src/urcu-bp.c

   1 /*
   2  * urcu-bp.c
   3  *
   4  * Userspace RCU library, "bulletproof" version.
   5  *
   6  * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
   7  * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
   8  *
   9  * This library is free software; you can redistribute it and/or
  10  * modify it under the terms of the GNU Lesser General Public
  11  * License as published by the Free Software Foundation; either
  12  * version 2.1 of the License, or (at your option) any later version.
  13  *
  14  * This library is distributed in the hope that it will be useful,
  15  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17  * Lesser General Public License for more details.
  18  *
  19  * You should have received a copy of the GNU Lesser General Public
  20  * License along with this library; if not, write to the Free Software
  21  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  22  *
  23  * IBM's contributions to this file may be relicensed under LGPLv2 or later.
  24  */
  25
  26 #define _LGPL_SOURCE
  27 #include <stdio.h>
  28 #include <pthread.h>
  29 #include <signal.h>
  30 #include <assert.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33 #include <errno.h>
  34 #include <poll.h>
  35 #include <unistd.h>
  36 #include <sys/mman.h>
  37
  38 #include "urcu/arch.h"
  39 #include "urcu/wfcqueue.h"
  40 #include "urcu/map/urcu-bp.h"
  41 #include "urcu/static/urcu-bp.h"
  42 #include "urcu-pointer.h"
  43 #include "urcu/tls-compat.h"
  44
  45 #include "urcu-die.h"
  46
  47 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
  48 #undef _LGPL_SOURCE
  49 #include "urcu-bp.h"
  50 #define _LGPL_SOURCE
  51
  52 #ifndef MAP_ANONYMOUS
  53 #define MAP_ANONYMOUS MAP_ANON
  54 #endif
  55
  56 #ifdef __linux__
  57 static
  58 void *mremap_wrapper(void *old_address, size_t old_size,
  59                 size_t new_size, int flags)
  60 {
  61         return mremap(old_address, old_size, new_size, flags);
  62 }
  63 #else
  64
  65 #define MREMAP_MAYMOVE  1
  66 #define MREMAP_FIXED    2
  67
  68 /*
  69  * mremap wrapper for non-Linux systems not allowing MAYMOVE.
  70  * This is not generic.
  71 */
  72 static
  73 void *mremap_wrapper(void *old_address, size_t old_size,
  74                 size_t new_size, int flags)
  75 {
  76         assert(!(flags & MREMAP_MAYMOVE));
  77
  78         return MAP_FAILED;
  79 }
  80 #endif
  81
  82 /* Sleep delay in ms */
  83 #define RCU_SLEEP_DELAY_MS      10
  84 #define INIT_NR_THREADS         8
  85 #define ARENA_INIT_ALLOC                \
  86         sizeof(struct registry_chunk)   \
  87         + INIT_NR_THREADS * sizeof(struct rcu_reader)
  88
  89 /*
  90  * Active attempts to check for reader Q.S. before calling sleep().
  91  */
  92 #define RCU_QS_ACTIVE_ATTEMPTS 100
  93
  94 static
  95 int rcu_bp_refcount;
  96
  97 /* If the headers do not support membarrier system call, fall back smp_mb. */
  98 #ifdef __NR_membarrier
  99 # define membarrier(...)                syscall(__NR_membarrier, __VA_ARGS__)
 100 #else
 101 # define membarrier(...)                -ENOSYS
 102 #endif
 103
 104 enum membarrier_cmd {
 105         MEMBARRIER_CMD_QUERY = 0,
 106         MEMBARRIER_CMD_SHARED = (1 << 0),
 107 };
 108
 109 static
 110 void __attribute__((constructor)) rcu_bp_init(void);
 111 static
 112 void __attribute__((destructor)) rcu_bp_exit(void);
 113
 114 int urcu_bp_has_sys_membarrier;
 115
 116 /*
 117  * rcu_gp_lock ensures mutual exclusion between threads calling
 118  * synchronize_rcu().
 119  */
 120 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
 121 /*
 122  * rcu_registry_lock ensures mutual exclusion between threads
 123  * registering and unregistering themselves to/from the registry, and
 124  * with threads reading that registry from synchronize_rcu(). However,
 125  * this lock is not held all the way through the completion of awaiting
 126  * for the grace period. It is sporadically released between iterations
 127  * on the registry.
