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_PREEMPT_RCU
  55
  56/*
  57 * Check for a task exiting while in a preemptible-RCU read-side
  58 * critical section, clean up if so.  No need to issue warnings,
  59 * as debug_check_no_locks_held() already does this if lockdep
  60 * is enabled.
  61 */
  62void exit_rcu(void)
  63{
  64        struct task_struct *t = current;
  65
  66        if (likely(list_empty(&current->rcu_node_entry)))
  67                return;
  68        t->rcu_read_lock_nesting = 1;
  69        barrier();
  70        t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
  71        __rcu_read_unlock();
  72}
  73
  74#else /* #ifdef CONFIG_PREEMPT_RCU */
  75
  76void exit_rcu(void)
  77{
  78}
  79
  80#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
  81
  82#ifdef CONFIG_DEBUG_LOCK_ALLOC
  83static struct lock_class_key rcu_lock_key;
  84struct lockdep_map rcu_lock_map =
  85        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
  86EXPORT_SYMBOL_GPL(rcu_lock_map);
  87
  88static struct lock_class_key rcu_bh_lock_key;
  89struct lockdep_map rcu_bh_lock_map =
  90        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
  91EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
  92
  93static struct lock_class_key rcu_sched_lock_key;
  94struct lockdep_map rcu_sched_lock_map =
  95        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
  96EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
  97#endif
  98
  99#ifdef CONFIG_DEBUG_LOCK_ALLOC
 100
 101int debug_lockdep_rcu_enabled(void)
 102{
 103        return rcu_scheduler_active && debug_locks &&
 104               current->lockdep_recursion == 0;
 105}
 106EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
 107
 108/**
 109 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
 110 *
 111 * Check for bottom half being disabled, which covers both the
 112 * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
 113 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
 114 * will show the situation.  This is useful for debug checks in functions
 115 * that require that they be called within an RCU read-side critical
 116 * section.
 117 *
 118 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
 119 *
 120 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
 121 * offline from an RCU perspective, so check for those as well.
 122 */
 123int rcu_read_lock_bh_held(void)
 124{
 125        if (!debug_lockdep_rcu_enabled())
 126                return 1;
 127        if (rcu_is_cpu_idle())
 128                return 0;
 129        if (!rcu_lockdep_current_cpu_online())
 130                return 0;
 131        return in_softirq() || irqs_disabled();
 132}
 133EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 134
 135#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 136
 137struct rcu_synchronize {
 138        struct rcu_head head;
 139        struct completion completion;
 140};
 141
 142/*
 143 * Awaken the corresponding synchronize_rcu() instance now that a
 144 * grace period has elapsed.
 145 */
 146static void wakeme_after_rcu(struct rcu_head  *head)
 147{
 148        struct rcu_synchronize *rcu;
 149
 150        rcu = container_of(head, struct rcu_synchronize, head);
 151        complete(&rcu->completion);
 152}
 153
 154void wait_rcu_gp(call_rcu_func_t crf)
 155{
 156        struct rcu_synchronize rcu;
 157
 158        init_rcu_head_on_stack(&rcu.head);
 159        init_completion(&rcu.completion);
 160        /* Will wake me after RCU finished. */
 161        crf(&rcu.head, wakeme_after_rcu);
 162        /* Wait for it. */
 163        wait_for_completion(&rcu.completion);
 164        destroy_rcu_head_on_stack(&rcu.head);
 165}
 166EXPORT_SYMBOL_GPL(wait_rcu_gp);
 167
 168#ifdef CONFIG_PROVE_RCU
 169/*
 170 * wrapper function to avoid #include problems.
 171 */
 172int rcu_my_thread_group_empty(void)
 173{
 174        return thread_group_empty(current);
 175}
 176EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 177#endif /* #ifdef CONFIG_PROVE_RCU */
 178
 179#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 180static inline void debug_init_rcu_head(struct rcu_head *head)
 181{
 182        debug_object_init(head, &rcuhead_debug_descr);
 183}
 184
 185static inline void debug_rcu_head_free(struct rcu_head *head)
 186{
 187        debug_object_free(head, &rcuhead_debug_descr);
 188}
 189
 190/*
 191 * fixup_init is called when:
 192 * - an active object is initialized
 193 */
 194static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
 195{
 196        struct rcu_head *head = addr;
 197
 198        switch (state) {
 199        case ODEBUG_STATE_ACTIVE:
 200                /*
 201                 * Ensure that queued callbacks are all executed.
 202                 * If we detect that we are nested in a RCU read-side critical
 203                 * section, we should simply fail, otherwise we would deadlock.
 204                 * In !PREEMPT configurations, there is no way to tell if we are
 205                 * in a RCU read-side critical section or not, so we never
 206                 * attempt any fixup and just print a warning.
