urcu-call-rcu-impl.h

   1 /*
   2  * urcu-call-rcu.c
   3  *
   4  * Userspace RCU library - batch memory reclamation with kernel API
   5  *
   6  * Copyright (c) 2010 Paul E. McKenney <paulmck@linux.vnet.ibm.com>
   7  *
   8  * This library is free software; you can redistribute it and/or
   9  * modify it under the terms of the GNU Lesser General Public
  10  * License as published by the Free Software Foundation; either
  11  * version 2.1 of the License, or (at your option) any later version.
  12  *
  13  * This library is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  16  * Lesser General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU Lesser General Public
  19  * License along with this library; if not, write to the Free Software
  20  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  21  */
  22
  23 #define _GNU_SOURCE
  24 #include <stdio.h>
  25 #include <pthread.h>
  26 #include <signal.h>
  27 #include <assert.h>
  28 #include <stdlib.h>
  29 #include <string.h>
  30 #include <errno.h>
  31 #include <poll.h>
  32 #include <sys/time.h>
  33 #include <syscall.h>
  34 #include <unistd.h>
  35 #include <sched.h>
  36
  37 #include "config.h"
  38 #include "urcu/wfqueue.h"
  39 #include "urcu-call-rcu.h"
  40 #include "urcu-pointer.h"
  41 #include "urcu/list.h"
  42 #include "urcu/urcu-futex.h"
  43
  44 /* Data structure that identifies a call_rcu thread. */
  45
  46 struct call_rcu_data {
  47         struct cds_wfq_queue cbs;
  48         unsigned long flags;
  49         int futex;
  50         unsigned long qlen; /* maintained for debugging. */
  51         pthread_t tid;
  52         int cpu_affinity;
  53         struct cds_list_head list;
  54 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
  55
  56 /*
  57  * List of all call_rcu_data structures to keep valgrind happy.
  58  * Protected by call_rcu_mutex.
  59  */
  60
  61 CDS_LIST_HEAD(call_rcu_data_list);
  62
  63 /* Link a thread using call_rcu() to its call_rcu thread. */
  64
  65 static __thread struct call_rcu_data *thread_call_rcu_data;
  66
  67 /* Guard call_rcu thread creation. */
  68
  69 static pthread_mutex_t call_rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
  70
  71 /* If a given thread does not have its own call_rcu thread, this is default. */
  72
  73 static struct call_rcu_data *default_call_rcu_data;
  74
  75 /*
  76  * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
  77  * available, then we can have call_rcu threads assigned to individual
  78  * CPUs rather than only to specific threads.
  79  */
  80
  81 #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
  82
  83 /*
  84  * Pointer to array of pointers to per-CPU call_rcu_data structures
  85  * and # CPUs.
  86  */
  87
  88 static struct call_rcu_data **per_cpu_call_rcu_data;
  89 static long maxcpus;
  90
  91 static void call_rcu_wait(struct call_rcu_data *crdp)
  92 {
  93         /* Read call_rcu list before read futex */
  94         cmm_smp_mb();
  95         if (uatomic_read(&crdp->futex) == -1)
  96                 futex_async(&crdp->futex, FUTEX_WAIT, -1,
  97                       NULL, NULL, 0);
  98 }
  99
 100 static void call_rcu_wake_up(struct call_rcu_data *crdp)
 101 {
 102         /* Write to call_rcu list before reading/writing futex */
 103         cmm_smp_mb();
 104         if (unlikely(uatomic_read(&crdp->futex) == -1)) {
 105                 uatomic_set(&crdp->futex, 0);
 106                 futex_async(&crdp->futex, FUTEX_WAKE, 1,
 107                       NULL, NULL, 0);
 108         }
 109 }
 110
 111 /* Allocate the array if it has not already been allocated. */
 112
 113 static void alloc_cpu_call_rcu_data(void)
 114 {
 115         struct call_rcu_data **p;
 116         static int warned = 0;
 117
 118         if (maxcpus != 0)
 119                 return;
 120         maxcpus = sysconf(_SC_NPROCESSORS_CONF);
 121         if (maxcpus <= 0) {
 122                 return;
 123         }
 124         p = malloc(maxcpus * sizeof(*per_cpu_call_rcu_data));
 125         if (p != NULL) {
 126                 memset(p, '\0', maxcpus * sizeof(*per_cpu_call_rcu_data));
 127                 per_cpu_call_rcu_data = p;
 128         } else {
