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
  49 struct rcu_synchronize {
  50         struct rcu_head head;
  51         struct completion completion;
  52 };
  53
  54 static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
  55 static atomic_t rcu_barrier_cpu_count;
  56 static DEFINE_MUTEX(rcu_barrier_mutex);
  57 static struct completion rcu_barrier_completion;
  58
  59 /*
  60  * Awaken the corresponding synchronize_rcu() instance now that a
  61  * grace period has elapsed.
  62  */
  63 static 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  */
  80 void 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 }
  91 EXPORT_SYMBOL_GPL(synchronize_rcu);
  92
  93 static 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  */
 102 static 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  */
 114 void 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 }
 135 EXPORT_SYMBOL_GPL(rcu_barrier);
 136
 137 void __init rcu_init(void)
 138 {
 139         __rcu_init();
 140 }
 141