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 URCU_NO_COMPAT_IDENTIFIERS
  27 #define _LGPL_SOURCE
  28 #include <stdio.h>
  29 #include <pthread.h>
  30 #include <signal.h>
  31 #include <assert.h>
  32 #include <stdlib.h>
  33 #include <string.h>
  34 #include <errno.h>
  35 #include <poll.h>
  36 #include <unistd.h>
  37 #include <stdbool.h>
  38 #include <sys/mman.h>
  39
  40 #include <urcu/arch.h>
  41 #include <urcu/wfcqueue.h>
  42 #include <urcu/map/urcu-bp.h>
  43 #include <urcu/static/urcu-bp.h>
  44 #include <urcu/pointer.h>
  45 #include <urcu/tls-compat.h>
  46
  47 #include "urcu-die.h"
  48 #include "urcu-utils.h"
  49
  50 #define URCU_API_MAP
  51 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
  52 #undef _LGPL_SOURCE
  53 #include <urcu/urcu-bp.h>
  54 #define _LGPL_SOURCE
  55
  56 #ifndef MAP_ANONYMOUS
  57 #define MAP_ANONYMOUS MAP_ANON
  58 #endif
  59
  60 #ifdef __linux__
  61 static
  62 void *mremap_wrapper(void *old_address, size_t old_size,
  63                 size_t new_size, int flags)
  64 {
  65         return mremap(old_address, old_size, new_size, flags);
  66 }
  67 #else
  68
  69 #define MREMAP_MAYMOVE  1
  70 #define MREMAP_FIXED    2
  71
  72 /*
  73  * mremap wrapper for non-Linux systems not allowing MAYMOVE.
  74  * This is not generic.
  75 */
  76 static
  77 void *mremap_wrapper(void *old_address, size_t old_size,
  78                 size_t new_size, int flags)
  79 {
  80         assert(!(flags & MREMAP_MAYMOVE));
  81
  82         return MAP_FAILED;
  83 }
  84 #endif
  85
  86 /* Sleep delay in ms */
  87 #define RCU_SLEEP_DELAY_MS      10
  88 #define INIT_NR_THREADS         8
  89 #define ARENA_INIT_ALLOC                \
  90         sizeof(struct registry_chunk)   \
  91         + INIT_NR_THREADS * sizeof(struct urcu_bp_reader)
  92
  93 /*
  94  * Active attempts to check for reader Q.S. before calling sleep().
  95  */
  96 #define RCU_QS_ACTIVE_ATTEMPTS 100
  97
  98 static
  99 int urcu_bp_refcount;
 100
 101 /* If the headers do not support membarrier system call, fall back smp_mb. */
 102 #ifdef __NR_membarrier
 103 # define membarrier(...)                syscall(__NR_membarrier, __VA_ARGS__)
 104 #else
 105 # define membarrier(...)                -ENOSYS
 106 #endif
 107
 108 enum membarrier_cmd {
 109         MEMBARRIER_CMD_QUERY                            = 0,
 110         MEMBARRIER_CMD_SHARED                           = (1 << 0),
 111         /* reserved for MEMBARRIER_CMD_SHARED_EXPEDITED (1 << 1) */
 112         /* reserved for MEMBARRIER_CMD_PRIVATE (1 << 2) */
 113         MEMBARRIER_CMD_PRIVATE_EXPEDITED                = (1 << 3),
 114         MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED       = (1 << 4),
 115 };
 116
 117 static
 118 void __attribute__((constructor)) _urcu_bp_init(void);
 119 static
 120 void __attribute__((destructor)) urcu_bp_exit(void);
 121
 122 #ifndef CONFIG_RCU_FORCE_SYS_MEMBARRIER
 123 int urcu_bp_has_sys_membarrier;
 124 #endif
 125
 126 /*
 127  * rcu_gp_lock ensures mutual exclusion between threads calling
 128  * synchronize_rcu().
