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Diffstat (limited to 'include/linux/srcutree.h')
| -rw-r--r-- | include/linux/srcutree.h | 368 |
1 files changed, 368 insertions, 0 deletions
diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h new file mode 100644 index 000000000000..d6f978b50472 --- /dev/null +++ b/include/linux/srcutree.h @@ -0,0 +1,368 @@ +/* SPDX-License-Identifier: GPL-2.0+ */ +/* + * Sleepable Read-Copy Update mechanism for mutual exclusion, + * tree variant. + * + * Copyright (C) IBM Corporation, 2017 + * + * Author: Paul McKenney <paulmck@linux.ibm.com> + */ + +#ifndef _LINUX_SRCU_TREE_H +#define _LINUX_SRCU_TREE_H + +#include <linux/rcu_node_tree.h> +#include <linux/completion.h> + +struct srcu_node; +struct srcu_struct; + +/* One element of the srcu_data srcu_ctrs array. */ +struct srcu_ctr { + atomic_long_t srcu_locks; /* Locks per CPU. */ + atomic_long_t srcu_unlocks; /* Unlocks per CPU. */ +}; + +/* + * Per-CPU structure feeding into leaf srcu_node, similar in function + * to rcu_node. + */ +struct srcu_data { + /* Read-side state. */ + struct srcu_ctr srcu_ctrs[2]; /* Locks and unlocks per CPU. */ + int srcu_reader_flavor; /* Reader flavor for srcu_struct structure? */ + /* Values: SRCU_READ_FLAVOR_.* */ + + /* Update-side state. */ + spinlock_t __private lock ____cacheline_internodealigned_in_smp; + struct rcu_segcblist srcu_cblist; /* List of callbacks.*/ + unsigned long srcu_gp_seq_needed; /* Furthest future GP needed. */ + unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ + bool srcu_cblist_invoking; /* Invoking these CBs? */ + struct timer_list delay_work; /* Delay for CB invoking */ + struct work_struct work; /* Context for CB invoking. */ + struct rcu_head srcu_barrier_head; /* For srcu_barrier() use. */ + struct rcu_head srcu_ec_head; /* For srcu_expedite_current() use. */ + int srcu_ec_state; /* State for srcu_expedite_current(). */ + struct srcu_node *mynode; /* Leaf srcu_node. */ + unsigned long grpmask; /* Mask for leaf srcu_node */ + /* ->srcu_data_have_cbs[]. */ + int cpu; + struct srcu_struct *ssp; +}; + +/* + * Node in SRCU combining tree, similar in function to rcu_data. + */ +struct srcu_node { + spinlock_t __private lock; + unsigned long srcu_have_cbs[4]; /* GP seq for children having CBs, but only */ + /* if greater than ->srcu_gp_seq. */ + unsigned long srcu_data_have_cbs[4]; /* Which srcu_data structs have CBs for given GP? */ + unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ + struct srcu_node *srcu_parent; /* Next up in tree. */ + int grplo; /* Least CPU for node. */ + int grphi; /* Biggest CPU for node. */ +}; + +/* + * Per-SRCU-domain structure, update-side data linked from srcu_struct. + */ +struct srcu_usage { + struct srcu_node *node; /* Combining tree. */ + struct srcu_node *level[RCU_NUM_LVLS + 1]; + /* First node at each level. */ + int srcu_size_state; /* Small-to-big transition state. */ + struct mutex srcu_cb_mutex; /* Serialize CB preparation. */ + spinlock_t __private lock; /* Protect counters and size state. */ + struct mutex srcu_gp_mutex; /* Serialize GP work. */ + unsigned long srcu_gp_seq; /* Grace-period seq #. */ + unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */ + unsigned long srcu_gp_seq_needed_exp; /* Furthest future exp GP. */ + unsigned long srcu_gp_start; /* Last GP start timestamp (jiffies) */ + unsigned long srcu_last_gp_end; /* Last GP end timestamp (ns) */ + unsigned long srcu_size_jiffies; /* Current contention-measurement interval. */ + unsigned long srcu_n_lock_retries; /* Contention events in current interval. */ + unsigned long srcu_n_exp_nodelay; /* # expedited no-delays in current GP phase. */ + bool sda_is_static; /* May ->sda be passed to free_percpu()? */ + unsigned long srcu_barrier_seq; /* srcu_barrier seq #. */ + struct mutex srcu_barrier_mutex; /* Serialize barrier ops. */ + struct completion srcu_barrier_completion; + /* Awaken barrier rq at end. */ + atomic_t