Peter Zijlstra proposed using SRCU to reduce mmap_sem contention [1], however, there are workloads that could result in a high volume of concurrent invocations of call_srcu(), which with current SRCU would result in excessive lock contention on the srcu_struct structure's ->queue_lock, which protects SRCU's callback lists. This commit therefore moves SRCU to per-CPU callback lists, thus greatly reducing contention.
Because a given SRCU instance no longer has a single centralized callback list, starting grace periods and invoking callbacks each require a bit more work. These are handled using an srcu_node tree that is in some ways similar to the rcu_node trees used by RCU-bh, RCU-preempt, and RCU-sched (for example, the srcu_node tree shape is controlled by exactly the same Kconfig options and boot parameters that control the shape of the rcu_node tree). In addition, the old per-CPU srcu_array structure is now named srcu_data and contains an rcu_segcblist structure named ->srcu_cblist for its callbacks (and a spinlock to protect this). The srcu_struct gets an srcu_gp_seq that is used to associate callback segments with the corresponding completion-time grace-period number. These completion-time grace-period numbers are propagated up the srcu_node tree so that the grace-period workqueue handler can determine whether additional grace periods are needed on the one hand and where to look for callbacks that are ready to be invoked. The srcu_barrier() function must now wait on all instances of the per-CPU ->srcu_cblist. Because each ->srcu_cblist is protected by ->lock, srcu_barrier() can remotely add the needed callbacks. In theory, it could also remotely start grace periods, but this gets complex and racy. And interestingly enough, it is never necessary to start a grace period in this case because srcu_barrier() only enqueues a callback when a callback is already present. And a grace period has to have already been started for this pre-existing callback. And it is only the callback that srcu_barrier() needs to wait on, not any particular grace period. Therefore, a new rcu_segcblist_entrain() function enqueues the srcu_barrier() function's callback into the same segment occupied by the pre-existing callback. The special case where all the pre-existing callbacks are on a different list being invoked is handled by enqueuing srcu_barrier()'s callback into the RCU_DONE_TAIL segment, relying on the done-callbacks check that takes place after all callbacks are inovked. Note that the readers use the same algorithm as before. Note that there is a separate srcu_idx that tells the readers what counter to increment. This unfortunately cannot be combined with srcu_gp_seq because they need to be incremented at different times. This commit introduces some ugly #ifdefs in rcutorture. These will go away when I feel good enough about Tree SRCU to ditch Classic SRCU. [1] https://lwn.net/Articles/309030/ Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> --- include/linux/rcu_segcblist.h | 42 ++- include/linux/srcutree.h | 80 ++++-- kernel/rcu/rcutorture.c | 20 +- kernel/rcu/srcutree.c | 639 +++++++++++++++++++++++++++++++++--------- kernel/rcu/tree.c | 6 + kernel/rcu/tree.h | 8 + 6 files changed, 645 insertions(+), 150 deletions(-) diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h index 74b1e7243955..ced8f313fd05 100644 --- a/include/linux/rcu_segcblist.h +++ b/include/linux/rcu_segcblist.h @@ -402,6 +402,37 @@ static inline void rcu_segcblist_enqueue(struct rcu_segcblist *rsclp, } /* + * Entrain the specified callback onto the specified rcu_segcblist at + * the end of the last non-empty segment. If the entire rcu_segcblist + * is empty, make no change, but return false. + * + * This is intended for use by rcu_barrier()-like primitives, -not- + * for normal grace-period use. IMPORTANT: The callback you enqueue + * will wait for all prior callbacks, NOT necessarily for a grace + * period. You have been warned. + */ +static inline bool rcu_segcblist_entrain(struct rcu_segcblist *rsclp, + struct rcu_head *rhp, bool lazy) +{ + int i; + + if (rcu_segcblist_n_cbs(rsclp) == 0) + return false; + WRITE_ONCE(rsclp->len, rsclp->len + 1); + if (lazy) + rsclp->len_lazy++; + 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]) + break; + *rsclp->tails[i] = rhp; + for (; i <= RCU_NEXT_TAIL; i++) + rsclp->tails[i] = &rhp->next; + return true; +} + +/* * 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 @@ -537,7 +568,8 @@ static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp, int i, j; WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp)); - WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)); + if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)) + return; /* * Find all callbacks whose ->gp_seq numbers indicate that they @@ -582,8 +614,9 @@ static inline void rcu_segcblist_advance(struct rcu_segcblist *rsclp, * them to complete at the end of the earlier grace period. * * This function operates on an rcu_segcblist structure, and also the - * grace-period sequence number at which new callbacks would become - * ready to invoke. + * grace-period sequence number seq at which new callbacks would become + * ready to invoke. Returns true if there are callbacks that won't be + * ready to invoke until seq, false otherwise. */ static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, unsigned long seq) @@ -591,7 +624,8 @@ static inline bool rcu_segcblist_accelerate(struct rcu_segcblist *rsclp, int i; WARN_ON_ONCE(!rcu_segcblist_is_enabled(rsclp)); - WARN_ON_ONCE(rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)); + if (rcu_segcblist_restempty(rsclp, RCU_DONE_TAIL)) + return false; /* * Find the segment preceding the oldest segment of callbacks diff --git a/include/linux/srcutree.h b/include/linux/srcutree.h index f2b3bd6c6bc2..0400e211aa44 100644 --- a/include/linux/srcutree.h +++ b/include/linux/srcutree.h @@ -24,25 +24,75 @@ #ifndef _LINUX_SRCU_TREE_H #define _LINUX_SRCU_TREE_H -struct srcu_array { - unsigned long lock_count[2]; - unsigned long unlock_count[2]; +#include <linux/rcu_node_tree.h> +#include <linux/completion.h> + +struct srcu_node; +struct srcu_struct; + +/* + * Per-CPU structure feeding into leaf srcu_node, similar in function + * to rcu_node. + */ +struct srcu_data { + /* Read-side state. */ + unsigned long srcu_lock_count[2]; /* Locks per CPU. */ + unsigned long srcu_unlock_count[2]; /* Unlocks per CPU. */ + + /* Update-side state. */ + spinlock_t lock ____cacheline_internodealigned_in_smp; + struct rcu_segcblist srcu_cblist; /* List of callbacks.*/ + unsigned long srcu_gp_seq_needed; /* Furthest future GP needed. */ + bool srcu_cblist_invoking; /* Invoking these CBs? */ + struct delayed_work work; /* Context for CB invoking. */ + struct rcu_head srcu_barrier_head; /* For srcu_barrier() use. */ + struct srcu_node *mynode; /* Leaf srcu_node. */ + int cpu; + struct srcu_struct *sp; }; +/* + * Node in SRCU combining tree, similar in function to rcu_data. + */ +struct srcu_node { + spinlock_t lock; + unsigned long srcu_have_cbs[4]; /* GP seq for children */ + /* having CBs, but only */ + /* is > ->srcu_gq_seq. */ + 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, similar in function to rcu_state. + */ struct srcu_struct { - unsigned long completed; - unsigned long srcu_gp_seq; - atomic_t srcu_exp_cnt; - struct srcu_array __percpu *per_cpu_ref; - spinlock_t queue_lock; /* protect ->srcu_cblist */ - struct rcu_segcblist srcu_cblist; + struct srcu_node node[NUM_RCU_NODES]; /* Combining tree. */ + struct srcu_node *level[RCU_NUM_LVLS + 1]; + /* First node at each level. */ + struct mutex srcu_cb_mutex; /* Serialize CB preparation. */ + spinlock_t gp_lock; /* protect ->srcu_cblist */ + struct mutex srcu_gp_mutex; /* Serialize GP work. */ + unsigned int srcu_idx; /* Current rdr array element. */ + unsigned long srcu_gp_seq; /* Grace-period seq #. */ + unsigned long srcu_gp_seq_needed; /* Latest gp_seq needed. */ + atomic_t srcu_exp_cnt; /* # ongoing expedited GPs. */ + struct srcu_data __percpu *sda; /* Per-CPU srcu_data array. */ + 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. */ struct delayed_work work; #ifdef CONFIG_DEBUG_LOCK_ALLOC struct lockdep_map dep_map; #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ }; -/* Values for -> state variable. */ +/* 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 @@ -51,11 +101,9 @@ void process_srcu(struct work_struct *work); #define __SRCU_STRUCT_INIT(name) \ { \ - .completed = -300, \ - .per_cpu_ref = &name##_srcu_array, \ - .queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock), \ - .srcu_cblist = RCU_SEGCBLIST_INITIALIZER(name.srcu_cblist),\ - .work = __DELAYED_WORK_INITIALIZER(name.work, process_srcu, 0),\ + .sda = &name##_srcu_data, \ + .gp_lock = __SPIN_LOCK_UNLOCKED(name.gp_lock), \ + .srcu_gp_seq_needed = 0 - 1, \ __SRCU_DEP_MAP_INIT(name) \ } @@ -79,7 +127,7 @@ void process_srcu(struct work_struct *work); * See include/linux/percpu-defs.h for the rules on per-CPU variables. */ #define __DEFINE_SRCU(name, is_static) \ - static DEFINE_PER_CPU(struct srcu_array, name##_srcu_array);\ + static DEFINE_PER_CPU(struct srcu_data, name##_srcu_data);\ is_static struct srcu_struct name = __SRCU_STRUCT_INIT(name) #define DEFINE_SRCU(name) __DEFINE_SRCU(name, /* not static */) #define DEFINE_STATIC_SRCU(name) __DEFINE_SRCU(name, static) diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c index 6f344b6748a8..e9d4527cdd43 100644 --- a/kernel/rcu/rcutorture.c +++ b/kernel/rcu/rcutorture.c @@ -563,17 +563,30 @@ static void srcu_torture_stats(void) int idx; #if defined(CONFIG_TREE_SRCU) || defined(CONFIG_CLASSIC_SRCU) +#ifdef CONFIG_TREE_SRCU + idx = srcu_ctlp->srcu_idx & 0x1; +#else /* #ifdef CONFIG_TREE_SRCU */ idx = srcu_ctlp->completed & 0x1; +#endif /* #else #ifdef CONFIG_TREE_SRCU */ pr_alert("%s%s Tree SRCU per-CPU(idx=%d):", torture_type, TORTURE_FLAG, idx); for_each_possible_cpu(cpu) { unsigned long l0, l1; unsigned long u0, u1; long c0, c1; - struct srcu_array *counts = per_cpu_ptr(srcu_ctlp->per_cpu_ref, cpu); +#ifdef CONFIG_TREE_SRCU + struct srcu_data *counts; + counts = per_cpu_ptr(srcu_ctlp->sda, cpu); + u0 = counts->srcu_unlock_count[!idx]; + u1 = counts->srcu_unlock_count[idx]; +#else /* #ifdef CONFIG_TREE_SRCU */ + struct srcu_array *counts; + + counts = per_cpu_ptr(srcu_ctlp->per_cpu_ref, cpu); u0 = counts->unlock_count[!idx]; u1 = counts->unlock_count[idx]; +#endif /* #else #ifdef CONFIG_TREE_SRCU */ /* * Make sure that a lock is always counted if the corresponding @@ -581,8 +594,13 @@ static void srcu_torture_stats(void) */ smp_rmb(); +#ifdef CONFIG_TREE_SRCU + l0 = counts->srcu_lock_count[!idx]; + l1 = counts->srcu_lock_count[idx]; +#else /* #ifdef CONFIG_TREE_SRCU */ l0 = counts->lock_count[!idx]; l1 = counts->lock_count[idx]; +#endif /* #else #ifdef CONFIG_TREE_SRCU */ c0 = l0 - u0; c1 = l1 - u1; diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index da676b0d016b..f9c684d79faa 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -36,19 +36,110 @@ #include <linux/delay.h> #include <linux/srcu.h> -#include <linux/rcu_node_tree.h> #include "rcu.h" -static int init_srcu_struct_fields(struct srcu_struct *sp) +static void srcu_invoke_callbacks(struct work_struct *work); +static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay); + +/* + * Initialize SRCU combining tree. 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 *sp, bool is_static) { - sp->completed = 0; + int cpu; + int i; + int level = 0; + int levelspread[RCU_NUM_LVLS]; + struct srcu_data *sdp; + struct srcu_node *snp; + struct srcu_node *snp_first; + + /* Work out the overall tree geometry. */ + sp->level[0] = &sp->node[0]; + for (i = 1; i < rcu_num_lvls; i++) + sp->level[i] = sp->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. */ + rcu_for_each_node_breadth_first(sp, snp) { + spin_lock_init(&snp->lock); + for (i = 0; i < ARRAY_SIZE(snp->srcu_have_cbs); i++) + snp->srcu_have_cbs[i] = 0; + snp->grplo = -1; + snp->grphi = -1; + if (snp == &sp->node[0]) { + /* Root node, special case. */ + snp->srcu_parent = NULL; + continue; + } + + /* Non-root node. */ + if (snp == sp->level[level + 1]) + level++; + snp->srcu_parent = sp->level[level - 1] + + (snp - sp->level[level]) / + levelspread[level - 1]; + } + + /* + * 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 = sp->level[level]; + for_each_possible_cpu(cpu) { + sdp = per_cpu_ptr(sp->sda, cpu); + spin_lock_init(&sdp->lock); + rcu_segcblist_init(&sdp->srcu_cblist); + sdp->srcu_cblist_invoking = false; + sdp->srcu_gp_seq_needed = sp->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_DELAYED_WORK(&sdp->work, srcu_invoke_callbacks); + sdp->sp = sp; + 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; + } + } +} + +/* + * 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. + */ +static int init_srcu_struct_fields(struct srcu_struct *sp, bool is_static) +{ + mutex_init(&sp->srcu_cb_mutex); + mutex_init(&sp->srcu_gp_mutex); + sp->srcu_idx = 0; sp->srcu_gp_seq = 0; atomic_set(&sp->srcu_exp_cnt, 0); - spin_lock_init(&sp->queue_lock); - rcu_segcblist_init(&sp->srcu_cblist); + sp->srcu_barrier_seq = 0; + mutex_init(&sp->srcu_barrier_mutex); + atomic_set(&sp->srcu_barrier_cpu_cnt, 0); INIT_DELAYED_WORK(&sp->work, process_srcu); - sp->per_cpu_ref = alloc_percpu(struct srcu_array); - return sp->per_cpu_ref ? 0 : -ENOMEM; + if (!is_static) + sp->sda = alloc_percpu(struct srcu_data); + init_srcu_struct_nodes(sp, is_static); + smp_store_release(&sp->srcu_gp_seq_needed, 0); /* Init done. */ + return sp->sda ? 0 : -ENOMEM; } #ifdef CONFIG_DEBUG_LOCK_ALLOC @@ -59,7 +150,8 @@ int __init_srcu_struct(struct srcu_struct *sp, const char *name, /* Don't re-initialize a lock while it is held. */ debug_check_no_locks_freed((void *)sp, sizeof(*sp)); lockdep_init_map(&sp->dep_map, name, key, 0); - return init_srcu_struct_fields(sp); + spin_lock_init(&sp->gp_lock); + return init_srcu_struct_fields(sp, false); } EXPORT_SYMBOL_GPL(__init_srcu_struct); @@ -75,15 +167,41 @@ EXPORT_SYMBOL_GPL(__init_srcu_struct); */ int init_srcu_struct(struct srcu_struct *sp) { - return init_srcu_struct_fields(sp); + spin_lock_init(&sp->gp_lock); + return init_srcu_struct_fields(sp, false); } EXPORT_SYMBOL_GPL(init_srcu_struct); #endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */ /* - * Returns approximate total of the readers' ->lock_count[] values for the - * rank of per-CPU counters specified by idx. + * 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 + * to each update-side SRCU primitive. Use ->gp_lock, which -is- + * compile-time initialized, to resolve races involving multiple + * CPUs trying to garner first-use privileges. + */ +static void check_init_srcu_struct(struct srcu_struct *sp) +{ + unsigned long flags; + + WARN_ON_ONCE(rcu_scheduler_active == RCU_SCHEDULER_INIT); + /* The smp_load_acquire() pairs with the smp_store_release(). */ + if (!rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq_needed))) /*^^^*/ + return; /* Already initialized. */ + spin_lock_irqsave(&sp->gp_lock, flags); + if (!rcu_seq_state(sp->srcu_gp_seq_needed)) { + spin_unlock_irqrestore(&sp->gp_lock, flags); + return; + } + init_srcu_struct_fields(sp, true); + spin_unlock_irqrestore(&sp->gp_lock, flags); +} + +/* + * Returns approximate total of the readers' ->srcu_lock_count[] values + * for the rank of per-CPU counters specified by idx. */ static unsigned long srcu_readers_lock_idx(struct srcu_struct *sp, int idx) { @@ -91,16 +209,16 @@ static unsigned long srcu_readers_lock_idx(struct srcu_struct *sp, int idx) unsigned long sum = 0; for_each_possible_cpu(cpu) { - struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu); + struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu); - sum += READ_ONCE(cpuc->lock_count[idx]); + sum += READ_ONCE(cpuc->srcu_lock_count[idx]); } return sum; } /* - * Returns approximate total of the readers' ->unlock_count[] values for the - * rank of per-CPU counters specified by idx. + * Returns approximate total of the readers' ->srcu_unlock_count[] values + * for the rank of per-CPU counters specified by idx. */ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *sp, int idx) { @@ -108,9 +226,9 @@ static unsigned long srcu_readers_unlock_idx(struct srcu_struct *sp, int idx) unsigned long sum = 0; for_each_possible_cpu(cpu) { - struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu); + struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu); - sum += READ_ONCE(cpuc->unlock_count[idx]); + sum += READ_ONCE(cpuc->srcu_unlock_count[idx]); } return sum; } @@ -145,14 +263,14 @@ static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx) * the current index but not have incremented the lock counter yet. * * Possible bug: There is no guarantee that there haven't been - * ULONG_MAX increments of ->lock_count[] since the unlocks were + * ULONG_MAX increments of ->srcu_lock_count[] since the unlocks were * counted, meaning that this could return true even if there are * still active readers. Since there are no memory barriers around - * srcu_flip(), the CPU is not required to increment ->completed + * srcu_flip(), the CPU is not required to increment ->srcu_idx * before running srcu_readers_unlock_idx(), which means that there * could be an arbitrarily large number of critical sections that * execute after srcu_readers_unlock_idx() but use the old value - * of ->completed. + * of ->srcu_idx. */ return srcu_readers_lock_idx(sp, idx) == unlocks; } @@ -172,12 +290,12 @@ static bool srcu_readers_active(struct srcu_struct *sp) unsigned long sum = 0; for_each_possible_cpu(cpu) { - struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu); + struct srcu_data *cpuc = per_cpu_ptr(sp->sda, cpu); - sum += READ_ONCE(cpuc->lock_count[0]); - sum += READ_ONCE(cpuc->lock_count[1]); - sum -= READ_ONCE(cpuc->unlock_count[0]); - sum -= READ_ONCE(cpuc->unlock_count[1]); + 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]); } return sum; } @@ -193,18 +311,21 @@ static bool srcu_readers_active(struct srcu_struct *sp) */ void cleanup_srcu_struct(struct srcu_struct *sp) { + int cpu; + WARN_ON_ONCE(atomic_read(&sp->srcu_exp_cnt)); if (WARN_ON(srcu_readers_active(sp))) return; /* Leakage unless caller handles error. */ - if (WARN_ON(!rcu_segcblist_empty(&sp->srcu_cblist))) - return; /* Leakage unless caller handles error. */ flush_delayed_work(&sp->work); - if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE)) { - pr_info("cleanup_srcu_struct: Active srcu_struct %lu CBs %c state: %d\n", rcu_segcblist_n_cbs(&sp->srcu_cblist), ".E"[rcu_segcblist_empty(&sp->srcu_cblist)], rcu_seq_state(READ_ONCE(sp->srcu_gp_seq))); + for_each_possible_cpu(cpu) + flush_delayed_work(&per_cpu_ptr(sp->sda, cpu)->work); + if (WARN_ON(rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) != SRCU_STATE_IDLE) || + WARN_ON(srcu_readers_active(sp))) { + pr_info("cleanup_srcu_struct: Active srcu_struct %p state: %d\n", sp, rcu_seq_state(READ_ONCE(sp->srcu_gp_seq))); return; /* Caller forgot to stop doing call_srcu()? */ } - free_percpu(sp->per_cpu_ref); - sp->per_cpu_ref = NULL; + free_percpu(sp->sda); + sp->sda = NULL; } EXPORT_SYMBOL_GPL(cleanup_srcu_struct); @@ -217,8 +338,8 @@ int __srcu_read_lock(struct srcu_struct *sp) { int idx; - idx = READ_ONCE(sp->completed) & 0x1; - __this_cpu_inc(sp->per_cpu_ref->lock_count[idx]); + idx = READ_ONCE(sp->srcu_idx) & 0x1; + __this_cpu_inc(sp->sda->srcu_lock_count[idx]); smp_mb(); /* B */ /* Avoid leaking the critical section. */ return idx; } @@ -233,7 +354,7 @@ EXPORT_SYMBOL_GPL(__srcu_read_lock); void __srcu_read_unlock(struct srcu_struct *sp, int idx) { smp_mb(); /* C */ /* Avoid leaking the critical section. */ - this_cpu_inc(sp->per_cpu_ref->unlock_count[idx]); + this_cpu_inc(sp->sda->srcu_unlock_count[idx]); } EXPORT_SYMBOL_GPL(__srcu_read_unlock); @@ -251,19 +372,207 @@ EXPORT_SYMBOL_GPL(__srcu_read_unlock); */ static void srcu_gp_start(struct srcu_struct *sp) { + struct srcu_data *sdp = this_cpu_ptr(sp->sda); int state; - rcu_segcblist_accelerate(&sp->srcu_cblist, - rcu_seq_snap(&sp->srcu_gp_seq)); + RCU_LOCKDEP_WARN(!lockdep_is_held(&sp->gp_lock), + "Invoked