 128  * rcu_registry_lock may nest inside rcu_gp_lock.
 129  */
 130 static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
 131
 132 static pthread_mutex_t init_lock = PTHREAD_MUTEX_INITIALIZER;
 133 static int initialized;
 134
 135 static pthread_key_t urcu_bp_key;
 136
 137 struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
 138
 139 /*
 140  * Pointer to registry elements. Written to only by each individual reader. Read
 141  * by both the reader and the writers.
 142  */
 143 DEFINE_URCU_TLS(struct rcu_reader *, rcu_reader);
 144
 145 static CDS_LIST_HEAD(registry);
 146
 147 struct registry_chunk {
 148         size_t data_len;                /* data length */
 149         size_t used;                    /* amount of data used */
 150         struct cds_list_head node;      /* chunk_list node */
 151         char data[];
 152 };
 153
 154 struct registry_arena {
 155         struct cds_list_head chunk_list;
 156 };
 157
 158 static struct registry_arena registry_arena = {
 159         .chunk_list = CDS_LIST_HEAD_INIT(registry_arena.chunk_list),
 160 };
 161
 162 /* Saved fork signal mask, protected by rcu_gp_lock */
 163 static sigset_t saved_fork_signal_mask;
 164
 165 static void mutex_lock(pthread_mutex_t *mutex)
 166 {
 167         int ret;
 168
 169 #ifndef DISTRUST_SIGNALS_EXTREME
 170         ret = pthread_mutex_lock(mutex);
 171         if (ret)
 172                 urcu_die(ret);
 173 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
 174         while ((ret = pthread_mutex_trylock(mutex)) != 0) {
 175                 if (ret != EBUSY && ret != EINTR)
 176                         urcu_die(ret);
 177                 poll(NULL,0,10);
 178         }
 179 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
 180 }
 181
 182 static void mutex_unlock(pthread_mutex_t *mutex)
 183 {
 184         int ret;
 185
 186         ret = pthread_mutex_unlock(mutex);
 187         if (ret)
 188                 urcu_die(ret);
 189 }
 190
 191 static void smp_mb_master(void)
 192 {
 193         if (caa_likely(urcu_bp_has_sys_membarrier))
 194                 (void) membarrier(MEMBARRIER_CMD_SHARED, 0);
 195         else
 196                 cmm_smp_mb();
 197 }
 198
 199 /*
 200  * Always called with rcu_registry lock held. Releases this lock between
 201  * iterations and grabs it again. Holds the lock when it returns.
 202  */
 203 static void wait_for_readers(struct cds_list_head *input_readers,
 204                         struct cds_list_head *cur_snap_readers,
 205                         struct cds_list_head *qsreaders)
 206 {
 207         unsigned int wait_loops = 0;
 208         struct rcu_reader *index, *tmp;
 209
 210         /*
 211          * Wait for each thread URCU_TLS(rcu_reader).ctr to either
 212          * indicate quiescence (not nested), or observe the current
 213          * rcu_gp.ctr value.
 214          */
 215         for (;;) {
 216                 if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
 217                         wait_loops++;
 218
 219                 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
 220                         switch (rcu_reader_state(&index->ctr)) {
 221                         case RCU_READER_ACTIVE_CURRENT:
 222                                 if (cur_snap_readers) {
 223                                         cds_list_move(&index->node,
 224                                                 cur_snap_readers);
 225                                         break;
 226                                 }
 227                                 /* Fall-through */
 228                         case RCU_READER_INACTIVE:
 229                                 cds_list_move(&index->node, qsreaders);
 230                                 break;
 231                         case RCU_READER_ACTIVE_OLD:
 232                                 /*
 233                                  * Old snapshot. Leaving node in
 234                                  * input_readers will make us busy-loop
 235                                  * until the snapshot becomes current or
 236                                  * the reader becomes inactive.
