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@ -1,668 +0,0 @@
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/*
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* Sleepable Read-Copy Update mechanism for mutual exclusion.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, you can access it online at
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* http://www.gnu.org/licenses/gpl-2.0.html.
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*
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* Copyright (C) IBM Corporation, 2006
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* Copyright (C) Fujitsu, 2012
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*
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* Author: Paul McKenney <paulmck@us.ibm.com>
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* Lai Jiangshan <laijs@cn.fujitsu.com>
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* Documentation/RCU/ *.txt
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*
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*/
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#include <linux/export.h>
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#include <linux/mutex.h>
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#include <linux/percpu.h>
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#include <linux/preempt.h>
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#include <linux/rcupdate_wait.h>
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#include <linux/sched.h>
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#include <linux/smp.h>
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#include <linux/delay.h>
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#include <linux/srcu.h>
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#include "rcu.h"
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/*
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* Initialize an rcu_batch structure to empty.
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*/
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static inline void rcu_batch_init(struct rcu_batch *b)
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{
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b->head = NULL;
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b->tail = &b->head;
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}
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/*
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* Enqueue a callback onto the tail of the specified rcu_batch structure.
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*/
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static inline void rcu_batch_queue(struct rcu_batch *b, struct rcu_head *head)
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{
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*b->tail = head;
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b->tail = &head->next;
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}
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/*
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* Is the specified rcu_batch structure empty?
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*/
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static inline bool rcu_batch_empty(struct rcu_batch *b)
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{
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return b->tail == &b->head;
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}
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/*
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* Remove the callback at the head of the specified rcu_batch structure
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* and return a pointer to it, or return NULL if the structure is empty.
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*/
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static inline struct rcu_head *rcu_batch_dequeue(struct rcu_batch *b)
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{
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struct rcu_head *head;
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if (rcu_batch_empty(b))
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return NULL;
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head = b->head;
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b->head = head->next;
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if (b->tail == &head->next)
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rcu_batch_init(b);
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return head;
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}
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/*
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* Move all callbacks from the rcu_batch structure specified by "from" to
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* the structure specified by "to".
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*/
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static inline void rcu_batch_move(struct rcu_batch *to, struct rcu_batch *from)
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{
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if (!rcu_batch_empty(from)) {
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*to->tail = from->head;
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to->tail = from->tail;
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rcu_batch_init(from);
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}
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}
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static int init_srcu_struct_fields(struct srcu_struct *sp)
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{
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sp->completed = 0;
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spin_lock_init(&sp->queue_lock);
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sp->running = false;
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rcu_batch_init(&sp->batch_queue);
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rcu_batch_init(&sp->batch_check0);
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rcu_batch_init(&sp->batch_check1);
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rcu_batch_init(&sp->batch_done);
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INIT_DELAYED_WORK(&sp->work, process_srcu);
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sp->per_cpu_ref = alloc_percpu(struct srcu_array);
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return sp->per_cpu_ref ? 0 : -ENOMEM;
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}
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#ifdef CONFIG_DEBUG_LOCK_ALLOC
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int __init_srcu_struct(struct srcu_struct *sp, const char *name,
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struct lock_class_key *key)
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{
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/* Don't re-initialize a lock while it is held. */
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debug_check_no_locks_freed((void *)sp, sizeof(*sp));
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lockdep_init_map(&sp->dep_map, name, key, 0);
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return init_srcu_struct_fields(sp);
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}
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EXPORT_SYMBOL_GPL(__init_srcu_struct);
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#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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/**
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* init_srcu_struct - initialize a sleep-RCU structure
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* @sp: structure to initialize.
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*
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* Must invoke this on a given srcu_struct before passing that srcu_struct
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* to any other function. Each srcu_struct represents a separate domain
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* of SRCU protection.
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*/
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int init_srcu_struct(struct srcu_struct *sp)
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{
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return init_srcu_struct_fields(sp);
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}
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EXPORT_SYMBOL_GPL(init_srcu_struct);
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#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
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/*
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* Returns approximate total of the readers' ->lock_count[] values for the
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* rank of per-CPU counters specified by idx.