srcu_gp_start() without ->gp_lock!"); + WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)); + rcu_segcblist_advance(&sdp->srcu_cblist, + rcu_seq_current(&sp->srcu_gp_seq)); + (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, + rcu_seq_snap(&sp->srcu_gp_seq)); rcu_seq_start(&sp->srcu_gp_seq); state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)); WARN_ON_ONCE(state != SRCU_STATE_SCAN1); } /* + * Track online CPUs to guide callback workqueue placement. + */ +DEFINE_PER_CPU(bool, srcu_online); + +void srcu_online_cpu(unsigned int cpu) +{ + WRITE_ONCE(per_cpu(srcu_online, cpu), true); +} + +void srcu_offline_cpu(unsigned int cpu) +{ + WRITE_ONCE(per_cpu(srcu_online, cpu), false); +} + +/* + * Place the workqueue handler on the specified CPU if online, otherwise + * just run it whereever. This is useful for placing workqueue handlers + * that are to invoke the specified CPU's callbacks. + */ +static bool srcu_queue_delayed_work_on(int cpu, struct workqueue_struct *wq, + struct delayed_work *dwork, + unsigned long delay) +{ + bool ret; + + preempt_disable(); + if (READ_ONCE(per_cpu(srcu_online, cpu))) + ret = queue_delayed_work_on(cpu, wq, dwork, delay); + else + ret = queue_delayed_work(wq, dwork, delay); + preempt_enable(); + return ret; +} + +/* + * Schedule callback invocation for the specified srcu_data structure, + * if possible, on the corresponding CPU. + */ +static void srcu_schedule_cbs_sdp(struct srcu_data *sdp, unsigned long delay) +{ + srcu_queue_delayed_work_on(sdp->cpu, system_power_efficient_wq, + &sdp->work, delay); +} + +/* + * Schedule callback invocation for all srcu_data structures associated + * with the specified srcu_node structure, if possible, on the corresponding + * CPUs. + */ +static void srcu_schedule_cbs_snp(struct srcu_struct *sp, struct srcu_node *snp) +{ + int cpu; + + for (cpu = snp->grplo; cpu <= snp->grphi; cpu++) + srcu_schedule_cbs_sdp(per_cpu_ptr(sp->sda, cpu), SRCU_INTERVAL); +} + +/* + * Note the end of an SRCU grace period. Initiates callback invocation + * and starts a new grace period if needed. + * + * The ->srcu_cb_mutex acquisition does not protect any data, but + * instead prevents more than one grace period from starting while we + * are initiating callback invocation. This allows the ->srcu_have_cbs[] + * array to have a finite number of elements. + */ +static void srcu_gp_end(struct srcu_struct *sp) +{ + bool cbs; + unsigned long gpseq; + int idx; + int idxnext; + struct srcu_node *snp; + + /* Prevent more than one additional grace period. */ + mutex_lock(&sp->srcu_cb_mutex); + + /* End the current grace period. */ + spin_lock_irq(&sp->gp_lock); + idx = rcu_seq_state(sp->srcu_gp_seq); + WARN_ON_ONCE(idx != SRCU_STATE_SCAN2); + rcu_seq_end(&sp->srcu_gp_seq); + gpseq = rcu_seq_current(&sp->srcu_gp_seq); + spin_unlock_irq(&sp->gp_lock); + mutex_unlock(&sp->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); + idxnext = (idx + 1) % ARRAY_SIZE(snp->srcu_have_cbs); + rcu_for_each_node_breadth_first(sp, snp) { + spin_lock_irq(&snp->lock); + cbs = false; + if (snp >= sp->level[rcu_num_lvls - 1]) + cbs = snp->srcu_have_cbs[idx] == gpseq; + snp->srcu_have_cbs[idx] = gpseq; + rcu_seq_set_state(&snp->srcu_have_cbs[idx], 1); + spin_unlock_irq(&snp->lock); + if (cbs) { + smp_mb(); /* GP end before CB invocation. */ + srcu_schedule_cbs_snp(sp, snp); + } + } + + /* Callback initiation done, allow grace periods after next. */ + mutex_unlock(&sp->srcu_cb_mutex); + + /* Start a new grace period if needed. */ + spin_lock_irq(&sp->gp_lock); + gpseq = rcu_seq_current(&sp->srcu_gp_seq); + if (!rcu_seq_state(gpseq) && + ULONG_CMP_LT(gpseq, sp->srcu_gp_seq_needed)) { + srcu_gp_start(sp); + spin_unlock_irq(&sp->gp_lock); + /* Throttle expedited grace periods: Should be rare! */ + srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) && + rcu_seq_ctr(gpseq) & 0xf + ? 0 + : SRCU_INTERVAL); + } else { + spin_unlock_irq(&sp->gp_lock); + } +} + +/* + * Funnel-locking scheme to scalably mediate many concurrent grace-period + * requests. The winner has to do the work of actually starting grace + * period s. Losers must either ensure that their desired grace-period + * number is recorded on at least their leaf srcu_node structure, or they + * must take steps to invoke their own callbacks. + */ +static void srcu_funnel_gp_start(struct srcu_struct *sp, + struct srcu_data *sdp, + unsigned long s) +{ + unsigned long flags; + int idx = rcu_seq_ctr(s) % ARRAY_SIZE(sdp->mynode->srcu_have_cbs); + struct srcu_node *snp = sdp->mynode; + unsigned long snp_seq; + + /* Each pass through the loop does one level of the srcu_node tree. */ + for (; snp != NULL; snp = snp->srcu_parent) { + if (rcu_seq_done(&sp->srcu_gp_seq, s) && snp != sdp->mynode) + return; /* GP already done and CBs recorded. */ + spin_lock_irqsave(&snp->lock, flags); + if (ULONG_CMP_GE(snp->srcu_have_cbs[idx], s)) { + snp_seq = snp->srcu_have_cbs[idx]; + spin_unlock_irqrestore(&snp->lock, flags); + if (snp == sdp->mynode && snp_seq != s) { + smp_mb(); /* CBs after GP! */ + srcu_schedule_cbs_sdp(sdp, 0); + } + return; + } + snp->srcu_have_cbs[idx] = s; + spin_unlock_irqrestore(&snp->lock, flags); + } + + /* Top of tree, must ensure the grace period will be started. */ + spin_lock_irqsave(&sp->gp_lock, flags); + if (ULONG_CMP_LT(sp->srcu_gp_seq_needed, s)) { + /* + * Record need for grace period s. Pair with load + * acquire setting up for initialization. + */ + smp_store_release(&sp->srcu_gp_seq_needed, s); /*^^^*/ + } + + /* If grace period not already done and none in progress, start it. */ + if (!rcu_seq_done(&sp->srcu_gp_seq, s) && + rcu_seq_state(sp->srcu_gp_seq) == SRCU_STATE_IDLE) { + WARN_ON_ONCE(ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)); + srcu_gp_start(sp); + queue_delayed_work(system_power_efficient_wq, &sp->work, + atomic_read(&sp->srcu_exp_cnt) + ? 0 + : SRCU_INTERVAL); + } + spin_unlock_irqrestore(&sp->gp_lock, flags); +} + +/* * Wait until all readers counted by array index idx complete, but * loop an additional time if there is an expedited grace period pending. - * The caller must ensure that ->completed is not changed while checking. + * The caller must ensure that ->srcu_idx is not changed while checking. */ static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount) { @@ -277,13 +586,13 @@ static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount) } /* - * Increment the ->completed counter so that future SRCU readers will - * use the other rank of the ->(un)lock_count[] arrays. This allows + * Increment the ->srcu_idx counter so that future SRCU readers will + * use the other rank of the ->srcu_(un)lock_count[] arrays. This allows * us to wait for pre-existing readers in a starvation-free manner. */ static void srcu_flip(struct srcu_struct *sp) { - WRITE_ONCE(sp->completed, sp->completed + 1); + WRITE_ONCE(sp->srcu_idx, sp->srcu_idx + 1); /* * Ensure that if the updater misses an __srcu_read_unlock() @@ -296,21 +605,9 @@ static void srcu_flip(struct srcu_struct *sp) } /* - * End an SRCU grace period. - */ -static void srcu_gp_end(struct srcu_struct *sp) -{ - rcu_seq_end(&sp->srcu_gp_seq); - - spin_lock_irq(&sp->queue_lock); - rcu_segcblist_advance(&sp->srcu_cblist, - rcu_seq_current(&sp->srcu_gp_seq)); - spin_unlock_irq(&sp->queue_lock); -} - -/* - * Enqueue an SRCU callback on the specified srcu_struct structure, - * initiating grace-period processing if it is not already running. + * 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. * * Note that all CPUs must agree that the grace period extended beyond * all pre-existing SRCU read-side critical section. On systems with @@ -335,33 +632,40 @@ static void srcu_gp_end(struct srcu_struct *sp) * srcu_read_lock(), and srcu_read_unlock() that are all passed the same * srcu_struct structure. */ -void call_srcu(struct srcu_struct *sp, struct rcu_head *head, +void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp, rcu_callback_t func) { unsigned long flags; - - head->next = NULL; - head->func = func; - spin_lock_irqsave(&sp->queue_lock, flags); - smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */ - rcu_segcblist_enqueue(&sp->srcu_cblist, head, false); - if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) { - srcu_gp_start(sp); - queue_delayed_work(system_power_efficient_wq, &sp->work, 0); + bool needgp = false; + unsigned long s; + struct srcu_data *sdp; + + check_init_srcu_struct(sp); + rhp->func = func; + local_irq_save(flags); + sdp = this_cpu_ptr(sp->sda); + spin_lock(&sdp->lock); + rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp, false); + rcu_segcblist_advance(&sdp->srcu_cblist, + rcu_seq_current(&sp->srcu_gp_seq)); + s = rcu_seq_snap(&sp->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; } - spin_unlock_irqrestore(&sp->queue_lock, flags); + spin_unlock_irqrestore(&sdp->lock, flags); + if (needgp) + srcu_funnel_gp_start(sp, sdp, s); } EXPORT_SYMBOL_GPL(call_srcu); -static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay); - /* * Helper function for synchronize_srcu() and synchronize_srcu_expedited(). */ static void __synchronize_srcu(struct srcu_struct *sp) { struct rcu_synchronize rcu; - struct rcu_head *head = &rcu.head; RCU_LOCKDEP_WARN(lock_is_held(&sp->dep_map) || lock_is_held(&rcu_bh_lock_map) || @@ -372,26 +676,12 @@ static void __synchronize_srcu(struct srcu_struct *sp) if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) return; might_sleep(); + check_init_srcu_struct(sp); init_completion(&rcu.completion); - - head->next = NULL; - head->func = wakeme_after_rcu; - spin_lock_irq(&sp->queue_lock); - smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */ - if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_IDLE) { - /* steal the processing owner */ - rcu_segcblist_enqueue(&sp->srcu_cblist, head, false); - srcu_gp_start(sp); - spin_unlock_irq(&sp->queue_lock); - /* give the processing owner to work_struct */ - srcu_reschedule(sp, 0); - } else { - rcu_segcblist_enqueue(&sp->srcu_cblist, head, false); - spin_unlock_irq(&sp->queue_lock); - } - + init_rcu_head_on_stack(&rcu.head); + call_srcu(sp, &rcu.head, wakeme_after_rcu); wait_for_completion(&rcu.completion); - smp_mb(); /* Caller's later accesses after GP. */ + destroy_rcu_head_on_stack(&rcu.head); } /** @@ -426,8 +716,8 @@ EXPORT_SYMBOL_GPL(synchronize_srcu_expedited); * * Wait for the count to drain to zero of both indexes. To avoid the * possible starvation of synchronize_srcu(), it waits for the count of - * the index=((->completed & 1) ^ 1) to drain to zero at first, - * and then flip the completed and wait for the count of the other index. + * the index=((->srcu_idx & 1) ^ 1) to drain to zero at first, + * and then flip the srcu_idx and wait for the count of the other index. * * Can block; must be called from process context. * @@ -468,13 +758,69 @@ void synchronize_srcu(struct srcu_struct *sp) } EXPORT_SYMBOL_GPL(synchronize_srcu); +/* + * Callback function for srcu_barrier() use. + */ +static void srcu_barrier_cb(struct rcu_head *rhp) +{ + struct srcu_data *sdp; + struct srcu_struct *sp; + + sdp = container_of(rhp, struct srcu_data, srcu_barrier_head); + sp = sdp->sp; + if (atomic_dec_and_test(&sp->srcu_barrier_cpu_cnt)) + complete(&sp->srcu_barrier_completion); +} + /** * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete. * @sp: srcu_struct on which to wait for in-flight callbacks. */ void srcu_barrier(struct srcu_struct *sp) { - synchronize_srcu(sp); + int cpu; + struct srcu_data *sdp; + unsigned long s = rcu_seq_snap(&sp->srcu_barrier_seq); + + check_init_srcu_struct(sp); + mutex_lock(&sp->srcu_barrier_mutex); + if (rcu_seq_done(&sp->srcu_barrier_seq, s)) { + smp_mb(); /* Force ordering following return. */ + mutex_unlock(&sp->srcu_barrier_mutex); + return; /* Someone else did our work for us. */ + } + rcu_seq_start(&sp->srcu_barrier_seq); + init_completion(&sp->srcu_barrier_completion); + + /* Initial count prevents reaching zero until all CBs are posted. */ + atomic_set(&sp->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(sp->sda, cpu); + spin_lock_irq(&sdp->lock); + atomic_inc(&sp->srcu_barrier_cpu_cnt); + sdp->srcu_barrier_head.func = srcu_barrier_cb; + if (!rcu_segcblist_entrain(&sdp->srcu_cblist, + &sdp->srcu_barrier_head, 0)) + atomic_dec(&sp->srcu_barrier_cpu_cnt); + spin_unlock_irq(&sdp->lock); + } + + /* Remove the initial count, at which point reaching zero can happen. */ + if (atomic_dec_and_test(&sp->srcu_barrier_cpu_cnt)) + complete(&sp->srcu_barrier_completion); + wait_for_completion(&sp->srcu_barrier_completion); + + rcu_seq_end(&sp->srcu_barrier_seq); + mutex_unlock(&sp->srcu_barrier_mutex); } EXPORT_SYMBOL_GPL(srcu_barrier); @@ -487,21 +833,24 @@ EXPORT_SYMBOL_GPL(srcu_barrier); */ unsigned long srcu_batches_completed(struct srcu_struct *sp) { - return sp->completed; + return sp->srcu_idx; } EXPORT_SYMBOL_GPL(srcu_batches_completed); /* - * Core SRCU state machine. Advance callbacks from ->batch_check0 to - * ->batch_check1 and then to ->batch_done as readers drain. + * Core SRCU state machine. Push state bits of ->srcu_gp_seq + * to SRCU_STATE_SCAN2, and invoke srcu_gp_end() when scan has + * completed in that state. */ -static void srcu_advance_batches(struct srcu_struct *sp) +static void srcu_advance_state(struct srcu_struct *sp) { int idx; + mutex_lock(&sp->srcu_gp_mutex); + /* * Because readers might be delayed for an extended period after - * fetching ->completed for their index, at any point in time there + * fetching ->srcu_idx for their index, at any point in time there * might well be readers using both idx=0 and idx=1. We therefore * need to wait for readers to clear from both index values before * invoking a callback. @@ -511,23 +860,29 @@ static void srcu_advance_batches(struct srcu_struct *sp) */ idx = rcu_seq_state(smp_load_acquire(&sp->srcu_gp_seq)); /* ^^^ */ if (idx == SRCU_STATE_IDLE) { - spin_lock_irq(&sp->queue_lock); - if (rcu_segcblist_empty(&sp->srcu_cblist)) { - spin_unlock_irq(&sp->queue_lock); + spin_lock_irq(&sp->gp_lock); + if (ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)) { + WARN_ON_ONCE(rcu_seq_state(sp->srcu_gp_seq)); + spin_unlock_irq(&sp->gp_lock); + mutex_unlock(&sp->srcu_gp_mutex); return; } idx = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)); if (idx == SRCU_STATE_IDLE) srcu_gp_start(sp); - spin_unlock_irq(&sp->queue_lock); - if (idx != SRCU_STATE_IDLE) + spin_unlock_irq(&sp->gp_lock); + if (idx != SRCU_STATE_IDLE) { + mutex_unlock(&sp->srcu_gp_mutex); return; /* Someone else started the grace period. */ + } } if (rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)) == SRCU_STATE_SCAN1) { - idx = 1 ^ (sp->completed & 1); - if (!try_check_zero(sp, idx, 1)) + idx = 1 ^ (sp->srcu_idx & 1); + if (!try_check_zero(sp, idx, 1)) { + mutex_unlock(&sp->srcu_gp_mutex); return; /* readers present, retry later. */ + } srcu_flip(sp); rcu_seq_set_state(&sp->srcu_gp_seq, SRCU_STATE_SCAN2); } @@ -538,10 +893,12 @@ static void srcu_advance_batches(struct srcu_struct *sp) * SRCU