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
  50 static struct lock_class_key rcu_lock_key;
  51 struct lockdep_map rcu_lock_map =
  52         STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
  53 EXPORT_SYMBOL_GPL(rcu_lock_map);
  54 #endif
  55
  56 int rcu_scheduler_active __read_mostly;
  57
  58 /*
  59  * Awaken the corresponding synchronize_rcu() instance now that a
  60  * grace period has elapsed.
  61  */
  62 void 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  */
  81 void 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 }
  94 EXPORT_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  */
 121 void 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 }
 134 EXPORT_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  */
 145 void 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 }
 158 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
 159
 160 static 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
 166 void __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
 182 void 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 }