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 #ifndef CONFIG_RCU_FORCE_SYS_MEMBARRIER
 115 int urcu_bp_has_sys_membarrier;
 116 #endif
 117
 118 /*
 119  * rcu_gp_lock ensures mutual exclusion between threads calling
 120  * synchronize_rcu().
 121  */
 122 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
 123 /*
 124  * rcu_registry_lock ensures mutual exclusion between threads
 125  * registering and unregistering themselves to/from the registry, and
 126  * with threads reading that registry from synchronize_rcu(). However,
 127  * this lock is not held all the way through the completion of awaiting
 128  * for the grace period. It is sporadically released between iterations
 129  * on the registry.
 130  * rcu_registry_lock may nest inside rcu_gp_lock.
 131  */
 132 static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
 133
 134 static pthread_mutex_t init_lock = PTHREAD_MUTEX_INITIALIZER;
 135 static int initialized;
 136
 137 static pthread_key_t urcu_bp_key;
 138
 139 struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
 140
 141 /*
 142  * Pointer to registry elements. Written to only by each individual reader. Read
 143  * by both the reader and the writers.
 144  */
 145 DEFINE_URCU_TLS(struct rcu_reader *, rcu_reader);
 146
 147 static CDS_LIST_HEAD(registry);
 148
 149 struct registry_chunk {
 150         size_t data_len;                /* data length */
 151         size_t used;                    /* amount of data used */
 152         struct cds_list_head node;      /* chunk_list node */
 153         char data[];
 154 };
 155
 156 struct registry_arena {
 157         struct cds_list_head chunk_list;
 158 };
 159
 160 static struct registry_arena registry_arena = {
 161         .chunk_list = CDS_LIST_HEAD_INIT(registry_arena.chunk_list),
 162 };
 163
 164 /* Saved fork signal mask, protected by rcu_gp_lock */
 165 static sigset_t saved_fork_signal_mask;
 166
 167 static void mutex_lock(pthread_mutex_t *mutex)
 168 {
 169         int ret;
 170
 171 #ifndef DISTRUST_SIGNALS_EXTREME
 172         ret = pthread_mutex_lock(mutex);
 173         if (ret)
 174                 urcu_die(ret);
 175 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
 176         while ((ret = pthread_mutex_trylock(mutex)) != 0) {
 177                 if (ret != EBUSY && ret != EINTR)
 178                         urcu_die(ret);
 179                 poll(NULL,0,10);
 180         }
 181 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
 182 }
 183
 184 static void mutex_unlock(pthread_mutex_t *mutex)
 185 {
 186         int ret;
 187
 188         ret = pthread_mutex_unlock(mutex);
 189         if (ret)
 190                 urcu_die(ret);
 191 }
 192
 193 static void smp_mb_master(void)
 194 {
 195         if (caa_likely(urcu_bp_has_sys_membarrier))
 196                 (void) membarrier(MEMBARRIER_CMD_SHARED, 0);
 197         else
 198                 cmm_smp_mb();
 199 }
 200
 201 /*
 202  * Always called with rcu_registry lock held. Releases this lock between
 203  * iterations and grabs it again. Holds the lock when it returns.
 204  */
 205 static void wait_for_readers(struct cds_list_head *input_readers,
 206                         struct cds_list_head *cur_snap_readers,
 207                         struct cds_list_head *qsreaders)
 208 {
 209         unsigned int wait_loops = 0;
 210         struct rcu_reader *index, *tmp;
 211
 212         /*
 213          * Wait for each thread URCU_TLS(rcu_reader).ctr to either
 214          * indicate quiescence (not nested), or observe the current
 215          * rcu_gp.ctr value.
 216          */
 217         for (;;) {
 218                 if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
 219                         wait_loops++;
 220
 221                 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
 222                         switch (rcu_reader_state(&index->ctr)) {
 223                         case RCU_READER_ACTIVE_CURRENT:
 224                                 if (cur_snap_readers) {
 225                                         cds_list_move(&index->node,
 226                                                 cur_snap_readers);
 227                                         break;
 228                                 }
 229                                 /* Fall-through */
 230                         case RCU_READER_INACTIVE:
 231                                 cds_list_move(&index->node, qsreaders);
 232                                 break;
 233                         case RCU_READER_ACTIVE_OLD:
 234                                 /*
 235                                  * Old snapshot. Leaving node in
 236                                  * input_readers will make us busy-loop
 237                                  * until the snapshot becomes current or
 238                                  * the reader becomes inactive.
