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 <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/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         int32_t 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 /* Allocate the array if it has not already been allocated. */
  92
  93 static void alloc_cpu_call_rcu_data(void)
  94 {
  95         struct call_rcu_data **p;
  96         static int warned = 0;
  97
  98         if (maxcpus != 0)
  99                 return;
 100         maxcpus = sysconf(_SC_NPROCESSORS_CONF);
 101         if (maxcpus <= 0) {
 102                 return;
 103         }
 104         p = malloc(maxcpus * sizeof(*per_cpu_call_rcu_data));
 105         if (p != NULL) {
 106                 memset(p, '\0', maxcpus * sizeof(*per_cpu_call_rcu_data));
 107                 per_cpu_call_rcu_data = p;
 108         } else {
 109                 if (!warned) {
 110                         fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
 111                 }
 112                 warned = 1;
 113         }
 114 }
 115
 116 #else /* #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
 117
 118 /*
 119  * per_cpu_call_rcu_data should be constant, but some functions below, used both
 120  * for cases where cpu number is available and not available, assume it it not
 121  * constant.
 122  */
 123 static struct call_rcu_data **per_cpu_call_rcu_data = NULL;
 124 static const long maxcpus = -1;
 125
 126 static void alloc_cpu_call_rcu_data(void)
 127 {
 128 }
 129
 130 static int sched_getcpu(void)
 131 {
 132         return -1;
 133 }
 134
 135 #endif /* #else #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
 136
 137 /* Acquire the specified pthread mutex. */
 138
 139 static void call_rcu_lock(pthread_mutex_t *pmp)
 140 {
 141         if (pthread_mutex_lock(pmp) != 0) {
 142                 perror("pthread_mutex_lock");
 143                 exit(-1);
 144         }
 145 }
 146
 147 /* Release the specified pthread mutex. */
 148
 149 static void call_rcu_unlock(pthread_mutex_t *pmp)
 150 {
 151         if (pthread_mutex_unlock(pmp) != 0) {
 152                 perror("pthread_mutex_unlock");
 153                 exit(-1);
 154         }
 155 }
 156
 157 #if HAVE_SCHED_SETAFFINITY
 158 static
 159 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
 160 {
 161         cpu_set_t mask;
 162
 163         if (crdp->cpu_affinity < 0)
 164                 return 0;
 165
 166         CPU_ZERO(&mask);
 167         CPU_SET(crdp->cpu_affinity, &mask);
 168 #if SCHED_SETAFFINITY_ARGS == 2
 169         return sched_setaffinity(0, &mask);
 170 #else
 171         return sched_setaffinity(0, sizeof(mask), &mask);
 172 #endif
 173 }
 174 #else
 175 static
 176 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
 177 {
 178         return 0;
 179 }
 180 #endif
 181
 182 static void call_rcu_wait(struct call_rcu_data *crdp)
 183 {
 184         /* Read call_rcu list before read futex */
 185         cmm_smp_mb();
 186         if (uatomic_read(&crdp->futex) == -1)
 187                 futex_async(&crdp->futex, FUTEX_WAIT, -1,
 188                       NULL, NULL, 0);
 189 }
 190
 191 static void call_rcu_wake_up(struct call_rcu_data *crdp)
 192 {
 193         /* Write to call_rcu list before reading/writing futex */
 194         cmm_smp_mb();
 195         if (unlikely(uatomic_read(&crdp->futex) == -1)) {
 196                 uatomic_set(&crdp->futex, 0);
 197                 futex_async(&crdp->futex, FUTEX_WAKE, 1,
 198                       NULL, NULL, 0);
 199         }
 200 }
 201
 202 /* This is the code run by each call_rcu thread. */
 203
 204 static void *call_rcu_thread(void *arg)
 205 {
 206         unsigned long cbcount;
 207         struct cds_wfq_node *cbs;
 208         struct cds_wfq_node **cbs_tail;
 209         struct call_rcu_data *crdp = (struct call_rcu_data *)arg;
 210         struct rcu_head *rhp;
 211         int rt = !!(uatomic_read(&crdp->flags) & URCU_CALL_RCU_RT);
 212
 213         if (set_thread_cpu_affinity(crdp) != 0) {
 214                 perror("pthread_setaffinity_np");
 215                 exit(-1);
 216         }
 217
 218         /*
 219          * If callbacks take a read-side lock, we need to be registered.