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*/
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static unsigned long srcu_readers_lock_idx(struct srcu_struct *sp, int idx)
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{
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int cpu;
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unsigned long sum = 0;
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for_each_possible_cpu(cpu) {
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struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
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sum += READ_ONCE(cpuc->lock_count[idx]);
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}
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return sum;
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}
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/*
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* Returns approximate total of the readers' ->unlock_count[] values for the
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* rank of per-CPU counters specified by idx.
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*/
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static unsigned long srcu_readers_unlock_idx(struct srcu_struct *sp, int idx)
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{
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int cpu;
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unsigned long sum = 0;
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for_each_possible_cpu(cpu) {
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struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
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sum += READ_ONCE(cpuc->unlock_count[idx]);
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}
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return sum;
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}
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/*
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* Return true if the number of pre-existing readers is determined to
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* be zero.
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*/
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static bool srcu_readers_active_idx_check(struct srcu_struct *sp, int idx)
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{
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unsigned long unlocks;
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unlocks = srcu_readers_unlock_idx(sp, idx);
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/*
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* Make sure that a lock is always counted if the corresponding unlock
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* is counted. Needs to be a smp_mb() as the read side may contain a
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* read from a variable that is written to before the synchronize_srcu()
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* in the write side. In this case smp_mb()s A and B act like the store
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* buffering pattern.
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*
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* This smp_mb() also pairs with smp_mb() C to prevent accesses after the
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* synchronize_srcu() from being executed before the grace period ends.
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*/
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smp_mb(); /* A */
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/*
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* If the locks are the same as the unlocks, then there must have
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* been no readers on this index at some time in between. This does not
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* mean that there are no more readers, as one could have read the
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* current index but not have incremented the lock counter yet.
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*
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* Possible bug: There is no guarantee that there haven't been ULONG_MAX
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* increments of ->lock_count[] since the unlocks were counted, meaning
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* that this could return true even if there are still active readers.
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* Since there are no memory barriers around srcu_flip(), the CPU is not
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* required to increment ->completed before running
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* srcu_readers_unlock_idx(), which means that there could be an
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* arbitrarily large number of critical sections that execute after
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* srcu_readers_unlock_idx() but use the old value of ->completed.
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*/
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return srcu_readers_lock_idx(sp, idx) == unlocks;
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}
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/**
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* srcu_readers_active - returns true if there are readers. and false
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* otherwise
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* @sp: which srcu_struct to count active readers (holding srcu_read_lock).
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*
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* Note that this is not an atomic primitive, and can therefore suffer
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* severe errors when invoked on an active srcu_struct. That said, it
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* can be useful as an error check at cleanup time.
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*/
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static bool srcu_readers_active(struct srcu_struct *sp)
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{
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int cpu;
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unsigned long sum = 0;
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for_each_possible_cpu(cpu) {
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struct srcu_array *cpuc = per_cpu_ptr(sp->per_cpu_ref, cpu);
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sum += READ_ONCE(cpuc->lock_count[0]);
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sum += READ_ONCE(cpuc->lock_count[1]);
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sum -= READ_ONCE(cpuc->unlock_count[0]);
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sum -= READ_ONCE(cpuc->unlock_count[1]);
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}
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return sum;
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}
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/**
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* cleanup_srcu_struct - deconstruct a sleep-RCU structure
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* @sp: structure to clean up.
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*
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* Must invoke this only after you are finished using a given srcu_struct
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* that was initialized via init_srcu_struct(). This code does some
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* probabalistic checking, spotting late uses of srcu_read_lock(),
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* synchronize_srcu(), synchronize_srcu_expedited(), and call_srcu().
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* If any such late uses are detected, the per-CPU memory associated with
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* the srcu_struct is simply leaked and WARN_ON() is invoked. If the
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* caller frees the srcu_struct itself, a use-after-free crash will likely
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* ensue, but at least there will be a warning printed.
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*/
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void cleanup_srcu_struct(struct srcu_struct *sp)
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{
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if (WARN_ON(srcu_readers_active(sp)))
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return; /* Leakage unless caller handles error. */
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free_percpu(sp->per_cpu_ref);
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sp->per_cpu_ref = NULL;
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}
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EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
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/*
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* Counts the new reader in the appropriate per-CPU element of the
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* srcu_struct.
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* Returns an index that must be passed to the matching srcu_read_unlock().
