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
  48 enum rcu_barrier {
  49         RCU_BARRIER_STD,
  50         RCU_BARRIER_BH,
  51         RCU_BARRIER_SCHED,
  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 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         init_completion(&rcu.completion);
  84         /* Will wake me after RCU finished. */
  85         call_rcu(&rcu.head, wakeme_after_rcu);
  86         /* Wait for it. */
  87         wait_for_completion(&rcu.completion);
  88 }
  89 EXPORT_SYMBOL_GPL(synchronize_rcu);
  90
  91 static void rcu_barrier_callback(struct rcu_head *notused)
  92 {
  93         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
  94                 complete(&rcu_barrier_completion);
  95 }
  96
  97 /*
  98  * Called with preemption disabled, and from cross-cpu IRQ context.
  99  */
 100 static void rcu_barrier_func(void *type)
 101 {
 102         int cpu = smp_processor_id();
 103         struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
 104
 105         atomic_inc(&rcu_barrier_cpu_count);
 106         switch ((enum rcu_barrier)type) {
 107         case RCU_BARRIER_STD:
 108                 call_rcu(head, rcu_barrier_callback);
 109                 break;
 110         case RCU_BARRIER_BH:
 111                 call_rcu_bh(head, rcu_barrier_callback);
 112                 break;
 113         case RCU_BARRIER_SCHED:
 114                 call_rcu_sched(head, rcu_barrier_callback);
 115                 break;
 116         }
 117 }
 118
 119 /*
 120  * Orchestrate the specified type of RCU barrier, waiting for all
 121  * RCU callbacks of the specified type to complete.
 122  */
 123 static void _rcu_barrier(enum rcu_barrier type)
 124 {
 125         BUG_ON(in_interrupt());
 126         /* Take cpucontrol mutex to protect against CPU hotplug */
 127         mutex_lock(&rcu_barrier_mutex);
 128         init_completion(&rcu_barrier_completion);
 129         /*
 130          * Initialize rcu_barrier_cpu_count to 1, then invoke
 131          * rcu_barrier_func() on each CPU, so that each CPU also has
 132          * incremented rcu_barrier_cpu_count.  Only then is it safe to
 133          * decrement rcu_barrier_cpu_count -- otherwise the first CPU
 134          * might complete its grace period before all of the other CPUs
 135          * did their increment, causing this function to return too
 136          * early.
 137          */
 138         atomic_set(&rcu_barrier_cpu_count, 1);
 139         on_each_cpu(rcu_barrier_func, (void *)type, 1);
 140         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
 141                 complete(&rcu_barrier_completion);
 142         wait_for_completion(&rcu_barrier_completion);
 143         mutex_unlock(&rcu_barrier_mutex);
 144 }
 145
 146 /**
 147  * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
 148  */
 149 void rcu_barrier(void)
 150 {
 151         _rcu_barrier(RCU_BARRIER_STD);
 152 }
 153 EXPORT_SYMBOL_GPL(rcu_barrier);
 154
 155 /**
 156  * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
 157  */
 158 void rcu_barrier_bh(void)
 159 {
 160         _rcu_barrier(RCU_BARRIER_BH);
 161 }
 162 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
 163
 164 /**
 165  * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
 166  */
 167 void rcu_barrier_sched(void)
 168 {
 169         _rcu_barrier(RCU_BARRIER_SCHED);
 170 }
 171 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
 172
 173 void __init rcu_init(void)
 174 {
 175         __rcu_init();
 176 }
 177