 220          */
 221         rcu_register_thread();
 222
 223         thread_call_rcu_data = crdp;
 224         if (!rt) {
 225                 uatomic_dec(&crdp->futex);
 226                 /* Decrement futex before reading call_rcu list */
 227                 cmm_smp_mb();
 228         }
 229         for (;;) {
 230                 if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
 231                         while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
 232                                 poll(NULL, 0, 1);
 233                         _CMM_STORE_SHARED(crdp->cbs.head, NULL);
 234                         cbs_tail = (struct cds_wfq_node **)
 235                                 uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
 236                         synchronize_rcu();
 237                         cbcount = 0;
 238                         do {
 239                                 while (cbs->next == NULL &&
 240                                        &cbs->next != cbs_tail)
 241                                         poll(NULL, 0, 1);
 242                                 if (cbs == &crdp->cbs.dummy) {
 243                                         cbs = cbs->next;
 244                                         continue;
 245                                 }
 246                                 rhp = (struct rcu_head *)cbs;
 247                                 cbs = cbs->next;
 248                                 rhp->func(rhp);
 249                                 cbcount++;
 250                         } while (cbs != NULL);
 251                         uatomic_sub(&crdp->qlen, cbcount);
 252                 }
 253                 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOP)
 254                         break;
 255                 rcu_thread_offline();
 256                 if (!rt) {
 257                         if (&crdp->cbs.head
 258                             == _CMM_LOAD_SHARED(crdp->cbs.tail)) {
 259                                 call_rcu_wait(crdp);
 260                                 poll(NULL, 0, 10);
 261                                 uatomic_dec(&crdp->futex);
 262                                 /*
 263                                  * Decrement futex before reading
 264                                  * call_rcu list.
 265                                  */
 266                                 cmm_smp_mb();
 267                         } else {
 268                                 poll(NULL, 0, 10);
 269                         }
 270                 } else {
 271                         poll(NULL, 0, 10);
 272                 }
 273                 rcu_thread_online();
 274         }
 275         if (!rt) {
 276                 /*
 277                  * Read call_rcu list before write futex.
 278                  */
 279                 cmm_smp_mb();
 280                 uatomic_set(&crdp->futex, 0);
 281         }
 282         uatomic_or(&crdp->flags, URCU_CALL_RCU_STOPPED);
 283         rcu_unregister_thread();
 284         return NULL;
 285 }
 286
 287 /*
 288  * Create both a call_rcu thread and the corresponding call_rcu_data
 289  * structure, linking the structure in as specified.  Caller must hold
 290  * call_rcu_mutex.
 291  */
 292
 293 static void call_rcu_data_init(struct call_rcu_data **crdpp,
 294                                unsigned long flags,
 295                                int cpu_affinity)
 296 {
 297         struct call_rcu_data *crdp;
 298
 299         crdp = malloc(sizeof(*crdp));
 300         if (crdp == NULL) {
 301                 fprintf(stderr, "Out of memory.\n");
 302                 exit(-1);
 303         }
 304         memset(crdp, '\0', sizeof(*crdp));
 305         cds_wfq_init(&crdp->cbs);
 306         crdp->qlen = 0;
 307         crdp->futex = 0;
 308         crdp->flags = flags;
 309         cds_list_add(&crdp->list, &call_rcu_data_list);
 310         crdp->cpu_affinity = cpu_affinity;
 311         cmm_smp_mb();  /* Structure initialized before pointer is planted. */
 312         *crdpp = crdp;
 313         if (pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp) != 0) {
 314                 perror("pthread_create");
 315                 exit(-1);
 316         }
 317 }
 318
 319 /*
 320  * Return a pointer to the call_rcu_data structure for the specified
 321  * CPU, returning NULL if there is none.  We cannot automatically
 322  * created it because the platform we are running on might not define
 323  * sched_getcpu().
