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         pthread_mutex_t mtx;
  50         int futex;
  51         unsigned long qlen;
  52         pthread_t tid;
  53         int cpu_affinity;
  54         struct cds_list_head list;
  55 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
  56
  57 /*
  58  * List of all call_rcu_data structures to keep valgrind happy.
  59  * Protected by call_rcu_mutex.
  60  */
  61
  62 CDS_LIST_HEAD(call_rcu_data_list);
  63
  64 /* Link a thread using call_rcu() to its call_rcu thread. */
  65
  66 static __thread struct call_rcu_data *thread_call_rcu_data;
  67
  68 /* Guard call_rcu thread creation. */
  69
  70 static pthread_mutex_t call_rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
  71
  72 /* If a given thread does not have its own call_rcu thread, this is default. */
  73
  74 static struct call_rcu_data *default_call_rcu_data;
  75
  76 /*
  77  * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
  78  * available, then we can have call_rcu threads assigned to individual
  79  * CPUs rather than only to specific threads.
  80  */
  81
  82 #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
  83
  84 /*
  85  * Pointer to array of pointers to per-CPU call_rcu_data structures
  86  * and # CPUs.
  87  */
  88
  89 static struct call_rcu_data **per_cpu_call_rcu_data;
  90 static long maxcpus;
  91
  92 static void call_rcu_wait(struct call_rcu_data *crdp)
  93 {
  94         /* Read call_rcu list before read futex */
  95         cmm_smp_mb();
  96         if (uatomic_read(&crdp->futex) == -1)
  97                 futex_async(&crdp->futex, FUTEX_WAIT, -1,
  98                       NULL, NULL, 0);
  99 }
 100
 101 static void call_rcu_wake_up(struct call_rcu_data *crdp)
 102 {
 103         /* Write to call_rcu list before reading/writing futex */
 104         cmm_smp_mb();
 105         if (unlikely(uatomic_read(&crdp->futex) == -1)) {
 106                 uatomic_set(&crdp->futex, 0);
 107                 futex_async(&crdp->futex, FUTEX_WAKE, 1,
 108                       NULL, NULL, 0);
 109         }
 110 }
 111
 112 /* Allocate the array if it has not already been allocated. */
 113
 114 static void alloc_cpu_call_rcu_data(void)
 115 {
 116         struct call_rcu_data **p;
 117         static int warned = 0;
 118
 119         if (maxcpus != 0)
 120                 return;
 121         maxcpus = sysconf(_SC_NPROCESSORS_CONF);
 122         if (maxcpus <= 0) {
 123                 return;
 124         }
 125         p = malloc(maxcpus * sizeof(*per_cpu_call_rcu_data));
 126         if (p != NULL) {
 127                 memset(p, '\0', maxcpus * sizeof(*per_cpu_call_rcu_data));
 128                 per_cpu_call_rcu_data = p;
 129         } else {
 130                 if (!warned) {
 131                         fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
 132                 }
 133                 warned = 1;
 134         }
 135 }
 136
 137 #else /* #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
 138
 139 static const struct call_rcu_data **per_cpu_call_rcu_data = NULL;
 140 static const long maxcpus = -1;
 141
 142 static void alloc_cpu_call_rcu_data(void)
 143 {
 144 }
 145
 146 static int sched_getcpu(void)
 147 {
 148         return -1;
 149 }
 150
 151 #endif /* #else #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
 152
 153 /* Acquire the specified pthread mutex. */
 154
 155 static void call_rcu_lock(pthread_mutex_t *pmp)
 156 {
 157         if (pthread_mutex_lock(pmp) != 0) {
 158                 perror("pthread_mutex_lock");
 159                 exit(-1);
 160         }
 161 }
 162
 163 /* Release the specified pthread mutex. */
 164
 165 static void call_rcu_unlock(pthread_mutex_t *pmp)
 166 {
 167         if (pthread_mutex_unlock(pmp) != 0) {
 168                 perror("pthread_mutex_unlock");
 169                 exit(-1);
 170         }
 171 }
 172
 173 #if HAVE_SCHED_SETAFFINITY
