src/urcu.c

   1 /*
   2  * urcu.c
   3  *
   4  * Userspace RCU library
   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 _BSD_SOURCE
  28 #define _LGPL_SOURCE
  29 #define _DEFAULT_SOURCE
  30 #include <stdio.h>
  31 #include <pthread.h>
  32 #include <signal.h>
  33 #include <assert.h>
  34 #include <stdlib.h>
  35 #include <stdint.h>
  36 #include <string.h>
  37 #include <errno.h>
  38 #include <stdbool.h>
  39 #include <poll.h>
  40
  41 #include <urcu/config.h>
  42 #include <urcu/arch.h>
  43 #include <urcu/wfcqueue.h>
  44 #include <urcu/map/urcu.h>
  45 #include <urcu/static/urcu.h>
  46 #include <urcu/pointer.h>
  47 #include <urcu/tls-compat.h>
  48
  49 #include "urcu-die.h"
  50 #include "urcu-wait.h"
  51 #include "urcu-utils.h"
  52
  53 #define URCU_API_MAP
  54 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
  55 #undef _LGPL_SOURCE
  56 #include <urcu/urcu.h>
  57 #define _LGPL_SOURCE
  58
  59 /*
  60  * If a reader is really non-cooperative and refuses to commit its
  61  * rcu_active_readers count to memory (there is no barrier in the reader
  62  * per-se), kick it after 10 loops waiting for it.
  63  */
  64 #define KICK_READER_LOOPS       10
  65
  66 /*
  67  * Active attempts to check for reader Q.S. before calling futex().
  68  */
  69 #define RCU_QS_ACTIVE_ATTEMPTS 100
  70
  71 /* If the headers do not support membarrier system call, fall back on RCU_MB */
  72 #ifdef __NR_membarrier
  73 # define membarrier(...)                syscall(__NR_membarrier, __VA_ARGS__)
  74 #else
  75 # define membarrier(...)                -ENOSYS
  76 #endif
  77
  78 enum membarrier_cmd {
  79         MEMBARRIER_CMD_QUERY                            = 0,
  80         MEMBARRIER_CMD_SHARED                           = (1 << 0),
  81         /* reserved for MEMBARRIER_CMD_SHARED_EXPEDITED (1 << 1) */
  82         /* reserved for MEMBARRIER_CMD_PRIVATE (1 << 2) */
  83         MEMBARRIER_CMD_PRIVATE_EXPEDITED                = (1 << 3),
  84         MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED       = (1 << 4),
  85 };
  86
  87 #ifdef RCU_MEMBARRIER
  88 static int init_done;
  89 static int urcu_memb_has_sys_membarrier_private_expedited;
  90
  91 #ifndef CONFIG_RCU_FORCE_SYS_MEMBARRIER
  92 /*
  93  * Explicitly initialize to zero because we can't alias a non-static
  94  * uninitialized variable.
  95  */
  96 int urcu_memb_has_sys_membarrier = 0;
  97 #endif
  98
  99 void __attribute__((constructor)) rcu_init(void);
 100 #endif
 101
 102 #ifdef RCU_MB
 103 void rcu_init(void)
 104 {
 105 }
 106 #endif
 107
 108 #ifdef RCU_SIGNAL
 109 static int init_done;
 110
 111 void __attribute__((constructor)) rcu_init(void);
 112 void __attribute__((destructor)) rcu_exit(void);
 113 #endif
 114
 115 /*
 116  * rcu_gp_lock ensures mutual exclusion between threads calling
 117  * synchronize_rcu().
 118  */
 119 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
 120 /*
 121  * rcu_registry_lock ensures mutual exclusion between threads
 122  * registering and unregistering themselves to/from the registry, and
 123  * with threads reading that registry from synchronize_rcu(). However,
 124  * this lock is not held all the way through the completion of awaiting
 125  * for the grace period. It is sporadically released between iterations
 126  * on the registry.
 127  * rcu_registry_lock may nest inside rcu_gp_lock.
 128  */
 129 static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
 130 struct urcu_gp rcu_gp = { .ctr = URCU_GP_COUNT };
 131
 132 /*
 133  * Written to only by each individual reader. Read by both the reader and the
 134  * writers.
 135  */
 136 DEFINE_URCU_TLS(struct urcu_reader, rcu_reader);
 137
 138 static CDS_LIST_HEAD(registry);
 139
 140 /*
 141  * Queue keeping threads awaiting to wait for a grace period. Contains
 142  * struct gp_waiters_thread objects.