 237                                  */
 238                                 break;
 239                         }
 240                 }
 241
 242                 if (cds_list_empty(input_readers)) {
 243                         break;
 244                 } else {
 245                         /* Temporarily unlock the registry lock. */
 246                         mutex_unlock(&rcu_registry_lock);
 247                         if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
 248                                 (void) poll(NULL, 0, RCU_SLEEP_DELAY_MS);
 249                         else
 250                                 caa_cpu_relax();
 251                         /* Re-lock the registry lock before the next loop. */
 252                         mutex_lock(&rcu_registry_lock);
 253                 }
 254         }
 255 }
 256
 257 void synchronize_rcu(void)
 258 {
 259         CDS_LIST_HEAD(cur_snap_readers);
 260         CDS_LIST_HEAD(qsreaders);
 261         sigset_t newmask, oldmask;
 262         int ret;
 263
 264         ret = sigfillset(&newmask);
 265         assert(!ret);
 266         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 267         assert(!ret);
 268
 269         mutex_lock(&rcu_gp_lock);
 270
 271         mutex_lock(&rcu_registry_lock);
 272
 273         if (cds_list_empty(&registry))
 274                 goto out;
 275
 276         /* All threads should read qparity before accessing data structure
 277          * where new ptr points to. */
 278         /* Write new ptr before changing the qparity */
 279         smp_mb_master();
 280
 281         /*
 282          * Wait for readers to observe original parity or be quiescent.
 283          * wait_for_readers() can release and grab again rcu_registry_lock
 284          * interally.
 285          */
 286         wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
 287
 288         /*
 289          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 290          * model easier to understand. It does not have a big performance impact
 291          * anyway, given this is the write-side.
 292          */
 293         cmm_smp_mb();
 294
 295         /* Switch parity: 0 -> 1, 1 -> 0 */
 296         CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE);
 297
 298         /*
 299          * Must commit qparity update to memory before waiting for other parity
 300          * quiescent state. Failure to do so could result in the writer waiting
 301          * forever while new readers are always accessing data (no progress).
 302          * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
 303          */
 304
 305         /*
 306          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 307          * model easier to understand. It does not have a big performance impact
 308          * anyway, given this is the write-side.
 309          */
 310         cmm_smp_mb();
 311
 312         /*
 313          * Wait for readers to observe new parity or be quiescent.
 314          * wait_for_readers() can release and grab again rcu_registry_lock
 315          * interally.
 316          */
 317         wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
 318
 319         /*
 320          * Put quiescent reader list back into registry.
 321          */
 322         cds_list_splice(&qsreaders, &registry);
 323
 324         /*
 325          * Finish waiting for reader threads before letting the old ptr being
 326          * freed.
 327          */
 328         smp_mb_master();
 329 out:
 330         mutex_unlock(&rcu_registry_lock);
 331         mutex_unlock(&rcu_gp_lock);
 332         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 333         assert(!ret);
 334 }
 335
 336 /*
 337  * library wrappers to be used by non-LGPL compatible source code.
 338  */
 339
 340 void rcu_read_lock(void)
 341 {
 342         _rcu_read_lock();
 343 }
 344
 345 void rcu_read_unlock(void)
 346 {
 347         _rcu_read_unlock();
 348 }
 349
 350 int rcu_read_ongoing(void)
 351 {
 352         return _rcu_read_ongoing();
 353 }
 354
 355 /*
 356  * Only grow for now. If empty, allocate a ARENA_INIT_ALLOC sized chunk.
 357  * Else, try expanding the last chunk. If this fails, allocate a new
 358  * chunk twice as big as the last chunk.
 359  * Memory used by chunks _never_ moves. A chunk could theoretically be
 360  * freed when all "used" slots are released, but we don't do it at this
 361  * point.
