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 <stdint.h>
  30 #include <string.h>
  31 #include <errno.h>
  32 #include <poll.h>
  33 #include <sys/time.h>
  34 #include <syscall.h>
  35 #include <unistd.h>
  36 #include <sched.h>
  37
  38 #include "config.h"
  39 #include "urcu/wfqueue.h"
  40 #include "urcu-call-rcu.h"
  41 #include "urcu-pointer.h"
  42 #include "urcu/list.h"
  43 #include "urcu/futex.h"
  44
  45 /* Data structure that identifies a call_rcu thread. */
  46
  47 struct call_rcu_data {
  48         struct cds_wfq_queue cbs;
  49         unsigned long flags;
  50         int32_t futex;
  51         unsigned long qlen; /* maintained for debugging. */
  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         int rt = !!(uatomic_read(&crdp->flags) & URCU_CALL_RCU_RT);
 208
 209         if (set_thread_cpu_affinity(crdp) != 0) {
 210                 perror("pthread_setaffinity_np");
 211                 exit(-1);
 212         }
 213
 214         thread_call_rcu_data = crdp;
 215         if (!rt) {
 216                 uatomic_dec(&crdp->futex);
 217                 /* Decrement futex before reading call_rcu list */
 218                 cmm_smp_mb();
 219         }
 220         for (;;) {
 221                 if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
 222                         while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
 223                                 poll(NULL, 0, 1);
 224                         _CMM_STORE_SHARED(crdp->cbs.head, NULL);
 225                         cbs_tail = (struct cds_wfq_node **)
 226                                 uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
 227                         synchronize_rcu();
 228                         cbcount = 0;
 229                         do {
 230                                 while (cbs->next == NULL &&
 231                                        &cbs->next != cbs_tail)
 232                                         poll(NULL, 0, 1);
 233                                 if (cbs == &crdp->cbs.dummy) {
 234                                         cbs = cbs->next;
 235                                         continue;
 236                                 }
 237                                 rhp = (struct rcu_head *)cbs;
 238                                 cbs = cbs->next;
 239                                 rhp->func(rhp);
 240                                 cbcount++;
 241                         } while (cbs != NULL);
 242                         uatomic_sub(&crdp->qlen, cbcount);
 243                 }
 244                 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOP)
 245                         break;
 246                 if (!rt) {
 247                         if (&crdp->cbs.head
 248                             == _CMM_LOAD_SHARED(crdp->cbs.tail)) {
 249                                 call_rcu_wait(crdp);
 250                                 poll(NULL, 0, 10);
 251                                 uatomic_dec(&crdp->futex);
 252                                 /*
 253                                  * Decrement futex before reading
 254                                  * call_rcu list.
 255                                  */
 256                                 cmm_smp_mb();
 257                         } else {
 258                                 poll(NULL, 0, 10);
 259                         }
 260                 } else {
 261                         poll(NULL, 0, 10);
 262                 }
 263         }
 264         if (!rt) {
 265                 /*
 266                  * Read call_rcu list before write futex.
 267                  */
 268                 cmm_smp_mb();
 269                 uatomic_set(&crdp->futex, 0);
 270         }
 271         uatomic_or(&crdp->flags, URCU_CALL_RCU_STOPPED);
 272         return NULL;
 273 }
 274
 275 /*
 276  * Create both a call_rcu thread and the corresponding call_rcu_data
 277  * structure, linking the structure in as specified.  Caller must hold
 278  * call_rcu_mutex.
 279  */
 280
 281 static void call_rcu_data_init(struct call_rcu_data **crdpp,
 282                                unsigned long flags,
 283                                int cpu_affinity)
 284 {
 285         struct call_rcu_data *crdp;
 286
 287         crdp = malloc(sizeof(*crdp));
 288         if (crdp == NULL) {
 289                 fprintf(stderr, "Out of memory.\n");
 290                 exit(-1);
 291         }
 292         memset(crdp, '\0', sizeof(*crdp));
 293         cds_wfq_init(&crdp->cbs);
 294         crdp->qlen = 0;
 295         crdp->futex = 0;
 296         crdp->flags = flags;
 297         cds_list_add(&crdp->list, &call_rcu_data_list);
 298         crdp->cpu_affinity = cpu_affinity;
 299         cmm_smp_mb();  /* Structure initialized before pointer is planted. */
 300         *crdpp = crdp;
 301         if (pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp) != 0) {
 302                 perror("pthread_create");
 303                 exit(-1);
 304         }
 305 }
 306
 307 /*
 308  * Return a pointer to the call_rcu_data structure for the specified
 309  * CPU, returning NULL if there is none.  We cannot automatically
 310  * created it because the platform we are running on might not define
 311  * sched_getcpu().
