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