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);     /* Makes kernel-doc tools happy */
  81 synchronize_rcu_xxx(synchronize_rcu, call_rcu)
  82 EXPORT_SYMBOL_GPL(synchronize_rcu);
  83
  84 static void rcu_barrier_callback(struct rcu_head *notused)
  85 {
  86         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
  87                 complete(&rcu_barrier_completion);
  88 }
  89
  90 /*
  91  * Called with preemption disabled, and from cross-cpu IRQ context.
  92  */
  93 static void rcu_barrier_func(void *type)
  94 {
  95         int cpu = smp_processor_id();
  96         struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
  97
  98         atomic_inc(&rcu_barrier_cpu_count);
  99         switch ((enum rcu_barrier)type) {
 100         case RCU_BARRIER_STD:
 101                 call_rcu(head, rcu_barrier_callback);
 102                 break;
 103         case RCU_BARRIER_BH:
 104                 call_rcu_bh(head, rcu_barrier_callback);
 105                 break;
 106         case RCU_BARRIER_SCHED:
 107                 call_rcu_sched(head, rcu_barrier_callback);
 108                 break;
 109         }
 110 }
 111
 112 /*
 113  * Orchestrate the specified type of RCU barrier, waiting for all
 114  * RCU callbacks of the specified type to complete.
 115  */
 116 static void _rcu_barrier(enum rcu_barrier type)
 117 {
 118         BUG_ON(in_interrupt());
 119         /* Take cpucontrol mutex to protect against CPU hotplug */
 120         mutex_lock(&rcu_barrier_mutex);
 121         init_completion(&rcu_barrier_completion);
 122         /*
 123          * Initialize rcu_barrier_cpu_count to 1, then invoke
 124          * rcu_barrier_func() on each CPU, so that each CPU also has
 125          * incremented rcu_barrier_cpu_count.  Only then is it safe to
 126          * decrement rcu_barrier_cpu_count -- otherwise the first CPU
 127          * might complete its grace period before all of the other CPUs
 128          * did their increment, causing this function to return too
 129          * early.
 130          */
 131         atomic_set(&rcu_barrier_cpu_count, 1);
 132         on_each_cpu(rcu_barrier_func, (void *)type, 1);
 133         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
 134                 complete(&rcu_barrier_completion);
 135         wait_for_completion(&rcu_barrier_completion);
 136         mutex_unlock(&rcu_barrier_mutex);
 137 }
 138
 139 /**
 140  * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
 141  */
 142 void rcu_barrier(void)
 143 {
 144         _rcu_barrier(RCU_BARRIER_STD);
 145 }
 146 EXPORT_SYMBOL_GPL(rcu_barrier);
 147
 148 /**
 149  * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
 150  */
 151 void rcu_barrier_bh(void)
 152 {
 153         _rcu_barrier(RCU_BARRIER_BH);
 154 }
 155 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
 156
 157 /**
 158  * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
 159  */
 160 void rcu_barrier_sched(void)
 161 {
 162         _rcu_barrier(RCU_BARRIER_SCHED);
 163 }
 164 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
 165
 166 void __init rcu_init(void)
 167 {
 168         __rcu_init();
 169 }
 170