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#endif /* #ifdef CONFIG_PREEMPT_RCU */
 108
 109#ifdef CONFIG_DEBUG_LOCK_ALLOC
 110static struct lock_class_key rcu_lock_key;
 111struct lockdep_map rcu_lock_map =
 112        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
 113EXPORT_SYMBOL_GPL(rcu_lock_map);
 114
 115static struct lock_class_key rcu_bh_lock_key;
 116struct lockdep_map rcu_bh_lock_map =
 117        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
 118EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
 119
 120static struct lock_class_key rcu_sched_lock_key;
 121struct lockdep_map rcu_sched_lock_map =
 122        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
 123EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
 124
 125int debug_lockdep_rcu_enabled(void)
 126{
 127        return rcu_scheduler_active && debug_locks &&
 128               current->lockdep_recursion == 0;
 129}
 130EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
 131
 132/**
 133 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
 134 *
 135 * Check for bottom half being disabled, which covers both the
 136 * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
 137 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
 138 * will show the situation.  This is useful for debug checks in functions
 139 * that require that they be called within an RCU read-side critical
 140 * section.
 141 *
 142 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
 143 *
 144 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
 145 * offline from an RCU perspective, so check for those as well.
 146 */
 147int rcu_read_lock_bh_held(void)
 148{
 149        if (!debug_lockdep_rcu_enabled())
 150                return 1;
 151        if (rcu_is_cpu_idle())
 152                return 0;
 153        if (!rcu_lockdep_current_cpu_online())
 154                return 0;
 155        return in_softirq() || irqs_disabled();
 156}
 157EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 158
 159#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 160
 161struct rcu_synchronize {
 162        struct rcu_head head;
 163        struct completion completion;
 164};
 165
 166/*
 167 * Awaken the corresponding synchronize_rcu() instance now that a
 168 * grace period has elapsed.
 169 */
 170static void wakeme_after_rcu(struct rcu_head  *head)
 171{
 172        struct rcu_synchronize *rcu;
 173
 174        rcu = container_of(head, struct rcu_synchronize, head);
 175        complete(&rcu->completion);
 176}
 177
 178void wait_rcu_gp(call_rcu_func_t crf)
 179{
 180        struct rcu_synchronize rcu;
 181
 182        init_rcu_head_on_stack(&rcu.head);
 183        init_completion(&rcu.completion);
 184        /* Will wake me after RCU finished. */
 185        crf(&rcu.head, wakeme_after_rcu);
 186        /* Wait for it. */
 187        wait_for_completion(&rcu.completion);
 188        destroy_rcu_head_on_stack(&rcu.head);
 189}
 190EXPORT_SYMBOL_GPL(wait_rcu_gp);
 191
 192#ifdef CONFIG_PROVE_RCU
 193/*
 194 * wrapper function to avoid #include problems.
 195 */
 196int rcu_my_thread_group_empty(void)
 197{
 198        return thread_group_empty(current);
 199}
 200EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 201#endif /* #ifdef CONFIG_PROVE_RCU */
 202
 203#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 204static inline void debug_init_rcu_head(struct rcu_head *head)
 205{
 206        debug_object_init(head, &rcuhead_debug_descr);
 207}
 208
 209static inline void debug_rcu_head_free(struct rcu_head *head)
 210{
 211        debug_object_free(head, &rcuhead_debug_descr);
 212}
 213
 214/*
 215 * fixup_init is called when:
 216 * - an active object is initialized
 217 */
 218static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
 219{
 220        struct rcu_head *head = addr;
 221
 222        switch (state) {
 223        case ODEBUG_STATE_ACTIVE:
 224                /*
 225                 * Ensure that queued callbacks are all executed.
 226                 * If we detect that we are nested in a RCU read-side critical
 227                 * section, we should simply fail, otherwise we would deadlock.
 228                 * In !PREEMPT configurations, there is no way to tell if we are
 229                 * in a RCU read-side critical section or not, so we never
 230                 * attempt any fixup and just print a warning.
 231                 */
 232#ifndef CONFIG_PREEMPT
 233                WARN_ON_ONCE(1);
 234                return 0;
 235#endif
 236                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 237                    irqs_disabled()) {
 238                        WARN_ON_ONCE(1);
 239                        return 0;
 240                }
 241                rcu_barrier();
 242                rcu_barrier_sched();
 243                rcu_barrier_bh();
 244                debug_object_init(head, &rcuhead_debug_descr);
 245                return 1;
 246        default:
 247                return 0;
 248        }
 249}
 250
 251/*
 252 * fixup_activate is called when:
 253 * - an active object is activated
 254 * - an unknown object is activated (might be a statically initialized object)
 255 * Activation is performed internally by call_rcu().
 256 */
 257static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 258{
 259        struct rcu_head *head = addr;
 260
 261        switch (state) {
 262
 263        case ODEBUG_STATE_NOTAVAILABLE:
 264                /*
 265                 * This is not really a fixup. We just make sure that it is
 266                 * tracked in the object tracker.
 267                 */
 268                debug_object_init(head, &rcuhead_debug_descr);
 269                debug_object_activate(head, &rcuhead_debug_descr);
 270                return 0;
 271
 272        case ODEBUG_STATE_ACTIVE:
 273                /*
 274                 * Ensure that queued callbacks are all executed.
