linux/kernel/rcupdate.c
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   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 <linux/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/export.h>
  47#include <linux/hardirq.h>
  48
  49#define CREATE_TRACE_POINTS
  50#include <trace/events/rcu.h>
  51
  52#include "rcu.h"
  53
  54#ifdef CONFIG_DEBUG_LOCK_ALLOC
  55static struct lock_class_key rcu_lock_key;
  56struct lockdep_map rcu_lock_map =
  57        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
  58EXPORT_SYMBOL_GPL(rcu_lock_map);
  59
  60static struct lock_class_key rcu_bh_lock_key;
  61struct lockdep_map rcu_bh_lock_map =
  62        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
  63EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
  64
  65static struct lock_class_key rcu_sched_lock_key;
  66struct lockdep_map rcu_sched_lock_map =
  67        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
  68EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
  69#endif
  70
  71#ifdef CONFIG_DEBUG_LOCK_ALLOC
  72
  73int debug_lockdep_rcu_enabled(void)
  74{
  75        return rcu_scheduler_active && debug_locks &&
  76               current->lockdep_recursion == 0;
  77}
  78EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
  79
  80/**
  81 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
  82 *
  83 * Check for bottom half being disabled, which covers both the
  84 * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
  85 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
  86 * will show the situation.  This is useful for debug checks in functions
  87 * that require that they be called within an RCU read-side critical
  88 * section.
  89 *
  90 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
  91 */
  92int rcu_read_lock_bh_held(void)
  93{
  94        if (!debug_lockdep_rcu_enabled())
  95                return 1;
  96        if (rcu_is_cpu_idle())
  97                return 0;
  98        return in_softirq() || irqs_disabled();
  99}
 100EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 101
 102#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 103
 104struct rcu_synchronize {
 105        struct rcu_head head;
 106        struct completion completion;
 107};
 108
 109/*
 110 * Awaken the corresponding synchronize_rcu() instance now that a
 111 * grace period has elapsed.
 112 */
 113static void wakeme_after_rcu(struct rcu_head  *head)
 114{
 115        struct rcu_synchronize *rcu;
 116
 117        rcu = container_of(head, struct rcu_synchronize, head);
 118        complete(&rcu->completion);
 119}
 120
 121void wait_rcu_gp(call_rcu_func_t crf)
 122{
 123        struct rcu_synchronize rcu;
 124
 125        init_rcu_head_on_stack(&rcu.head);
 126        init_completion(&rcu.completion);
 127        /* Will wake me after RCU finished. */
 128        crf(&rcu.head, wakeme_after_rcu);
 129        /* Wait for it. */
 130        wait_for_completion(&rcu.completion);
 131        destroy_rcu_head_on_stack(&rcu.head);
 132}
 133EXPORT_SYMBOL_GPL(wait_rcu_gp);
 134
 135#ifdef CONFIG_PROVE_RCU
 136/*
 137 * wrapper function to avoid #include problems.
 138 */
 139int rcu_my_thread_group_empty(void)
 140{
 141        return thread_group_empty(current);
 142}
 143EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 144#endif /* #ifdef CONFIG_PROVE_RCU */
 145
 146#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 147static inline void debug_init_rcu_head(struct rcu_head *head)
 148{
 149        debug_object_init(head, &rcuhead_debug_descr);
 150}
 151
 152static inline void debug_rcu_head_free(struct rcu_head *head)
 153{
 154        debug_object_free(head, &rcuhead_debug_descr);
 155}
 156
 157/*
 158 * fixup_init is called when:
 159 * - an active object is initialized
 160 */
 161static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
 162{
 163        struct rcu_head *head = addr;
 164
 165        switch (state) {
 166        case ODEBUG_STATE_ACTIVE:
 167                /*
 168                 * Ensure that queued callbacks are all executed.
 169                 * If we detect that we are nested in a RCU read-side critical
 170                 * section, we should simply fail, otherwise we would deadlock.
 171                 * In !PREEMPT configurations, there is no way to tell if we are
 172                 * in a RCU read-side critical section or not, so we never
 173                 * attempt any fixup and just print a warning.
 174                 */
 175#ifndef CONFIG_PREEMPT
 176                WARN_ON_ONCE(1);
 177                return 0;
 178#endif
 179                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 180                    irqs_disabled()) {
 181                        WARN_ON_ONCE(1);
 182                        return 0;
 183                }
 184                rcu_barrier();
 185                rcu_barrier_sched();
 186                rcu_barrier_bh();
 187                debug_object_init(head, &rcuhead_debug_descr);
 188                return 1;
 189        default:
 190                return 0;
 191        }
 192}
 193
 194/*
 195 * fixup_activate is called when:
 196 * - an active object is activated
 197 * - an unknown object is activated (might be a statically initialized object)
 198 * Activation is performed internally by call_rcu().
