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 <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
  50#define CREATE_TRACE_POINTS
  51#include <trace/events/rcu.h>
  52
  53#include "rcu.h"
  54
  55#ifdef CONFIG_PREEMPT_RCU
  56
  57/*
  58 * Preemptible RCU implementation for rcu_read_lock().
  59 * Just increment ->rcu_read_lock_nesting, shared state will be updated
  60 * if we block.
  61 */
  62void __rcu_read_lock(void)
  63{
  64        current->rcu_read_lock_nesting++;
  65        barrier();  /* critical section after entry code. */
  66}
  67EXPORT_SYMBOL_GPL(__rcu_read_lock);
  68
  69/*
  70 * Preemptible RCU implementation for rcu_read_unlock().
  71 * Decrement ->rcu_read_lock_nesting.  If the result is zero (outermost
  72 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
  73 * invoke rcu_read_unlock_special() to clean up after a context switch
  74 * in an RCU read-side critical section and other special cases.
  75 */
  76void __rcu_read_unlock(void)
  77{
  78        struct task_struct *t = current;
  79
  80        if (t->rcu_read_lock_nesting != 1) {
  81                --t->rcu_read_lock_nesting;
  82        } else {
  83                barrier();  /* critical section before exit code. */
  84                t->rcu_read_lock_nesting = INT_MIN;
  85#ifdef CONFIG_PROVE_RCU_DELAY
  86                udelay(10); /* Make preemption more probable. */
  87#endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
  88                barrier();  /* assign before ->rcu_read_unlock_special load */
  89                if (unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
  90                        rcu_read_unlock_special(t);
  91                barrier();  /* ->rcu_read_unlock_special load before assign */
  92                t->rcu_read_lock_nesting = 0;
  93        }
  94#ifdef CONFIG_PROVE_LOCKING
  95        {
  96                int rrln = ACCESS_ONCE(t->rcu_read_lock_nesting);
  97
  98                WARN_ON_ONCE(rrln < 0 && rrln > INT_MIN / 2);
  99        }
 100#endif /* #ifdef CONFIG_PROVE_LOCKING */
 101}
 102EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 103
 104/*
 105 * Check for a task exiting while in a preemptible-RCU read-side
 106 * critical section, clean up if so.  No need to issue warnings,
 107 * as debug_check_no_locks_held() already does this if lockdep
 108 * is enabled.
 109 */
 110void exit_rcu(void)
 111{
 112        struct task_struct *t = current;
 113
 114        if (likely(list_empty(&current->rcu_node_entry)))
 115                return;
 116        t->rcu_read_lock_nesting = 1;
 117        barrier();
 118        t->rcu_read_unlock_special = RCU_READ_UNLOCK_BLOCKED;
 119        __rcu_read_unlock();
 120}
 121
 122#else /* #ifdef CONFIG_PREEMPT_RCU */
 123
 124void exit_rcu(void)
 125{
 126}
 127
 128#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
 129
 130#ifdef CONFIG_DEBUG_LOCK_ALLOC
 131static struct lock_class_key rcu_lock_key;
 132struct lockdep_map rcu_lock_map =
 133        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
 134EXPORT_SYMBOL_GPL(rcu_lock_map);
 135
 136static struct lock_class_key rcu_bh_lock_key;
 137struct lockdep_map rcu_bh_lock_map =
 138        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_bh", &rcu_bh_lock_key);
 139EXPORT_SYMBOL_GPL(rcu_bh_lock_map);
 140
 141static struct lock_class_key rcu_sched_lock_key;
 142struct lockdep_map rcu_sched_lock_map =
 143        STATIC_LOCKDEP_MAP_INIT("rcu_read_lock_sched", &rcu_sched_lock_key);
 144EXPORT_SYMBOL_GPL(rcu_sched_lock_map);
 145#endif
 146
 147#ifdef CONFIG_DEBUG_LOCK_ALLOC
 148
 149int debug_lockdep_rcu_enabled(void)
 150{
 151        return rcu_scheduler_active && debug_locks &&
 152               current->lockdep_recursion == 0;
 153}
 154EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
 155
 156/**
 157 * rcu_read_lock_bh_held() - might we be in RCU-bh read-side critical section?
 158 *
 159 * Check for bottom half being disabled, which covers both the
 160 * CONFIG_PROVE_RCU and not cases.  Note that if someone uses
 161 * rcu_read_lock_bh(), but then later enables BH, lockdep (if enabled)
 162 * will show the situation.  This is useful for debug checks in functions
 163 * that require that they be called within an RCU read-side critical
 164 * section.
