linux/kernel/rcupdate.c
<<
>>
Prefs
   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/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                 */
 146                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 147                    irqs_disabled()) {
 148                        WARN_ON(1);
 149                        return 0;
 150                }
 151                rcu_barrier();
 152                rcu_barrier_sched();
 153                rcu_barrier_bh();
 154                debug_object_init(head, &rcuhead_debug_descr);
 155                return 1;
 156        default:
 157                return 0;
 158        }
 159}
 160
 161/*
 162 * fixup_activate is called when:
 163 * - an active object is activated
 164 * - an unknown object is activated (might be a statically initialized object)
 165 * Activation is performed internally by call_rcu().
 166 */
 167static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 168{
 169        struct rcu_head *head = addr;
 170
 171        switch (state) {
 172
 173        case ODEBUG_STATE_NOTAVAILABLE:
 174                /*
 175                 * This is not really a fixup. We just make sure that it is
 176                 * tracked in the object tracker.
 177                 */
 178                debug_object_init(head, &rcuhead_debug_descr);
 179                debug_object_activate(head, &rcuhead_debug_descr);
 180                return 0;
 181
 182        case ODEBUG_STATE_ACTIVE:
 183                /*
 184                 * Ensure that queued callbacks are all executed.
 185                 * If we detect that we are nested in a RCU read-side critical
 186                 * section, we should simply fail, otherwise we would deadlock.
 187                 */
 188                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 189                    irqs_disabled()) {
 190                        WARN_ON(1);
 191                        return 0;
 192                }
 193                rcu_barrier();
 194                rcu_barrier_sched();
 195                rcu_barrier_bh();
 196                debug_object_activate(head, &rcuhead_debug_descr);
 197                return 1;
 198        default:
 199                return 0;
 200        }
 201}
 202
 203/*
 204 * fixup_free is called when:
 205 * - an active object is freed
 206 */
 207static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 208{
 209        struct rcu_head *head = addr;
 210
 211        switch (state) {
 212        case ODEBUG_STATE_ACTIVE:
 213                /*
 214                 * Ensure that queued callbacks are all executed.
 215                 * If we detect that we are nested in a RCU read-side critical
 216                 * section, we should simply fail, otherwise we would deadlock.
 217                 * Note that the machinery to reliably determine whether
 218                 * or not we are in an RCU read-side critical section
 219                 * exists only in the preemptible RCU implementations
 220                 * (TINY_PREEMPT_RCU and TREE_PREEMPT_RCU), which is why
 221                 * DEBUG_OBJECTS_RCU_HEAD is disallowed if !PREEMPT.
 222                 */
 223                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 224                    irqs_disabled()) {
 225                        WARN_ON(1);
 226                        return 0;
 227                }
 228                rcu_barrier();
 229                rcu_barrier_sched();
 230                rcu_barrier_bh();
 231                debug_object_free(head, &rcuhead_debug_descr);
 232                return 1;
 233        default:
 234                return 0;
 235        }
 236}
 237
 238/**
 239 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 240 * @head: pointer to rcu_head structure to be initialized
 241 *
 242 * This function informs debugobjects of a new rcu_head structure that
 243 * has been allocated as an auto variable on the stack.  This function
 244 * is not required for rcu_head structures that are statically defined or
 245 * that are dynamically allocated on the heap.  This function has no
 246 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 247 */
 248void init_rcu_head_on_stack(struct rcu_head *head)
 249{
 250        debug_object_init_on_stack(head, &rcuhead_debug_descr);
 251}
 252EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 253
 254/**
 255 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 256 * @head: pointer to rcu_head structure to be initialized
 257 *
 258 * This function informs debugobjects that an on-stack rcu_head structure
 259 * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 260 * function is not required for rcu_head structures that are statically
 261 * defined or that are dynamically allocated on the heap.  Also as with
 262 * init_rcu_head_on_stack(), this function has no effect for
 263 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 264 */
 265void destroy_rcu_head_on_stack(struct rcu_head *head)
 266{
 267        debug_object_free(head, &rcuhead_debug_descr);
 268}
 269EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 270
 271struct debug_obj_descr rcuhead_debug_descr = {
 272        .name = "rcu_head",
 273        .fixup_init = rcuhead_fixup_init,
 274        .fixup_activate = rcuhead_fixup_activate,
 275        .fixup_free = rcuhead_fixup_free,
 276};
 277EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 278#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 279