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*/
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int __srcu_read_lock(struct srcu_struct *sp)
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{
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int idx;
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idx = READ_ONCE(sp->completed) & 0x1;
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this_cpu_inc(sp->per_cpu_ref->lock_count[idx]);
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smp_mb(); /* B */ /* Avoid leaking the critical section. */
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return idx;
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}
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EXPORT_SYMBOL_GPL(__srcu_read_lock);
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/*
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* Removes the count for the old reader from the appropriate per-CPU
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* element of the srcu_struct. Note that this may well be a different
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* CPU than that which was incremented by the corresponding srcu_read_lock().
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*/
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void __srcu_read_unlock(struct srcu_struct *sp, int idx)
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{
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smp_mb(); /* C */ /* Avoid leaking the critical section. */
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this_cpu_inc(sp->per_cpu_ref->unlock_count[idx]);
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}
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EXPORT_SYMBOL_GPL(__srcu_read_unlock);
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/*
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* We use an adaptive strategy for synchronize_srcu() and especially for
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* synchronize_srcu_expedited(). We spin for a fixed time period
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* (defined below) to allow SRCU readers to exit their read-side critical
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* sections. If there are still some readers after 10 microseconds,
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* we repeatedly block for 1-millisecond time periods. This approach
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* has done well in testing, so there is no need for a config parameter.
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*/
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#define SRCU_RETRY_CHECK_DELAY 5
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#define SYNCHRONIZE_SRCU_TRYCOUNT 2
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#define SYNCHRONIZE_SRCU_EXP_TRYCOUNT 12
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/*
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* @@@ Wait until all pre-existing readers complete. Such readers
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* will have used the index specified by "idx".
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* the caller should ensures the ->completed is not changed while checking
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* and idx = (->completed & 1) ^ 1
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*/
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static bool try_check_zero(struct srcu_struct *sp, int idx, int trycount)
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{
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for (;;) {
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if (srcu_readers_active_idx_check(sp, idx))
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return true;
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if (--trycount <= 0)
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return false;
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udelay(SRCU_RETRY_CHECK_DELAY);
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}
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}
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/*
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* Increment the ->completed counter so that future SRCU readers will
|
|
|
|
|
* use the other rank of the ->(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);
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* Ensure that if the updater misses an __srcu_read_unlock()
|
|
|
|
|
* increment, that task's next __srcu_read_lock() will see the
|
|
|
|
|
* above counter update. Note that both this memory barrier
|
|
|
|
|
* and the one in srcu_readers_active_idx_check() provide the
|
|
|
|
|
* guarantee for __srcu_read_lock().
|
|
|
|
|
*/
|
|
|
|
|
smp_mb(); /* D */ /* Pairs with C. */
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/*
|
|
|
|
|
* Enqueue an SRCU callback on 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
|
|
|
|
|
* more than one CPU, this means that when "func()" is invoked, each CPU
|
|
|
|
|
* is guaranteed to have executed a full memory barrier since the end of
|
|
|
|
|
* its last corresponding SRCU read-side critical section whose beginning
|
|
|
|
|
* preceded the call to call_rcu(). It also means that each CPU executing
|
|
|
|
|
* an SRCU read-side critical section that continues beyond the start of
|
|
|
|
|
* "func()" must have executed a memory barrier after the call_rcu()
|
|
|
|
|
* but before the beginning of that SRCU read-side critical section.
|
|
|
|
|
* Note that these guarantees include CPUs that are offline, idle, or
|
|
|
|
|
* executing in user mode, as well as CPUs that are executing in the kernel.
|
|
|
|
|
*
|
|
|
|
|
* Furthermore, if CPU A invoked call_rcu() and CPU B invoked the
|
|
|
|
|
* resulting SRCU callback function "func()", then both CPU A and CPU
|
|
|
|
|
* B are guaranteed to execute a full memory barrier during the time
|
|
|
|
|
* interval between the call to call_rcu() and the invocation of "func()".
|
|
|
|
|
* This guarantee applies even if CPU A and CPU B are the same CPU (but
|
|
|
|
|
* again only if the system has more than one CPU).
