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 enum rcu_barrier {
  50         RCU_BARRIER_STD,
  51         RCU_BARRIER_BH,
  52         RCU_BARRIER_SCHED,
  53 };
  54
  55 static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
  56 static atomic_t rcu_barrier_cpu_count;
  57 static DEFINE_MUTEX(rcu_barrier_mutex);
  58 static struct completion rcu_barrier_completion;
  59 int rcu_scheduler_active __read_mostly;
  60
  61 static atomic_t rcu_migrate_type_count = ATOMIC_INIT(0);
  62 static struct rcu_head rcu_migrate_head[3];
  63 static DECLARE_WAIT_QUEUE_HEAD(rcu_migrate_wq);
  64
  65 /*
  66  * Awaken the corresponding synchronize_rcu() instance now that a
  67  * grace period has elapsed.
  68  */
  69 void wakeme_after_rcu(struct rcu_head  *head)
  70 {
  71         struct rcu_synchronize *rcu;
  72
  73         rcu = container_of(head, struct rcu_synchronize, head);
  74         complete(&rcu->completion);
  75 }
  76
  77 /**
  78  * synchronize_rcu - wait until a grace period has elapsed.
  79  *
  80  * Control will return to the caller some time after a full grace
  81  * period has elapsed, in other words after all currently executing RCU
  82  * read-side critical sections have completed.  RCU read-side critical
  83  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
  84  * and may be nested.
  85  */
  86 void synchronize_rcu(void)
  87 {
  88         struct rcu_synchronize rcu;
  89
  90         if (rcu_blocking_is_gp())
  91                 return;
  92
  93         init_completion(&rcu.completion);
  94         /* Will wake me after RCU finished. */
  95         call_rcu(&rcu.head, wakeme_after_rcu);
  96         /* Wait for it. */
  97         wait_for_completion(&rcu.completion);
  98 }
  99 EXPORT_SYMBOL_GPL(synchronize_rcu);
 100
 101 static void rcu_barrier_callback(struct rcu_head *notused)
 102 {
 103         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
 104                 complete(&rcu_barrier_completion);
 105 }
 106
 107 /*
 108  * Called with preemption disabled, and from cross-cpu IRQ context.
 109  */
 110 static void rcu_barrier_func(void *type)
 111 {
 112         int cpu = smp_processor_id();
 113         struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
 114
 115         atomic_inc(&rcu_barrier_cpu_count);
 116         switch ((enum rcu_barrier)type) {
 117         case RCU_BARRIER_STD:
 118                 call_rcu(head, rcu_barrier_callback);
 119                 break;
 120         case RCU_BARRIER_BH:
 121                 call_rcu_bh(head, rcu_barrier_callback);
 122                 break;
 123         case RCU_BARRIER_SCHED:
 124                 call_rcu_sched(head, rcu_barrier_callback);
 125                 break;
 126         }
 127 }
 128
 129 static inline void wait_migrated_callbacks(void)
 130 {
 131         wait_event(rcu_migrate_wq, !atomic_read(&rcu_migrate_type_count));
 132 }
 133
 134 /*
 135  * Orchestrate the specified type of RCU barrier, waiting for all
 136  * RCU callbacks of the specified type to complete.
 137  */
 138 static void _rcu_barrier(enum rcu_barrier type)
 139 {
 140         BUG_ON(in_interrupt());
 141         /* Take cpucontrol mutex to protect against CPU hotplug */
 142         mutex_lock(&rcu_barrier_mutex);
 143         init_completion(&rcu_barrier_completion);
 144         /*
 145          * Initialize rcu_barrier_cpu_count to 1, then invoke
 146          * rcu_barrier_func() on each CPU, so that each CPU also has
 147          * incremented rcu_barrier_cpu_count.  Only then is it safe to
 148          * decrement rcu_barrier_cpu_count -- otherwise the first CPU
 149          * might complete its grace period before all of the other CPUs
 150          * did their increment, causing this function to return too
 151          * early.
 152          */
 153         atomic_set(&rcu_barrier_cpu_count, 1);
 154         on_each_cpu(rcu_barrier_func, (void *)type, 1);
 155         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
 156                 complete(&rcu_barrier_completion);
 157         wait_for_completion(&rcu_barrier_completion);
 158         mutex_unlock(&rcu_barrier_mutex);
 159         wait_migrated_callbacks();
 160 }
 161
 162 /**
 163  * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
 164  */
 165 void rcu_barrier(void)
 166 {
 167         _rcu_barrier(RCU_BARRIER_STD);
 168 }
 169 EXPORT_SYMBOL_GPL(rcu_barrier);
 170
 171 /**
 172  * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
 173  */
 174 void rcu_barrier_bh(void)
 175 {
 176         _rcu_barrier(RCU_BARRIER_BH);
 177 }
 178 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
 179
 180 /**
 181  * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
 182  */
 183 void rcu_barrier_sched(void)
 184 {
 185         _rcu_barrier(RCU_BARRIER_SCHED);
 186 }
 187 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
 188
 189 static void rcu_migrate_callback(struct rcu_head *notused)
 190 {
 191         if (atomic_dec_and_test(&rcu_migrate_type_count))
 192                 wake_up(&rcu_migrate_wq);
 193 }
 194
 195 static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
 196                 unsigned long action, void *hcpu)
 197 {
 198         if (action == CPU_DYING) {
 199                 /*
 200                  * preempt_disable() in on_each_cpu() prevents stop_machine(),
 201                  * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);"
 202                  * returns, all online cpus have queued rcu_barrier_func(),
 203                  * and the dead cpu(if it exist) queues rcu_migrate_callback()s.
 204                  *
 205                  * These callbacks ensure _rcu_barrier() waits for all
 206                  * RCU callbacks of the specified type to complete.
 207                  */
 208                 atomic_set(&rcu_migrate_type_count, 3);
 209                 call_rcu_bh(rcu_migrate_head, rcu_migrate_callback);
 210                 call_rcu_sched(rcu_migrate_head + 1, rcu_migrate_callback);
 211                 call_rcu(rcu_migrate_head + 2, rcu_migrate_callback);
 212         } else if (action == CPU_POST_DEAD) {
 213                 /* rcu_migrate_head is protected by cpu_add_remove_lock */
 214                 wait_migrated_callbacks();
 215         }
 216
 217         return NOTIFY_OK;
 218 }
 219
 220 void __init rcu_init(void)
 221 {
 222         __rcu_init();
 223         hotcpu_notifier(rcu_barrier_cpu_hotplug, 0);
 224 }
 225
 226 void rcu_scheduler_starting(void)
 227 {
 228         WARN_ON(num_online_cpus() != 1);
 229         WARN_ON(nr_context_switches() > 0);
 230         rcu_scheduler_active = 1;
 231 }