 239                                  */
 240                                 break;
 241                         }
 242                 }
 243
 244                 if (cds_list_empty(input_readers)) {
 245                         break;
 246                 } else {
 247                         /* Temporarily unlock the registry lock. */
 248                         mutex_unlock(&rcu_registry_lock);
 249                         if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
 250                                 (void) poll(NULL, 0, RCU_SLEEP_DELAY_MS);
 251                         else
 252                                 caa_cpu_relax();
 253                         /* Re-lock the registry lock before the next loop. */
 254                         mutex_lock(&rcu_registry_lock);
 255                 }
 256         }
 257 }
 258
 259 void synchronize_rcu(void)
 260 {
 261         CDS_LIST_HEAD(cur_snap_readers);
 262         CDS_LIST_HEAD(qsreaders);
 263         sigset_t newmask, oldmask;
 264         int ret;
 265
 266         ret = sigfillset(&newmask);
 267         assert(!ret);
 268         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 269         assert(!ret);
 270
 271         mutex_lock(&rcu_gp_lock);
 272
 273         mutex_lock(&rcu_registry_lock);
 274
 275         if (cds_list_empty(&registry))
 276                 goto out;
 277
 278         /* All threads should read qparity before accessing data structure
 279          * where new ptr points to. */
 280         /* Write new ptr before changing the qparity */
 281         smp_mb_master();
 282
 283         /*
 284          * Wait for readers to observe original parity or be quiescent.
 285          * wait_for_readers() can release and grab again rcu_registry_lock
 286          * interally.
 287          */
 288         wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
 289
 290         /*
 291          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 292          * model easier to understand. It does not have a big performance impact
 293          * anyway, given this is the write-side.
 294          */
 295         cmm_smp_mb();
 296
 297         /* Switch parity: 0 -> 1, 1 -> 0 */
 298         CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE);
 299
 300         /*
 301          * Must commit qparity update to memory before waiting for other parity
 302          * quiescent state. Failure to do so could result in the writer waiting
 303          * forever while new readers are always accessing data (no progress).
 304          * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
 305          */
 306
 307         /*
 308          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 309          * model easier to understand. It does not have a big performance impact
 310          * anyway, given this is the write-side.
 311          */
 312         cmm_smp_mb();
 313
 314         /*
 315          * Wait for readers to observe new parity or be quiescent.
 316          * wait_for_readers() can release and grab again rcu_registry_lock
 317          * interally.
 318          */
 319         wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
 320
 321         /*
 322          * Put quiescent reader list back into registry.
 323          */
 324         cds_list_splice(&qsreaders, &registry);
 325
 326         /*
 327          * Finish waiting for reader threads before letting the old ptr being
 328          * freed.
 329          */
 330         smp_mb_master();
 331 out:
 332         mutex_unlock(&rcu_registry_lock);
 333         mutex_unlock(&rcu_gp_lock);
 334         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 335         assert(!ret);
 336 }
 337
 338 /*
 339  * library wrappers to be used by non-LGPL compatible source code.
 340  */
 341
 342 void rcu_read_lock(void)
 343 {
 344         _rcu_read_lock();
 345 }
 346
 347 void rcu_read_unlock(void)
 348 {
 349         _rcu_read_unlock();
 350 }
 351
 352 int rcu_read_ongoing(void)
 353 {
 354         return _rcu_read_ongoing();
 355 }
 356
 357 /*
 358  * Only grow for now. If empty, allocate a ARENA_INIT_ALLOC sized chunk.
 359  * Else, try expanding the last chunk. If this fails, allocate a new
 360  * chunk twice as big as the last chunk.
 361  * Memory used by chunks _never_ moves. A chunk could theoretically be
 362  * freed when all "used" slots are released, but we don't do it at this
 363  * point.
