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#include <linux/delay.h>
  49#include <linux/module.h>
  50
  51#define CREATE_TRACE_POINTS
  52#include <trace/events/rcu.h>
  53
  54#include "rcu.h"
  55
  56module_param(rcu_expedited, int, 0);
  57
  58#ifdef CONFIG_PREEMPT_RCU
  59
  60/*
  61 * Preemptible RCU implementation for rcu_read_lock().
  62 * Just increment ->rcu_read_lock_nesting, shared state will be updated
  63 * if we block.
  64 */
  65void __rcu_read_lock(void)
  66{
  67        current->rcu_read_lock_nesting++;
  68        barrier();  /* critical section after entry code. */
  69}
  70EXPORT_SYMBOL_GPL(__rcu_read_lock);
  71
  72/*
  73 * Preemptible RCU implementation for rcu_read_unlock().
  74 * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
  75 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
  76 * invoke rcu_read_unlock_special() to clean up after a context switch
  77 * in an RCU read-side critical section and other special cases.
  78 */
  79void __rcu_read_unlock(void)
  80{
  81        struct task_struct *t = current;
  82
  83        if (t->rcu_read_lock_nesting != 1) {
  84                --t->rcu_read_lock_nesting;
  85        } else {
  86                barrier();  /* critical section before exit code. */
  87                t->rcu_read_lock_nesting = INT_MIN;
  88#ifdef CONFIG_PROVE_RCU_DELAY
  89                udelay(10); /* Make preemption more probable. */
  90#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
  91                barrier();  /* assign before ->rcu_read_unlock_special load */
  92                if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
  93                        rcu_read_unlock_special(t);
  94                barrier();  /* ->rcu_read_unlock_special load before assign */
  95                t->rcu_read_lock_nesting = 0;
  96        }
  97#ifdef CONFIG_PROVE_LOCKING
  98        {
  99                int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
 100
 101                WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
 102        }
 103#endif /* #ifdef CONFIG_PROVE_LOCKING */
 104}
 105EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 106
 107/*
 108 * Check for a task exiting while in a preemptible-RCU read-side
 109 * critical section, clean up if so.  No need to issue warnings,
 110 * as debug_check_no_locks_held() already does this if lockdep
 111 * is enabled.
 112 */
 113void exit_rcu(void)
 114{
 115        struct task_struct *t = current;
 116
 117        if (likely(list_empty(&current->rcu_node_entry)))
 118                return;
 119        t->rcu_read_lock_nesting = 1;
 120        barrier();
 121        t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
 122        __rcu_read_unlock();
 123}
 124
 125#else /* #ifdef CONFIG_PREEMPT_RCU */
 126
 127void exit_rcu(void)
 128{
 129}
 130
 131#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 132
 133#ifdef CONFIG_DEBUG_LOCK_ALLOC
 134static struct lock_class_key rcu_lock_key;
 135struct lockdep_map rcu_lock_map =
 136        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
 137EXPORT_SYMBOL_GPL(rcu_lock_map);
 138
 139static struct lock_class_key rcu_bh_lock_key;
 140struct lockdep_map rcu_bh_lock_map =
 141        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
 142EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
 143
 144static struct lock_class_key rcu_sched_lock_key;
 145struct lockdep_map rcu_sched_lock_map =
 146        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
 147EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
 148#endif
 149
 150#ifdef CONFIG_DEBUG_LOCK_ALLOC
 151
 152int debug_lockdep_rcu_enabled(void)
 153{
 154        return rcu_scheduler_active && debug_locks &&
 155               current->lockdep_recursion == 0;
 156}
 157EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
 158
 159/**
 160 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
 161 *
 162 * Check for bottom half being disabled, which covers both the
 163 * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
 164 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
 165 * will show the situation.  This is useful for debug checks in functions
 166 * that require that they be called within an RCU read-side critical
 167 * section.