 129  */
 130 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
 131 /*
 132  * rcu_registry_lock ensures mutual exclusion between threads
 133  * registering and unregistering themselves to/from the registry, and
 134  * with threads reading that registry from synchronize_rcu(). However,
 135  * this lock is not held all the way through the completion of awaiting
 136  * for the grace period. It is sporadically released between iterations
 137  * on the registry.
 138  * rcu_registry_lock may nest inside rcu_gp_lock.
 139  */
 140 static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
 141
 142 static pthread_mutex_t init_lock = PTHREAD_MUTEX_INITIALIZER;
 143 static int initialized;
 144
 145 static pthread_key_t urcu_bp_key;
 146
 147 struct urcu_bp_gp urcu_bp_gp = { .ctr = URCU_BP_GP_COUNT };
 148 URCU_ATTR_ALIAS("urcu_bp_gp") extern struct urcu_bp_gp rcu_gp_bp;
 149
 150 /*
 151  * Pointer to registry elements. Written to only by each individual reader. Read
 152  * by both the reader and the writers.
 153  */
 154 DEFINE_URCU_TLS(struct urcu_bp_reader *, urcu_bp_reader);
 155 DEFINE_URCU_TLS_ALIAS(struct urcu_bp_reader *, urcu_bp_reader, rcu_reader_bp);
 156
 157 static CDS_LIST_HEAD(registry);
 158
 159 struct registry_chunk {
 160         size_t data_len;                /* data length */
 161         size_t used;                    /* amount of data used */
 162         struct cds_list_head node;      /* chunk_list node */
 163         char data[];
 164 };
 165
 166 struct registry_arena {
 167         struct cds_list_head chunk_list;
 168 };
 169
 170 static struct registry_arena registry_arena = {
 171         .chunk_list = CDS_LIST_HEAD_INIT(registry_arena.chunk_list),
 172 };
 173
 174 /* Saved fork signal mask, protected by rcu_gp_lock */
 175 static sigset_t saved_fork_signal_mask;
 176
 177 static void mutex_lock(pthread_mutex_t *mutex)
 178 {
 179         int ret;
 180
 181 #ifndef DISTRUST_SIGNALS_EXTREME
 182         ret = pthread_mutex_lock(mutex);
 183         if (ret)
 184                 urcu_die(ret);
 185 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
 186         while ((ret = pthread_mutex_trylock(mutex)) != 0) {
 187                 if (ret != EBUSY && ret != EINTR)
 188                         urcu_die(ret);
 189                 poll(NULL,0,10);
 190         }
 191 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
 192 }
 193
 194 static void mutex_unlock(pthread_mutex_t *mutex)
 195 {
 196         int ret;
 197
 198         ret = pthread_mutex_unlock(mutex);
 199         if (ret)
 200                 urcu_die(ret);
 201 }
 202
 203 static void smp_mb_master(void)
 204 {
 205         if (caa_likely(urcu_bp_has_sys_membarrier)) {
 206                 if (membarrier(MEMBARRIER_CMD_PRIVATE_EXPEDITED, 0))
 207                         urcu_die(errno);
 208         } else {
 209                 cmm_smp_mb();
 210         }
 211 }
 212
 213 /*
 214  * Always called with rcu_registry lock held. Releases this lock between
 215  * iterations and grabs it again. Holds the lock when it returns.
 216  */
 217 static void wait_for_readers(struct cds_list_head *input_readers,
 218                         struct cds_list_head *cur_snap_readers,
 219                         struct cds_list_head *qsreaders)
 220 {
 221         unsigned int wait_loops = 0;
 222         struct urcu_bp_reader *index, *tmp;
 223
 224         /*
 225          * Wait for each thread URCU_TLS(urcu_bp_reader).ctr to either
 226          * indicate quiescence (not nested), or observe the current
 227          * rcu_gp.ctr value.
