active variable is initialized to the value @@ -510,74 +507,6 @@ static const char *gp_state_getname(short gs) return gp_state_names[gs]; } -/* - * Show the state of the grace-period kthreads. - */ -void show_rcu_gp_kthreads(void) -{ - int cpu; - unsigned long j; - unsigned long ja; - unsigned long jr; - unsigned long jw; - struct rcu_data *rdp; - struct rcu_node *rnp; - - j = jiffies; - ja = j - READ_ONCE(rcu_state.gp_activity); - jr = j - READ_ONCE(rcu_state.gp_req_activity); - jw = j - READ_ONCE(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", - rcu_state.name, gp_state_getname(rcu_state.gp_state), - rcu_state.gp_state, - rcu_state.gp_kthread ? rcu_state.gp_kthread->state : 0x1ffffL, - ja, jr, jw, (long)READ_ONCE(rcu_state.gp_wake_seq), - (long)READ_ONCE(rcu_state.gp_seq), - (long)READ_ONCE(rcu_get_root()->gp_seq_needed), - READ_ONCE(rcu_state.gp_flags)); - rcu_for_each_node_breadth_first(rnp) { - if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed)) - continue; - pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n", - rnp->grplo, rnp->grphi, (long)rnp->gp_seq, - (long)rnp->gp_seq_needed); - if (!rcu_is_leaf_node(rnp)) - continue; - for_each_leaf_node_possible_cpu(rnp, cpu) { - rdp = per_cpu_ptr(&rcu_data, cpu); - if (rdp->gpwrap || - ULONG_CMP_GE(rcu_state.gp_seq, - rdp->gp_seq_needed)) - continue; - pr_info("\tcpu %d ->gp_seq_needed %ld\n", - cpu, (long)rdp->gp_seq_needed); - } - } - /* sched_show_task(rcu_state.gp_kthread); */ -} -EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads); - -/* Dump grace-period-request information due to commandeered sysrq. */ -static void sysrq_show_rcu(int key) -{ - show_rcu_gp_kthreads(); -} - -static struct sysrq_key_op sysrq_rcudump_op = { - .handler = sysrq_show_rcu, - .help_msg = "show-rcu(y)", - .action_msg = "Show RCU tree", - .enable_mask = SYSRQ_ENABLE_DUMP, -}; - -static int __init rcu_sysrq_init(void) -{ - if (sysrq_rcu) - return register_sysrq_key('y', &sysrq_rcudump_op); - return 0; -} -early_initcall(rcu_sysrq_init); - /* * Send along grace-period-related data for rcutorture diagnostics. */ @@ -2323,101 +2252,6 @@ void rcu_force_quiescent_state(void) } EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); -/* - * This function checks for grace-period requests that fail to motivate - * RCU to come out of its idle mode. - */ -void -rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, - const unsigned long gpssdelay) -{ - unsigned long flags; - unsigned long j; - struct rcu_node *rnp_root = rcu_get_root(); - static atomic_t warned = ATOMIC_INIT(0); - - if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() || - ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed)) - return; - j = jiffies; /* Expensive access, and in common case don't get here. */ - if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || - time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || - atomic_read(&warned)) - return; - - raw_spin_lock_irqsave_rcu_node(rnp, flags); - j = jiffies; - if (rcu_gp_in_progress() || - ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) || - time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || - time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || - atomic_read(&warned)) { - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - return; - } - /* Hold onto the leaf lock to make others see warned==1. */ - - if (rnp_root != rnp) - raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */ - j = jiffies; - if (rcu_gp_in_progress() || - ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) || - time_before(j, rcu_state.gp_req_activity + gpssdelay) || - time_before(j, rcu_state.gp_activity + gpssdelay) || - atomic_xchg(&warned, 1)) { - raw_spin_unlock_rcu_node(rnp_root); /* irqs remain disabled. */ - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - return; - } - WARN_ON(1); - if (rnp_root != rnp) - raw_spin_unlock_rcu_node(rnp_root); - raw_spin_unlock_irqrestore_rcu_node(rnp, flags); - show_rcu_gp_kthreads(); -} - -/* - * Do a forward-progress check for rcutorture. This is normally invoked - * due to an OOM event. The argument "j" gives the time period during - * which rcutorture would like progress to have been made. - */ -void rcu_fwd_progress_check(unsigned long j) -{ - unsigned long cbs; - int cpu; - unsigned long max_cbs = 0; - int max_cpu = -1; - struct rcu_data *rdp; - - if (rcu_gp_in_progress()) { - pr_info("%s: GP age %lu jiffies\n", - __func__, jiffies - 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); - preempt_disable(); - rdp = this_cpu_ptr(&rcu_data); - rcu_check_gp_start_stall(rdp->mynode, rdp, j); - preempt_enable(); - } - for_each_possible_cpu(cpu) { - cbs = rcu_get_n_cbs_cpu(cpu); - if (!cbs) - continue; - if (max_cpu < 0) - pr_info("%s: callbacks", __func__); - pr_cont(" %d: %lu", cpu, cbs); - if (cbs <= max_cbs) - continue; - max_cbs = cbs; - max_cpu = cpu; - } - if (max_cpu >= 0) - pr_cont("\n"); -} -EXPORT_SYMBOL_GPL(rcu_fwd_progress_check); - /* Perform RCU core processing work for the current CPU. */ static __latent_entropy void rcu_core(struct softirq_action *unused) { -- cgit