 174 static
 175 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
 176 {
 177         cpu_set_t mask;
 178
 179         if (crdp->cpu_affinity < 0)
 180                 return 0;
 181
 182         CPU_ZERO(&mask);
 183         CPU_SET(crdp->cpu_affinity, &mask);
 184 #if SCHED_SETAFFINITY_ARGS == 2
 185         return sched_setaffinity(0, &mask);
 186 #else
 187         return sched_setaffinity(0, sizeof(mask), &mask);
 188 #endif
 189 }
 190 #else
 191 static
 192 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
 193 {
 194         return 0;
 195 }
 196 #endif
 197
 198 /* This is the code run by each call_rcu thread. */
 199
 200 static void *call_rcu_thread(void *arg)
 201 {
 202         unsigned long cbcount;
 203         struct cds_wfq_node *cbs;
 204         struct cds_wfq_node **cbs_tail;
 205         struct call_rcu_data *crdp = (struct call_rcu_data *)arg;
 206         struct rcu_head *rhp;
 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 (!(crdp->flags & URCU_CALL_RCU_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 (crdp->flags & URCU_CALL_RCU_STOP) {
 244                         if (!(crdp->flags & URCU_CALL_RCU_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 (!(crdp->flags & URCU_CALL_RCU_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         call_rcu_lock(&crdp->mtx);
 260         crdp->flags |= URCU_CALL_RCU_STOPPED;
 261         call_rcu_unlock(&crdp->mtx);
 262         return NULL;
 263 }
 264
 265 /*
 266  * Create both a call_rcu thread and the corresponding call_rcu_data
 267  * structure, linking the structure in as specified.  Caller must hold
 268  * call_rcu_mutex.
 269  */
 270
 271 static void call_rcu_data_init(struct call_rcu_data **crdpp,
 272                                unsigned long flags,
 273                                int cpu_affinity)
 274 {
 275         struct call_rcu_data *crdp;
 276
 277         crdp = malloc(sizeof(*crdp));
 278         if (crdp == NULL) {
 279                 fprintf(stderr, "Out of memory.\n");
 280                 exit(-1);
 281         }
 282         memset(crdp, '\0', sizeof(*crdp));
 283         cds_wfq_init(&crdp->cbs);
 284         crdp->qlen = 0;
 285         if (pthread_mutex_init(&crdp->mtx, NULL) != 0) {
 286                 perror("pthread_mutex_init");
 287                 exit(-1);
 288         }
 289         crdp->futex = 0;
 290         crdp->flags = flags;
 291         cds_list_add(&crdp->list, &call_rcu_data_list);
 292         crdp->cpu_affinity = cpu_affinity;
 293         cmm_smp_mb();  /* Structure initialized before pointer is planted. */
 294         *crdpp = crdp;
 295         if (pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp) != 0) {
 296                 perror("pthread_create");
 297                 exit(-1);
 298         }
 299 }
 300
 301 /*
 302  * Return a pointer to the call_rcu_data structure for the specified
 303  * CPU, returning NULL if there is none.  We cannot automatically
 304  * created it because the platform we are running on might not define
 305  * sched_getcpu().
 306  */
 307
 308 struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
 309 {
 310         static int warned = 0;
 311
 312         if (per_cpu_call_rcu_data == NULL)
 313                 return NULL;
 314         if (!warned && maxcpus > 0 && (cpu < 0 || maxcpus <= cpu)) {
 315                 fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
 316                 warned = 1;
 317         }
 318         if (cpu < 0 || maxcpus <= cpu)
 319                 return NULL;
 320         return per_cpu_call_rcu_data[cpu];
 321 }
 322
 323 /*
 324  * Return the tid corresponding to the call_rcu thread whose
 325  * call_rcu_data structure is specified.
 326  */
 327
 328 pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
 329 {
 330         return crdp->tid;
 331 }
 332
 333 /*
 334  * Create a call_rcu_data structure (with thread) and return a pointer.
