+++ /dev/null
-/*
- * Sleepable Read-Copy Update mechanism for mutual exclusion.
- *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation; either version 2 of the License, or
- * (at your option) any later version.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with this program; if not, write to the Free Software
- * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
- *
- * Copyright (C) IBM Corporation, 2006
- * Copyright (C) Fujitsu, 2012
- *
- * Author: Paul McKenney <paulmck@us.ibm.com>
- * Lai Jiangshan <laijs@cn.fujitsu.com>
- *
- * For detailed explanation of Read-Copy Update mechanism see -
- * Documentation/RCU/ *.txt
- *
- */
-
-#include <linux/export.h>
-#include <linux/mutex.h>
-#include <linux/percpu.h>
-#include <linux/preempt.h>
-#include <linux/rcupdate.h>
-#include <linux/sched.h>
-#include <linux/smp.h>
-#include <linux/delay.h>
-#include <linux/srcu.h>
-
-#include <trace/events/rcu.h>
-
-#include "rcu.h"
-
-/*
- * Initialize an rcu_batch structure to empty.
- */
-static inline void rcu_batch_init(struct rcu_batch *b)
-{
- b->head = NULL;
- b->tail = &b->head;
-}
-
-/*
- * Enqueue a callback onto the tail of the specified rcu_batch structure.
- */
-static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
-{
- *b->tail = head;
- b->tail = &head->next;
-}
-
-/*
- * Is the specified rcu_batch structure empty?
- */
-static inline bool rcu_batch_empty(struct rcu_batch *b)
-{
- return b->tail == &b->head;
-}
-
-/*
- * Remove the callback at the head of the specified rcu_batch structure
- * and return a pointer to it, or return NULL if the structure is empty.
- */
-static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
-{
- struct rcu_head *head;
-
- if (rcu_batch_empty(b))
- return NULL;
-
- head = b->head;
- b->head = head->next;
- if (b->tail == &head->next)
- rcu_batch_init(b);
-
- return head;
-}
-
-/*
- * Move all callbacks from the rcu_batch structure specified by "from" to
- * the structure specified by "to".
- */
-static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
-{
- if (!rcu_batch_empty(from)) {
- *to->tail = from->head;
- to->tail = from->tail;
- rcu_batch_init(from);
- }
-}
-
-static int init_srcu_struct_fields(struct srcu_struct *sp)
-{
- sp->completed = 0;
- spin_lock_init(&sp->queue_lock);
- sp->running = false;
- rcu_batch_init(&sp->batch_queue);
- rcu_batch_init(&sp->batch_check0);
- rcu_batch_init(&sp->batch_check1);
- rcu_batch_init(&sp->batch_done);
- INIT_DELAYED_WORK(&sp->work, process_srcu);
- sp->per_cpu_ref = alloc_percpu(struct srcu_struct_array);
- return sp->per_cpu_ref ? 0 : -ENOMEM;
-}
-
-#ifdef CONFIG_DEBUG_LOCK_ALLOC
-
-int __init_srcu_struct(struct srcu_struct *sp, const char *name,
- struct lock_class_key *key)
-{
- /* 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);
-}
-EXPORT_SYMBOL_GPL(__init_srcu_struct);
-
-#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-
-/**
- * init_srcu_struct - initialize a sleep-RCU structure
- * @sp: structure to initialize.
- *
- * Must invoke this on a given srcu_struct before passing that srcu_struct
- * to any other function. Each srcu_struct represents a separate domain
- * of SRCU protection.
- */
-int init_srcu_struct(struct srcu_struct *sp)
-{
- return init_srcu_struct_fields(sp);
-}
-EXPORT_SYMBOL_GPL(init_srcu_struct);
-
-#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
-
-/*
- * Returns approximate total of the readers' ->seq[] values for the
- * rank of per-CPU counters specified by idx.
- */
-static unsigned long srcu_readers_seq_idx(struct srcu_struct *sp, int idx)
-{
- int cpu;
- unsigned long sum = 0;
- unsigned long t;
-
- for_each_possible_cpu(cpu) {
- t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->seq[idx]);
- sum += t;
- }
- return sum;
-}
-
-/*
- * Returns approximate number of readers active on the specified rank
- * of the per-CPU ->c[] counters.