 129                 if (!warned) {
 130                         fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
 131                 }
 132                 warned = 1;
 133         }
 134 }
 135
 136 #else /* #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
 137
 138 static const struct call_rcu_data **per_cpu_call_rcu_data = NULL;
 139 static const long maxcpus = -1;
 140
 141 static void alloc_cpu_call_rcu_data(void)
 142 {
 143 }
 144
 145 static int sched_getcpu(void)
 146 {
 147         return -1;
 148 }
 149
 150 #endif /* #else #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
 151
 152 /* Acquire the specified pthread mutex. */
 153
 154 static void call_rcu_lock(pthread_mutex_t *pmp)
 155 {
 156         if (pthread_mutex_lock(pmp) != 0) {
 157                 perror("pthread_mutex_lock");
 158                 exit(-1);
 159         }
 160 }
 161
 162 /* Release the specified pthread mutex. */
 163
 164 static void call_rcu_unlock(pthread_mutex_t *pmp)
 165 {
 166         if (pthread_mutex_unlock(pmp) != 0) {
 167                 perror("pthread_mutex_unlock");
 168                 exit(-1);
 169         }
 170 }
 171
 172 #if HAVE_SCHED_SETAFFINITY
 173 static
 174 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
 175 {
 176         cpu_set_t mask;
 177
 178         if (crdp->cpu_affinity < 0)
 179                 return 0;
 180
 181         CPU_ZERO(&mask);
 182         CPU_SET(crdp->cpu_affinity, &mask);
 183 #if SCHED_SETAFFINITY_ARGS == 2
 184         return sched_setaffinity(0, &mask);
 185 #else
 186         return sched_setaffinity(0, sizeof(mask), &mask);
 187 #endif
 188 }
 189 #else
 190 static
 191 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
 192 {
 193         return 0;
 194 }
 195 #endif
 196
 197 /* This is the code run by each call_rcu thread. */
 198
 199 static void *call_rcu_thread(void *arg)
 200 {
 201         unsigned long cbcount;
 202         struct cds_wfq_node *cbs;
 203         struct cds_wfq_node **cbs_tail;
 204         struct call_rcu_data *crdp = (struct call_rcu_data *)arg;
 205         struct rcu_head *rhp;
 206         int rt = !!(uatomic_read(&crdp->flags) & URCU_CALL_RCU_RT);
 207
 208         if (set_thread_cpu_affinity(crdp) != 0) {
 209                 perror("pthread_setaffinity_np");
 210                 exit(-1);
 211         }
 212
 213         thread_call_rcu_data = crdp;
 214         for (;;) {
 215                 if (!rt) {
 216                         uatomic_dec(&crdp->futex);
 217                         /* Decrement futex before reading call_rcu list */
 218                         cmm_smp_mb();
 219                 }
 220                 if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
 221                         while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
 222                                 poll(NULL, 0, 1);
 223                         _CMM_STORE_SHARED(crdp->cbs.head, NULL);
 224                         cbs_tail = (struct cds_wfq_node **)
 225                                 uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
 226                         synchronize_rcu();
 227                         cbcount = 0;
 228                         do {
 229                                 while (cbs->next == NULL &&
 230                                        &cbs->next != cbs_tail)
 231                                         poll(NULL, 0, 1);
 232                                 if (cbs == &crdp->cbs.dummy) {
 233                                         cbs = cbs->next;
 234                                         continue;
 235                                 }
 236                                 rhp = (struct rcu_head *)cbs;
 237                                 cbs = cbs->next;
 238                                 rhp->func(rhp);
 239                                 cbcount++;
 240                         } while (cbs != NULL);
 241                         uatomic_sub(&crdp->qlen, cbcount);
 242                 }
 243                 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOP) {
 244                         if (!rt) {
 245                                 /*
 246                                  * Read call_rcu list before write futex.