 165 *
 166 * Check debug_lockdep_rcu_enabled() to prevent false positives during boot.
 167 *
 168 * Note that rcu_read_lock() is disallowed if the CPU is either idle or
 169 * offline from an RCU perspective, so check for those as well.
 170 */
 171int rcu_read_lock_bh_held(void)
 172{
 173        if (!debug_lockdep_rcu_enabled())
 174                return 1;
 175        if (rcu_is_cpu_idle())
 176                return 0;
 177        if (!rcu_lockdep_current_cpu_online())
 178                return 0;
 179        return in_softirq() || irqs_disabled();
 180}
 181EXPORT_SYMBOL_GPL(rcu_read_lock_bh_held);
 182
 183#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
 184
 185struct rcu_synchronize {
 186        struct rcu_head head;
 187        struct completion completion;
 188};
 189
 190/*
 191 * Awaken the corresponding synchronize_rcu() instance now that a
 192 * grace period has elapsed.
 193 */
 194static void wakeme_after_rcu(struct rcu_head  *head)
 195{
 196        struct rcu_synchronize *rcu;
 197
 198        rcu = container_of(head, struct rcu_synchronize, head);
 199        complete(&rcu->completion);
 200}
 201
 202void wait_rcu_gp(call_rcu_func_t crf)
 203{
 204        struct rcu_synchronize rcu;
 205
 206        init_rcu_head_on_stack(&rcu.head);
 207        init_completion(&rcu.completion);
 208        /* Will wake me after RCU finished. */
 209        crf(&rcu.head, wakeme_after_rcu);
 210        /* Wait for it. */
 211        wait_for_completion(&rcu.completion);
 212        destroy_rcu_head_on_stack(&rcu.head);
 213}
 214EXPORT_SYMBOL_GPL(wait_rcu_gp);
 215
 216#ifdef CONFIG_PROVE_RCU
 217/*
 218 * wrapper function to avoid #include problems.
 219 */
 220int rcu_my_thread_group_empty(void)
 221{
 222        return thread_group_empty(current);
 223}
 224EXPORT_SYMBOL_GPL(rcu_my_thread_group_empty);
 225#endif /* #ifdef CONFIG_PROVE_RCU */
 226
 227#ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD
 228static inline void debug_init_rcu_head(struct rcu_head *head)
 229{
 230        debug_object_init(head, &rcuhead_debug_descr);
 231}
 232
 233static inline void debug_rcu_head_free(struct rcu_head *head)
 234{
 235        debug_object_free(head, &rcuhead_debug_descr);
 236}
 237
 238/*
 239 * fixup_init is called when:
 240 * - an active object is initialized
 241 */
 242static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
 243{
 244        struct rcu_head *head = addr;
 245
 246        switch (state) {
 247        case ODEBUG_STATE_ACTIVE:
 248                /*
 249                 * Ensure that queued callbacks are all executed.
 250                 * If we detect that we are nested in a RCU read-side critical
 251                 * section, we should simply fail, otherwise we would deadlock.
 252                 * In !PREEMPT configurations, there is no way to tell if we are
 253                 * in a RCU read-side critical section or not, so we never
 254                 * attempt any fixup and just print a warning.
 255                 */
 256#ifndef CONFIG_PREEMPT
 257                WARN_ON_ONCE(1);
 258                return 0;
 259#endif
 260                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 261                    irqs_disabled()) {
 262                        WARN_ON_ONCE(1);
 263                        return 0;
 264                }
 265                rcu_barrier();
 266                rcu_barrier_sched();
 267                rcu_barrier_bh();
 268                debug_object_init(head, &rcuhead_debug_descr);
 269                return 1;
 270        default:
 271                return 0;
 272        }
 273}
 274
 275/*
 276 * fixup_activate is called when:
 277 * - an active object is activated
 278 * - an unknown object is activated (might be a statically initialized object)
 279 * Activation is performed internally by call_rcu().
 280 */
 281static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
 282{
 283        struct rcu_head *head = addr;
 284
 285        switch (state) {
 286
 287        case ODEBUG_STATE_NOTAVAILABLE:
 288                /*
 289                 * This is not really a fixup. We just make sure that it is
 290                 * tracked in the object tracker.
 291                 */
 292                debug_object_init(head, &rcuhead_debug_descr);
 293                debug_object_activate(head, &rcuhead_debug_descr);
 294                return 0;
 295
 296        case ODEBUG_STATE_ACTIVE:
 297                /*
 298                 * Ensure that queued callbacks are all executed.