 199 */
 200static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 201{
 202        struct rcu_head *head = addr;
 203
 204        switch (state) {
 205
 206        case ODEBUG_STATE_NOTAVAILABLE:
 207                /*
 208                 * This is not really a fixup. We just make sure that it is
 209                 * tracked in the object tracker.
 210                 */
 211                debug_object_init(head, &rcuhead_debug_descr);
 212                debug_object_activate(head, &rcuhead_debug_descr);
 213                return 0;
 214
 215        case ODEBUG_STATE_ACTIVE:
 216                /*
 217                 * Ensure that queued callbacks are all executed.
 218                 * If we detect that we are nested in a RCU read-side critical
 219                 * section, we should simply fail, otherwise we would deadlock.
 220                 * In !PREEMPT configurations, there is no way to tell if we are
 221                 * in a RCU read-side critical section or not, so we never
 222                 * attempt any fixup and just print a warning.
 223                 */
 224#ifndef CONFIG_PREEMPT
 225                WARN_ON_ONCE(1);
 226                return 0;
 227#endif
 228                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 229                    irqs_disabled()) {
 230                        WARN_ON_ONCE(1);
 231                        return 0;
 232                }
 233                rcu_barrier();
 234                rcu_barrier_sched();
 235                rcu_barrier_bh();
 236                debug_object_activate(head, &rcuhead_debug_descr);
 237                return 1;
 238        default:
 239                return 0;
 240        }
 241}
 242
 243/*
 244 * fixup_free is called when:
 245 * - an active object is freed
 246 */
 247static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 248{
 249        struct rcu_head *head = addr;
 250
 251        switch (state) {
 252        case ODEBUG_STATE_ACTIVE:
 253                /*
 254                 * Ensure that queued callbacks are all executed.
 255                 * If we detect that we are nested in a RCU read-side critical
 256                 * section, we should simply fail, otherwise we would deadlock.
 257                 * In !PREEMPT configurations, there is no way to tell if we are
 258                 * in a RCU read-side critical section or not, so we never
 259                 * attempt any fixup and just print a warning.
 260                 */
 261#ifndef CONFIG_PREEMPT
 262                WARN_ON_ONCE(1);
 263                return 0;
 264#endif
 265                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 266                    irqs_disabled()) {
 267                        WARN_ON_ONCE(1);
 268                        return 0;
 269                }
 270                rcu_barrier();
 271                rcu_barrier_sched();
 272                rcu_barrier_bh();
 273                debug_object_free(head, &rcuhead_debug_descr);
 274                return 1;
 275        default:
 276                return 0;
 277        }
 278}
 279
 280/**
 281 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 282 * @head: pointer to rcu_head structure to be initialized
 283 *
 284 * This function informs debugobjects of a new rcu_head structure that
 285 * has been allocated as an auto variable on the stack.  This function
 286 * is not required for rcu_head structures that are statically defined or
 287 * that are dynamically allocated on the heap.  This function has no
 288 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 289 */
 290void init_rcu_head_on_stack(struct rcu_head *head)
 291{
 292        debug_object_init_on_stack(head, &rcuhead_debug_descr);
 293}
 294EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 295
 296/**
 297 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 298 * @head: pointer to rcu_head structure to be initialized
 299 *
 300 * This function informs debugobjects that an on-stack rcu_head structure
 301 * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 302 * function is not required for rcu_head structures that are statically
 303 * defined or that are dynamically allocated on the heap.  Also as with
 304 * init_rcu_head_on_stack(), this function has no effect for
 305 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 306 */
 307void destroy_rcu_head_on_stack(struct rcu_head *head)
 308{
 309        debug_object_free(head, &rcuhead_debug_descr);
 310}
 311EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 312
 313struct debug_obj_descr rcuhead_debug_descr = {
 314        .name = "rcu_head",
 315        .fixup_init = rcuhead_fixup_init,
 316        .fixup_activate = rcuhead_fixup_activate,
 317        .fixup_free = rcuhead_fixup_free,
 318};
 319EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 320#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 321
 322#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
 323void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
 324{
 325        trace_rcu_torture_read(rcutorturename, rhp);
 326}
 327EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 328#else
 329#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
 330#endif
 331