 247                                  */
 248                                 cmm_smp_mb();
 249                                 uatomic_set(&crdp->futex, 0);
 250                         }
 251                         break;
 252                 }
 253                 if (!rt) {
 254                         if (&crdp->cbs.head == _CMM_LOAD_SHARED(crdp->cbs.tail))
 255                                 call_rcu_wait(crdp);
 256                 }
 257                 poll(NULL, 0, 10);
 258         }
 259         uatomic_or(&crdp->flags, URCU_CALL_RCU_STOPPED);
 260         return NULL;
 261 }
 262
 263 /*
 264  * Create both a call_rcu thread and the corresponding call_rcu_data
 265  * structure, linking the structure in as specified.  Caller must hold
 266  * call_rcu_mutex.
 267  */
 268
 269 static void call_rcu_data_init(struct call_rcu_data **crdpp,
 270                                unsigned long flags,
 271                                int cpu_affinity)
 272 {
 273         struct call_rcu_data *crdp;
 274
 275         crdp = malloc(sizeof(*crdp));
 276         if (crdp == NULL) {
 277                 fprintf(stderr, "Out of memory.\n");
 278                 exit(-1);
 279         }
 280         memset(crdp, '\0', sizeof(*crdp));
 281         cds_wfq_init(&crdp->cbs);
 282         crdp->qlen = 0;
 283         crdp->futex = 0;
 284         crdp->flags = flags;
 285         cds_list_add(&crdp->list, &call_rcu_data_list);
 286         crdp->cpu_affinity = cpu_affinity;
 287         cmm_smp_mb();  /* Structure initialized before pointer is planted. */
 288         *crdpp = crdp;
 289         if (pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp) != 0) {
 290                 perror("pthread_create");
 291                 exit(-1);
 292         }
 293 }
 294
 295 /*
 296  * Return a pointer to the call_rcu_data structure for the specified
 297  * CPU, returning NULL if there is none.  We cannot automatically
 298  * created it because the platform we are running on might not define
 299  * sched_getcpu().
 300  */
 301
 302 struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
 303 {
 304         static int warned = 0;
 305
 306         if (per_cpu_call_rcu_data == NULL)
 307                 return NULL;
 308         if (!warned && maxcpus > 0 && (cpu < 0 || maxcpus <= cpu)) {
 309                 fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
 310                 warned = 1;
 311         }
 312         if (cpu < 0 || maxcpus <= cpu)
 313                 return NULL;
 314         return per_cpu_call_rcu_data[cpu];
 315 }
 316
 317 /*
 318  * Return the tid corresponding to the call_rcu thread whose
 319  * call_rcu_data structure is specified.
 320  */
 321
 322 pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
 323 {
 324         return crdp->tid;
 325 }
 326
 327 /*
 328  * Create a call_rcu_data structure (with thread) and return a pointer.
 329  */
 330
 331 static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
 332                                                     int cpu_affinity)
 333 {
 334         struct call_rcu_data *crdp;
 335
 336         call_rcu_data_init(&crdp, flags, cpu_affinity);
 337         return crdp;
 338 }
 339
 340 struct call_rcu_data *create_call_rcu_data(unsigned long flags,
 341                                            int cpu_affinity)
 342 {
 343         struct call_rcu_data *crdp;
 344
 345         call_rcu_lock(&call_rcu_mutex);
 346         crdp = __create_call_rcu_data(flags, cpu_affinity);
 347         call_rcu_unlock(&call_rcu_mutex);
 348         return crdp;
 349 }
 350
 351 /*
 352  * Set the specified CPU to use the specified call_rcu_data structure.