 312  */
 313
 314 struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
 315 {
 316         static int warned = 0;
 317
 318         if (per_cpu_call_rcu_data == NULL)
 319                 return NULL;
 320         if (!warned && maxcpus > 0 && (cpu < 0 || maxcpus <= cpu)) {
 321                 fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
 322                 warned = 1;
 323         }
 324         if (cpu < 0 || maxcpus <= cpu)
 325                 return NULL;
 326         return per_cpu_call_rcu_data[cpu];
 327 }
 328
 329 /*
 330  * Return the tid corresponding to the call_rcu thread whose
 331  * call_rcu_data structure is specified.
 332  */
 333
 334 pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
 335 {
 336         return crdp->tid;
 337 }
 338
 339 /*
 340  * Create a call_rcu_data structure (with thread) and return a pointer.
 341  */
 342
 343 static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
 344                                                     int cpu_affinity)
 345 {
 346         struct call_rcu_data *crdp;
 347
 348         call_rcu_data_init(&crdp, flags, cpu_affinity);
 349         return crdp;
 350 }
 351
 352 struct call_rcu_data *create_call_rcu_data(unsigned long flags,
 353                                            int cpu_affinity)
 354 {
 355         struct call_rcu_data *crdp;
 356
 357         call_rcu_lock(&call_rcu_mutex);
 358         crdp = __create_call_rcu_data(flags, cpu_affinity);
 359         call_rcu_unlock(&call_rcu_mutex);
 360         return crdp;
 361 }
 362
 363 /*
 364  * Set the specified CPU to use the specified call_rcu_data structure.
 365  *
 366  * Use NULL to remove a CPU's call_rcu_data structure, but it is
 367  * the caller's responsibility to dispose of the removed structure.
 368  * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
 369  * (prior to NULLing it out, of course).
 370  */
 371
 372 int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
 373 {
 374         int warned = 0;
 375
 376         call_rcu_lock(&call_rcu_mutex);
 377         if (cpu < 0 || maxcpus <= cpu) {
 378                 if (!warned) {
 379                         fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
 380                         warned = 1;
 381                 }
 382                 call_rcu_unlock(&call_rcu_mutex);
 383                 errno = EINVAL;
 384                 return -EINVAL;
 385         }
 386         alloc_cpu_call_rcu_data();
 387         call_rcu_unlock(&call_rcu_mutex);
 388         if (per_cpu_call_rcu_data == NULL) {
 389                 errno = ENOMEM;
 390                 return -ENOMEM;
 391         }
 392         per_cpu_call_rcu_data[cpu] = crdp;
 393         return 0;
 394 }
 395
 396 /*
 397  * Return a pointer to the default call_rcu_data structure, creating
 398  * one if need be.  Because we never free call_rcu_data structures,
 399  * we don't need to be in an RCU read-side critical section.
 400  */
 401
 402 struct call_rcu_data *get_default_call_rcu_data(void)
 403 {
 404         if (default_call_rcu_data != NULL)
 405                 return rcu_dereference(default_call_rcu_data);
 406         call_rcu_lock(&call_rcu_mutex);
 407         if (default_call_rcu_data != NULL) {
 408                 call_rcu_unlock(&call_rcu_mutex);
 409                 return default_call_rcu_data;
 410         }
 411         call_rcu_data_init(&default_call_rcu_data, 0, -1);
 412         call_rcu_unlock(&call_rcu_mutex);
 413         return default_call_rcu_data;
 414 }
 415
 416 /*
 417  * Return the call_rcu_data structure that applies to the currently
 418  * running thread.  Any call_rcu_data structure assigned specifically
 419  * to this thread has first priority, followed by any call_rcu_data
 420  * structure assigned to the CPU on which the thread is running,
 421  * followed by the default call_rcu_data structure.  If there is not
 422  * yet a default call_rcu_data structure, one will be created.