- */
-static unsigned long srcu_readers_active_idx(struct srcu_struct *sp, int idx)
-{
- int cpu;
- unsigned long sum = 0;
- unsigned long t;
-
- for_each_possible_cpu(cpu) {
- t = ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[idx]);
- sum += t;
- }
- return sum;
-}
-
-/*
- * Return true if the number of pre-existing readers is determined to
- * be stably zero. An example unstable zero can occur if the call
- * to srcu_readers_active_idx() misses an __srcu_read_lock() increment,
- * but due to task migration, sees the corresponding __srcu_read_unlock()
- * decrement. This can happen because srcu_readers_active_idx() takes
- * time to sum the array, and might in fact be interrupted or preempted
- * partway through the summation.
- */
-static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
-{
- unsigned long seq;
-
- seq = srcu_readers_seq_idx(sp, idx);
-
- /*
- * The following smp_mb() A pairs with the smp_mb() B located in
- * __srcu_read_lock(). This pairing ensures that if an
- * __srcu_read_lock() increments its counter after the summation
- * in srcu_readers_active_idx(), then the corresponding SRCU read-side
- * critical section will see any changes made prior to the start
- * of the current SRCU grace period.
- *
- * Also, if the above call to srcu_readers_seq_idx() saw the
- * increment of ->seq[], then the call to srcu_readers_active_idx()
- * must see the increment of ->c[].
- */
- smp_mb(); /* A */
-
- /*
- * Note that srcu_readers_active_idx() can incorrectly return
- * zero even though there is a pre-existing reader throughout.
- * To see this, suppose that task A is in a very long SRCU
- * read-side critical section that started on CPU 0, and that
- * no other reader exists, so that the sum of the counters
- * is equal to one. Then suppose that task B starts executing
- * srcu_readers_active_idx(), summing up to CPU 1, and then that
- * task C starts reading on CPU 0, so that its increment is not
- * summed, but finishes reading on CPU 2, so that its decrement
- * -is- summed. Then when task B completes its sum, it will
- * incorrectly get zero, despite the fact that task A has been
- * in its SRCU read-side critical section the whole time.
- *
- * We therefore do a validation step should srcu_readers_active_idx()
- * return zero.
- */
- if (srcu_readers_active_idx(sp, idx) != 0)
- return false;
-
- /*
- * The remainder of this function is the validation step.
- * The following smp_mb() D pairs with the smp_mb() C in
- * __srcu_read_unlock(). If the __srcu_read_unlock() was seen
- * by srcu_readers_active_idx() above, then any destructive
- * operation performed after the grace period will happen after
- * the corresponding SRCU read-side critical section.
- *
- * Note that there can be at most NR_CPUS worth of readers using
- * the old index, which is not enough to overflow even a 32-bit
- * integer. (Yes, this does mean that systems having more than
- * a billion or so CPUs need to be 64-bit systems.) Therefore,
- * the sum of the ->seq[] counters cannot possibly overflow.
- * Therefore, the only way that the return values of the two
- * calls to srcu_readers_seq_idx() can be equal is if there were
- * no increments of the corresponding rank of ->seq[] counts
- * in the interim. But the missed-increment scenario laid out
- * above includes an increment of the ->seq[] counter by
- * the corresponding __srcu_read_lock(). Therefore, if this
- * scenario occurs, the return values from the two calls to
- * srcu_readers_seq_idx() will differ, and thus the validation
- * step below suffices.
- */
- smp_mb(); /* D */
-
- return srcu_readers_seq_idx(sp, idx) == seq;
-}
-
-/**
- * srcu_readers_active - returns approximate number of readers.
- * @sp: which srcu_struct to count active readers (holding srcu_read_lock).
- *
- * Note that this is not an atomic primitive, and can therefore suffer
- * severe errors when invoked on an active srcu_struct. That said, it
- * can be useful as an error check at cleanup time.
- */
-static int srcu_readers_active(struct srcu_struct *sp)
-{
- int cpu;
- unsigned long sum = 0;
-
- for_each_possible_cpu(cpu) {
- sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[0]);
- sum += ACCESS_ONCE(per_cpu_ptr(sp->per_cpu_ref, cpu)->c[1]);
- }
- return sum;
-}
-
-/**
- * cleanup_srcu_struct - deconstruct a sleep-RCU structure
- * @sp: structure to clean up.