 335  */
 336
 337 static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
 338                                                     int cpu_affinity)
 339 {
 340         struct call_rcu_data *crdp;
 341
 342         call_rcu_data_init(&crdp, flags, cpu_affinity);
 343         return crdp;
 344 }
 345
 346 struct call_rcu_data *create_call_rcu_data(unsigned long flags,
 347                                            int cpu_affinity)
 348 {
 349         struct call_rcu_data *crdp;
 350
 351         call_rcu_lock(&call_rcu_mutex);
 352         crdp = __create_call_rcu_data(flags, cpu_affinity);
 353         call_rcu_unlock(&call_rcu_mutex);
 354         return crdp;
 355 }
 356
 357 /*
 358  * Set the specified CPU to use the specified call_rcu_data structure.
 359  *
 360  * Use NULL to remove a CPU's call_rcu_data structure, but it is
 361  * the caller's responsibility to dispose of the removed structure.
 362  * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
 363  * (prior to NULLing it out, of course).
 364  */
 365
 366 int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
 367 {
 368         int warned = 0;
 369
 370         call_rcu_lock(&call_rcu_mutex);
 371         if (cpu < 0 || maxcpus <= cpu) {
 372                 if (!warned) {
 373                         fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
 374                         warned = 1;
 375                 }
 376                 call_rcu_unlock(&call_rcu_mutex);
 377                 errno = EINVAL;
 378                 return -EINVAL;
 379         }
 380         alloc_cpu_call_rcu_data();
 381         call_rcu_unlock(&call_rcu_mutex);
 382         if (per_cpu_call_rcu_data == NULL) {
 383                 errno = ENOMEM;
 384                 return -ENOMEM;
 385         }
 386         per_cpu_call_rcu_data[cpu] = crdp;
 387         return 0;
 388 }
 389
 390 /*
 391  * Return a pointer to the default call_rcu_data structure, creating
 392  * one if need be.  Because we never free call_rcu_data structures,
 393  * we don't need to be in an RCU read-side critical section.
 394  */
 395
 396 struct call_rcu_data *get_default_call_rcu_data(void)
 397 {
 398         if (default_call_rcu_data != NULL)
 399                 return rcu_dereference(default_call_rcu_data);
 400         call_rcu_lock(&call_rcu_mutex);
 401         if (default_call_rcu_data != NULL) {
 402                 call_rcu_unlock(&call_rcu_mutex);
 403                 return default_call_rcu_data;
 404         }
 405         call_rcu_data_init(&default_call_rcu_data, 0, -1);
 406         call_rcu_unlock(&call_rcu_mutex);
 407         return default_call_rcu_data;
 408 }
 409
 410 /*
 411  * Return the call_rcu_data structure that applies to the currently
 412  * running thread.  Any call_rcu_data structure assigned specifically
 413  * to this thread has first priority, followed by any call_rcu_data
 414  * structure assigned to the CPU on which the thread is running,
 415  * followed by the default call_rcu_data structure.  If there is not
 416  * yet a default call_rcu_data structure, one will be created.
 417  */
 418 struct call_rcu_data *get_call_rcu_data(void)
 419 {
 420         int curcpu;
 421         static int warned = 0;
 422
 423         if (thread_call_rcu_data != NULL)
 424                 return thread_call_rcu_data;
 425         if (maxcpus <= 0)
 426                 return get_default_call_rcu_data();
 427         curcpu = sched_getcpu();
 428         if (!warned && (curcpu < 0 || maxcpus <= curcpu)) {
 429                 fprintf(stderr, "[error] liburcu: gcrd CPU # out of range\n");
 430                 warned = 1;
 431         }
 432         if (curcpu >= 0 && maxcpus > curcpu &&
 433             per_cpu_call_rcu_data != NULL &&
 434             per_cpu_call_rcu_data[curcpu] != NULL)
 435                 return per_cpu_call_rcu_data[curcpu];
 436         return get_default_call_rcu_data();
 437 }
 438
 439 /*
 440  * Return a pointer to this task's call_rcu_data if there is one.
 441  */
 442
 443 struct call_rcu_data *get_thread_call_rcu_data(void)
 444 {
 445         return thread_call_rcu_data;
 446 }
 447
 448 /*
 449  * Set this task's call_rcu_data structure as specified, regardless
 450  * of whether or not this task already had one.  (This allows switching
 451  * to and from real-time call_rcu threads, for example.)
