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 /*
  62  * Awaken the corresponding synchronize_rcu() instance now that a
  63  * grace period has elapsed.
  64  */
  65 void wakeme_after_rcu(struct rcu_head  *head)
  66 {
  67         struct rcu_synchronize *rcu;
  68
  69         rcu = container_of(head, struct rcu_synchronize, head);
  70         complete(&rcu->completion);
  71 }
  72
  73 /**
  74  * synchronize_rcu - wait until a grace period has elapsed.
  75  *
  76  * Control will return to the caller some time after a full grace
  77  * period has elapsed, in other words after all currently executing RCU
  78  * read-side critical sections have completed.  RCU read-side critical
  79  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
  80  * and may be nested.
  81  */
  82 void synchronize_rcu(void)
  83 {
  84         struct rcu_synchronize rcu;
  85
  86         if (rcu_blocking_is_gp())
  87                 return;
  88
  89         init_completion(&rcu.completion);
  90         /* Will wake me after RCU finished. */
  91         call_rcu(&rcu.head, wakeme_after_rcu);
  92         /* Wait for it. */
  93         wait_for_completion(&rcu.completion);
  94 }
  95 EXPORT_SYMBOL_GPL(synchronize_rcu);
  96
  97 static void rcu_barrier_callback(struct rcu_head *notused)
  98 {
  99         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
 100                 complete(&rcu_barrier_completion);
 101 }
 102
 103 /*
 104  * Called with preemption disabled, and from cross-cpu IRQ context.
 105  */
 106 static void rcu_barrier_func(void *type)
 107 {
 108         int cpu = smp_processor_id();
 109         struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
 110
 111         atomic_inc(&rcu_barrier_cpu_count);
 112         switch ((enum rcu_barrier)type) {
 113         case RCU_BARRIER_STD:
 114                 call_rcu(head, rcu_barrier_callback);
 115                 break;
 116         case RCU_BARRIER_BH:
 117                 call_rcu_bh(head, rcu_barrier_callback);
 118                 break;
 119         case RCU_BARRIER_SCHED:
 120                 call_rcu_sched(head, rcu_barrier_callback);
 121                 break;
 122         }
 123 }
 124
 125 static inline void wait_migrated_callbacks(void);
 126
 127 /*
 128  * Orchestrate the specified type of RCU barrier, waiting for all
 129  * RCU callbacks of the specified type to complete.
 130  */
 131 static void _rcu_barrier(enum rcu_barrier type)
 132 {
 133         BUG_ON(in_interrupt());
 134         /* Take cpucontrol mutex to protect against CPU hotplug */
 135         mutex_lock(&rcu_barrier_mutex);
 136         init_completion(&rcu_barrier_completion);
 137         /*
 138          * Initialize rcu_barrier_cpu_count to 1, then invoke
 139          * rcu_barrier_func() on each CPU, so that each CPU also has
 140          * incremented rcu_barrier_cpu_count.  Only then is it safe to
 141          * decrement rcu_barrier_cpu_count -- otherwise the first CPU
 142          * might complete its grace period before all of the other CPUs
 143          * did their increment, causing this function to return too
 144          * early.
 145          */
 146         atomic_set(&rcu_barrier_cpu_count, 1);
 147         on_each_cpu(rcu_barrier_func, (void *)type, 1);
 148         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
 149                 complete(&rcu_barrier_completion);
 150         wait_for_completion(&rcu_barrier_completion);
 151         mutex_unlock(&rcu_barrier_mutex);
 152         wait_migrated_callbacks();
 153 }
 154
 155 /**
 156  * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
 157  */
 158 void rcu_barrier(void)
 159 {
 160         _rcu_barrier(RCU_BARRIER_STD);
 161 }
 162 EXPORT_SYMBOL_GPL(rcu_barrier);
 163
 164 /**
 165  * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
 166  */
 167 void rcu_barrier_bh(void)
 168 {
 169         _rcu_barrier(RCU_BARRIER_BH);
 170 }
 171 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
 172
 173 /**
 174  * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
 175  */
 176 void rcu_barrier_sched(void)
 177 {
 178         _rcu_barrier(RCU_BARRIER_SCHED);
 179 }
 180 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
 181
 182 static atomic_t rcu_migrate_type_count = ATOMIC_INIT(0);
 183 static struct rcu_head rcu_migrate_head[3];
 184 static DECLARE_WAIT_QUEUE_HEAD(rcu_migrate_wq);
 185
 186 static void rcu_migrate_callback(struct rcu_head *notused)
 187 {
 188         if (atomic_dec_and_test(&rcu_migrate_type_count))
 189                 wake_up(&rcu_migrate_wq);
 190 }
 191
 192 static inline void wait_migrated_callbacks(void)
 193 {
 194         wait_event(rcu_migrate_wq, !atomic_read(&rcu_migrate_type_count));
 195 }
 196
 197 static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
 198                 unsigned long action, void *hcpu)
 199 {
 200         if (action == CPU_DYING) {
 201                 /*
 202                  * preempt_disable() in on_each_cpu() prevents stop_machine(),
 203                  * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);"
 204                  * returns, all online cpus have queued rcu_barrier_func(),
 205                  * and the dead cpu(if it exist) queues rcu_migrate_callback()s.
 206                  *
 207                  * These callbacks ensure _rcu_barrier() waits for all
 208                  * RCU callbacks of the specified type to complete.
 209                  */
 210                 atomic_set(&rcu_migrate_type_count, 3);
 211                 call_rcu_bh(rcu_migrate_head, rcu_migrate_callback);
 212                 call_rcu_sched(rcu_migrate_head + 1, rcu_migrate_callback);
 213                 call_rcu(rcu_migrate_head + 2, rcu_migrate_callback);
 214         } else if (action == CPU_POST_DEAD) {
 215                 /* rcu_migrate_head is protected by cpu_add_remove_lock */
 216                 wait_migrated_callbacks();
 217         }
 218
 219         return NOTIFY_OK;
 220 }
 221
 222 void __init rcu_init(void)
 223 {
 224         __rcu_init();
 225         hotcpu_notifier(rcu_barrier_cpu_hotplug, 0);
 226 }
 227
 228 void rcu_scheduler_starting(void)
 229 {
 230         WARN_ON(num_online_cpus() != 1);
 231         WARN_ON(nr_context_switches() > 0);
 232         rcu_scheduler_active = 1;
 233 }