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 /* Because of FASTCALL declaration of complete, we use this wrapper */
  60 static void wakeme_after_rcu(struct rcu_head  *head)
  61 {
  62         struct rcu_synchronize *rcu;
  63
  64         rcu = container_of(head, struct rcu_synchronize, head);
  65         complete(&rcu->completion);
  66 }
  67
  68 /**
  69  * synchronize_rcu - wait until a grace period has elapsed.
  70  *
  71  * Control will return to the caller some time after a full grace
  72  * period has elapsed, in other words after all currently executing RCU
  73  * read-side critical sections have completed.  RCU read-side critical
  74  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
  75  * and may be nested.
  76  */
  77 void synchronize_rcu(void)
  78 {
  79         struct rcu_synchronize rcu;
  80
  81         init_completion(&rcu.completion);
  82         /* Will wake me after RCU finished */
  83         call_rcu(&rcu.head, wakeme_after_rcu);
  84
  85         /* Wait for it */
  86         wait_for_completion(&rcu.completion);
  87 }
  88 EXPORT_SYMBOL_GPL(synchronize_rcu);
  89
  90 static void rcu_barrier_callback(struct rcu_head *notused)
  91 {
  92         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
  93                 complete(&rcu_barrier_completion);
  94 }
  95
  96 /*
  97  * Called with preemption disabled, and from cross-cpu IRQ context.
  98  */
  99 static void rcu_barrier_func(void *notused)
 100 {
 101         int cpu = smp_processor_id();
 102         struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
 103
 104         atomic_inc(&rcu_barrier_cpu_count);
 105         call_rcu(head, rcu_barrier_callback);
 106 }
 107
 108 /**
 109  * rcu_barrier - Wait until all the in-flight RCUs are complete.
 110  */
 111 void rcu_barrier(void)
 112 {
 113         BUG_ON(in_interrupt());
 114         /* Take cpucontrol mutex to protect against CPU hotplug */
 115         mutex_lock(&rcu_barrier_mutex);
 116         init_completion(&rcu_barrier_completion);
 117         atomic_set(&rcu_barrier_cpu_count, 0);
 118         /*
 119          * The queueing of callbacks in all CPUs must be atomic with
 120          * respect to RCU, otherwise one CPU may queue a callback,
 121          * wait for a grace period, decrement barrier count and call
 122          * complete(), while other CPUs have not yet queued anything.
 123          * So, we need to make sure that grace periods cannot complete
 124          * until all the callbacks are queued.
 125          */
 126         rcu_read_lock();
 127         on_each_cpu(rcu_barrier_func, NULL, 0, 1);
 128         rcu_read_unlock();
 129         wait_for_completion(&rcu_barrier_completion);
 130         mutex_unlock(&rcu_barrier_mutex);
 131 }
 132 EXPORT_SYMBOL_GPL(rcu_barrier);
 133
 134 void __init rcu_init(void)
 135 {
 136         __rcu_init();
 137 }
 138