srcu_barrier_cpu_cnt; /* # CPUs not yet posting a */ + /* callback for the barrier */ + /* operation. */ + unsigned long reschedule_jiffies; + unsigned long reschedule_count; + struct delayed_work work; + struct srcu_struct *srcu_ssp; +}; + +/* + * Per-SRCU-domain structure, similar in function to rcu_state. + */ +struct srcu_struct { + struct srcu_ctr __percpu *srcu_ctrp; + struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ + u8 srcu_reader_flavor; + struct lockdep_map dep_map; + struct srcu_usage *srcu_sup; /* Update-side data. */ +}; + +// Values for size state variable (->srcu_size_state). Once the state +// has been set to SRCU_SIZE_ALLOC, the grace-period code advances through +// this state machine one step per grace period until the SRCU_SIZE_BIG state +// is reached. Otherwise, the state machine remains in the SRCU_SIZE_SMALL +// state indefinitely. +#define SRCU_SIZE_SMALL 0 // No srcu_node combining tree, ->node == NULL +#define SRCU_SIZE_ALLOC 1 // An srcu_node tree is being allocated, initialized, + // and then referenced by ->node. It will not be used. +#define SRCU_SIZE_WAIT_BARRIER 2 // The srcu_node tree starts being used by everything + // except call_srcu(), especially by srcu_barrier(). + // By the end of this state, all CPUs and threads + // are aware of this tree's existence. +#define SRCU_SIZE_WAIT_CALL 3 // The srcu_node tree starts being used by call_srcu(). + // By the end of this state, all of the call_srcu() + // invocations that were running on a non-boot CPU + // and using the boot CPU's callback queue will have + // completed. +#define SRCU_SIZE_WAIT_CBS1 4 // Don't trust the ->srcu_have_cbs[] grace-period +#define SRCU_SIZE_WAIT_CBS2 5 // sequence elements or the ->srcu_data_have_cbs[] +#define SRCU_SIZE_WAIT_CBS3 6 // CPU-bitmask elements until all four elements of +#define SRCU_SIZE_WAIT_CBS4 7 // each array have been initialized. +#define SRCU_SIZE_BIG 8 // The srcu_node combining tree is fully initialized + // and all aspects of it are being put to use. + +/* Values for state variable (bottom bits of ->srcu_gp_seq). */ +#define SRCU_STATE_IDLE 0 +#define SRCU_STATE_SCAN1 1 +#define SRCU_STATE_SCAN2 2 + +/* Values for srcu_expedite_current() state (->srcu_ec_state). */ +#define SRCU_EC_IDLE 0 +#define SRCU_EC_PENDING 1 +#define SRCU_EC_REPOST 2 + +/* + * Values for initializing gp sequence fields. Higher values allow wrap arounds to + * occur earlier. + * The second value with state is useful in the case of static initialization of + * srcu_usage where srcu_gp_seq_needed is expected to have some state value in its + * lower bits (or else it will appear to be already initialized within + * the call check_init_srcu_struct()). + */ +#define SRCU_GP_SEQ_INITIAL_VAL ((0UL - 100UL) << RCU_SEQ_CTR_SHIFT) +#define SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE (SRCU_GP_SEQ_INITIAL_VAL - 1) + +#define __SRCU_USAGE_INIT(name) \ +{ \ + .lock = __SPIN_LOCK_UNLOCKED(name.lock), \ + .srcu_gp_seq = SRCU_GP_SEQ_INITIAL_VAL, \ + .srcu_gp_seq_needed = SRCU_GP_SEQ_INITIAL_VAL_WITH_STATE, \ + .srcu_gp_seq_needed_exp = SRCU_GP_SEQ_INITIAL_VAL, \ + .work = __DELAYED_WORK_INITIALIZER(name.work, NULL, 0), \ +} + +#define __SRCU_STRUCT_INIT_COMMON(name, usage_name, fast) \ + .srcu_sup = &usage_name, \ + .srcu_reader_flavor = fast, \ + __SRCU_DEP_MAP_INIT(name) + +#define __SRCU_STRUCT_INIT_MODULE(name, usage_name, fast) \ +{ \ + __SRCU_STRUCT_INIT_COMMON(name, usage_name, fast) \ +} + +#define __SRCU_STRUCT_INIT(name, usage_name, pcpu_name, fast) \ +{ \ + .sda = &pcpu_name, \ + .srcu_ctrp = &pcpu_name.srcu_ctrs[0], \ + __SRCU_STRUCT_INIT_COMMON(name, usage_name, fast) \ +} + +/* + * Define and initialize a srcu struct at build time. + * Do -not- call init_srcu_struct() nor cleanup_srcu_struct() on it. + * + * Note that although DEFINE_STATIC_SRCU() hides the name from other + * files, the per-CPU variable rules nevertheless require that the + * chosen name be