 362  */
 363 static
 364 void expand_arena(struct registry_arena *arena)
 365 {
 366         struct registry_chunk *new_chunk, *last_chunk;
 367         size_t old_chunk_len, new_chunk_len;
 368
 369         /* No chunk. */
 370         if (cds_list_empty(&arena->chunk_list)) {
 371                 assert(ARENA_INIT_ALLOC >=
 372                         sizeof(struct registry_chunk)
 373                         + sizeof(struct rcu_reader));
 374                 new_chunk_len = ARENA_INIT_ALLOC;
 375                 new_chunk = mmap(NULL, new_chunk_len,
 376                         PROT_READ | PROT_WRITE,
 377                         MAP_ANONYMOUS | MAP_PRIVATE,
 378                         -1, 0);
 379                 if (new_chunk == MAP_FAILED)
 380                         abort();
 381                 memset(new_chunk, 0, new_chunk_len);
 382                 new_chunk->data_len =
 383                         new_chunk_len - sizeof(struct registry_chunk);
 384                 cds_list_add_tail(&new_chunk->node, &arena->chunk_list);
 385                 return;         /* We're done. */
 386         }
 387
 388         /* Try expanding last chunk. */
 389         last_chunk = cds_list_entry(arena->chunk_list.prev,
 390                 struct registry_chunk, node);
 391         old_chunk_len =
 392                 last_chunk->data_len + sizeof(struct registry_chunk);
 393         new_chunk_len = old_chunk_len << 1;
 394
 395         /* Don't allow memory mapping to move, just expand. */
 396         new_chunk = mremap_wrapper(last_chunk, old_chunk_len,
 397                 new_chunk_len, 0);
 398         if (new_chunk != MAP_FAILED) {
 399                 /* Should not have moved. */
 400                 assert(new_chunk == last_chunk);
 401                 memset((char *) last_chunk + old_chunk_len, 0,
 402                         new_chunk_len - old_chunk_len);
 403                 last_chunk->data_len =
 404                         new_chunk_len - sizeof(struct registry_chunk);
 405                 return;         /* We're done. */
 406         }
 407
 408         /* Remap did not succeed, we need to add a new chunk. */
 409         new_chunk = mmap(NULL, new_chunk_len,
 410                 PROT_READ | PROT_WRITE,
 411                 MAP_ANONYMOUS | MAP_PRIVATE,
 412                 -1, 0);
 413         if (new_chunk == MAP_FAILED)
 414                 abort();
 415         memset(new_chunk, 0, new_chunk_len);
 416         new_chunk->data_len =
 417                 new_chunk_len - sizeof(struct registry_chunk);
 418         cds_list_add_tail(&new_chunk->node, &arena->chunk_list);
 419 }
 420
 421 static
 422 struct rcu_reader *arena_alloc(struct registry_arena *arena)
 423 {
 424         struct registry_chunk *chunk;
 425         struct rcu_reader *rcu_reader_reg;
 426         int expand_done = 0;    /* Only allow to expand once per alloc */
 427         size_t len = sizeof(struct rcu_reader);
 428
 429 retry:
 430         cds_list_for_each_entry(chunk, &arena->chunk_list, node) {
 431                 if (chunk->data_len - chunk->used < len)
 432                         continue;
 433                 /* Find spot */
 434                 for (rcu_reader_reg = (struct rcu_reader *) &chunk->data[0];
 435                                 rcu_reader_reg < (struct rcu_reader *) &chunk->data[chunk->data_len];
 436                                 rcu_reader_reg++) {
 437                         if (!rcu_reader_reg->alloc) {
 438                                 rcu_reader_reg->alloc = 1;
 439                                 chunk->used += len;
 440                                 return rcu_reader_reg;
 441                         }
 442                 }
 443         }
 444
 445         if (!expand_done) {
 446                 expand_arena(arena);
 447                 expand_done = 1;
 448                 goto retry;
 449         }
 450
 451         return NULL;
 452 }
 453
 454 /* Called with signals off and mutex locked */
 455 static
 456 void add_thread(void)
 457 {
 458         struct rcu_reader *rcu_reader_reg;
 459         int ret;
 460
 461         rcu_reader_reg = arena_alloc(&registry_arena);
 462         if (!rcu_reader_reg)
 463                 abort();
 464         ret = pthread_setspecific(urcu_bp_key, rcu_reader_reg);
 465         if (ret)
 466                 abort();
 467
 468         /* Add to registry */
 469         rcu_reader_reg->tid = pthread_self();
 470         assert(rcu_reader_reg->ctr == 0);
 471         cds_list_add(&rcu_reader_reg->node, &registry);
 472         /*
 473          * Reader threads are pointing to the reader registry. This is
 474          * why its memory should never be relocated.