 364  */
 365 static
 366 void expand_arena(struct registry_arena *arena)
 367 {
 368         struct registry_chunk *new_chunk, *last_chunk;
 369         size_t old_chunk_len, new_chunk_len;
 370
 371         /* No chunk. */
 372         if (cds_list_empty(&arena->chunk_list)) {
 373                 assert(ARENA_INIT_ALLOC >=
 374                         sizeof(struct registry_chunk)
 375                         + sizeof(struct rcu_reader));
 376                 new_chunk_len = ARENA_INIT_ALLOC;
 377                 new_chunk = (struct registry_chunk *) mmap(NULL,
 378                         new_chunk_len,
 379                         PROT_READ | PROT_WRITE,
 380                         MAP_ANONYMOUS | MAP_PRIVATE,
 381                         -1, 0);
 382                 if (new_chunk == MAP_FAILED)
 383                         abort();
 384                 memset(new_chunk, 0, new_chunk_len);
 385                 new_chunk->data_len =
 386                         new_chunk_len - sizeof(struct registry_chunk);
 387                 cds_list_add_tail(&new_chunk->node, &arena->chunk_list);
 388                 return;         /* We're done. */
 389         }
 390
 391         /* Try expanding last chunk. */
 392         last_chunk = cds_list_entry(arena->chunk_list.prev,
 393                 struct registry_chunk, node);
 394         old_chunk_len =
 395                 last_chunk->data_len + sizeof(struct registry_chunk);
 396         new_chunk_len = old_chunk_len << 1;
 397
 398         /* Don't allow memory mapping to move, just expand. */
 399         new_chunk = mremap_wrapper(last_chunk, old_chunk_len,
 400                 new_chunk_len, 0);
 401         if (new_chunk != MAP_FAILED) {
 402                 /* Should not have moved. */
 403                 assert(new_chunk == last_chunk);
 404                 memset((char *) last_chunk + old_chunk_len, 0,
 405                         new_chunk_len - old_chunk_len);
 406                 last_chunk->data_len =
 407                         new_chunk_len - sizeof(struct registry_chunk);
 408                 return;         /* We're done. */
 409         }
 410
 411         /* Remap did not succeed, we need to add a new chunk. */
 412         new_chunk = (struct registry_chunk *) mmap(NULL,
 413                 new_chunk_len,
 414                 PROT_READ | PROT_WRITE,
 415                 MAP_ANONYMOUS | MAP_PRIVATE,
 416                 -1, 0);
 417         if (new_chunk == MAP_FAILED)
 418                 abort();
 419         memset(new_chunk, 0, new_chunk_len);
 420         new_chunk->data_len =
 421                 new_chunk_len - sizeof(struct registry_chunk);
 422         cds_list_add_tail(&new_chunk->node, &arena->chunk_list);
 423 }
 424
 425 static
 426 struct rcu_reader *arena_alloc(struct registry_arena *arena)
 427 {
 428         struct registry_chunk *chunk;
 429         struct rcu_reader *rcu_reader_reg;
 430         int expand_done = 0;    /* Only allow to expand once per alloc */
 431         size_t len = sizeof(struct rcu_reader);
 432
 433 retry:
 434         cds_list_for_each_entry(chunk, &arena->chunk_list, node) {
 435                 if (chunk->data_len - chunk->used < len)
 436                         continue;
 437                 /* Find spot */
 438                 for (rcu_reader_reg = (struct rcu_reader *) &chunk->data[0];
 439                                 rcu_reader_reg < (struct rcu_reader *) &chunk->data[chunk->data_len];
 440                                 rcu_reader_reg++) {
 441                         if (!rcu_reader_reg->alloc) {
 442                                 rcu_reader_reg->alloc = 1;
 443                                 chunk->used += len;
 444                                 return rcu_reader_reg;
 445                         }
 446                 }
 447         }
 448
 449         if (!expand_done) {
 450                 expand_arena(arena);
 451                 expand_done = 1;
 452                 goto retry;
 453         }
 454
 455         return NULL;
 456 }
 457
 458 /* Called with signals off and mutex locked */
 459 static
 460 void add_thread(void)
 461 {
 462         struct rcu_reader *rcu_reader_reg;
 463         int ret;
 464
 465         rcu_reader_reg = arena_alloc(&registry_arena);
 466         if (!rcu_reader_reg)
 467                 abort();
 468         ret = pthread_setspecific(urcu_bp_key, rcu_reader_reg);
 469         if (ret)
 470                 abort();
 471
 472         /* Add to registry */
 473         rcu_reader_reg->tid = pthread_self();
 474         assert(rcu_reader_reg->ctr == 0);
 475         cds_list_add(&rcu_reader_reg->node, &registry);
 476         /*
 477          * Reader threads are pointing to the reader registry. This is
 478          * why its memory should never be relocated.