 299                 * If we detect that we are nested in a RCU read-side critical
 300                 * section, we should simply fail, otherwise we would deadlock.
 301                 * In !PREEMPT configurations, there is no way to tell if we are
 302                 * in a RCU read-side critical section or not, so we never
 303                 * attempt any fixup and just print a warning.
 304                 */
 305#ifndef CONFIG_PREEMPT
 306                WARN_ON_ONCE(1);
 307                return 0;
 308#endif
 309                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 310                    irqs_disabled()) {
 311                        WARN_ON_ONCE(1);
 312                        return 0;
 313                }
 314                rcu_barrier();
 315                rcu_barrier_sched();
 316                rcu_barrier_bh();
 317                debug_object_activate(head, &rcuhead_debug_descr);
 318                return 1;
 319        default:
 320                return 0;
 321        }
 322}
 323
 324/*
 325 * fixup_free is called when:
 326 * - an active object is freed
 327 */
 328static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
 329{
 330        struct rcu_head *head = addr;
 331
 332        switch (state) {
 333        case ODEBUG_STATE_ACTIVE:
 334                /*
 335                 * Ensure that queued callbacks are all executed.
 336                 * If we detect that we are nested in a RCU read-side critical
 337                 * section, we should simply fail, otherwise we would deadlock.
 338                 * In !PREEMPT configurations, there is no way to tell if we are
 339                 * in a RCU read-side critical section or not, so we never
 340                 * attempt any fixup and just print a warning.
 341                 */
 342#ifndef CONFIG_PREEMPT
 343                WARN_ON_ONCE(1);
 344                return 0;
 345#endif
 346                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
 347                    irqs_disabled()) {
 348                        WARN_ON_ONCE(1);
 349                        return 0;
 350                }
 351                rcu_barrier();
 352                rcu_barrier_sched();
 353                rcu_barrier_bh();
 354                debug_object_free(head, &rcuhead_debug_descr);
 355                return 1;
 356        default:
 357                return 0;
 358        }
 359}
 360
 361/**
 362 * init_rcu_head_on_stack() - initialize on-stack rcu_head for debugobjects
 363 * @head: pointer to rcu_head structure to be initialized
 364 *
 365 * This function informs debugobjects of a new rcu_head structure that
 366 * has been allocated as an auto variable on the stack.  This function
 367 * is not required for rcu_head structures that are statically defined or
 368 * that are dynamically allocated on the heap.  This function has no
 369 * effect for !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 370 */
 371void init_rcu_head_on_stack(struct rcu_head *head)
 372{
 373        debug_object_init_on_stack(head, &rcuhead_debug_descr);
 374}
 375EXPORT_SYMBOL_GPL(init_rcu_head_on_stack);
 376
 377/**
 378 * destroy_rcu_head_on_stack() - destroy on-stack rcu_head for debugobjects
 379 * @head: pointer to rcu_head structure to be initialized
 380 *
 381 * This function informs debugobjects that an on-stack rcu_head structure
 382 * is about to go out of scope.  As with init_rcu_head_on_stack(), this
 383 * function is not required for rcu_head structures that are statically
 384 * defined or that are dynamically allocated on the heap.  Also as with
 385 * init_rcu_head_on_stack(), this function has no effect for
 386 * !CONFIG_DEBUG_OBJECTS_RCU_HEAD kernel builds.
 387 */
 388void destroy_rcu_head_on_stack(struct rcu_head *head)
 389{
 390        debug_object_free(head, &rcuhead_debug_descr);
 391}
 392EXPORT_SYMBOL_GPL(destroy_rcu_head_on_stack);
 393
 394struct debug_obj_descr rcuhead_debug_descr = {
 395        .name = "rcu_head",
 396        .fixup_init = rcuhead_fixup_init,
 397        .fixup_activate = rcuhead_fixup_activate,
 398        .fixup_free = rcuhead_fixup_free,
 399};
 400EXPORT_SYMBOL_GPL(rcuhead_debug_descr);
 401#endif /* #ifdef CONFIG_DEBUG_OBJECTS_RCU_HEAD */
 402
 403#if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) || defined(CONFIG_RCU_TRACE)
 404void do_trace_rcu_torture_read(char *rcutorturename, struct rcu_head *rhp)
 405{
 406        trace_rcu_torture_read(rcutorturename, rhp);
 407}
 408EXPORT_SYMBOL_GPL(do_trace_rcu_torture_read);
 409#else
 410#define do_trace_rcu_torture_read(rcutorturename, rhp) do { } while (0)
 411#endif
 412
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.