 475          */
 476         URCU_TLS(rcu_reader) = rcu_reader_reg;
 477 }
 478
 479 /* Called with mutex locked */
 480 static
 481 void cleanup_thread(struct registry_chunk *chunk,
 482                 struct rcu_reader *rcu_reader_reg)
 483 {
 484         rcu_reader_reg->ctr = 0;
 485         cds_list_del(&rcu_reader_reg->node);
 486         rcu_reader_reg->tid = 0;
 487         rcu_reader_reg->alloc = 0;
 488         chunk->used -= sizeof(struct rcu_reader);
 489 }
 490
 491 static
 492 struct registry_chunk *find_chunk(struct rcu_reader *rcu_reader_reg)
 493 {
 494         struct registry_chunk *chunk;
 495
 496         cds_list_for_each_entry(chunk, &registry_arena.chunk_list, node) {
 497                 if (rcu_reader_reg < (struct rcu_reader *) &chunk->data[0])
 498                         continue;
 499                 if (rcu_reader_reg >= (struct rcu_reader *) &chunk->data[chunk->data_len])
 500                         continue;
 501                 return chunk;
 502         }
 503         return NULL;
 504 }
 505
 506 /* Called with signals off and mutex locked */
 507 static
 508 void remove_thread(struct rcu_reader *rcu_reader_reg)
 509 {
 510         cleanup_thread(find_chunk(rcu_reader_reg), rcu_reader_reg);
 511         URCU_TLS(rcu_reader) = NULL;
 512 }
 513
 514 /* Disable signals, take mutex, add to registry */
 515 void rcu_bp_register(void)
 516 {
 517         sigset_t newmask, oldmask;
 518         int ret;
 519
 520         ret = sigfillset(&newmask);
 521         if (ret)
 522                 abort();
 523         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 524         if (ret)
 525                 abort();
 526
 527         /*
 528          * Check if a signal concurrently registered our thread since
 529          * the check in rcu_read_lock().
 530          */
 531         if (URCU_TLS(rcu_reader))
 532                 goto end;
 533
 534         /*
 535          * Take care of early registration before urcu_bp constructor.
 536          */
 537         rcu_bp_init();
 538
 539         mutex_lock(&rcu_registry_lock);
 540         add_thread();
 541         mutex_unlock(&rcu_registry_lock);
 542 end:
 543         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 544         if (ret)
 545                 abort();
 546 }
 547
 548 /* Disable signals, take mutex, remove from registry */
 549 static
 550 void rcu_bp_unregister(struct rcu_reader *rcu_reader_reg)
 551 {
 552         sigset_t newmask, oldmask;
 553         int ret;
 554
 555         ret = sigfillset(&newmask);
 556         if (ret)
 557                 abort();
 558         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 559         if (ret)
 560                 abort();
 561
 562         mutex_lock(&rcu_registry_lock);
 563         remove_thread(rcu_reader_reg);
 564         mutex_unlock(&rcu_registry_lock);
 565         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 566         if (ret)
 567                 abort();
 568         rcu_bp_exit();
 569 }
 570
 571 /*
 572  * Remove thread from the registry when it exits, and flag it as
 573  * destroyed so garbage collection can take care of it.