 228          */
 229         for (;;) {
 230                 if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
 231                         wait_loops++;
 232
 233                 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
 234                         switch (urcu_bp_reader_state(&index->ctr)) {
 235                         case URCU_BP_READER_ACTIVE_CURRENT:
 236                                 if (cur_snap_readers) {
 237                                         cds_list_move(&index->node,
 238                                                 cur_snap_readers);
 239                                         break;
 240                                 }
 241                                 /* Fall-through */
 242                         case URCU_BP_READER_INACTIVE:
 243                                 cds_list_move(&index->node, qsreaders);
 244                                 break;
 245                         case URCU_BP_READER_ACTIVE_OLD:
 246                                 /*
 247                                  * Old snapshot. Leaving node in
 248                                  * input_readers will make us busy-loop
 249                                  * until the snapshot becomes current or
 250                                  * the reader becomes inactive.
 251                                  */
 252                                 break;
 253                         }
 254                 }
 255
 256                 if (cds_list_empty(input_readers)) {
 257                         break;
 258                 } else {
 259                         /* Temporarily unlock the registry lock. */
 260                         mutex_unlock(&rcu_registry_lock);
 261                         if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
 262                                 (void) poll(NULL, 0, RCU_SLEEP_DELAY_MS);
 263                         else
 264                                 caa_cpu_relax();
 265                         /* Re-lock the registry lock before the next loop. */
 266                         mutex_lock(&rcu_registry_lock);
 267                 }
 268         }
 269 }
 270
 271 void urcu_bp_synchronize_rcu(void)
 272 {
 273         CDS_LIST_HEAD(cur_snap_readers);
 274         CDS_LIST_HEAD(qsreaders);
 275         sigset_t newmask, oldmask;
 276         int ret;
 277
 278         ret = sigfillset(&newmask);
 279         assert(!ret);
 280         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 281         assert(!ret);
 282
 283         mutex_lock(&rcu_gp_lock);
 284
 285         mutex_lock(&rcu_registry_lock);
 286
 287         if (cds_list_empty(&registry))
 288                 goto out;
 289
 290         /* All threads should read qparity before accessing data structure
 291          * where new ptr points to. */
 292         /* Write new ptr before changing the qparity */
 293         smp_mb_master();
 294
 295         /*
 296          * Wait for readers to observe original parity or be quiescent.
 297          * wait_for_readers() can release and grab again rcu_registry_lock
 298          * interally.
 299          */
 300         wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
 301
 302         /*
 303          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 304          * model easier to understand. It does not have a big performance impact
 305          * anyway, given this is the write-side.
 306          */
 307         cmm_smp_mb();
 308
 309         /* Switch parity: 0 -> 1, 1 -> 0 */
 310         CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ URCU_BP_GP_CTR_PHASE);
 311
 312         /*
 313          * Must commit qparity update to memory before waiting for other parity
 314          * quiescent state. Failure to do so could result in the writer waiting
 315          * forever while new readers are always accessing data (no progress).
 316          * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
 317          */
 318
 319         /*
 320          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 321          * model easier to understand. It does not have a big performance impact
 322          * anyway, given this is the write-side.
 323          */
 324         cmm_smp_mb();
 325
 326         /*
 327          * Wait for readers to observe new parity or be quiescent.
 328          * wait_for_readers() can release and grab again rcu_registry_lock
 329          * interally.
 330          */
 331         wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
 332
 333         /*
 334          * Put quiescent reader list back into registry.
 335          */
 336         cds_list_splice(&qsreaders, &registry);
 337
 338         /*
 339          * Finish waiting for reader threads before letting the old ptr being
 340          * freed.
 341          */
 342         smp_mb_master();
 343 out:
 344         mutex_unlock(&rcu_registry_lock);
 345         mutex_unlock(&rcu_gp_lock);
 346         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 347         assert(!ret);
 348 }
 349 URCU_ATTR_ALIAS("urcu_bp_synchronize_rcu") void synchronize_rcu_bp();
 350
 351 /*
 352  * library wrappers to be used by non-LGPL compatible source code.