 324  */
 325
 326 struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
 327 {
 328         static int warned = 0;
 329
 330         if (per_cpu_call_rcu_data == NULL)
 331                 return NULL;
 332         if (!warned && maxcpus > 0 && (cpu < 0 || maxcpus <= cpu)) {
 333                 fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
 334                 warned = 1;
 335         }
 336         if (cpu < 0 || maxcpus <= cpu)
 337                 return NULL;
 338         return per_cpu_call_rcu_data[cpu];
 339 }
 340
 341 /*
 342  * Return the tid corresponding to the call_rcu thread whose
 343  * call_rcu_data structure is specified.
 344  */
 345
 346 pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
 347 {
 348         return crdp->tid;
 349 }
 350
 351 /*
 352  * Create a call_rcu_data structure (with thread) and return a pointer.
 353  */
 354
 355 static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
 356                                                     int cpu_affinity)
 357 {
 358         struct call_rcu_data *crdp;
 359
 360         call_rcu_data_init(&crdp, flags, cpu_affinity);
 361         return crdp;
 362 }
 363
 364 struct call_rcu_data *create_call_rcu_data(unsigned long flags,
 365                                            int cpu_affinity)
 366 {
 367         struct call_rcu_data *crdp;
 368
 369         call_rcu_lock(&call_rcu_mutex);
 370         crdp = __create_call_rcu_data(flags, cpu_affinity);
 371         call_rcu_unlock(&call_rcu_mutex);
 372         return crdp;
 373 }
 374
 375 /*
 376  * Set the specified CPU to use the specified call_rcu_data structure.
 377  *
 378  * Use NULL to remove a CPU's call_rcu_data structure, but it is
 379  * the caller's responsibility to dispose of the removed structure.
 380  * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
 381  * (prior to NULLing it out, of course).
 382  */
 383
 384 int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
 385 {
 386         static int warned = 0;
 387
 388         call_rcu_lock(&call_rcu_mutex);
 389         alloc_cpu_call_rcu_data();
 390         if (cpu < 0 || maxcpus <= cpu) {
 391                 if (!warned) {
 392                         fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
 393                         warned = 1;
 394                 }
 395                 call_rcu_unlock(&call_rcu_mutex);
 396                 errno = EINVAL;
 397                 return -EINVAL;
 398         }
 399         call_rcu_unlock(&call_rcu_mutex);
 400         if (per_cpu_call_rcu_data == NULL) {
 401                 errno = ENOMEM;
 402                 return -ENOMEM;
 403         }
 404         per_cpu_call_rcu_data[cpu] = crdp;
 405         return 0;
 406 }
 407
 408 /*
 409  * Return a pointer to the default call_rcu_data structure, creating
 410  * one if need be.  Because we never free call_rcu_data structures,
 411  * we don't need to be in an RCU read-side critical section.
 412  */
 413
 414 struct call_rcu_data *get_default_call_rcu_data(void)
 415 {
 416         if (default_call_rcu_data != NULL)
 417                 return rcu_dereference(default_call_rcu_data);
 418         call_rcu_lock(&call_rcu_mutex);
 419         if (default_call_rcu_data != NULL) {
 420                 call_rcu_unlock(&call_rcu_mutex);
 421                 return default_call_rcu_data;
 422         }
 423         call_rcu_data_init(&default_call_rcu_data, 0, -1);
 424         call_rcu_unlock(&call_rcu_mutex);
 425         return default_call_rcu_data;
 426 }
 427
 428 /*
 429  * Return the call_rcu_data structure that applies to the currently
 430  * running thread.  Any call_rcu_data structure assigned specifically
 431  * to this thread has first priority, followed by any call_rcu_data
 432  * structure assigned to the CPU on which the thread is running,
 433  * followed by the default call_rcu_data structure.  If there is not
 434  * yet a default call_rcu_data structure, one will be created.
