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/percpu.h>
  43#include <linux/notifier.h>
  44#include <linux/cpu.h>
  45#include <linux/mutex.h>
  46#include <linux/module.h>
  47#include <linux/kernel_stat.h>
  48
  49#ifdef CONFIG_DEBUG_LOCK_ALLOC
  50static struct lock_class_key rcu_lock_key;
  51struct lockdep_map rcu_lock_map =
  52        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
  53EXPORT_SYMBOL_GPL(rcu_lock_map);
  54#endif
  55
  56int rcu_scheduler_active __read_mostly;
  57
  58/*
  59 * Awaken the corresponding synchronize_rcu() instance now that a
  60 * grace period has elapsed.
  61 */
  62void wakeme_after_rcu(struct rcu_head  *head)
  63{
  64        struct rcu_synchronize *rcu;
  65
  66        rcu = container_of(head, struct rcu_synchronize, head);
  67        complete(&rcu->completion);
  68}
  69
  70#ifdef CONFIG_TREE_PREEMPT_RCU
  71
  72/**
  73 * synchronize_rcu - wait until a grace period has elapsed.
  74 *
  75 * Control will return to the caller some time after a full grace
  76 * period has elapsed, in other words after all currently executing RCU
  77 * read-side critical sections have completed.  RCU read-side critical
  78 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
  79 * and may be nested.
  80 */
  81void synchronize_rcu(void)
  82{
  83        struct rcu_synchronize rcu;
  84
  85        if (!rcu_scheduler_active)
  86                return;
  87
  88        init_completion(&rcu.completion);
  89        /* Will wake me after RCU finished. */
  90        call_rcu(&rcu.head, wakeme_after_rcu);
  91        /* Wait for it. */
  92        wait_for_completion(&rcu.completion);
  93}
  94EXPORT_SYMBOL_GPL(synchronize_rcu);
  95
  96#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
  97
  98/**
  99 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
 100 *
 101 * Control will return to the caller some time after a full rcu-sched
 102 * grace period has elapsed, in other words after all currently executing
 103 * rcu-sched read-side critical sections have completed.   These read-side
 104 * critical sections are delimited by rcu_read_lock_sched() and
 105 * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
 106 * local_irq_disable(), and so on may be used in place of
 107 * rcu_read_lock_sched().
 108 *
 109 * This means that all preempt_disable code sequences, including NMI and
 110 * hardware-interrupt handlers, in progress on entry will have completed
 111 * before this primitive returns.  However, this does not guarantee that
 112 * softirq handlers will have completed, since in some kernels, these
 113 * handlers can run in process context, and can block.
 114 *
 115 * This primitive provides the guarantees made by the (now removed)
 116 * synchronize_kernel() API.  In contrast, synchronize_rcu() only
 117 * guarantees that rcu_read_lock() sections will have completed.
 118 * In "classic RCU", these two guarantees happen to be one and
 119 * the same, but can differ in realtime RCU implementations.
 120 */
 121void synchronize_sched(void)
 122{
 123        struct rcu_synchronize rcu;
 124
 125        if (rcu_blocking_is_gp())
 126                return;
 127
 128        init_completion(&rcu.completion);
 129        /* Will wake me after RCU finished. */
 130        call_rcu_sched(&rcu.head, wakeme_after_rcu);
 131        /* Wait for it. */
 132        wait_for_completion(&rcu.completion);
 133}
 134EXPORT_SYMBOL_GPL(synchronize_sched);
 135
 136/**
 137 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
 138 *
 139 * Control will return to the caller some time after a full rcu_bh grace
 140 * period has elapsed, in other words after all currently executing rcu_bh
 141 * read-side critical sections have completed.  RCU read-side critical
 142 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
 143 * and may be nested.
 144 */
 145void synchronize_rcu_bh(void)
 146{
 147        struct rcu_synchronize rcu;
 148
 149        if (rcu_blocking_is_gp())
 150                return;
 151
 152        init_completion(&rcu.completion);
 153        /* Will wake me after RCU finished. */
 154        call_rcu_bh(&rcu.head, wakeme_after_rcu);
 155        /* Wait for it. */
 156        wait_for_completion(&rcu.completion);
 157}
 158EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
 159
 160static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
 161                unsigned long action, void *hcpu)
 162{
 163        return rcu_cpu_notify(self, action, hcpu);
 164}
 165
 166void __init rcu_init(void)
 167{
 168        int i;
 169
 170        __rcu_init();
 171        cpu_notifier(rcu_barrier_cpu_hotplug, 0);
 172
 173        /*
 174         * We don't need protection against CPU-hotplug here because
 175         * this is called early in boot, before either interrupts
 176         * or the scheduler are operational.
 177         */
 178        for_each_online_cpu(i)
 179                rcu_barrier_cpu_hotplug(NULL, CPU_UP_PREPARE, (void *)(long)i);
 180}
 181
 182void rcu_scheduler_starting(void)
 183{
 184        WARN_ON(num_online_cpus() != 1);
 185        WARN_ON(nr_context_switches() > 0);
 186        rcu_scheduler_active = 1;
 187}
 188