 353  */
 354
 355 void urcu_bp_read_lock(void)
 356 {
 357         _urcu_bp_read_lock();
 358 }
 359 URCU_ATTR_ALIAS("urcu_bp_read_lock") void rcu_read_lock_bp();
 360
 361 void urcu_bp_read_unlock(void)
 362 {
 363         _urcu_bp_read_unlock();
 364 }
 365 URCU_ATTR_ALIAS("urcu_bp_read_unlock") void rcu_read_unlock_bp();
 366
 367 int urcu_bp_read_ongoing(void)
 368 {
 369         return _urcu_bp_read_ongoing();
 370 }
 371 URCU_ATTR_ALIAS("urcu_bp_read_ongoing") int rcu_read_ongoing_bp();
 372
 373 /*
 374  * Only grow for now. If empty, allocate a ARENA_INIT_ALLOC sized chunk.
 375  * Else, try expanding the last chunk. If this fails, allocate a new
 376  * chunk twice as big as the last chunk.
 377  * Memory used by chunks _never_ moves. A chunk could theoretically be
 378  * freed when all "used" slots are released, but we don't do it at this
 379  * point.
 380  */
 381 static
 382 void expand_arena(struct registry_arena *arena)
 383 {
 384         struct registry_chunk *new_chunk, *last_chunk;
 385         size_t old_chunk_len, new_chunk_len;
 386
 387         /* No chunk. */
 388         if (cds_list_empty(&arena->chunk_list)) {
 389                 assert(ARENA_INIT_ALLOC >=
 390                         sizeof(struct registry_chunk)
 391                         + sizeof(struct rcu_reader));
 392                 new_chunk_len = ARENA_INIT_ALLOC;
 393                 new_chunk = (struct registry_chunk *) mmap(NULL,
 394                         new_chunk_len,
 395                         PROT_READ | PROT_WRITE,
 396                         MAP_ANONYMOUS | MAP_PRIVATE,
 397                         -1, 0);
 398                 if (new_chunk == MAP_FAILED)
 399                         abort();
 400                 memset(new_chunk, 0, new_chunk_len);
 401                 new_chunk->data_len =
 402                         new_chunk_len - sizeof(struct registry_chunk);
 403                 cds_list_add_tail(&new_chunk->node, &arena->chunk_list);
 404                 return;         /* We're done. */
 405         }
 406
 407         /* Try expanding last chunk. */
 408         last_chunk = cds_list_entry(arena->chunk_list.prev,
 409                 struct registry_chunk, node);
 410         old_chunk_len =
 411                 last_chunk->data_len + sizeof(struct registry_chunk);
 412         new_chunk_len = old_chunk_len << 1;
 413
 414         /* Don't allow memory mapping to move, just expand. */
 415         new_chunk = mremap_wrapper(last_chunk, old_chunk_len,
 416                 new_chunk_len, 0);
 417         if (new_chunk != MAP_FAILED) {
 418                 /* Should not have moved. */
 419                 assert(new_chunk == last_chunk);
 420                 memset((char *) last_chunk + old_chunk_len, 0,
 421                         new_chunk_len - old_chunk_len);
 422                 last_chunk->data_len =
 423                         new_chunk_len - sizeof(struct registry_chunk);
 424                 return;         /* We're done. */
 425         }
 426
 427         /* Remap did not succeed, we need to add a new chunk. */
 428         new_chunk = (struct registry_chunk *) mmap(NULL,
 429                 new_chunk_len,
 430                 PROT_READ | PROT_WRITE,
 431                 MAP_ANONYMOUS | MAP_PRIVATE,
 432                 -1, 0);
 433         if (new_chunk == MAP_FAILED)
 434                 abort();
 435         memset(new_chunk, 0, new_chunk_len);
 436         new_chunk->data_len =
 437                 new_chunk_len - sizeof(struct registry_chunk);
 438         cds_list_add_tail(&new_chunk->node, &arena->chunk_list);
 439 }
 440
 441 static
 442 struct rcu_reader *arena_alloc(struct registry_arena *arena)
 443 {
 444         struct registry_chunk *chunk;
 445         struct rcu_reader *rcu_reader_reg;
 446         int expand_done = 0;    /* Only allow to expand once per alloc */