 143  */
 144 static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
 145
 146 static void mutex_lock(pthread_mutex_t *mutex)
 147 {
 148         int ret;
 149
 150 #ifndef DISTRUST_SIGNALS_EXTREME
 151         ret = pthread_mutex_lock(mutex);
 152         if (ret)
 153                 urcu_die(ret);
 154 #else /* #ifndef DISTRUST_SIGNALS_EXTREME */
 155         while ((ret = pthread_mutex_trylock(mutex)) != 0) {
 156                 if (ret != EBUSY && ret != EINTR)
 157                         urcu_die(ret);
 158                 if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) {
 159                         cmm_smp_mb();
 160                         _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
 161                         cmm_smp_mb();
 162                 }
 163                 (void) poll(NULL, 0, 10);
 164         }
 165 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
 166 }
 167
 168 static void mutex_unlock(pthread_mutex_t *mutex)
 169 {
 170         int ret;
 171
 172         ret = pthread_mutex_unlock(mutex);
 173         if (ret)
 174                 urcu_die(ret);
 175 }
 176
 177 #ifdef RCU_MEMBARRIER
 178 static void smp_mb_master(void)
 179 {
 180         if (caa_likely(urcu_memb_has_sys_membarrier)) {
 181                 if (membarrier(urcu_memb_has_sys_membarrier_private_expedited ?
 182                                 MEMBARRIER_CMD_PRIVATE_EXPEDITED :
 183                                 MEMBARRIER_CMD_SHARED, 0))
 184                         urcu_die(errno);
 185         } else {
 186                 cmm_smp_mb();
 187         }
 188 }
 189 #endif
 190
 191 #ifdef RCU_MB
 192 static void smp_mb_master(void)
 193 {
 194         cmm_smp_mb();
 195 }
 196 #endif
 197
 198 #ifdef RCU_SIGNAL
 199 static void force_mb_all_readers(void)
 200 {
 201         struct urcu_reader *index;
 202
 203         /*
 204          * Ask for each threads to execute a cmm_smp_mb() so we can consider the
 205          * compiler barriers around rcu read lock as real memory barriers.
 206          */
 207         if (cds_list_empty(&registry))
 208                 return;
 209         /*
 210          * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
 211          * a cache flush on architectures with non-coherent cache. Let's play
 212          * safe and don't assume anything : we use cmm_smp_mc() to make sure the
 213          * cache flush is enforced.
 214          */
 215         cds_list_for_each_entry(index, &registry, node) {
 216                 CMM_STORE_SHARED(index->need_mb, 1);
 217                 pthread_kill(index->tid, SIGRCU);
 218         }
 219         /*
 220          * Wait for sighandler (and thus mb()) to execute on every thread.
 221          *
 222          * Note that the pthread_kill() will never be executed on systems
 223          * that correctly deliver signals in a timely manner.  However, it
 224          * is not uncommon for kernels to have bugs that can result in
 225          * lost or unduly delayed signals.
 226          *
 227          * If you are seeing the below pthread_kill() executing much at
 228          * all, we suggest testing the underlying kernel and filing the
 229          * relevant bug report.  For Linux kernels, we recommend getting
 230          * the Linux Test Project (LTP).
 231          */
 232         cds_list_for_each_entry(index, &registry, node) {
 233                 while (CMM_LOAD_SHARED(index->need_mb)) {
 234                         pthread_kill(index->tid, SIGRCU);
 235                         (void) poll(NULL, 0, 1);
 236                 }
 237         }
 238         cmm_smp_mb();   /* read ->need_mb before ending the barrier */
 239 }
 240
 241 static void smp_mb_master(void)
 242 {
 243         force_mb_all_readers();
 244 }
 245 #endif /* #ifdef RCU_SIGNAL */
 246
 247 /*
 248  * synchronize_rcu() waiting. Single thread.
 249  * Always called with rcu_registry lock held. Releases this lock and
 250  * grabs it again. Holds the lock when it returns.
 251  */
 252 static void wait_gp(void)
 253 {
 254         /*
 255          * Read reader_gp before read futex. smp_mb_master() needs to
 256          * be called with the rcu registry lock held in RCU_SIGNAL
 257          * flavor.
