LXR linux/kernel/rcupdate.c

   1/*
   2 * Read-Copy Update mechanism for mutual exclusion
   3 *
   4 * This program is free software; you can redistribute it and/or modify
   5 * it under the terms of the GNU General Public License as published by
   6 * the Free Software Foundation; either version 2 of the License, or
   7 * (at your option) any later version.
   8 *
   9 * This program is distributed in the hope that it will be useful,
  10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 * GNU General Public License for more details.
  13 *
  14 * You should have received a copy of the GNU General Public License
  15 * along with this program; if not, write to the Free Software
  16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
  17 *
  18 * Copyright IBM Corporation, 2001
  19 *
  20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
  21 *          Manfred Spraul <manfred@colorfullife.com>
  22 * 
  23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
  24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
  25 * Papers:
  26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
  27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
  28 *
  29 * For detailed explanation of Read-Copy Update mechanism see -
  30 *              http://lse.sourceforge.net/locking/rcupdate.html
  31 *
  32 */
  33#include <linux/types.h>
  34#include <linux/kernel.h>
  35#include <linux/init.h>
  36#include <linux/spinlock.h>
  37#include <linux/smp.h>
  38#include <linux/interrupt.h>
  39#include <linux/sched.h>
  40#include <asm/atomic.h>
  41#include <linux/bitops.h>
  42#include <linux/completion.h>
  43#include <linux/percpu.h>
  44#include <linux/notifier.h>
  45#include <linux/cpu.h>
  46#include <linux/mutex.h>
  47#include <linux/module.h>
  48
  49struct rcu_synchronize {
  50        struct rcu_head head;
  51        struct completion completion;
  52};
  53
  54static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
  55static atomic_t rcu_barrier_cpu_count;
  56static DEFINE_MUTEX(rcu_barrier_mutex);
  57static struct completion rcu_barrier_completion;
  58
  59/*
  60 * Awaken the corresponding synchronize_rcu() instance now that a
  61 * grace period has elapsed.
  62 */
  63static void wakeme_after_rcu(struct rcu_head  *head)
  64{
  65        struct rcu_synchronize *rcu;
  66
  67        rcu = container_of(head, struct rcu_synchronize, head);
  68        complete(&rcu->completion);
  69}
  70
  71/**
  72 * synchronize_rcu - wait until a grace period has elapsed.
  73 *
  74 * Control will return to the caller some time after a full grace
  75 * period has elapsed, in other words after all currently executing RCU
  76 * read-side critical sections have completed.  RCU read-side critical
  77 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
  78 * and may be nested.
  79 */
  80void synchronize_rcu(void)
  81{
  82        struct rcu_synchronize rcu;
  83
  84        init_completion(&rcu.completion);
  85        /* Will wake me after RCU finished */
  86        call_rcu(&rcu.head, wakeme_after_rcu);
  87
  88        /* Wait for it */
  89        wait_for_completion(&rcu.completion);
  90}
  91EXPORT_SYMBOL_GPL(synchronize_rcu);
  92
  93static void rcu_barrier_callback(struct rcu_head *notused)
  94{
  95        if (atomic_dec_and_test(&rcu_barrier_cpu_count))
  96                complete(&rcu_barrier_completion);
  97}
  98
  99/*
 100 * Called with preemption disabled, and from cross-cpu IRQ context.
 101 */
 102static void rcu_barrier_func(void *notused)
 103{
 104        int cpu = smp_processor_id();
 105        struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
 106
 107        atomic_inc(&rcu_barrier_cpu_count);
 108        call_rcu(head, rcu_barrier_callback);
 109}
 110
 111/**
 112 * rcu_barrier - Wait until all the in-flight RCUs are complete.
 113 */
 114void rcu_barrier(void)
 115{
 116        BUG_ON(in_interrupt());
 117        /* Take cpucontrol mutex to protect against CPU hotplug */
 118        mutex_lock(&rcu_barrier_mutex);
 119        init_completion(&rcu_barrier_completion);
 120        atomic_set(&rcu_barrier_cpu_count, 0);
 121        /*
 122         * The queueing of callbacks in all CPUs must be atomic with
 123         * respect to RCU, otherwise one CPU may queue a callback,
 124         * wait for a grace period, decrement barrier count and call
 125         * complete(), while other CPUs have not yet queued anything.
 126         * So, we need to make sure that grace periods cannot complete
 127         * until all the callbacks are queued.
 128         */
 129        rcu_read_lock();
 130        on_each_cpu(rcu_barrier_func, NULL, 0, 1);
 131        rcu_read_unlock();
 132        wait_for_completion(&rcu_barrier_completion);
 133        mutex_unlock(&rcu_barrier_mutex);
 134}
 135EXPORT_SYMBOL_GPL(rcu_barrier);
 136
 137void __init rcu_init(void)
 138{
 139        __rcu_init();
 140}
 141
 142