read-side critical sections are normally short, * so check at least twice in quick succession after a flip. */ - idx = 1 ^ (sp->completed & 1); - if (!try_check_zero(sp, idx, 2)) - return; /* readers present, retry after later. */ - srcu_gp_end(sp); + idx = 1 ^ (sp->srcu_idx & 1); + if (!try_check_zero(sp, idx, 2)) { + mutex_unlock(&sp->srcu_gp_mutex); + return; /* readers present, retry later. */ + } + srcu_gp_end(sp); /* Releases ->srcu_gp_mutex. */ } } @@ -551,28 +908,51 @@ static void srcu_advance_batches(struct srcu_struct *sp) * the workqueue. Note that needed memory barriers have been executed * in this task's context by srcu_readers_active_idx_check(). */ -static void srcu_invoke_callbacks(struct srcu_struct *sp) +static void srcu_invoke_callbacks(struct work_struct *work) { + bool more; struct rcu_cblist ready_cbs; struct rcu_head *rhp; + struct srcu_data *sdp; + struct srcu_struct *sp; - spin_lock_irq(&sp->queue_lock); - if (!rcu_segcblist_ready_cbs(&sp->srcu_cblist)) { - spin_unlock_irq(&sp->queue_lock); - return; - } + sdp = container_of(work, struct srcu_data, work.work); + sp = sdp->sp; rcu_cblist_init(&ready_cbs); - rcu_segcblist_extract_done_cbs(&sp->srcu_cblist, &ready_cbs); - spin_unlock_irq(&sp->queue_lock); + spin_lock_irq(&sdp->lock); + smp_mb(); /* Old grace periods before callback invocation! */ + rcu_segcblist_advance(&sdp->srcu_cblist, + rcu_seq_current(&sp->srcu_gp_seq)); + if (sdp->srcu_cblist_invoking || + !rcu_segcblist_ready_cbs(&sdp->srcu_cblist)) { + spin_unlock_irq(&sdp->lock); + return; /* Someone else on the job or nothing to do. */ + } + + /* 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); + spin_unlock_irq(&sdp->lock); rhp = rcu_cblist_dequeue(&ready_cbs); for (; rhp != NULL; rhp = rcu_cblist_dequeue(&ready_cbs)) { local_bh_disable(); rhp->func(rhp); local_bh_enable(); } - spin_lock_irq(&sp->queue_lock); - rcu_segcblist_insert_count(&sp->srcu_cblist, &ready_cbs); - spin_unlock_irq(&sp->queue_lock); + + /* + * Update counts, accelerate new callbacks, and if needed, + * schedule another round of callback invocation. + */ + spin_lock_irq(&sdp->lock); + rcu_segcblist_insert_count(&sdp->srcu_cblist, &ready_cbs); + (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, + rcu_seq_snap(&sp->srcu_gp_seq)); + sdp->srcu_cblist_invoking = false; + more = rcu_segcblist_ready_cbs(&sdp->srcu_cblist); + spin_unlock_irq(&sdp->lock); + if (more) + srcu_schedule_cbs_sdp(sdp, 0); } /* @@ -581,19 +961,21 @@ static void srcu_invoke_callbacks(struct srcu_struct *sp) */ static void srcu_reschedule(struct srcu_struct *sp, unsigned long delay) { - bool pending = true; - int state; + bool pushgp = true; - if (rcu_segcblist_empty(&sp->srcu_cblist)) { - spin_lock_irq(&sp->queue_lock); - state = rcu_seq_state(READ_ONCE(sp->srcu_gp_seq)); - if (rcu_segcblist_empty(&sp->srcu_cblist) && - state == SRCU_STATE_IDLE) - pending = false; - spin_unlock_irq(&sp->queue_lock); + spin_lock_irq(&sp->gp_lock); + if (ULONG_CMP_GE(sp->srcu_gp_seq, sp->srcu_gp_seq_needed)) { + if (!WARN_ON_ONCE(rcu_seq_state(sp->srcu_gp_seq))) { + /* All requests fulfilled, time to go idle. */ + pushgp = false; + } + } else if (!rcu_seq_state(sp->srcu_gp_seq)) { + /* Outstanding request and no GP. Start one. */ + srcu_gp_start(sp); } + spin_unlock_irq(&sp->gp_lock); - if (pending) + if (pushgp) queue_delayed_work(system_power_efficient_wq, &sp->work, delay); } @@ -606,8 +988,7 @@ void process_srcu(struct work_struct *work) sp = container_of(work, struct srcu_struct, work.work); - srcu_advance_batches(sp); - srcu_invoke_callbacks(sp); + srcu_advance_state(sp); srcu_reschedule(sp, atomic_read(&sp->srcu_exp_cnt) ? 0 : SRCU_INTERVAL); } EXPORT_SYMBOL_GPL(process_srcu); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index e0eb798181bc..75ca946734e6 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3783,12 +3783,16 @@ int rcutree_online_cpu(unsigned int cpu) { sync_sched_exp_online_cleanup(cpu); rcutree_affinity_setting(cpu, -1); + if (IS_ENABLED(CONFIG_TREE_SRCU)) + srcu_online_cpu(cpu); return 0; } int rcutree_offline_cpu(unsigned int cpu) { rcutree_affinity_setting(cpu, cpu); + if (IS_ENABLED(CONFIG_TREE_SRCU)) + srcu_offline_cpu(cpu); return 0; } @@ -4164,6 +4168,8 @@ void __init rcu_init(void) for_each_online_cpu(cpu) { rcutree_prepare_cpu(cpu); rcu_cpu_starting(cpu); + if (IS_ENABLED(CONFIG_TREE_SRCU)) + srcu_online_cpu(cpu); } } diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index a2a45cb629d6..0e598ab08fea 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -541,6 +541,14 @@ static bool rcu_nohz_full_cpu(struct rcu_state *rsp); static void rcu_dynticks_task_enter(void); static void rcu_dynticks_task_exit(void); +#ifdef CONFIG_SRCU +void srcu_online_cpu(unsigned int cpu); +void srcu_offline_cpu(unsigned int cpu); +#else /* #ifdef CONFIG_SRCU */ +void srcu_online_cpu(unsigned int cpu) { } +void srcu_offline_cpu(unsigned int cpu) { } +#endif /* #else #ifdef CONFIG_SRCU */ + #endif /* #ifndef RCU_TREE_NONCORE */ #ifdef CONFIG_RCU_TRACE -- 2.5.2
