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 #ifdef CONFIG_TREE_PREEMPT_RCU
  78
  79 /**
  80  * synchronize_rcu - wait until a grace period has elapsed.
  81  *
  82  * Control will return to the caller some time after a full grace
  83  * period has elapsed, in other words after all currently executing RCU
  84  * read-side critical sections have completed.  RCU read-side critical
  85  * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
  86  * and may be nested.
  87  */
  88 void synchronize_rcu(void)
  89 {
  90         struct rcu_synchronize rcu;
  91
  92         if (!rcu_scheduler_active)
  93                 return;
  94
  95         init_completion(&rcu.completion);
  96         /* Will wake me after RCU finished. */
  97         call_rcu(&rcu.head, wakeme_after_rcu);
  98         /* Wait for it. */
  99         wait_for_completion(&rcu.completion);
 100 }
 101 EXPORT_SYMBOL_GPL(synchronize_rcu);
 102
 103 #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
 104
 105 /**
 106  * synchronize_sched - wait until an rcu-sched grace period has elapsed.
 107  *
 108  * Control will return to the caller some time after a full rcu-sched
 109  * grace period has elapsed, in other words after all currently executing
 110  * rcu-sched read-side critical sections have completed.   These read-side
 111  * critical sections are delimited by rcu_read_lock_sched() and
 112  * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
 113  * local_irq_disable(), and so on may be used in place of
 114  * rcu_read_lock_sched().
 115  *
 116  * This means that all preempt_disable code sequences, including NMI and
 117  * hardware-interrupt handlers, in progress on entry will have completed
 118  * before this primitive returns.  However, this does not guarantee that
 119  * softirq handlers will have completed, since in some kernels, these
 120  * handlers can run in process context, and can block.
 121  *
 122  * This primitive provides the guarantees made by the (now removed)
 123  * synchronize_kernel() API.  In contrast, synchronize_rcu() only
 124  * guarantees that rcu_read_lock() sections will have completed.
 125  * In "classic RCU", these two guarantees happen to be one and
 126  * the same, but can differ in realtime RCU implementations.
 127  */
 128 void synchronize_sched(void)
 129 {
 130         struct rcu_synchronize rcu;
 131
 132         if (rcu_blocking_is_gp())
 133                 return;
 134
 135         init_completion(&rcu.completion);
 136         /* Will wake me after RCU finished. */
 137         call_rcu_sched(&rcu.head, wakeme_after_rcu);
 138         /* Wait for it. */
 139         wait_for_completion(&rcu.completion);
 140 }
 141 EXPORT_SYMBOL_GPL(synchronize_sched);
 142
 143 /**
 144  * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
 145  *
 146  * Control will return to the caller some time after a full rcu_bh grace
 147  * period has elapsed, in other words after all currently executing rcu_bh
 148  * read-side critical sections have completed.  RCU read-side critical
 149  * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
 150  * and may be nested.
 151  */
 152 void synchronize_rcu_bh(void)
 153 {
 154         struct rcu_synchronize rcu;
 155
 156         if (rcu_blocking_is_gp())
 157                 return;
 158
 159         init_completion(&rcu.completion);
 160         /* Will wake me after RCU finished. */
 161         call_rcu_bh(&rcu.head, wakeme_after_rcu);
 162         /* Wait for it. */
 163         wait_for_completion(&rcu.completion);
 164 }
 165 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
 166
 167 static void rcu_barrier_callback(struct rcu_head *notused)
 168 {
 169         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
 170                 complete(&rcu_barrier_completion);
 171 }
 172
 173 /*
 174  * Called with preemption disabled, and from cross-cpu IRQ context.
 175  */
 176 static void rcu_barrier_func(void *type)
 177 {
 178         int cpu = smp_processor_id();
 179         struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
 180
 181         atomic_inc(&rcu_barrier_cpu_count);
 182         switch ((enum rcu_barrier)type) {
 183         case RCU_BARRIER_STD:
 184                 call_rcu(head, rcu_barrier_callback);
 185                 break;
 186         case RCU_BARRIER_BH:
 187                 call_rcu_bh(head, rcu_barrier_callback);
 188                 break;
 189         case RCU_BARRIER_SCHED:
 190                 call_rcu_sched(head, rcu_barrier_callback);
 191                 break;
 192         }
 193 }
 194
 195 static inline void wait_migrated_callbacks(void)
 196 {
 197         wait_event(rcu_migrate_wq, !atomic_read(&rcu_migrate_type_count));
 198         smp_mb(); /* In case we didn't sleep. */
 199 }
 200
 201 /*
 202  * Orchestrate the specified type of RCU barrier, waiting for all
 203  * RCU callbacks of the specified type to complete.