 168 *
 169 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
 170 *
 171 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
 172 * offline from an RCU perspective, so check for those as well.
 173 */
 174int rcu_read_lock_bh_held(void)
 175{
 176        if (!debug_lockdep_rcu_enabled())
 177                return 1;
 178        if (rcu_is_cpu_idle())
 179                return 0;
 180        if (!rcu_lockdep_current_cpu_online())
 181                return 0;
 182        return in_softirq() || irqs_disabled();
 183}
 184EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 185
 186#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 187
 188struct rcu_synchronize {
 189        struct rcu_head head;
 190        struct completion completion;
 191};
 192
 193/*
 194 * Awaken the corresponding synchronize_rcu() instance now that a
 195 * grace period has elapsed.
 196 */
 197static void wakeme_after_rcu(struct rcu_head  *head)
 198{
 199        struct rcu_synchronize *rcu;
 200
 201        rcu = container_of(head, struct rcu_synchronize, head);
 202        complete(&rcu->completion);
 203}
 204
 205void wait_rcu_gp(call_rcu_func_t crf)
 206{
 207        struct rcu_synchronize rcu;
 208
 209        init_rcu_head_on_stack(&rcu.head);
 210        init_completion(&rcu.completion);
 211        /* Will wake me after RCU finished. */
 212        crf(&rcu.head, wakeme_after_rcu);
 213        /* Wait for it. */
 214        wait_for_completion(&rcu.completion);
 215        destroy_rcu_head_on_stack(&rcu.head);
 216}
 217EXPORT_SYMBOL_GPL(wait_rcu_gp);
 218
 219#ifdef CONFIG_PROVE_RCU
 220/*
 221 * wrapper function to avoid #include problems.
 222 */
 223int rcu_my_thread_group_empty(void)
 224{
 225        return thread_group_empty(current);
 226}
 227EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 228#endif /* #ifdef CONFIG_PROVE_RCU */
 229
 230#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 231static inline void debug_init_rcu_head(struct rcu_head *head)
 232{
 233        debug_object_init(head, &rcuhead_debug_descr);
 234}
 235
 236static inline void debug_rcu_head_free(struct rcu_head *head)
 237{
 238        debug_object_free(head, &rcuhead_debug_descr);
 239}
 240
 241/*
 242 * fixup_init is called when:
 243 * - an active object is initialized
 244 */
 245static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
 246{
 247        struct rcu_head *head = addr;
 248
 249        switch (state) {
 250        case ODEBUG_STATE_ACTIVE:
 251                /*
 252                 * Ensure that queued callbacks are all executed.
 253                 * If we detect that we are nested in a RCU read-side critical
 254                 * section, we should simply fail, otherwise we would deadlock.
 255                 * In !PREEMPT configurations, there is no way to tell if we are
 256                 * in a RCU read-side critical section or not, so we never
 257                 * attempt any fixup and just print a warning.
 258                 */
 259#ifndef CONFIG_PREEMPT
 260                WARN_ON_ONCE(1);
 261                return 0;
 262#endif
 263                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 264                    irqs_disabled()) {
 265                        WARN_ON_ONCE(1);
 266                        return 0;
 267                }
 268                rcu_barrier();
 269                rcu_barrier_sched();
 270                rcu_barrier_bh();
 271                debug_object_init(head, &rcuhead_debug_descr);
 272                return 1;
 273        default:
 274                return 0;
 275        }
 276}
 277
 278/*
 279 * fixup_activate is called when:
 280 * - an active object is activated
 281 * - an unknown object is activated (might be a statically initialized object)
 282 * Activation is performed internally by call_rcu().
 283 */
 284static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 285{
 286        struct rcu_head *head = addr;
 287
 288        switch (state) {
 289
 290        case ODEBUG_STATE_NOTAVAILABLE:
 291                /*
 292                 * This is not really a fixup. We just make sure that it is
 293                 * tracked in the object tracker.