globally unique. These rules also prohibit use of + * DEFINE_STATIC_SRCU() within a function. If these rules are too + * restrictive, declare the srcu_struct manually. For example, in + * each file: + * + * static struct srcu_struct my_srcu; + * + * Then, before the first use of each my_srcu, manually initialize it: + * + * init_srcu_struct(&my_srcu); + * + * See include/linux/percpu-defs.h for the rules on per-CPU variables. + * + * DEFINE_SRCU_FAST() and DEFINE_STATIC_SRCU_FAST create an srcu_struct + * and associated structures whose readers must be of the SRCU-fast variety. + * DEFINE_SRCU_FAST_UPDOWN() and DEFINE_STATIC_SRCU_FAST_UPDOWN() create + * an srcu_struct and associated structures whose readers must be of the + * SRCU-fast-updown variety. The key point (aside from error checking) with + * both varieties is that the grace periods must use synchronize_rcu() + * instead of smp_mb(), and given that the first (for example) + * srcu_read_lock_fast() might race with the first synchronize_srcu(), + * this different must be specified at initialization time. + */ +#ifdef MODULE +# define __DEFINE_SRCU(name, fast, is_static) \ + static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ + is_static struct srcu_struct name = __SRCU_STRUCT_INIT_MODULE(name, name##_srcu_usage, \ + fast); \ + extern struct srcu_struct * const __srcu_struct_##name; \ + struct srcu_struct * const __srcu_struct_##name \ + __section("___srcu_struct_ptrs") = &name +#else +# define __DEFINE_SRCU(name, fast, is_static) \ + static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data); \ + static struct srcu_usage name##_srcu_usage = __SRCU_USAGE_INIT(name##_srcu_usage); \ + is_static struct srcu_struct name = \ + __SRCU_STRUCT_INIT(name, name##_srcu_usage, name##_srcu_data, fast) +#endif +#define DEFINE_SRCU(name) __DEFINE_SRCU(name, 0, /* not static */) +#define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, 0, static) +#define DEFINE_SRCU_FAST(name) __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST, /* not static */) +#define DEFINE_STATIC_SRCU_FAST(name) __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST, static) +#define DEFINE_SRCU_FAST_UPDOWN(name) __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST_UPDOWN, \ + /* not static */) +#define DEFINE_STATIC_SRCU_FAST_UPDOWN(name) \ + __DEFINE_SRCU(name, SRCU_READ_FLAVOR_FAST_UPDOWN, static) + +int __srcu_read_lock(struct srcu_struct *ssp) __acquires(ssp); +void synchronize_srcu_expedited(struct srcu_struct *ssp); +void srcu_barrier(struct srcu_struct *ssp); +void srcu_expedite_current(struct srcu_struct *ssp); +void srcu_torture_stats_print(struct srcu_struct *ssp, char *tt, char *tf); + +// Converts a per-CPU pointer to an ->srcu_ctrs[] array element to that +// element's index. +static inline bool __srcu_ptr_to_ctr(struct srcu_struct *ssp, struct srcu_ctr __percpu *scpp) +{ + return scpp - &ssp->sda->srcu_ctrs[0]; +} + +// Converts an integer to a per-CPU pointer to the corresponding +// ->srcu_ctrs[] array element. +static inline struct srcu_ctr __percpu *__srcu_ctr_to_ptr(struct srcu_struct *ssp, int idx) +{ + return &ssp->sda->srcu_ctrs[idx]; +} + +/* + * Counts the new reader in the appropriate per-CPU element of the + * srcu_struct. Returns a pointer that must be passed to the matching + * srcu_read_unlock_fast(). + * + * Note that both this_cpu_inc() and atomic_long_inc() are RCU read-side + * critical sections either because they disables interrupts, because + * they are a single instruction, or because they are read-modify-write + * atomic operations, depending on the whims of the architecture. + * This matters because the SRCU-fast grace-period mechanism uses either + * synchronize_rcu() or synchronize_rcu_expedited(), that is, RCU, + * *not* SRCU, in order to eliminate the need for the read-side smp_mb() + * invocations that are used by srcu_read_lock() and srcu_read_unlock(). + * The __srcu_read_unlock_fast() function