 447         size_t len = sizeof(struct rcu_reader);
 448
 449 retry:
 450         cds_list_for_each_entry(chunk, &arena->chunk_list, node) {
 451                 if (chunk->data_len - chunk->used < len)
 452                         continue;
 453                 /* Find spot */
 454                 for (rcu_reader_reg = (struct rcu_reader *) &chunk->data[0];
 455                                 rcu_reader_reg < (struct rcu_reader *) &chunk->data[chunk->data_len];
 456                                 rcu_reader_reg++) {
 457                         if (!rcu_reader_reg->alloc) {
 458                                 rcu_reader_reg->alloc = 1;
 459                                 chunk->used += len;
 460                                 return rcu_reader_reg;
 461                         }
 462                 }
 463         }
 464
 465         if (!expand_done) {
 466                 expand_arena(arena);
 467                 expand_done = 1;
 468                 goto retry;
 469         }
 470
 471         return NULL;
 472 }
 473
 474 /* Called with signals off and mutex locked */
 475 static
 476 void add_thread(void)
 477 {
 478         struct rcu_reader *rcu_reader_reg;
 479         int ret;
 480
 481         rcu_reader_reg = arena_alloc(&registry_arena);
 482         if (!rcu_reader_reg)
 483                 abort();
 484         ret = pthread_setspecific(urcu_bp_key, rcu_reader_reg);
 485         if (ret)
 486                 abort();
 487
 488         /* Add to registry */
 489         rcu_reader_reg->tid = pthread_self();
 490         assert(rcu_reader_reg->ctr == 0);
 491         cds_list_add(&rcu_reader_reg->node, &registry);
 492         /*
 493          * Reader threads are pointing to the reader registry. This is
 494          * why its memory should never be relocated.
 495          */
 496         URCU_TLS(urcu_bp_reader) = rcu_reader_reg;
 497 }
 498
 499 /* Called with mutex locked */
 500 static
 501 void cleanup_thread(struct registry_chunk *chunk,
 502                 struct rcu_reader *rcu_reader_reg)
 503 {
 504         rcu_reader_reg->ctr = 0;
 505         cds_list_del(&rcu_reader_reg->node);
 506         rcu_reader_reg->tid = 0;
 507         rcu_reader_reg->alloc = 0;
 508         chunk->used -= sizeof(struct rcu_reader);
 509 }
 510
 511 static
 512 struct registry_chunk *find_chunk(struct rcu_reader *rcu_reader_reg)
 513 {
 514         struct registry_chunk *chunk;
 515
 516         cds_list_for_each_entry(chunk, &registry_arena.chunk_list, node) {
 517                 if (rcu_reader_reg < (struct rcu_reader *) &chunk->data[0])
 518                         continue;
 519                 if (rcu_reader_reg >= (struct rcu_reader *) &chunk->data[chunk->data_len])
 520                         continue;
 521                 return chunk;
 522         }
 523         return NULL;
 524 }
 525
 526 /* Called with signals off and mutex locked */
 527 static
 528 void remove_thread(struct rcu_reader *rcu_reader_reg)
 529 {
 530         cleanup_thread(find_chunk(rcu_reader_reg), rcu_reader_reg);
 531         URCU_TLS(urcu_bp_reader) = NULL;
 532 }
 533
 534 /* Disable signals, take mutex, add to registry */
 535 void urcu_bp_register(void)
 536 {
 537         sigset_t newmask, oldmask;
 538         int ret;
 539
 540         ret = sigfillset(&newmask);
 541         if (ret)
 542                 abort();
 543         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 544         if (ret)
 545                 abort();
 546
 547         /*
 548          * Check if a signal concurrently registered our thread since
 549          * the check in rcu_read_lock().
 550          */
 551         if (URCU_TLS(urcu_bp_reader))
 552                 goto end;
 553
 554         /*
 555          * Take care of early registration before urcu_bp constructor.