 452  *
 453  * Use NULL to remove a thread's call_rcu_data structure, but it is
 454  * the caller's responsibility to dispose of the removed structure.
 455  * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
 456  * (prior to NULLing it out, of course).
 457  */
 458
 459 void set_thread_call_rcu_data(struct call_rcu_data *crdp)
 460 {
 461         thread_call_rcu_data = crdp;
 462 }
 463
 464 /*
 465  * Create a separate call_rcu thread for each CPU.  This does not
 466  * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
 467  * function if you want that behavior.
 468  */
 469
 470 int create_all_cpu_call_rcu_data(unsigned long flags)
 471 {
 472         int i;
 473         struct call_rcu_data *crdp;
 474         int ret;
 475
 476         call_rcu_lock(&call_rcu_mutex);
 477         alloc_cpu_call_rcu_data();
 478         call_rcu_unlock(&call_rcu_mutex);
 479         if (maxcpus <= 0) {
 480                 errno = EINVAL;
 481                 return -EINVAL;
 482         }
 483         if (per_cpu_call_rcu_data == NULL) {
 484                 errno = ENOMEM;
 485                 return -ENOMEM;
 486         }
 487         for (i = 0; i < maxcpus; i++) {
 488                 call_rcu_lock(&call_rcu_mutex);
 489                 if (get_cpu_call_rcu_data(i)) {
 490                         call_rcu_unlock(&call_rcu_mutex);
 491                         continue;
 492                 }
 493                 crdp = __create_call_rcu_data(flags, i);
 494                 if (crdp == NULL) {
 495                         call_rcu_unlock(&call_rcu_mutex);
 496                         errno = ENOMEM;
 497                         return -ENOMEM;
 498                 }
 499                 call_rcu_unlock(&call_rcu_mutex);
 500                 if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
 501                         /* FIXME: Leaks crdp for now. */
 502                         return ret; /* Can happen on race. */
 503                 }
 504         }
 505         return 0;
 506 }
 507
 508 /*
 509  * Wake up the call_rcu thread corresponding to the specified
 510  * call_rcu_data structure.
 511  */
 512 static void wake_call_rcu_thread(struct call_rcu_data *crdp)
 513 {
 514         if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT))
 515                 call_rcu_wake_up(crdp);
 516 }
 517
 518 /*
 519  * Schedule a function to be invoked after a following grace period.
 520  * This is the only function that must be called -- the others are
 521  * only present to allow applications to tune their use of RCU for
 522  * maximum performance.
 523  *
 524  * Note that unless a call_rcu thread has not already been created,
 525  * the first invocation of call_rcu() will create one.  So, if you
 526  * need the first invocation of call_rcu() to be fast, make sure
 527  * to create a call_rcu thread first.  One way to accomplish this is
 528  * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
 529  */
 530
 531 void call_rcu(struct rcu_head *head,
 532               void (*func)(struct rcu_head *head))
 533 {
 534         struct call_rcu_data *crdp;
 535
 536         cds_wfq_node_init(&head->next);
 537         head->func = func;
 538         crdp = get_call_rcu_data();
 539         cds_wfq_enqueue(&crdp->cbs, &head->next);
 540         uatomic_inc(&crdp->qlen);
 541         wake_call_rcu_thread(crdp);
 542 }
 543
 544 /*
 545  * Free up the specified call_rcu_data structure, terminating the
 546  * associated call_rcu thread.  The caller must have previously
 547  * removed the call_rcu_data structure from per-thread or per-CPU
 548  * usage.  For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
 549  * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
 550  * per-thread call_rcu_data structures.
 551  *
 552  * We silently refuse to free up the default call_rcu_data structure
 553  * because that is where we put any leftover callbacks.  Note that
 554  * the possibility of self-spawning callbacks makes it impossible
 555  * to execute all the callbacks in finite time without putting any
 556  * newly spawned callbacks somewhere else.  The "somewhere else" of
 557  * last resort is the default call_rcu_data structure.
 558  *
 559  * We also silently refuse to free NULL pointers.  This simplifies
 560  * the calling code.