 258          */
 259         smp_mb_master();
 260         /* Temporarily unlock the registry lock. */
 261         mutex_unlock(&rcu_registry_lock);
 262         if (uatomic_read(&rcu_gp.futex) != -1)
 263                 goto end;
 264         while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
 265                         NULL, NULL, 0)) {
 266                 switch (errno) {
 267                 case EWOULDBLOCK:
 268                         /* Value already changed. */
 269                         goto end;
 270                 case EINTR:
 271                         /* Retry if interrupted by signal. */
 272                         break;  /* Get out of switch. */
 273                 default:
 274                         /* Unexpected error. */
 275                         urcu_die(errno);
 276                 }
 277         }
 278 end:
 279         /*
 280          * Re-lock the registry lock before the next loop.
 281          */
 282         mutex_lock(&rcu_registry_lock);
 283 }
 284
 285 /*
 286  * Always called with rcu_registry lock held. Releases this lock between
 287  * iterations and grabs it again. Holds the lock when it returns.
 288  */
 289 static void wait_for_readers(struct cds_list_head *input_readers,
 290                         struct cds_list_head *cur_snap_readers,
 291                         struct cds_list_head *qsreaders)
 292 {
 293         unsigned int wait_loops = 0;
 294         struct urcu_reader *index, *tmp;
 295 #ifdef HAS_INCOHERENT_CACHES
 296         unsigned int wait_gp_loops = 0;
 297 #endif /* HAS_INCOHERENT_CACHES */
 298
 299         /*
 300          * Wait for each thread URCU_TLS(rcu_reader).ctr to either
 301          * indicate quiescence (not nested), or observe the current
 302          * rcu_gp.ctr value.
 303          */
 304         for (;;) {
 305                 if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
 306                         wait_loops++;
 307                 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 308                         uatomic_dec(&rcu_gp.futex);
 309                         /* Write futex before read reader_gp */
 310                         smp_mb_master();
 311                 }
 312
 313                 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
 314                         switch (urcu_common_reader_state(&rcu_gp, &index->ctr)) {
 315                         case URCU_READER_ACTIVE_CURRENT:
 316                                 if (cur_snap_readers) {
 317                                         cds_list_move(&index->node,
 318                                                 cur_snap_readers);
 319                                         break;
 320                                 }
 321                                 /* Fall-through */
 322                         case URCU_READER_INACTIVE:
 323                                 cds_list_move(&index->node, qsreaders);
 324                                 break;
 325                         case URCU_READER_ACTIVE_OLD:
 326                                 /*
 327                                  * Old snapshot. Leaving node in
 328                                  * input_readers will make us busy-loop
 329                                  * until the snapshot becomes current or
 330                                  * the reader becomes inactive.
 331                                  */
 332                                 break;
 333                         }
 334                 }
 335
 336 #ifndef HAS_INCOHERENT_CACHES
 337                 if (cds_list_empty(input_readers)) {
 338                         if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 339                                 /* Read reader_gp before write futex */
 340                                 smp_mb_master();
 341                                 uatomic_set(&rcu_gp.futex, 0);
 342                         }
 343                         break;
 344                 } else {
 345                         if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 346                                 /* wait_gp unlocks/locks registry lock. */
 347                                 wait_gp();
 348                         } else {
 349                                 /* Temporarily unlock the registry lock. */
 350                                 mutex_unlock(&rcu_registry_lock);
 351                                 caa_cpu_relax();
 352                                 /*
 353                                  * Re-lock the registry lock before the
 354                                  * next loop.
 355                                  */
 356                                 mutex_lock(&rcu_registry_lock);
 357                         }
 358                 }
 359 #else /* #ifndef HAS_INCOHERENT_CACHES */
 360                 /*
 361                  * BUSY-LOOP. Force the reader thread to commit its
 362                  * URCU_TLS(rcu_reader).ctr update to memory if we wait
 363                  * for too long.
 364                  */
 365                 if (cds_list_empty(input_readers)) {
 366                         if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 367                                 /* Read reader_gp before write futex */
 368                                 smp_mb_master();
 369                                 uatomic_set(&rcu_gp.futex, 0);
 370                         }
 371                         break;
 372                 } else {
 373                         if (wait_gp_loops == KICK_READER_LOOPS) {
 374                                 smp_mb_master();
 375                                 wait_gp_loops = 0;
 376                         }
 377                         if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
 378                                 /* wait_gp unlocks/locks registry lock. */
 379                                 wait_gp();
 380                                 wait_gp_loops++;
 381                         } else {
 382                                 /* Temporarily unlock the registry lock. */
 383                                 mutex_unlock(&rcu_registry_lock);
 384                                 caa_cpu_relax();
 385                                 /*
 386                                  * Re-lock the registry lock before the
 387                                  * next loop.