- *
- * Must invoke this after you are finished using a given srcu_struct that
- * was initialized via init_srcu_struct(), else you leak memory.
- */
-void cleanup_srcu_struct(struct srcu_struct *sp)
-{
- if (WARN_ON(srcu_readers_active(sp)))
- return; /* Leakage unless caller handles error. */
- free_percpu(sp->per_cpu_ref);
- sp->per_cpu_ref = NULL;
-}
-EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
-
-/*
- * Counts the new reader in the appropriate per-CPU element of the
- * srcu_struct. Must be called from process context.
- * Returns an index that must be passed to the matching srcu_read_unlock().
- */
-int __srcu_read_lock(struct srcu_struct *sp)
-{
- int idx;
-
- idx = ACCESS_ONCE(sp->completed) & 0x1;
- preempt_disable();
- ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->c[idx]) += 1;
- smp_mb(); /* B */ /* Avoid leaking the critical section. */
- ACCESS_ONCE(this_cpu_ptr(sp->per_cpu_ref)->seq[idx]) += 1;
- preempt_enable();
- return idx;
-}
-EXPORT_SYMBOL_GPL(__srcu_read_lock);
-
-/*
- * 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().
- * Must be called from process context.
- */
-void __srcu_read_unlock(struct srcu_struct *sp, int idx)
-{
- smp_mb(); /* C */ /* Avoid leaking the critical section. */
- this_cpu_dec(sp->per_cpu_ref->c[idx]);
-}
-EXPORT_SYMBOL_GPL(__srcu_read_unlock);
-
-/*
- * 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 10 microseconds,
- * we repeatedly block for 1-millisecond time periods. This approach
- * has done well in testing, so there is no need for a config parameter.
- */
-#define SRCU_RETRY_CHECK_DELAY 5
-#define SYNCHRONIZE_SRCU_TRYCOUNT 2
-#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT 12
-
-/*
- * @@@ Wait until all pre-existing readers complete. Such readers
- * will have used the index specified by "idx".
- * the caller should ensures the ->completed is not changed while checking
- * and idx = (->completed & 1) ^ 1
- */
-static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
-{
- for (;;) {
- if (srcu_readers_active_idx_check(sp, idx))
- return true;
- if (--trycount <= 0)
- return false;
- udelay(SRCU_RETRY_CHECK_DELAY);
- }
-}
-
-/*
- * Increment the ->completed counter so that future SRCU readers will
- * use the other rank of the ->c[] and ->seq[] arrays. This allows
- * us to wait for pre-existing readers in a starvation-free manner.
- */
-static void srcu_flip(struct srcu_struct *sp)
-{
- sp->completed++;
-}
-
-/*
- * Enqueue an SRCU callback on the specified srcu_struct structure,
- * initiating grace-period processing if it is not already running.
- */
-void call_srcu(struct srcu_struct *sp, struct rcu_head *head,
- void (*func)(struct rcu_head *head))
-{
- unsigned long flags;
-
- head->next = NULL;
- head->func = func;
- spin_lock_irqsave(&sp->queue_lock, flags);
- rcu_batch_queue(&sp->batch_queue, head);
- if (!sp->running) {
- sp->running = true;
- schedule_delayed_work(&sp->work, 0);
- }
- spin_unlock_irqrestore(&sp->queue_lock, flags);
-}
-EXPORT_SYMBOL_GPL(call_srcu);
-
-struct rcu_synchronize {
- struct rcu_head head;
- struct completion completion;
-};
-
-/*
- * Awaken the corresponding synchronize_srcu() instance now that a
- * grace period has elapsed.
- */
-static void wakeme_after_rcu(struct rcu_head *head)
-{
- struct rcu_synchronize *rcu;
-
- rcu = container_of(head, struct rcu_synchronize, head);
- complete(&rcu->completion);
-}
-
-static void srcu_advance_batches(struct srcu_struct *sp, int trycount);
-static void srcu_reschedule(struct srcu_struct *sp);
-
-/*
- * Helper function for synchronize_srcu() and synchronize_srcu_expedited().