 353  *
 354  * Use NULL to remove a CPU's call_rcu_data structure, but it is
 355  * the caller's responsibility to dispose of the removed structure.
 356  * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
 357  * (prior to NULLing it out, of course).
 358  */
 359
 360 int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
 361 {
 362         int warned = 0;
 363
 364         call_rcu_lock(&call_rcu_mutex);
 365         if (cpu < 0 || maxcpus <= cpu) {
 366                 if (!warned) {
 367                         fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
 368                         warned = 1;
 369                 }
 370                 call_rcu_unlock(&call_rcu_mutex);
 371                 errno = EINVAL;
 372                 return -EINVAL;
 373         }
 374         alloc_cpu_call_rcu_data();
 375         call_rcu_unlock(&call_rcu_mutex);
 376         if (per_cpu_call_rcu_data == NULL) {
 377                 errno = ENOMEM;
 378                 return -ENOMEM;
 379         }
 380         per_cpu_call_rcu_data[cpu] = crdp;
 381         return 0;
 382 }
 383
 384 /*
 385  * Return a pointer to the default call_rcu_data structure, creating
 386  * one if need be.  Because we never free call_rcu_data structures,
 387  * we don't need to be in an RCU read-side critical section.
 388  */
 389
 390 struct call_rcu_data *get_default_call_rcu_data(void)
 391 {
 392         if (default_call_rcu_data != NULL)
 393                 return rcu_dereference(default_call_rcu_data);
 394         call_rcu_lock(&call_rcu_mutex);
 395         if (default_call_rcu_data != NULL) {
 396                 call_rcu_unlock(&call_rcu_mutex);
 397                 return default_call_rcu_data;
 398         }
 399         call_rcu_data_init(&default_call_rcu_data, 0, -1);
 400         call_rcu_unlock(&call_rcu_mutex);
 401         return default_call_rcu_data;
 402 }
 403
 404 /*
 405  * Return the call_rcu_data structure that applies to the currently
 406  * running thread.  Any call_rcu_data structure assigned specifically
 407  * to this thread has first priority, followed by any call_rcu_data
 408  * structure assigned to the CPU on which the thread is running,
 409  * followed by the default call_rcu_data structure.  If there is not
 410  * yet a default call_rcu_data structure, one will be created.
 411  */
 412 struct call_rcu_data *get_call_rcu_data(void)
 413 {
 414         int curcpu;
 415         static int warned = 0;
 416
 417         if (thread_call_rcu_data != NULL)
 418                 return thread_call_rcu_data;
 419         if (maxcpus <= 0)
 420                 return get_default_call_rcu_data();
 421         curcpu = sched_getcpu();
 422         if (!warned && (curcpu < 0 || maxcpus <= curcpu)) {
 423                 fprintf(stderr, "[error] liburcu: gcrd CPU # out of range\n");
 424                 warned = 1;
 425         }
 426         if (curcpu >= 0 && maxcpus > curcpu &&
 427             per_cpu_call_rcu_data != NULL &&
 428             per_cpu_call_rcu_data[curcpu] != NULL)
 429                 return per_cpu_call_rcu_data[curcpu];
 430         return get_default_call_rcu_data();
 431 }
 432
 433 /*
 434  * Return a pointer to this task's call_rcu_data if there is one.
 435  */
 436
 437 struct call_rcu_data *get_thread_call_rcu_data(void)
 438 {
 439         return thread_call_rcu_data;
 440 }
 441
 442 /*
 443  * Set this task's call_rcu_data structure as specified, regardless
 444  * of whether or not this task already had one.  (This allows switching
 445  * to and from real-time call_rcu threads, for example.)
 446  *
 447  * Use NULL to remove a thread's call_rcu_data structure, but it is
 448  * the caller's responsibility to dispose of the removed structure.