 556          */
 557         _urcu_bp_init();
 558
 559         mutex_lock(&rcu_registry_lock);
 560         add_thread();
 561         mutex_unlock(&rcu_registry_lock);
 562 end:
 563         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 564         if (ret)
 565                 abort();
 566 }
 567 URCU_ATTR_ALIAS("urcu_bp_register") void rcu_bp_register();
 568
 569 void urcu_bp_register_thread(void)
 570 {
 571         if (caa_unlikely(!URCU_TLS(urcu_bp_reader)))
 572                 urcu_bp_register(); /* If not yet registered. */
 573 }
 574
 575 /* Disable signals, take mutex, remove from registry */
 576 static
 577 void urcu_bp_unregister(struct rcu_reader *rcu_reader_reg)
 578 {
 579         sigset_t newmask, oldmask;
 580         int ret;
 581
 582         ret = sigfillset(&newmask);
 583         if (ret)
 584                 abort();
 585         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 586         if (ret)
 587                 abort();
 588
 589         mutex_lock(&rcu_registry_lock);
 590         remove_thread(rcu_reader_reg);
 591         mutex_unlock(&rcu_registry_lock);
 592         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 593         if (ret)
 594                 abort();
 595         urcu_bp_exit();
 596 }
 597
 598 /*
 599  * Remove thread from the registry when it exits, and flag it as
 600  * destroyed so garbage collection can take care of it.
 601  */
 602 static
 603 void urcu_bp_thread_exit_notifier(void *rcu_key)
 604 {
 605         urcu_bp_unregister(rcu_key);
 606 }
 607
 608 #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
 609 static
 610 void urcu_bp_sys_membarrier_status(bool available)
 611 {
 612         if (!available)
 613                 abort();
 614 }
 615 #else
 616 static
 617 void urcu_bp_sys_membarrier_status(bool available)
 618 {
 619         if (!available)
 620                 return;
 621         urcu_bp_has_sys_membarrier = 1;
 622 }
 623 #endif
 624
 625 static
 626 void urcu_bp_sys_membarrier_init(void)
 627 {
 628         bool available = false;
 629         int mask;
 630
 631         mask = membarrier(MEMBARRIER_CMD_QUERY, 0);
 632         if (mask >= 0) {
 633                 if (mask & MEMBARRIER_CMD_PRIVATE_EXPEDITED) {
 634                         if (membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0))
 635                                 urcu_die(errno);
 636                         available = true;
 637                 }
 638         }
 639         urcu_bp_sys_membarrier_status(available);
 640 }
 641
 642 static
 643 void _urcu_bp_init(void)
 644 {
 645         mutex_lock(&init_lock);
 646         if (!urcu_bp_refcount++) {
 647                 int ret;
 648
 649                 ret = pthread_key_create(&urcu_bp_key,
 650                                 urcu_bp_thread_exit_notifier);
 651                 if (ret)
 652                         abort();
 653                 urcu_bp_sys_membarrier_init();
 654                 initialized = 1;
 655         }
 656         mutex_unlock(&init_lock);
 657 }
 658
 659 static
 660 void urcu_bp_exit(void)
 661 {
 662         mutex_lock(&init_lock);
 663         if (!--urcu_bp_refcount) {
 664                 struct registry_chunk *chunk, *tmp;
 665                 int ret;
 666
 667                 cds_list_for_each_entry_safe(chunk, tmp,
 668                                 &registry_arena.chunk_list, node) {
 669                         munmap((void *) chunk, chunk->data_len
 670                                         + sizeof(struct registry_chunk));
 671                 }
 672                 CDS_INIT_LIST_HEAD(&registry_arena.chunk_list);
 673                 ret = pthread_key_delete(urcu_bp_key);
 674                 if (ret)
 675                         abort();
 676         }
 677         mutex_unlock(&init_lock);
 678 }
 679
 680 /*
 681  * Holding the rcu_gp_lock and rcu_registry_lock across fork will make
 682  * sure we fork() don't race with a concurrent thread executing with
 683  * any of those locks held. This ensures that the registry and data
 684  * protected by rcu_gp_lock are in a coherent state in the child.