- */
-static void __synchronize_srcu(struct srcu_struct *sp, int trycount)
-{
- struct rcu_synchronize rcu;
- struct rcu_head *head = &rcu.head;
- bool done = false;
-
- rcu_lockdep_assert(!lock_is_held(&sp->dep_map) &&
- !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 RCU) read-side critical section");
-
- might_sleep();
- init_completion(&rcu.completion);
-
- head->next = NULL;
- head->func = wakeme_after_rcu;
- spin_lock_irq(&sp->queue_lock);
- if (!sp->running) {
- /* steal the processing owner */
- sp->running = true;
- rcu_batch_queue(&sp->batch_check0, head);
- spin_unlock_irq(&sp->queue_lock);
-
- srcu_advance_batches(sp, trycount);
- if (!rcu_batch_empty(&sp->batch_done)) {
- BUG_ON(sp->batch_done.head != head);
- rcu_batch_dequeue(&sp->batch_done);
- done = true;
- }
- /* give the processing owner to work_struct */
- srcu_reschedule(sp);
- } else {
- rcu_batch_queue(&sp->batch_queue, head);
- spin_unlock_irq(&sp->queue_lock);
- }
-
- if (!done)
- wait_for_completion(&rcu.completion);
-}
-
-/**
- * synchronize_srcu - wait for prior SRCU read-side critical-section completion
- * @sp: srcu_struct with which to synchronize.
- *
- * 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.
- *
- * Can block; must be called from process context.
- *
- * Note that it is illegal to call synchronize_srcu() from the corresponding
- * SRCU read-side critical section; doing so will result in deadlock.
- * However, it is perfectly legal to call synchronize_srcu() on one
- * srcu_struct from some other srcu_struct's read-side critical section.
- */
-void synchronize_srcu(struct srcu_struct *sp)
-{
- __synchronize_srcu(sp, rcu_expedited
- ? SYNCHRONIZE_SRCU_EXP_TRYCOUNT
- : SYNCHRONIZE_SRCU_TRYCOUNT);
-}
-EXPORT_SYMBOL_GPL(synchronize_srcu);
-
-/**
- * synchronize_srcu_expedited - Brute-force SRCU grace period
- * @sp: srcu_struct with which to synchronize.
- *
- * Wait for an SRCU grace period to elapse, but be more aggressive about
- * spinning rather than blocking when waiting.
- *
- * Note that it is also illegal to call synchronize_srcu_expedited()
- * from the corresponding SRCU read-side critical section;
- * doing so will result in deadlock. However, it is perfectly legal
- * to call synchronize_srcu_expedited() on one srcu_struct from some
- * other srcu_struct's read-side critical section, as long as
- * the resulting graph of srcu_structs is acyclic.
- */
-void synchronize_srcu_expedited(struct srcu_struct *sp)
-{
- __synchronize_srcu(sp, SYNCHRONIZE_SRCU_EXP_TRYCOUNT);
-}
-EXPORT_SYMBOL_GPL(synchronize_srcu_expedited);
-
-/**
- * srcu_barrier - Wait until all in-flight call_srcu() callbacks complete.
- */
-void srcu_barrier(struct srcu_struct *sp)
-{
- synchronize_srcu(sp);
-}
-EXPORT_SYMBOL_GPL(srcu_barrier);
-
-/**
- * srcu_batches_completed - return batches completed.
- * @sp: srcu_struct on which to report batch completion.
- *
- * Report the number of batches, correlated with, but not necessarily
- * precisely the same as, the number of grace periods that have elapsed.
- */
-long srcu_batches_completed(struct srcu_struct *sp)
-{
- return sp->completed;
-}
-EXPORT_SYMBOL_GPL(srcu_batches_completed);
-
-#define SRCU_CALLBACK_BATCH 10
-#define SRCU_INTERVAL 1
-
-/*
- * Move any new SRCU callbacks to the first stage of the SRCU grace
- * period pipeline.
- */
-static void srcu_collect_new(struct srcu_struct *sp)
-{
- if (!rcu_batch_empty(&sp->batch_queue)) {
- spin_lock_irq(&sp->queue_lock);
- rcu_batch_move(&sp->batch_check0, &sp->batch_queue);
- spin_unlock_irq(&sp->queue_lock);
- }
-}
-
-/*
- * Core SRCU state machine. Advance callbacks from ->batch_check0 to
- * ->batch_check1 and then to ->batch_done as readers drain.