 207                 */
 208#ifndef CONFIG_PREEMPT
 209                WARN_ON_ONCE(1);
 210                return 0;
 211#endif
 212                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 213                    irqs_disabled()) {
 214                        WARN_ON_ONCE(1);
 215                        return 0;
 216                }
 217                rcu_barrier();
 218                rcu_barrier_sched();
 219                rcu_barrier_bh();
 220                debug_object_init(head, &rcuhead_debug_descr);
 221                return 1;
 222        default:
 223                return 0;
 224        }
 225}
 226
 227/*
 228 * fixup_activate is called when:
 229 * - an active object is activated
 230 * - an unknown object is activated (might be a statically initialized object)
 231 * Activation is performed internally by call_rcu().
 232 */
 233static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 234{
 235        struct rcu_head *head = addr;
 236
 237        switch (state) {
 238
 239        case ODEBUG_STATE_NOTAVAILABLE:
 240                /*
 241                 * This is not really a fixup. We just make sure that it is
 242                 * tracked in the object tracker.
 243                 */
 244                debug_object_init(head, &rcuhead_debug_descr);
 245                debug_object_activate(head, &rcuhead_debug_descr);
 246                return 0;
 247
 248        case ODEBUG_STATE_ACTIVE:
 249                /*
 250                 * Ensure that queued callbacks are all executed.
 251                 * If we detect that we are nested in a RCU read-side critical
 252                 * section, we should simply fail, otherwise we would deadlock.
 253                 * In !PREEMPT configurations, there is no way to tell if we are
 254                 * in a RCU read-side critical section or not, so we never
 255                 * attempt any fixup and just print a warning.
 256                 */
 257#ifndef CONFIG_PREEMPT
 258                WARN_ON_ONCE(1);
 259                return 0;
 260#endif
 261                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 262                    irqs_disabled()) {
 263                        WARN_ON_ONCE(1);
 264                        return 0;
 265                }
 266                rcu_barrier();
 267                rcu_barrier_sched();
 268                rcu_barrier_bh();
 269                debug_object_activate(head, &rcuhead_debug_descr);
 270                return 1;
 271        default:
 272                return 0;
 273        }
 274}
 275
 276/*
 277 * fixup_free is called when:
 278 * - an active object is freed
 279 */
 280static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 281{
 282        struct rcu_head *head = addr;
 283
 284        switch (state) {
 285        case ODEBUG_STATE_ACTIVE:
 286                /*
 287                 * Ensure that queued callbacks are all executed.
 288                 * If we detect that we are nested in a RCU read-side critical
 289                 * section, we should simply fail, otherwise we would deadlock.
 290                 * In !PREEMPT configurations, there is no way to tell if we are
 291                 * in a RCU read-side critical section or not, so we never
 292                 * attempt any fixup and just print a warning.
 293                 */
 294#ifndef CONFIG_PREEMPT
 295                WARN_ON_ONCE(1);
 296                return 0;
 297#endif
 298                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 299                    irqs_disabled()) {
 300                        WARN_ON_ONCE(1);
 301                        return 0;
 302                }
 303                rcu_barrier();
 304                rcu_barrier_sched();
 305                rcu_barrier_bh();
 306                debug_object_free(head, &rcuhead_debug_descr);
 307                return 1;
 308        default:
 309                return 0;
 310        }
 311}
 312
 313/**
 314 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 315 * @head: pointer to rcu_head structure to be initialized
 316 *
 317 * This function informs debugobjects of a new rcu_head structure that
 318 * has been allocated as an auto variable on the stack.  This function
 319 * is not required for rcu_head structures that are statically defined or
 320 * that are dynamically allocated on the heap.  This function has no
 321 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 322 */
 323void init_rcu_head_on_stack(struct rcu_head *head)
 324{
 325        debug_object_init_on_stack(head, &rcuhead_debug_descr);
 326}
 327EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 328
 329/**
 330 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 331 * @head: pointer to rcu_head structure to be initialized
 332 *
 333 * This function informs debugobjects that an on-stack rcu_head structure
 334 * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 335 * function is not required for rcu_head structures that are statically
 336 * defined or that are dynamically allocated on the heap.  Also as with
 337 * init_rcu_head_on_stack(), this function has no effect for
 338 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 339 */
 340void destroy_rcu_head_on_stack(struct rcu_head *head)
 341{
 342        debug_object_free(head, &rcuhead_debug_descr);
 343}
 344EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 345
 346struct debug_obj_descr rcuhead_debug_descr = {
 347        .name = "rcu_head",
 348        .fixup_init = rcuhead_fixup_init,
 349        .fixup_activate = rcuhead_fixup_activate,
 350        .fixup_free = rcuhead_fixup_free,
 351};
 352EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 353#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 354
 355#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
 356void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
 357{
 358        trace_rcu_torture_read(rcutorturename, rhp);
 359}
 360EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 361#else
 362#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
 363#endif
 364
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