 388                                  */
 389                                 mutex_lock(&rcu_registry_lock);
 390                         }
 391                 }
 392 #endif /* #else #ifndef HAS_INCOHERENT_CACHES */
 393         }
 394 }
 395
 396 void synchronize_rcu(void)
 397 {
 398         CDS_LIST_HEAD(cur_snap_readers);
 399         CDS_LIST_HEAD(qsreaders);
 400         DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
 401         struct urcu_waiters waiters;
 402
 403         /*
 404          * Add ourself to gp_waiters queue of threads awaiting to wait
 405          * for a grace period. Proceed to perform the grace period only
 406          * if we are the first thread added into the queue.
 407          * The implicit memory barrier before urcu_wait_add()
 408          * orders prior memory accesses of threads put into the wait
 409          * queue before their insertion into the wait queue.
 410          */
 411         if (urcu_wait_add(&gp_waiters, &wait) != 0) {
 412                 /* Not first in queue: will be awakened by another thread. */
 413                 urcu_adaptative_busy_wait(&wait);
 414                 /* Order following memory accesses after grace period. */
 415                 cmm_smp_mb();
 416                 return;
 417         }
 418         /* We won't need to wake ourself up */
 419         urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
 420
 421         mutex_lock(&rcu_gp_lock);
 422
 423         /*
 424          * Move all waiters into our local queue.
 425          */
 426         urcu_move_waiters(&waiters, &gp_waiters);
 427
 428         mutex_lock(&rcu_registry_lock);
 429
 430         if (cds_list_empty(&registry))
 431                 goto out;
 432
 433         /*
 434          * All threads should read qparity before accessing data structure
 435          * where new ptr points to. Must be done within rcu_registry_lock
 436          * because it iterates on reader threads.
 437          */
 438         /* Write new ptr before changing the qparity */
 439         smp_mb_master();
 440
 441         /*
 442          * Wait for readers to observe original parity or be quiescent.
 443          * wait_for_readers() can release and grab again rcu_registry_lock
 444          * interally.
 445          */
 446         wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
 447
 448         /*
 449          * Must finish waiting for quiescent state for original parity before
 450          * committing next rcu_gp.ctr update to memory. Failure to do so could
 451          * result in the writer waiting forever while new readers are always
 452          * accessing data (no progress).  Enforce compiler-order of load
 453          * URCU_TLS(rcu_reader).ctr before store to rcu_gp.ctr.
 454          */
 455         cmm_barrier();
 456
 457         /*
 458          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 459          * model easier to understand. It does not have a big performance impact
 460          * anyway, given this is the write-side.
 461          */
 462         cmm_smp_mb();
 463
 464         /* Switch parity: 0 -> 1, 1 -> 0 */
 465         CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ URCU_GP_CTR_PHASE);
 466
 467         /*
 468          * Must commit rcu_gp.ctr update to memory before waiting for quiescent
 469          * state. Failure to do so could result in the writer waiting forever
 470          * while new readers are always accessing data (no progress). Enforce
 471          * compiler-order of store to rcu_gp.ctr before load rcu_reader ctr.
 472          */
 473         cmm_barrier();
 474
 475         /*
 476          *
 477          * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
 478          * model easier to understand. It does not have a big performance impact
 479          * anyway, given this is the write-side.
 480          */
 481         cmm_smp_mb();
 482
 483         /*
 484          * Wait for readers to observe new parity or be quiescent.
 485          * wait_for_readers() can release and grab again rcu_registry_lock
 486          * interally.
 487          */
 488         wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
 489
 490         /*
 491          * Put quiescent reader list back into registry.
 492          */
 493         cds_list_splice(&qsreaders, &registry);
 494
 495         /*
 496          * Finish waiting for reader threads before letting the old ptr
 497          * being freed. Must be done within rcu_registry_lock because it
 498          * iterates on reader threads.
 499          */
 500         smp_mb_master();
 501 out:
 502         mutex_unlock(&rcu_registry_lock);
 503         mutex_unlock(&rcu_gp_lock);
 504
 505         /*
 506          * Wakeup waiters only after we have completed the grace period
 507          * and have ensured the memory barriers at the end of the grace
 508          * period have been issued.
 509          */
 510         urcu_wake_all_waiters(&waiters);
 511 }
 512
 513 /*
 514  * library wrappers to be used by non-LGPL compatible source code.
