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