|
|
|
|
|
*
|
|
|
|
|
* Of course, these guarantees apply only for invocations of call_srcu(),
|
|
|
|
|
* 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,
|
|
|
|
|
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_batch_queue(&sp->batch_queue, head);
|
|
|
|
|
if (!sp->running) {
|
|
|
|
|
sp->running = true;
|
|
|
|
|
queue_delayed_work(system_power_efficient_wq, &sp->work, 0);
|
|
|
|
|
}
|
|
|
|
|
spin_unlock_irqrestore(&sp->queue_lock, flags);
|
|
|
|
|
}
|
|
|
|
|
EXPORT_SYMBOL_GPL(call_srcu);
|
|
|
|
|
|
|
|
|
|
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_WARN(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 in 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);
|
|
|
|
|
smp_mb__after_unlock_lock(); /* Caller's prior accesses before GP. */
|
|
|
|
|
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);
|
|
|
|
|
smp_mb(); /* Caller's later accesses after GP. */
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
}
|
|
|
|
|
|
|
|
|
|
/**
|
|
|
|
|
* 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,
|
|
|
|
|
* as long as the resulting graph of srcu_structs is acyclic.
|
|
|
|
|
*
|
|
|
|
|
* There are memory-ordering constraints implied by synchronize_srcu().
|
|
|
|
|
* On systems with more than one CPU, when synchronize_srcu() returns,
|
|
|
|
|
* each CPU is guaranteed to have executed a full memory barrier since
|
|
|
|
|
* the end of its last corresponding SRCU-sched read-side critical section
|
|
|
|
|
* whose beginning preceded the call to synchronize_srcu(). In addition,
|
|
|
|
|
* each CPU having an SRCU read-side critical section that extends beyond
|
|
|
|
|
* the return from synchronize_srcu() is guaranteed to have executed a
|
|
|
|
|
* full memory barrier after the beginning of synchronize_srcu() and before
|
|
|
|
|
* the beginning of that SRCU read-side critical section. Note that these
|
|
|
|
|
* guarantees include CPUs that are offline, idle, or executing in user mode,
|
|
|
|
|
* as well as CPUs that are executing in the kernel.
|
|
|
|
|
*
|
|
|
|
|
* Furthermore, if CPU A invoked synchronize_srcu(), which returned
|
|
|
|
|
* to its caller on CPU B, then both CPU A and CPU B are guaranteed
|
|
|
|
|
* to have executed a full memory barrier during the execution of
|
|
|
|
|
* synchronize_srcu(). This guarantee applies even if CPU A and CPU B
|
|
|
|
|
* are the same CPU, but again only if the system has more than one CPU.
|
|
|
|
|
*
|
|
|
|
|
* Of course, these memory-ordering guarantees apply only when
|
|
|
|
|
* synchronize_srcu(), srcu_read_lock(), and srcu_read_unlock() are
|
|
|
|
|
* passed the same srcu_struct structure.
|
|
|
|
|
*/
|
|
|
|
|
void synchronize_srcu(struct srcu_struct *sp)
|
|
|
|
|
{
|
|
|
|
|
__synchronize_srcu(sp, (rcu_gp_is_expedited() && !rcu_gp_is_normal())
|
|
|
|
|
? 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 synchronize_srcu_expedited() has the same deadlock and
|
|
|
|
|
* memory-ordering properties as does synchronize_srcu().
|
|
|
|
|
*/
|
|
|
|
|
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.
|
|
|
|
|
* @sp: srcu_struct on which to wait for in-flight callbacks.
|
|
|
|
|
*/
|
|
|
|
|
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.
|
|
|
|
|
*/
|
|
|
|
|
unsigned 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. 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)
|
|
|
|
|
{
|
|
|
|
|
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) &&
|
|
|
|
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rcu_batch_empty(&sp->batch_queue)) {
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|
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spin_lock_irq(&sp->queue_lock);
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|
|
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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)) {
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|
|
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sp->running = false;
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|
|
|
|
pending = false;
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|
|
|
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}
|
|
|
|
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spin_unlock_irq(&sp->queue_lock);
|
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|
|
|
}
|
|
|
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|
|
|
|
if (pending)
|
|
|
|
|
queue_delayed_work(system_power_efficient_wq,
|
|
|
|
|
&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);
|
|
|
|
|
|
|
|
|
|
static int __init srcu_bootup_announce(void)
|
|
|
|
|
{
|
|
|
|
|
pr_info("Classic SRCU implementation.\n");
|
|
|
|
|
return 0;
|
|
|
|
|
}
|
|
|
|
|
early_initcall(srcu_bootup_announce);
|
Paul E. McKenney