 449  * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
 450  * (prior to NULLing it out, of course).
 451  */
 452
 453 void set_thread_call_rcu_data(struct call_rcu_data *crdp)
 454 {
 455         thread_call_rcu_data = crdp;
 456 }
 457
 458 /*
 459  * Create a separate call_rcu thread for each CPU.  This does not
 460  * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
 461  * function if you want that behavior.
 462  */
 463
 464 int create_all_cpu_call_rcu_data(unsigned long flags)
 465 {
 466         int i;
 467         struct call_rcu_data *crdp;
 468         int ret;
 469
 470         call_rcu_lock(&call_rcu_mutex);
 471         alloc_cpu_call_rcu_data();
 472         call_rcu_unlock(&call_rcu_mutex);
 473         if (maxcpus <= 0) {
 474                 errno = EINVAL;
 475                 return -EINVAL;
 476         }
 477         if (per_cpu_call_rcu_data == NULL) {
 478                 errno = ENOMEM;
 479                 return -ENOMEM;
 480         }
 481         for (i = 0; i < maxcpus; i++) {
 482                 call_rcu_lock(&call_rcu_mutex);
 483                 if (get_cpu_call_rcu_data(i)) {
 484                         call_rcu_unlock(&call_rcu_mutex);
 485                         continue;
 486                 }
 487                 crdp = __create_call_rcu_data(flags, i);
 488                 if (crdp == NULL) {
 489                         call_rcu_unlock(&call_rcu_mutex);
 490                         errno = ENOMEM;
 491                         return -ENOMEM;
 492                 }
 493                 call_rcu_unlock(&call_rcu_mutex);
 494                 if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
 495                         /* FIXME: Leaks crdp for now. */
 496                         return ret; /* Can happen on race. */
 497                 }
 498         }
 499         return 0;
 500 }
 501
 502 /*
 503  * Wake up the call_rcu thread corresponding to the specified
 504  * call_rcu_data structure.
 505  */
 506 static void wake_call_rcu_thread(struct call_rcu_data *crdp)
 507 {
 508         if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT))
 509                 call_rcu_wake_up(crdp);
 510 }
 511
 512 /*
 513  * Schedule a function to be invoked after a following grace period.
 514  * This is the only function that must be called -- the others are
 515  * only present to allow applications to tune their use of RCU for
 516  * maximum performance.
 517  *
 518  * Note that unless a call_rcu thread has not already been created,
 519  * the first invocation of call_rcu() will create one.  So, if you
 520  * need the first invocation of call_rcu() to be fast, make sure
 521  * to create a call_rcu thread first.  One way to accomplish this is
 522  * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
 523  */
 524
 525 void call_rcu(struct rcu_head *head,
 526               void (*func)(struct rcu_head *head))
 527 {
 528         struct call_rcu_data *crdp;
 529
 530         cds_wfq_node_init(&head->next);
 531         head->func = func;
 532         crdp = get_call_rcu_data();
 533         cds_wfq_enqueue(&crdp->cbs, &head->next);
 534         uatomic_inc(&crdp->qlen);
 535         wake_call_rcu_thread(crdp);
 536 }
 537
 538 /*
 539  * Free up the specified call_rcu_data structure, terminating the
 540  * associated call_rcu thread.  The caller must have previously
 541  * removed the call_rcu_data structure from per-thread or per-CPU
 542  * usage.  For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
 543  * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
 544  * per-thread call_rcu_data structures.
 545  *
 546  * We silently refuse to free up the default call_rcu_data structure
 547  * because that is where we put any leftover callbacks.  Note that
 548  * the possibility of self-spawning callbacks makes it impossible
 549  * to execute all the callbacks in finite time without putting any
 550  * newly spawned callbacks somewhere else.  The "somewhere else" of
 551  * last resort is the default call_rcu_data structure.