 479          */
 480         URCU_TLS(rcu_reader) = rcu_reader_reg;
 481 }
 482
 483 /* Called with mutex locked */
 484 static
 485 void cleanup_thread(struct registry_chunk *chunk,
 486                 struct rcu_reader *rcu_reader_reg)
 487 {
 488         rcu_reader_reg->ctr = 0;
 489         cds_list_del(&rcu_reader_reg->node);
 490         rcu_reader_reg->tid = 0;
 491         rcu_reader_reg->alloc = 0;
 492         chunk->used -= sizeof(struct rcu_reader);
 493 }
 494
 495 static
 496 struct registry_chunk *find_chunk(struct rcu_reader *rcu_reader_reg)
 497 {
 498         struct registry_chunk *chunk;
 499
 500         cds_list_for_each_entry(chunk, &registry_arena.chunk_list, node) {
 501                 if (rcu_reader_reg < (struct rcu_reader *) &chunk->data[0])
 502                         continue;
 503                 if (rcu_reader_reg >= (struct rcu_reader *) &chunk->data[chunk->data_len])
 504                         continue;
 505                 return chunk;
 506         }
 507         return NULL;
 508 }
 509
 510 /* Called with signals off and mutex locked */
 511 static
 512 void remove_thread(struct rcu_reader *rcu_reader_reg)
 513 {
 514         cleanup_thread(find_chunk(rcu_reader_reg), rcu_reader_reg);
 515         URCU_TLS(rcu_reader) = NULL;
 516 }
 517
 518 /* Disable signals, take mutex, add to registry */
 519 void rcu_bp_register(void)
 520 {
 521         sigset_t newmask, oldmask;
 522         int ret;
 523
 524         ret = sigfillset(&newmask);
 525         if (ret)
 526                 abort();
 527         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 528         if (ret)
 529                 abort();
 530
 531         /*
 532          * Check if a signal concurrently registered our thread since
 533          * the check in rcu_read_lock().
 534          */
 535         if (URCU_TLS(rcu_reader))
 536                 goto end;
 537
 538         /*
 539          * Take care of early registration before urcu_bp constructor.
 540          */
 541         rcu_bp_init();
 542
 543         mutex_lock(&rcu_registry_lock);
 544         add_thread();
 545         mutex_unlock(&rcu_registry_lock);
 546 end:
 547         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 548         if (ret)
 549                 abort();
 550 }
 551
 552 /* Disable signals, take mutex, remove from registry */
 553 static
 554 void rcu_bp_unregister(struct rcu_reader *rcu_reader_reg)
 555 {
 556         sigset_t newmask, oldmask;
 557         int ret;
 558
 559         ret = sigfillset(&newmask);
 560         if (ret)
 561                 abort();
 562         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 563         if (ret)
 564                 abort();
 565
 566         mutex_lock(&rcu_registry_lock);
 567         remove_thread(rcu_reader_reg);
 568         mutex_unlock(&rcu_registry_lock);
 569         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 570         if (ret)
 571                 abort();
 572         rcu_bp_exit();
 573 }
 574
 575 /*
 576  * Remove thread from the registry when it exits, and flag it as
 577  * destroyed so garbage collection can take care of it.
 578  */
 579 static
 580 void urcu_bp_thread_exit_notifier(void *rcu_key)
 581 {
 582         rcu_bp_unregister(rcu_key);
 583 }
 584
 585 #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
 586 static
 587 void rcu_sys_membarrier_status(int available)
 588 {
 589         if (!available)
 590                 abort();
 591 }
 592 #else
 593 static
 594 void rcu_sys_membarrier_status(int available)
 595 {
 596         /*
 597          * membarrier has blocking behavior, which changes the
 598          * application behavior too much compared to using barriers when
 599          * synchronize_rcu is used repeatedly (without using call_rcu).
 600          * Don't use membarrier for now, unless its use has been
 601          * explicitly forced when building liburcu.