 423  */
 424 struct call_rcu_data *get_call_rcu_data(void)
 425 {
 426         int curcpu;
 427         static int warned = 0;
 428
 429         if (thread_call_rcu_data != NULL)
 430                 return thread_call_rcu_data;
 431         if (maxcpus <= 0)
 432                 return get_default_call_rcu_data();
 433         curcpu = sched_getcpu();
 434         if (!warned && (curcpu < 0 || maxcpus <= curcpu)) {
 435                 fprintf(stderr, "[error] liburcu: gcrd CPU # out of range\n");
 436                 warned = 1;
 437         }
 438         if (curcpu >= 0 && maxcpus > curcpu &&
 439             per_cpu_call_rcu_data != NULL &&
 440             per_cpu_call_rcu_data[curcpu] != NULL)
 441                 return per_cpu_call_rcu_data[curcpu];
 442         return get_default_call_rcu_data();
 443 }
 444
 445 /*
 446  * Return a pointer to this task's call_rcu_data if there is one.
 447  */
 448
 449 struct call_rcu_data *get_thread_call_rcu_data(void)
 450 {
 451         return thread_call_rcu_data;
 452 }
 453
 454 /*
 455  * Set this task's call_rcu_data structure as specified, regardless
 456  * of whether or not this task already had one.  (This allows switching
 457  * to and from real-time call_rcu threads, for example.)
 458  *
 459  * Use NULL to remove a thread's call_rcu_data structure, but it is
 460  * the caller's responsibility to dispose of the removed structure.
 461  * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
 462  * (prior to NULLing it out, of course).
 463  */
 464
 465 void set_thread_call_rcu_data(struct call_rcu_data *crdp)
 466 {
 467         thread_call_rcu_data = crdp;
 468 }
 469
 470 /*
 471  * Create a separate call_rcu thread for each CPU.  This does not
 472  * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
 473  * function if you want that behavior.
 474  */
 475
 476 int create_all_cpu_call_rcu_data(unsigned long flags)
 477 {
 478         int i;
 479         struct call_rcu_data *crdp;
 480         int ret;
 481
 482         call_rcu_lock(&call_rcu_mutex);
 483         alloc_cpu_call_rcu_data();
 484         call_rcu_unlock(&call_rcu_mutex);
 485         if (maxcpus <= 0) {
 486                 errno = EINVAL;
 487                 return -EINVAL;
 488         }
 489         if (per_cpu_call_rcu_data == NULL) {
 490                 errno = ENOMEM;
 491                 return -ENOMEM;
 492         }
 493         for (i = 0; i < maxcpus; i++) {
 494                 call_rcu_lock(&call_rcu_mutex);
 495                 if (get_cpu_call_rcu_data(i)) {
 496                         call_rcu_unlock(&call_rcu_mutex);
 497                         continue;
 498                 }
 499                 crdp = __create_call_rcu_data(flags, i);
 500                 if (crdp == NULL) {
 501                         call_rcu_unlock(&call_rcu_mutex);
 502                         errno = ENOMEM;
 503                         return -ENOMEM;
 504                 }
 505                 call_rcu_unlock(&call_rcu_mutex);
 506                 if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
 507                         /* FIXME: Leaks crdp for now. */
 508                         return ret; /* Can happen on race. */
 509                 }
 510         }
 511         return 0;
 512 }
 513
 514 /*
 515  * Wake up the call_rcu thread corresponding to the specified
 516  * call_rcu_data structure.
 517  */
 518 static void wake_call_rcu_thread(struct call_rcu_data *crdp)
 519 {
 520         if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT))
 521                 call_rcu_wake_up(crdp);
 522 }
 523
 524 /*
 525  * Schedule a function to be invoked after a following grace period.
 526  * This is the only function that must be called -- the others are
 527  * only present to allow applications to tune their use of RCU for
 528  * maximum performance.
 529  *
 530  * Note that unless a call_rcu thread has not already been created,
 531  * the first invocation of call_rcu() will create one.  So, if you
 532  * need the first invocation of call_rcu() to be fast, make sure
 533  * to create a call_rcu thread first.  One way to accomplish this is
 534  * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
 535  */
 536
 537 void call_rcu(struct rcu_head *head,
 538               void (*func)(struct rcu_head *head))
 539 {
 540         struct call_rcu_data *crdp;
 541
 542         cds_wfq_node_init(&head->next);
 543         head->func = func;
 544         crdp = get_call_rcu_data();
 545         cds_wfq_enqueue(&crdp->cbs, &head->next);
 546         uatomic_inc(&crdp->qlen);
 547         wake_call_rcu_thread(crdp);
 548 }
 549
 550 /*
 551  * Free up the specified call_rcu_data structure, terminating the
 552  * associated call_rcu thread.  The caller must have previously
 553  * removed the call_rcu_data structure from per-thread or per-CPU
 554  * usage.  For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
 555  * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
 556  * per-thread call_rcu_data structures.