 552  *
 553  * We also silently refuse to free NULL pointers.  This simplifies
 554  * the calling code.
 555  */
 556 void call_rcu_data_free(struct call_rcu_data *crdp)
 557 {
 558         struct cds_wfq_node *cbs;
 559         struct cds_wfq_node **cbs_tail;
 560         struct cds_wfq_node **cbs_endprev;
 561
 562         if (crdp == NULL || crdp == default_call_rcu_data) {
 563                 return;
 564         }
 565         if ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0) {
 566                 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOP);
 567                 wake_call_rcu_thread(crdp);
 568                 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
 569                         poll(NULL, 0, 1);
 570         }
 571         if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
 572                 while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
 573                         poll(NULL, 0, 1);
 574                 _CMM_STORE_SHARED(crdp->cbs.head, NULL);
 575                 cbs_tail = (struct cds_wfq_node **)
 576                         uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
 577                 cbs_endprev = (struct cds_wfq_node **)
 578                         uatomic_xchg(&default_call_rcu_data, cbs_tail);
 579                 *cbs_endprev = cbs;
 580                 uatomic_add(&default_call_rcu_data->qlen,
 581                             uatomic_read(&crdp->qlen));
 582                 cds_list_del(&crdp->list);
 583                 free(crdp);
 584         }
 585 }
 586
 587 /*
 588  * Clean up all the per-CPU call_rcu threads.
 589  */
 590 void free_all_cpu_call_rcu_data(void)
 591 {
 592         int cpu;
 593         struct call_rcu_data *crdp;
 594
 595         if (maxcpus <= 0)
 596                 return;
 597         for (cpu = 0; cpu < maxcpus; cpu++) {
 598                 crdp = get_cpu_call_rcu_data(cpu);
 599                 if (crdp == NULL)
 600                         continue;
 601                 set_cpu_call_rcu_data(cpu, NULL);
 602                 call_rcu_data_free(crdp);
 603         }
 604 }
 605
 606 /*
 607  * Acquire the call_rcu_mutex in order to ensure that the child sees
 608  * all of the call_rcu() data structures in a consistent state.
 609  * Suitable for pthread_atfork() and friends.
 610  */
 611 void call_rcu_before_fork(void)
 612 {
 613         call_rcu_lock(&call_rcu_mutex);
 614 }
 615
 616 /*
 617  * Clean up call_rcu data structures in the parent of a successful fork()
 618  * that is not followed by exec() in the child.  Suitable for
 619  * pthread_atfork() and friends.
 620  */
 621 void call_rcu_after_fork_parent(void)
 622 {
 623         call_rcu_unlock(&call_rcu_mutex);
 624 }
 625
 626 /*
 627  * Clean up call_rcu data structures in the child of a successful fork()
 628  * that is not followed by exec().  Suitable for pthread_atfork() and
 629  * friends.
 630  */
 631 void call_rcu_after_fork_child(void)
 632 {
 633         struct call_rcu_data *crdp;
 634
 635         /* Release the mutex. */
 636         call_rcu_unlock(&call_rcu_mutex);
 637
 638         /*
 639          * Allocate a new default call_rcu_data structure in order
 640          * to get a working call_rcu thread to go with it.
 641          */
 642         default_call_rcu_data = NULL;
 643         (void)get_default_call_rcu_data();
 644
 645         /* Dispose of all of the rest of the call_rcu_data structures. */
 646         while (call_rcu_data_list.next != call_rcu_data_list.prev) {
 647                 crdp = cds_list_entry(call_rcu_data_list.prev,
 648                                       struct call_rcu_data, list);
 649                 if (crdp == default_call_rcu_data)
 650                         crdp = cds_list_entry(crdp->list.prev,
 651                                               struct call_rcu_data, list);
 652                 uatomic_set(&crdp->flags, URCU_CALL_RCU_STOPPED);
 653                 call_rcu_data_free(crdp);
 654         }
 655 }