also relies on this same RCU + * (again, *not* SRCU) trick to eliminate the need for smp_mb(). + * + * The key point behind this RCU trick is that if any part of a given + * RCU reader precedes the beginning of a given RCU grace period, then + * the entirety of that RCU reader and everything preceding it happens + * before the end of that same RCU grace period. Similarly, if any part + * of a given RCU reader follows the end of a given RCU grace period, + * then the entirety of that RCU reader and everything following it + * happens after the beginning of that same RCU grace period. Therefore, + * the operations labeled Y in __srcu_read_lock_fast() and those labeled Z + * in __srcu_read_unlock_fast() are ordered against the corresponding SRCU + * read-side critical section from the viewpoint of the SRCU grace period. + * This is all the ordering that is required, hence no calls to smp_mb(). + * + * This means that __srcu_read_lock_fast() is not all that fast + * on architectures that support NMIs but do not supply NMI-safe + * implementations of this_cpu_inc(). + */ +static inline struct srcu_ctr __percpu notrace *__srcu_read_lock_fast(struct srcu_struct *ssp) +{ + struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp); + + if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) + this_cpu_inc(scp->srcu_locks.counter); // Y, and implicit RCU reader. + else + atomic_long_inc(raw_cpu_ptr(&scp->srcu_locks)); // Y, and implicit RCU reader. + barrier(); /* Avoid leaking the critical section. */ + return scp; +} + +/* + * 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_fast(), but it must be within the same task. + * + * Please see the __srcu_read_lock_fast() function's header comment for + * information on implicit RCU readers and NMI safety. + */ +static inline void notrace +__srcu_read_unlock_fast(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp) +{ + barrier(); /* Avoid leaking the critical section. */ + if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) + this_cpu_inc(scp->srcu_unlocks.counter); // Z, and implicit RCU reader. + else + atomic_long_inc(raw_cpu_ptr(&scp->srcu_unlocks)); // Z, and implicit RCU reader. +} + +/* + * Counts the new reader in the appropriate per-CPU element of the + * srcu_struct. Returns a pointer that must be passed to the matching + * srcu_read_unlock_fast_updown(). This type of reader is compatible + * with srcu_down_read_fast() and srcu_up_read_fast(). + * + * See the __srcu_read_lock_fast() comment for more details. + */ +static inline +struct srcu_ctr __percpu notrace *__srcu_read_lock_fast_updown(struct srcu_struct *ssp) +{ + struct srcu_ctr __percpu *scp = READ_ONCE(ssp->srcu_ctrp); + + if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) + this_cpu_inc(scp->srcu_locks.counter); // Y, and implicit RCU reader. + else + atomic_long_inc(raw_cpu_ptr(&scp->srcu_locks)); // Y, and implicit RCU reader. + barrier(); /* Avoid leaking the critical section. */ + return scp; +} + +/* + * 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_fast(), but it must be within the same task. + * + * Please see the __srcu_read_lock_fast() function's header comment for + * information on implicit RCU readers and NMI safety. + */ +static inline void notrace +__srcu_read_unlock_fast_updown(struct srcu_struct *ssp, struct srcu_ctr __percpu *scp) +{ + barrier(); /* Avoid leaking the critical section. */ + if (!IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) + this_cpu_inc(scp->srcu_unlocks.counter); // Z, and implicit RCU reader. + else + atomic_long_inc(raw_cpu_ptr(&scp->srcu_unlocks)); // Z, and implicit RCU reader. +} + +void __srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor); + +// Record SRCU-reader usage type only for CONFIG_PROVE_RCU=y kernels. +static inline void srcu_check_read_flavor(struct srcu_struct *ssp, int read_flavor) +{ + if (IS_ENABLED(CONFIG_PROVE_RCU)) + __srcu_check_read_flavor(ssp, read_flavor); +} + +#endif |