 574  */
 575 static
 576 void urcu_bp_thread_exit_notifier(void *rcu_key)
 577 {
 578         rcu_bp_unregister(rcu_key);
 579 }
 580
 581 static
 582 void rcu_bp_init(void)
 583 {
 584         mutex_lock(&init_lock);
 585         if (!rcu_bp_refcount++) {
 586                 int ret;
 587
 588                 ret = pthread_key_create(&urcu_bp_key,
 589                                 urcu_bp_thread_exit_notifier);
 590                 if (ret)
 591                         abort();
 592                 ret = membarrier(MEMBARRIER_CMD_QUERY, 0);
 593                 if (ret >= 0 && (ret & MEMBARRIER_CMD_SHARED)) {
 594                         urcu_bp_has_sys_membarrier = 1;
 595                 }
 596                 initialized = 1;
 597         }
 598         mutex_unlock(&init_lock);
 599 }
 600
 601 static
 602 void rcu_bp_exit(void)
 603 {
 604         mutex_lock(&init_lock);
 605         if (!--rcu_bp_refcount) {
 606                 struct registry_chunk *chunk, *tmp;
 607                 int ret;
 608
 609                 cds_list_for_each_entry_safe(chunk, tmp,
 610                                 &registry_arena.chunk_list, node) {
 611                         munmap(chunk, chunk->data_len
 612                                         + sizeof(struct registry_chunk));
 613                 }
 614                 CDS_INIT_LIST_HEAD(&registry_arena.chunk_list);
 615                 ret = pthread_key_delete(urcu_bp_key);
 616                 if (ret)
 617                         abort();
 618         }
 619         mutex_unlock(&init_lock);
 620 }
 621
 622 /*
 623  * Holding the rcu_gp_lock and rcu_registry_lock across fork will make
 624  * sure we fork() don't race with a concurrent thread executing with
 625  * any of those locks held. This ensures that the registry and data
 626  * protected by rcu_gp_lock are in a coherent state in the child.
 627  */
 628 void rcu_bp_before_fork(void)
 629 {
 630         sigset_t newmask, oldmask;
 631         int ret;
 632
 633         ret = sigfillset(&newmask);
 634         assert(!ret);
 635         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 636         assert(!ret);
 637         mutex_lock(&rcu_gp_lock);
 638         mutex_lock(&rcu_registry_lock);
 639         saved_fork_signal_mask = oldmask;
 640 }
 641
 642 void rcu_bp_after_fork_parent(void)
 643 {
 644         sigset_t oldmask;
 645         int ret;
 646
 647         oldmask = saved_fork_signal_mask;
 648         mutex_unlock(&rcu_registry_lock);
 649         mutex_unlock(&rcu_gp_lock);
 650         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 651         assert(!ret);
 652 }
 653
 654 /*
 655  * Prune all entries from registry except our own thread. Fits the Linux
 656  * fork behavior. Called with rcu_gp_lock and rcu_registry_lock held.
 657  */
 658 static
 659 void urcu_bp_prune_registry(void)
 660 {
 661         struct registry_chunk *chunk;
 662         struct rcu_reader *rcu_reader_reg;
 663
 664         cds_list_for_each_entry(chunk, &registry_arena.chunk_list, node) {
 665                 for (rcu_reader_reg = (struct rcu_reader *) &chunk->data[0];
 666                                 rcu_reader_reg < (struct rcu_reader *) &chunk->data[chunk->data_len];
 667                                 rcu_reader_reg++) {
 668                         if (!rcu_reader_reg->alloc)
 669                                 continue;
 670                         if (rcu_reader_reg->tid == pthread_self())
 671                                 continue;
 672                         cleanup_thread(chunk, rcu_reader_reg);
 673                 }
 674         }
 675 }
 676
 677 void rcu_bp_after_fork_child(void)
 678 {
 679         sigset_t oldmask;
 680         int ret;
 681
 682         urcu_bp_prune_registry();
 683         oldmask = saved_fork_signal_mask;
 684         mutex_unlock(&rcu_registry_lock);
 685         mutex_unlock(&rcu_gp_lock);
 686         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 687         assert(!ret);
 688 }
 689
 690 void *rcu_dereference_sym_bp(void *p)
 691 {
 692         return _rcu_dereference(p);
 693 }
 694
 695 void *rcu_set_pointer_sym_bp(void **p, void *v)
 696 {
 697         cmm_wmb();
 698         uatomic_set(p, v);
 699         return v;
 700 }
 701
 702 void *rcu_xchg_pointer_sym_bp(void **p, void *v)
 703 {
 704         cmm_wmb();
 705         return uatomic_xchg(p, v);
 706 }
 707
 708 void *rcu_cmpxchg_pointer_sym_bp(void **p, void *old, void *_new)
 709 {
 710         cmm_wmb();
 711         return uatomic_cmpxchg(p, old, _new);
 712 }
 713
 714 DEFINE_RCU_FLAVOR(rcu_flavor);
 715
 716 #include "urcu-call-rcu-impl.h"
 717 #include "urcu-defer-impl.h"