 294                 */
 295                debug_object_init(head, &rcuhead_debug_descr);
 296                debug_object_activate(head, &rcuhead_debug_descr);
 297                return 0;
 298
 299        case ODEBUG_STATE_ACTIVE:
 300                /*
 301                 * Ensure that queued callbacks are all executed.
 302                 * If we detect that we are nested in a RCU read-side critical
 303                 * section, we should simply fail, otherwise we would deadlock.
 304                 * In !PREEMPT configurations, there is no way to tell if we are
 305                 * in a RCU read-side critical section or not, so we never
 306                 * attempt any fixup and just print a warning.
 307                 */
 308#ifndef CONFIG_PREEMPT
 309                WARN_ON_ONCE(1);
 310                return 0;
 311#endif
 312                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 313                    irqs_disabled()) {
 314                        WARN_ON_ONCE(1);
 315                        return 0;
 316                }
 317                rcu_barrier();
 318                rcu_barrier_sched();
 319                rcu_barrier_bh();
 320                debug_object_activate(head, &rcuhead_debug_descr);
 321                return 1;
 322        default:
 323                return 0;
 324        }
 325}
 326
 327/*
 328 * fixup_free is called when:
 329 * - an active object is freed
 330 */
 331static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 332{
 333        struct rcu_head *head = addr;
 334
 335        switch (state) {
 336        case ODEBUG_STATE_ACTIVE:
 337                /*
 338                 * Ensure that queued callbacks are all executed.
 339                 * If we detect that we are nested in a RCU read-side critical
 340                 * section, we should simply fail, otherwise we would deadlock.
 341                 * In !PREEMPT configurations, there is no way to tell if we are
 342                 * in a RCU read-side critical section or not, so we never
 343                 * attempt any fixup and just print a warning.
 344                 */
 345#ifndef CONFIG_PREEMPT
 346                WARN_ON_ONCE(1);
 347                return 0;
 348#endif
 349                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 350                    irqs_disabled()) {
 351                        WARN_ON_ONCE(1);
 352                        return 0;
 353                }
 354                rcu_barrier();
 355                rcu_barrier_sched();
 356                rcu_barrier_bh();
 357                debug_object_free(head, &rcuhead_debug_descr);
 358                return 1;
 359        default:
 360                return 0;
 361        }
 362}
 363
 364/**
 365 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 366 * @head: pointer to rcu_head structure to be initialized
 367 *
 368 * This function informs debugobjects of a new rcu_head structure that
 369 * has been allocated as an auto variable on the stack.  This function
 370 * is not required for rcu_head structures that are statically defined or
 371 * that are dynamically allocated on the heap.  This function has no
 372 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 373 */
 374void init_rcu_head_on_stack(struct rcu_head *head)
 375{
 376        debug_object_init_on_stack(head, &rcuhead_debug_descr);
 377}
 378EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 379
 380/**
 381 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 382 * @head: pointer to rcu_head structure to be initialized
 383 *
 384 * This function informs debugobjects that an on-stack rcu_head structure
 385 * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 386 * function is not required for rcu_head structures that are statically
 387 * defined or that are dynamically allocated on the heap.  Also as with
 388 * init_rcu_head_on_stack(), this function has no effect for
 389 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 390 */
 391void destroy_rcu_head_on_stack(struct rcu_head *head)
 392{
 393        debug_object_free(head, &rcuhead_debug_descr);
 394}
 395EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 396
 397struct debug_obj_descr rcuhead_debug_descr = {
 398        .name = "rcu_head",
 399        .fixup_init = rcuhead_fixup_init,
 400        .fixup_activate = rcuhead_fixup_activate,
 401        .fixup_free = rcuhead_fixup_free,
 402};
 403EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 404#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 405
 406#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
 407void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
 408{
 409        trace_rcu_torture_read(rcutorturename, rhp);
 410}
 411EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 412#else
 413#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
 414#endif
 415
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