- */
-static void srcu_advance_batches(struct srcu_struct *sp, int trycount)
-{
- int idx = 1 ^ (sp->completed & 1);
-
- /*
- * Because readers might be delayed for an extended period after
- * fetching ->completed 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.
- */
-
- if (rcu_batch_empty(&sp->batch_check0) &&
- rcu_batch_empty(&sp->batch_check1))
- return; /* no callbacks need to be advanced */
-
- if (!try_check_zero(sp, idx, trycount))
- return; /* failed to advance, will try after SRCU_INTERVAL */
-
- /*
- * The callbacks in ->batch_check1 have already done with their
- * first zero check and flip back when they were enqueued on
- * ->batch_check0 in a previous invocation of srcu_advance_batches().
- * (Presumably try_check_zero() returned false during that
- * invocation, leaving the callbacks stranded on ->batch_check1.)
- * They are therefore ready to invoke, so move them to ->batch_done.
- */
- rcu_batch_move(&sp->batch_done, &sp->batch_check1);
-
- if (rcu_batch_empty(&sp->batch_check0))
- return; /* no callbacks need to be advanced */
- srcu_flip(sp);
-
- /*
- * The callbacks in ->batch_check0 just finished their
- * first check zero and flip, so move them to ->batch_check1
- * for future checking on the other idx.
- */
- rcu_batch_move(&sp->batch_check1, &sp->batch_check0);
-
- /*
- * SRCU read-side critical sections are normally short, so check
- * at least twice in quick succession after a flip.
- */
- trycount = trycount < 2 ? 2 : trycount;
- if (!try_check_zero(sp, idx^1, trycount))
- return; /* failed to advance, will try after SRCU_INTERVAL */
-
- /*
- * The callbacks in ->batch_check1 have now waited for all
- * pre-existing readers using both idx values. They are therefore
- * ready to invoke, so move them to ->batch_done.
- */
- rcu_batch_move(&sp->batch_done, &sp->batch_check1);
-}
-
-/*
- * Invoke a limited number of SRCU callbacks that have passed through
- * their grace period. If there are more to do, SRCU will reschedule
- * the workqueue.
- */
-static void srcu_invoke_callbacks(struct srcu_struct *sp)
-{
- int i;
- struct rcu_head *head;
-
- for (i = 0; i < SRCU_CALLBACK_BATCH; i++) {
- head = rcu_batch_dequeue(&sp->batch_done);
- if (!head)
- break;
- local_bh_disable();
- head->func(head);
- local_bh_enable();
- }
-}
-
-/*
- * Finished one round of SRCU grace period. Start another if there are
- * more SRCU callbacks queued, otherwise put SRCU into not-running state.
- */
-static void srcu_reschedule(struct srcu_struct *sp)
-{
- bool pending = true;
-
- if (rcu_batch_empty(&sp->batch_done) &&
- rcu_batch_empty(&sp->batch_check1) &&
- rcu_batch_empty(&sp->batch_check0) &&
- rcu_batch_empty(&sp->batch_queue)) {
- spin_lock_irq(&sp->queue_lock);
- if (rcu_batch_empty(&sp->batch_done) &&
- rcu_batch_empty(&sp->batch_check1) &&
- rcu_batch_empty(&sp->batch_check0) &&
- rcu_batch_empty(&sp->batch_queue)) {
- sp->running = false;
- pending = false;
- }
- spin_unlock_irq(&sp->queue_lock);
- }
-
- if (pending)
- schedule_delayed_work(&sp->work, SRCU_INTERVAL);
-}
-
-/*
- * This is the work-queue function that handles SRCU grace periods.
- */
-void process_srcu(struct work_struct *work)
-{
- struct srcu_struct *sp;
-
- sp = container_of(work, struct srcu_struct, work.work);
-
- srcu_collect_new(sp);
- srcu_advance_batches(sp, 1);
- srcu_invoke_callbacks(sp);
- srcu_reschedule(sp);
-}
-EXPORT_SYMBOL_GPL(process_srcu);
projects / firefly-linux-kernel-4.4.55.git / blobdiff