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