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