 515  */
 516
 517 void rcu_read_lock(void)
 518 {
 519         _rcu_read_lock();
 520 }
 521
 522 void rcu_read_unlock(void)
 523 {
 524         _rcu_read_unlock();
 525 }
 526
 527 int rcu_read_ongoing(void)
 528 {
 529         return _rcu_read_ongoing();
 530 }
 531
 532 void rcu_register_thread(void)
 533 {
 534         URCU_TLS(rcu_reader).tid = pthread_self();
 535         assert(URCU_TLS(rcu_reader).need_mb == 0);
 536         assert(!(URCU_TLS(rcu_reader).ctr & URCU_GP_CTR_NEST_MASK));
 537
 538         mutex_lock(&rcu_registry_lock);
 539         assert(!URCU_TLS(rcu_reader).registered);
 540         URCU_TLS(rcu_reader).registered = 1;
 541         rcu_init();     /* In case gcc does not support constructor attribute */
 542         cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
 543         mutex_unlock(&rcu_registry_lock);
 544 }
 545
 546 void rcu_unregister_thread(void)
 547 {
 548         mutex_lock(&rcu_registry_lock);
 549         assert(URCU_TLS(rcu_reader).registered);
 550         URCU_TLS(rcu_reader).registered = 0;
 551         cds_list_del(&URCU_TLS(rcu_reader).node);
 552         mutex_unlock(&rcu_registry_lock);
 553 }
 554
 555 #ifdef RCU_MEMBARRIER
 556
 557 #ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
 558 static
 559 void rcu_sys_membarrier_status(bool available)
 560 {
 561         if (!available)
 562                 abort();
 563 }
 564 #else
 565 static
 566 void rcu_sys_membarrier_status(bool available)
 567 {
 568         if (!available)
 569                 return;
 570         urcu_memb_has_sys_membarrier = 1;
 571 }
 572 #endif
 573
 574 static
 575 void rcu_sys_membarrier_init(void)
 576 {
 577         bool available = false;
 578         int mask;
 579
 580         mask = membarrier(MEMBARRIER_CMD_QUERY, 0);
 581         if (mask >= 0) {
 582                 if (mask & MEMBARRIER_CMD_PRIVATE_EXPEDITED) {
 583                         if (membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0))
 584                                 urcu_die(errno);
 585                         urcu_memb_has_sys_membarrier_private_expedited = 1;
 586                         available = true;
 587                 } else if (mask & MEMBARRIER_CMD_SHARED) {
 588                         available = true;
 589                 }
 590         }
 591         rcu_sys_membarrier_status(available);
 592 }
 593
 594 void rcu_init(void)
 595 {
 596         if (init_done)
 597                 return;
 598         init_done = 1;
 599         rcu_sys_membarrier_init();
 600 }
 601 #endif
 602
 603 #ifdef RCU_SIGNAL
 604 static void sigrcu_handler(int signo __attribute__((unused)),
 605                 siginfo_t *siginfo __attribute__((unused)),
 606                 void *context __attribute__((unused)))
 607 {
 608         /*
 609          * Executing this cmm_smp_mb() is the only purpose of this signal handler.
 610          * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
 611          * executed on.
 612          */
 613         cmm_smp_mb();
 614         _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
 615         cmm_smp_mb();
 616 }
 617
 618 /*
 619  * rcu_init constructor. Called when the library is linked, but also when
 620  * reader threads are calling rcu_register_thread().
 621  * Should only be called by a single thread at a given time. This is ensured by
 622  * holing the rcu_registry_lock from rcu_register_thread() or by running
 623  * at library load time, which should not be executed by multiple
 624  * threads nor concurrently with rcu_register_thread() anyway.
 625  */
 626 void rcu_init(void)
 627 {
 628         struct sigaction act;
 629         int ret;
 630
 631         if (init_done)
 632                 return;
 633         init_done = 1;
 634
 635         act.sa_sigaction = sigrcu_handler;
 636         act.sa_flags = SA_SIGINFO | SA_RESTART;
 637         sigemptyset(&act.sa_mask);
 638         ret = sigaction(SIGRCU, &act, NULL);
 639         if (ret)
 640                 urcu_die(errno);
 641 }
 642
 643 void rcu_exit(void)
 644 {
 645         /*
 646          * Don't unregister the SIGRCU signal handler anymore, because
 647          * call_rcu threads could still be using it shortly before the
 648          * application exits.
 649          * Assertion disabled because call_rcu threads are now rcu
 650          * readers, and left running at exit.
 651          * assert(cds_list_empty(&registry));
 652          */
 653 }
 654
 655 #endif /* #ifdef RCU_SIGNAL */
 656
 657 DEFINE_RCU_FLAVOR(rcu_flavor);
 658
 659 #include "urcu-call-rcu-impl.h"
 660 #include "urcu-defer-impl.h"