 435  */
 436 struct call_rcu_data *get_call_rcu_data(void)
 437 {
 438         struct call_rcu_data *crd;
 439
 440         if (thread_call_rcu_data != NULL)
 441                 return thread_call_rcu_data;
 442
 443         if (maxcpus > 0) {
 444                 crd = get_cpu_call_rcu_data(sched_getcpu());
 445                 if (crd)
 446                         return crd;
 447         }
 448
 449         return get_default_call_rcu_data();
 450 }
 451
 452 /*
 453  * Return a pointer to this task's call_rcu_data if there is one.
 454  */
 455
 456 struct call_rcu_data *get_thread_call_rcu_data(void)
 457 {
 458         return thread_call_rcu_data;
 459 }
 460
 461 /*
 462  * Set this task's call_rcu_data structure as specified, regardless
 463  * of whether or not this task already had one.  (This allows switching
 464  * to and from real-time call_rcu threads, for example.)
 465  *
 466  * Use NULL to remove a thread's call_rcu_data structure, but it is
 467  * the caller's responsibility to dispose of the removed structure.
 468  * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
 469  * (prior to NULLing it out, of course).
 470  */
 471
 472 void set_thread_call_rcu_data(struct call_rcu_data *crdp)
 473 {
 474         thread_call_rcu_data = crdp;
 475 }
 476
 477 /*
 478  * Create a separate call_rcu thread for each CPU.  This does not
 479  * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
 480  * function if you want that behavior. Should be paired with
 481  * free_all_cpu_call_rcu_data() to teardown these call_rcu worker
 482  * threads.
 483  */
 484
 485 int create_all_cpu_call_rcu_data(unsigned long flags)
 486 {
 487         int i;
 488         struct call_rcu_data *crdp;
 489         int ret;
 490
 491         call_rcu_lock(&call_rcu_mutex);
 492         alloc_cpu_call_rcu_data();
 493         call_rcu_unlock(&call_rcu_mutex);
 494         if (maxcpus <= 0) {
 495                 errno = EINVAL;
 496                 return -EINVAL;
 497         }
 498         if (per_cpu_call_rcu_data == NULL) {
 499                 errno = ENOMEM;
 500                 return -ENOMEM;
 501         }
 502         for (i = 0; i < maxcpus; i++) {
 503                 call_rcu_lock(&call_rcu_mutex);
 504                 if (get_cpu_call_rcu_data(i)) {
 505                         call_rcu_unlock(&call_rcu_mutex);
 506                         continue;
 507                 }
 508                 crdp = __create_call_rcu_data(flags, i);
 509                 if (crdp == NULL) {
 510                         call_rcu_unlock(&call_rcu_mutex);
 511                         errno = ENOMEM;
 512                         return -ENOMEM;
 513                 }
 514                 call_rcu_unlock(&call_rcu_mutex);
 515                 if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
 516                         /* FIXME: Leaks crdp for now. */
 517                         return ret; /* Can happen on race. */
 518                 }
 519         }
 520         return 0;
 521 }
 522
 523 /*
 524  * Wake up the call_rcu thread corresponding to the specified
 525  * call_rcu_data structure.
 526  */
 527 static void wake_call_rcu_thread(struct call_rcu_data *crdp)
 528 {
 529         if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT))
 530                 call_rcu_wake_up(crdp);
 531 }
 532
 533 /*
 534  * Schedule a function to be invoked after a following grace period.
 535  * This is the only function that must be called -- the others are
 536  * only present to allow applications to tune their use of RCU for
 537  * maximum performance.
 538  *
 539  * Note that unless a call_rcu thread has not already been created,
 540  * the first invocation of call_rcu() will create one.  So, if you
 541  * need the first invocation of call_rcu() to be fast, make sure
 542  * to create a call_rcu thread first.  One way to accomplish this is
 543  * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
 544  */
 545
 546 void call_rcu(struct rcu_head *head,
 547               void (*func)(struct rcu_head *head))
 548 {
 549         struct call_rcu_data *crdp;
 550
 551         cds_wfq_node_init(&head->next);
 552         head->func = func;
 553         crdp = get_call_rcu_data();
 554         cds_wfq_enqueue(&crdp->cbs, &head->next);
 555         uatomic_inc(&crdp->qlen);
 556         wake_call_rcu_thread(crdp);
 557 }
 558
 559 /*
 560  * Free up the specified call_rcu_data structure, terminating the
 561  * associated call_rcu thread.  The caller must have previously
 562  * removed the call_rcu_data structure from per-thread or per-CPU
 563  * usage.  For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
 564  * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
 565  * per-thread call_rcu_data structures.