 685  */
 686 void urcu_bp_before_fork(void)
 687 {
 688         sigset_t newmask, oldmask;
 689         int ret;
 690
 691         ret = sigfillset(&newmask);
 692         assert(!ret);
 693         ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 694         assert(!ret);
 695         mutex_lock(&rcu_gp_lock);
 696         mutex_lock(&rcu_registry_lock);
 697         saved_fork_signal_mask = oldmask;
 698 }
 699 URCU_ATTR_ALIAS("urcu_bp_before_fork") void rcu_bp_before_fork();
 700
 701 void urcu_bp_after_fork_parent(void)
 702 {
 703         sigset_t oldmask;
 704         int ret;
 705
 706         oldmask = saved_fork_signal_mask;
 707         mutex_unlock(&rcu_registry_lock);
 708         mutex_unlock(&rcu_gp_lock);
 709         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 710         assert(!ret);
 711 }
 712 URCU_ATTR_ALIAS("urcu_bp_after_fork_parent")
 713 void rcu_bp_after_fork_parent(void);
 714
 715 /*
 716  * Prune all entries from registry except our own thread. Fits the Linux
 717  * fork behavior. Called with rcu_gp_lock and rcu_registry_lock held.
 718  */
 719 static
 720 void urcu_bp_prune_registry(void)
 721 {
 722         struct registry_chunk *chunk;
 723         struct urcu_bp_reader *rcu_reader_reg;
 724
 725         cds_list_for_each_entry(chunk, &registry_arena.chunk_list, node) {
 726                 for (rcu_reader_reg = (struct urcu_bp_reader *) &chunk->data[0];
 727                                 rcu_reader_reg < (struct urcu_bp_reader *) &chunk->data[chunk->data_len];
 728                                 rcu_reader_reg++) {
 729                         if (!rcu_reader_reg->alloc)
 730                                 continue;
 731                         if (rcu_reader_reg->tid == pthread_self())
 732                                 continue;
 733                         cleanup_thread(chunk, rcu_reader_reg);
 734                 }
 735         }
 736 }
 737
 738 void urcu_bp_after_fork_child(void)
 739 {
 740         sigset_t oldmask;
 741         int ret;
 742
 743         urcu_bp_prune_registry();
 744         oldmask = saved_fork_signal_mask;
 745         mutex_unlock(&rcu_registry_lock);
 746         mutex_unlock(&rcu_gp_lock);
 747         ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 748         assert(!ret);
 749 }
 750 URCU_ATTR_ALIAS("urcu_bp_after_fork_child")
 751 void rcu_bp_after_fork_child(void);
 752
 753 void *urcu_bp_dereference_sym(void *p)
 754 {
 755         return _rcu_dereference(p);
 756 }
 757 URCU_ATTR_ALIAS("urcu_bp_dereference_sym")
 758 void *rcu_dereference_sym_bp();
 759
 760 void *urcu_bp_set_pointer_sym(void **p, void *v)
 761 {
 762         cmm_wmb();
 763         uatomic_set(p, v);
 764         return v;
 765 }
 766 URCU_ATTR_ALIAS("urcu_bp_set_pointer_sym")
 767 void *rcu_set_pointer_sym_bp();
 768
 769 void *urcu_bp_xchg_pointer_sym(void **p, void *v)
 770 {
 771         cmm_wmb();
 772         return uatomic_xchg(p, v);
 773 }
 774 URCU_ATTR_ALIAS("urcu_bp_xchg_pointer_sym")
 775 void *rcu_xchg_pointer_sym_bp();
 776
 777 void *urcu_bp_cmpxchg_pointer_sym(void **p, void *old, void *_new)
 778 {
 779         cmm_wmb();
 780         return uatomic_cmpxchg(p, old, _new);
 781 }
 782 URCU_ATTR_ALIAS("urcu_bp_cmpxchg_pointer_sym")
 783 void *rcu_cmpxchg_pointer_sym_bp();
 784
 785 DEFINE_RCU_FLAVOR(rcu_flavor);
 786 DEFINE_RCU_FLAVOR_ALIAS(rcu_flavor, alias_rcu_flavor);
 787
 788 #include "urcu-call-rcu-impl.h"
 789 #include "urcu-defer-impl.h"