 602          */
 603 }
 604 #endif
 605
 606 static
 607 void rcu_bp_init(void)
 608 {
 609         mutex_lock(&init_lock);
 610         if (!rcu_bp_refcount++) {
 611                 int ret;
 612
 613                 ret = pthread_key_create(&urcu_bp_key,
 614                                 urcu_bp_thread_exit_notifier);
 615                 if (ret)
 616                         abort();
 617                 ret = membarrier(MEMBARRIER_CMD_QUERY, 0);
 618                 rcu_sys_membarrier_status(ret >= 0
 619                                 && (ret & MEMBARRIER_CMD_SHARED));
 620                 initialized = 1;
 621         }
 622         mutex_unlock(&init_lock);
 623 }
 624
 625 static
 626 void rcu_bp_exit(void)
 627 {
 628         mutex_lock(&init_lock);
 629         if (!--rcu_bp_refcount) {
 630                 struct registry_chunk *chunk, *tmp;
 631                 int ret;
 632
 633                 cds_list_for_each_entry_safe(chunk, tmp,
 634                                 &registry_arena.chunk_list, node) {
 635                         munmap((void *) chunk, chunk->data_len
 636                                         + sizeof(struct registry_chunk));
 637                 }
 638                 CDS_INIT_LIST_HEAD(&registry_arena.chunk_list);
 639                 ret = pthread_key_delete(urcu_bp_key);
 640                 if (ret)
 641                         abort();
 642         }
 643         mutex_unlock(&init_lock);
 644 }
 645
 646 /*
 647  * Holding the rcu_gp_lock and rcu_registry_lock across fork will make
 648  * sure we fork() don't race with a concurrent thread executing with
 649  * any of those locks held. This ensures that the registry and data
 650  * protected by rcu_gp_lock are in a coherent state in the child.
 651  */
 652 void rcu_bp_before_fork(void)
 653 {
 654         sigset_t newmask, oldmask;
 655         int ret;
 656
 657         ret = sigfillset(&newmask);
 658         assert(!ret);
 659         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 660         assert(!ret);
 661         mutex_lock(&rcu_gp_lock);
 662         mutex_lock(&rcu_registry_lock);
 663         saved_fork_signal_mask = oldmask;
 664 }
 665
 666 void rcu_bp_after_fork_parent(void)
 667 {
 668         sigset_t oldmask;
 669         int ret;
 670
 671         oldmask = saved_fork_signal_mask;
 672         mutex_unlock(&rcu_registry_lock);
 673         mutex_unlock(&rcu_gp_lock);
 674         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 675         assert(!ret);
 676 }
 677
 678 /*
 679  * Prune all entries from registry except our own thread. Fits the Linux
 680  * fork behavior. Called with rcu_gp_lock and rcu_registry_lock held.
 681  */
 682 static
 683 void urcu_bp_prune_registry(void)
 684 {
 685         struct registry_chunk *chunk;
 686         struct rcu_reader *rcu_reader_reg;
 687
 688         cds_list_for_each_entry(chunk, &registry_arena.chunk_list, node) {
 689                 for (rcu_reader_reg = (struct rcu_reader *) &chunk->data[0];
 690                                 rcu_reader_reg < (struct rcu_reader *) &chunk->data[chunk->data_len];
 691                                 rcu_reader_reg++) {
 692                         if (!rcu_reader_reg->alloc)
 693                                 continue;
 694                         if (rcu_reader_reg->tid == pthread_self())
 695                                 continue;
 696                         cleanup_thread(chunk, rcu_reader_reg);
 697                 }
 698         }
 699 }
 700
 701 void rcu_bp_after_fork_child(void)
 702 {
 703         sigset_t oldmask;
 704         int ret;
 705
 706         urcu_bp_prune_registry();
 707         oldmask = saved_fork_signal_mask;
 708         mutex_unlock(&rcu_registry_lock);
 709         mutex_unlock(&rcu_gp_lock);
 710         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 711         assert(!ret);
 712 }
 713
 714 void *rcu_dereference_sym_bp(void *p)
 715 {
 716         return _rcu_dereference(p);
 717 }
 718
 719 void *rcu_set_pointer_sym_bp(void **p, void *v)
 720 {
 721         cmm_wmb();
 722         uatomic_set(p, v);
 723         return v;
 724 }
 725
 726 void *rcu_xchg_pointer_sym_bp(void **p, void *v)
 727 {
 728         cmm_wmb();
 729         return uatomic_xchg(p, v);
 730 }
 731
 732 void *rcu_cmpxchg_pointer_sym_bp(void **p, void *old, void *_new)
 733 {
 734         cmm_wmb();
 735         return uatomic_cmpxchg(p, old, _new);
 736 }
 737
 738 DEFINE_RCU_FLAVOR(rcu_flavor);
 739
 740 #include "urcu-call-rcu-impl.h"
 741 #include "urcu-defer-impl.h"