 561  */
 562 void call_rcu_data_free(struct call_rcu_data *crdp)
 563 {
 564         struct cds_wfq_node *cbs;
 565         struct cds_wfq_node **cbs_tail;
 566         struct cds_wfq_node **cbs_endprev;
 567
 568         if (crdp == NULL || crdp == default_call_rcu_data) {
 569                 return;
 570         }
 571         if ((crdp->flags & URCU_CALL_RCU_STOPPED) == 0) {
 572                 call_rcu_lock(&crdp->mtx);
 573                 crdp->flags |= URCU_CALL_RCU_STOP;
 574                 call_rcu_unlock(&crdp->mtx);
 575                 wake_call_rcu_thread(crdp);
 576                 while ((crdp->flags & URCU_CALL_RCU_STOPPED) == 0)
 577                         poll(NULL, 0, 1);
 578         }
 579         if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
 580                 while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
 581                         poll(NULL, 0, 1);
 582                 _CMM_STORE_SHARED(crdp->cbs.head, NULL);
 583                 cbs_tail = (struct cds_wfq_node **)
 584                         uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
 585                 cbs_endprev = (struct cds_wfq_node **)
 586                         uatomic_xchg(&default_call_rcu_data, cbs_tail);
 587                 *cbs_endprev = cbs;
 588                 uatomic_add(&default_call_rcu_data->qlen,
 589                             uatomic_read(&crdp->qlen));
 590                 cds_list_del(&crdp->list);
 591                 free(crdp);
 592         }
 593 }
 594
 595 /*
 596  * Clean up all the per-CPU call_rcu threads.
 597  */
 598 void free_all_cpu_call_rcu_data(void)
 599 {
 600         int cpu;
 601         struct call_rcu_data *crdp;
 602
 603         if (maxcpus <= 0)
 604                 return;
 605         for (cpu = 0; cpu < maxcpus; cpu++) {
 606                 crdp = get_cpu_call_rcu_data(cpu);
 607                 if (crdp == NULL)
 608                         continue;
 609                 set_cpu_call_rcu_data(cpu, NULL);
 610                 call_rcu_data_free(crdp);
 611         }
 612 }
 613
 614 /*
 615  * Acquire the call_rcu_mutex in order to ensure that the child sees
 616  * all of the call_rcu() data structures in a consistent state.
 617  * Suitable for pthread_atfork() and friends.
 618  */
 619 void call_rcu_before_fork(void)
 620 {
 621         call_rcu_lock(&call_rcu_mutex);
 622 }
 623
 624 /*
 625  * Clean up call_rcu data structures in the parent of a successful fork()
 626  * that is not followed by exec() in the child.  Suitable for
 627  * pthread_atfork() and friends.
 628  */
 629 void call_rcu_after_fork_parent(void)
 630 {
 631         call_rcu_unlock(&call_rcu_mutex);
 632 }
 633
 634 /*
 635  * Clean up call_rcu data structures in the child of a successful fork()
 636  * that is not followed by exec().  Suitable for pthread_atfork() and
 637  * friends.
 638  */
 639 void call_rcu_after_fork_child(void)
 640 {
 641         struct call_rcu_data *crdp;
 642
 643         /* Release the mutex. */
 644         call_rcu_unlock(&call_rcu_mutex);
 645
 646         /*
 647          * Allocate a new default call_rcu_data structure in order
 648          * to get a working call_rcu thread to go with it.
 649          */
 650         default_call_rcu_data = NULL;
 651         (void)get_default_call_rcu_data();
 652
 653         /* Dispose of all of the rest of the call_rcu_data structures. */
 654         while (call_rcu_data_list.next != call_rcu_data_list.prev) {
 655                 crdp = cds_list_entry(call_rcu_data_list.prev,
 656                                       struct call_rcu_data, list);
 657                 if (crdp == default_call_rcu_data)
 658                         crdp = cds_list_entry(crdp->list.prev,
 659                                               struct call_rcu_data, list);
 660                 crdp->flags = URCU_CALL_RCU_STOPPED;
 661                 call_rcu_data_free(crdp);
 662         }
 663 }