 275                 * If we detect that we are nested in a RCU read-side critical
 276                 * section, we should simply fail, otherwise we would deadlock.
 277                 * In !PREEMPT configurations, there is no way to tell if we are
 278                 * in a RCU read-side critical section or not, so we never
 279                 * attempt any fixup and just print a warning.
 280                 */
 281#ifndef CONFIG_PREEMPT
 282                WARN_ON_ONCE(1);
 283                return 0;
 284#endif
 285                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 286                    irqs_disabled()) {
 287                        WARN_ON_ONCE(1);
 288                        return 0;
 289                }
 290                rcu_barrier();
 291                rcu_barrier_sched();
 292                rcu_barrier_bh();
 293                debug_object_activate(head, &rcuhead_debug_descr);
 294                return 1;
 295        default:
 296                return 0;
 297        }
 298}
 299
 300/*
 301 * fixup_free is called when:
 302 * - an active object is freed
 303 */
 304static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 305{
 306        struct rcu_head *head = addr;
 307
 308        switch (state) {
 309        case ODEBUG_STATE_ACTIVE:
 310                /*
 311                 * Ensure that queued callbacks are all executed.
 312                 * If we detect that we are nested in a RCU read-side critical
 313                 * section, we should simply fail, otherwise we would deadlock.
 314                 * In !PREEMPT configurations, there is no way to tell if we are
 315                 * in a RCU read-side critical section or not, so we never
 316                 * attempt any fixup and just print a warning.
 317                 */
 318#ifndef CONFIG_PREEMPT
 319                WARN_ON_ONCE(1);
 320                return 0;
 321#endif
 322                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 323                    irqs_disabled()) {
 324                        WARN_ON_ONCE(1);
 325                        return 0;
 326                }
 327                rcu_barrier();
 328                rcu_barrier_sched();
 329                rcu_barrier_bh();
 330                debug_object_free(head, &rcuhead_debug_descr);
 331                return 1;
 332        default:
 333                return 0;
 334        }
 335}
 336
 337/**
 338 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 339 * @head: pointer to rcu_head structure to be initialized
 340 *
 341 * This function informs debugobjects of a new rcu_head structure that
 342 * has been allocated as an auto variable on the stack.  This function
 343 * is not required for rcu_head structures that are statically defined or
 344 * that are dynamically allocated on the heap.  This function has no
 345 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 346 */
 347void init_rcu_head_on_stack(struct rcu_head *head)
 348{
 349        debug_object_init_on_stack(head, &rcuhead_debug_descr);
 350}
 351EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 352
 353/**
 354 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 355 * @head: pointer to rcu_head structure to be initialized
 356 *
 357 * This function informs debugobjects that an on-stack rcu_head structure
 358 * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 359 * function is not required for rcu_head structures that are statically
 360 * defined or that are dynamically allocated on the heap.  Also as with
 361 * init_rcu_head_on_stack(), this function has no effect for
 362 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 363 */
 364void destroy_rcu_head_on_stack(struct rcu_head *head)
 365{
 366        debug_object_free(head, &rcuhead_debug_descr);
 367}
 368EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 369
 370struct debug_obj_descr rcuhead_debug_descr = {
 371        .name = "rcu_head",
 372        .fixup_init = rcuhead_fixup_init,
 373        .fixup_activate = rcuhead_fixup_activate,
 374        .fixup_free = rcuhead_fixup_free,
 375};
 376EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 377#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 378
 379#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
 380void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp,
 381                               unsigned long secs,
 382                               unsigned long c_old, unsigned long c)
 383{
 384        trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c);
 385}
 386EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 387#else
 388#define do_trace_rcu_torture_read(rcutorturename, rhp, secs, c_old, c) \
 389        do { } while (0)
 390#endif
 391
 392#ifdef CONFIG_RCU_STALL_COMMON
 393
 394#ifdef CONFIG_PROVE_RCU
 395#define RCU_STALL_DELAY_DELTA          (5 * HZ)
 396#else
 397#define RCU_STALL_DELAY_DELTA          0
 398#endif
 399
 400int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
 401int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
 402
 403module_param(rcu_cpu_stall_suppress, int, 0644);
 404module_param(rcu_cpu_stall_timeout, int, 0644);
 405
 406int rcu_jiffies_till_stall_check(void)
 407{
 408        int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
 409
 410        /*
 411         * Limit check must be consistent with the Kconfig limits
 412         * for CONFIG_RCU_CPU_STALL_TIMEOUT.
 413         */
 414        if (till_stall_check < 3) {
 415                ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
 416                till_stall_check = 3;
 417        } else if (till_stall_check > 300) {
 418                ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
 419                till_stall_check = 300;
 420        }
 421        return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
 422}
 423
 424static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
 425{
 426        rcu_cpu_stall_suppress = 1;
 427        return NOTIFY_DONE;
 428}
 429
 430static struct notifier_block rcu_panic_block = {
 431        .notifier_call = rcu_panic,
 432};
 433
 434static int __init check_cpu_stall_init(void)
 435{
 436        atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
 437        return 0;
 438}
 439early_initcall(check_cpu_stall_init);
 440
 441#endif /* #ifdef CONFIG_RCU_STALL_COMMON */
 442
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