 204  */
 205 static void _rcu_barrier(enum rcu_barrier type)
 206 {
 207         BUG_ON(in_interrupt());
 208         /* Take cpucontrol mutex to protect against CPU hotplug */
 209         mutex_lock(&rcu_barrier_mutex);
 210         init_completion(&rcu_barrier_completion);
 211         /*
 212          * Initialize rcu_barrier_cpu_count to 1, then invoke
 213          * rcu_barrier_func() on each CPU, so that each CPU also has
 214          * incremented rcu_barrier_cpu_count.  Only then is it safe to
 215          * decrement rcu_barrier_cpu_count -- otherwise the first CPU
 216          * might complete its grace period before all of the other CPUs
 217          * did their increment, causing this function to return too
 218          * early.
 219          */
 220         atomic_set(&rcu_barrier_cpu_count, 1);
 221         on_each_cpu(rcu_barrier_func, (void *)type, 1);
 222         if (atomic_dec_and_test(&rcu_barrier_cpu_count))
 223                 complete(&rcu_barrier_completion);
 224         wait_for_completion(&rcu_barrier_completion);
 225         mutex_unlock(&rcu_barrier_mutex);
 226         wait_migrated_callbacks();
 227 }
 228
 229 /**
 230  * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
 231  */
 232 void rcu_barrier(void)
 233 {
 234         _rcu_barrier(RCU_BARRIER_STD);
 235 }
 236 EXPORT_SYMBOL_GPL(rcu_barrier);
 237
 238 /**
 239  * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
 240  */
 241 void rcu_barrier_bh(void)
 242 {
 243         _rcu_barrier(RCU_BARRIER_BH);
 244 }
 245 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
 246
 247 /**
 248  * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
 249  */
 250 void rcu_barrier_sched(void)
 251 {
 252         _rcu_barrier(RCU_BARRIER_SCHED);
 253 }
 254 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
 255
 256 static void rcu_migrate_callback(struct rcu_head *notused)
 257 {
 258         if (atomic_dec_and_test(&rcu_migrate_type_count))
 259                 wake_up(&rcu_migrate_wq);
 260 }
 261
 262 extern int rcu_cpu_notify(struct notifier_block *self,
 263                           unsigned long action, void *hcpu);
 264
 265 static int __cpuinit rcu_barrier_cpu_hotplug(struct notifier_block *self,
 266                 unsigned long action, void *hcpu)
 267 {
 268         rcu_cpu_notify(self, action, hcpu);
 269         if (action == CPU_DYING) {
 270                 /*
 271                  * preempt_disable() in on_each_cpu() prevents stop_machine(),
 272                  * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);"
 273                  * returns, all online cpus have queued rcu_barrier_func(),
 274                  * and the dead cpu(if it exist) queues rcu_migrate_callback()s.
 275                  *
 276                  * These callbacks ensure _rcu_barrier() waits for all
 277                  * RCU callbacks of the specified type to complete.
 278                  */
 279                 atomic_set(&rcu_migrate_type_count, 3);
 280                 call_rcu_bh(rcu_migrate_head, rcu_migrate_callback);
 281                 call_rcu_sched(rcu_migrate_head + 1, rcu_migrate_callback);
 282                 call_rcu(rcu_migrate_head + 2, rcu_migrate_callback);
 283         } else if (action == CPU_DOWN_PREPARE) {
 284                 /* Don't need to wait until next removal operation. */
 285                 /* rcu_migrate_head is protected by cpu_add_remove_lock */
 286                 wait_migrated_callbacks();
 287         }
 288
 289         return NOTIFY_OK;
 290 }
 291
 292 void __init rcu_init(void)
 293 {
 294         int i;
 295
 296         __rcu_init();
 297         cpu_notifier(rcu_barrier_cpu_hotplug, 0);
 298
 299         /*
 300          * We don't need protection against CPU-hotplug here because
 301          * this is called early in boot, before either interrupts
 302          * or the scheduler are operational.
 303          */
 304         for_each_online_cpu(i)
 305                 rcu_barrier_cpu_hotplug(NULL, CPU_UP_PREPARE, (void *)(long)i);
 306 }
 307
 308 void rcu_scheduler_starting(void)
 309 {
 310         WARN_ON(num_online_cpus() != 1);
 311         WARN_ON(nr_context_switches() > 0);
 312         rcu_scheduler_active = 1;
 313 }