 557  *
 558  * We silently refuse to free up the default call_rcu_data structure
 559  * because that is where we put any leftover callbacks.  Note that
 560  * the possibility of self-spawning callbacks makes it impossible
 561  * to execute all the callbacks in finite time without putting any
 562  * newly spawned callbacks somewhere else.  The "somewhere else" of
 563  * last resort is the default call_rcu_data structure.
 564  *
 565  * We also silently refuse to free NULL pointers.  This simplifies
 566  * the calling code.
 567  */
 568 void call_rcu_data_free(struct call_rcu_data *crdp)
 569 {
 570         struct cds_wfq_node *cbs;
 571         struct cds_wfq_node **cbs_tail;
 572         struct cds_wfq_node **cbs_endprev;
 573
 574         if (crdp == NULL || crdp == default_call_rcu_data) {
 575                 return;
 576         }
 577         if ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0) {
 578                 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOP);
 579                 wake_call_rcu_thread(crdp);
 580                 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
 581                         poll(NULL, 0, 1);
 582         }
 583         if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
 584                 while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
 585                         poll(NULL, 0, 1);
 586                 _CMM_STORE_SHARED(crdp->cbs.head, NULL);
 587                 cbs_tail = (struct cds_wfq_node **)
 588                         uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
 589                 cbs_endprev = (struct cds_wfq_node **)
 590                         uatomic_xchg(&default_call_rcu_data, cbs_tail);
 591                 *cbs_endprev = cbs;
 592                 uatomic_add(&default_call_rcu_data->qlen,
 593                             uatomic_read(&crdp->qlen));
 594                 cds_list_del(&crdp->list);
 595                 free(crdp);
 596         }
 597 }
 598
 599 /*
 600  * Clean up all the per-CPU call_rcu threads.
 601  */
 602 void free_all_cpu_call_rcu_data(void)
 603 {
 604         int cpu;
 605         struct call_rcu_data *crdp;
 606
 607         if (maxcpus <= 0)
 608                 return;
 609         for (cpu = 0; cpu < maxcpus; cpu++) {
 610                 crdp = get_cpu_call_rcu_data(cpu);
 611                 if (crdp == NULL)
 612                         continue;
 613                 set_cpu_call_rcu_data(cpu, NULL);
 614                 call_rcu_data_free(crdp);
 615         }
 616 }
 617
 618 /*
 619  * Acquire the call_rcu_mutex in order to ensure that the child sees
 620  * all of the call_rcu() data structures in a consistent state.
 621  * Suitable for pthread_atfork() and friends.
 622  */
 623 void call_rcu_before_fork(void)
 624 {
 625         call_rcu_lock(&call_rcu_mutex);
 626 }
 627
 628 /*
 629  * Clean up call_rcu data structures in the parent of a successful fork()
 630  * that is not followed by exec() in the child.  Suitable for
 631  * pthread_atfork() and friends.
 632  */
 633 void call_rcu_after_fork_parent(void)
 634 {
 635         call_rcu_unlock(&call_rcu_mutex);
 636 }
 637
 638 /*
 639  * Clean up call_rcu data structures in the child of a successful fork()
 640  * that is not followed by exec().  Suitable for pthread_atfork() and
 641  * friends.
 642  */
 643 void call_rcu_after_fork_child(void)
 644 {
 645         struct call_rcu_data *crdp;
 646
 647         /* Release the mutex. */
 648         call_rcu_unlock(&call_rcu_mutex);
 649
 650         /*
 651          * Allocate a new default call_rcu_data structure in order
 652          * to get a working call_rcu thread to go with it.
 653          */
 654         default_call_rcu_data = NULL;
 655         (void)get_default_call_rcu_data();
 656
 657         /* Dispose of all of the rest of the call_rcu_data structures. */
 658         while (call_rcu_data_list.next != call_rcu_data_list.prev) {
 659                 crdp = cds_list_entry(call_rcu_data_list.prev,
 660                                       struct call_rcu_data, list);
 661                 if (crdp == default_call_rcu_data)
 662                         crdp = cds_list_entry(crdp->list.prev,
 663                                               struct call_rcu_data, list);
 664                 uatomic_set(&crdp->flags, URCU_CALL_RCU_STOPPED);
 665                 call_rcu_data_free(crdp);
 666         }
 667 }