 566  *
 567  * We silently refuse to free up the default call_rcu_data structure
 568  * because that is where we put any leftover callbacks.  Note that
 569  * the possibility of self-spawning callbacks makes it impossible
 570  * to execute all the callbacks in finite time without putting any
 571  * newly spawned callbacks somewhere else.  The "somewhere else" of
 572  * last resort is the default call_rcu_data structure.
 573  *
 574  * We also silently refuse to free NULL pointers.  This simplifies
 575  * the calling code.
 576  */
 577 void call_rcu_data_free(struct call_rcu_data *crdp)
 578 {
 579         struct cds_wfq_node *cbs;
 580         struct cds_wfq_node **cbs_tail;
 581         struct cds_wfq_node **cbs_endprev;
 582
 583         if (crdp == NULL || crdp == default_call_rcu_data) {
 584                 return;
 585         }
 586         if ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0) {
 587                 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOP);
 588                 wake_call_rcu_thread(crdp);
 589                 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
 590                         poll(NULL, 0, 1);
 591         }
 592         if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
 593                 while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
 594                         poll(NULL, 0, 1);
 595                 _CMM_STORE_SHARED(crdp->cbs.head, NULL);
 596                 cbs_tail = (struct cds_wfq_node **)
 597                         uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
 598                 cbs_endprev = (struct cds_wfq_node **)
 599                         uatomic_xchg(&default_call_rcu_data, cbs_tail);
 600                 *cbs_endprev = cbs;
 601                 uatomic_add(&default_call_rcu_data->qlen,
 602                             uatomic_read(&crdp->qlen));
 603                 cds_list_del(&crdp->list);
 604                 free(crdp);
 605         }
 606 }
 607
 608 /*
 609  * Clean up all the per-CPU call_rcu threads.
 610  */
 611 void free_all_cpu_call_rcu_data(void)
 612 {
 613         int cpu;
 614         struct call_rcu_data *crdp;
 615
 616         if (maxcpus <= 0)
 617                 return;
 618         for (cpu = 0; cpu < maxcpus; cpu++) {
 619                 crdp = get_cpu_call_rcu_data(cpu);
 620                 if (crdp == NULL)
 621                         continue;
 622                 set_cpu_call_rcu_data(cpu, NULL);
 623                 call_rcu_data_free(crdp);
 624         }
 625 }
 626
 627 /*
 628  * Acquire the call_rcu_mutex in order to ensure that the child sees
 629  * all of the call_rcu() data structures in a consistent state.
 630  * Suitable for pthread_atfork() and friends.
 631  */
 632 void call_rcu_before_fork(void)
 633 {
 634         call_rcu_lock(&call_rcu_mutex);
 635 }
 636
 637 /*
 638  * Clean up call_rcu data structures in the parent of a successful fork()
 639  * that is not followed by exec() in the child.  Suitable for
 640  * pthread_atfork() and friends.
 641  */
 642 void call_rcu_after_fork_parent(void)
 643 {
 644         call_rcu_unlock(&call_rcu_mutex);
 645 }
 646
 647 /*
 648  * Clean up call_rcu data structures in the child of a successful fork()
 649  * that is not followed by exec().  Suitable for pthread_atfork() and
 650  * friends.
 651  */
 652 void call_rcu_after_fork_child(void)
 653 {
 654         struct call_rcu_data *crdp;
 655
 656         /* Release the mutex. */
 657         call_rcu_unlock(&call_rcu_mutex);
 658
 659         /*
 660          * Allocate a new default call_rcu_data structure in order
 661          * to get a working call_rcu thread to go with it.
 662          */
 663         default_call_rcu_data = NULL;
 664         (void)get_default_call_rcu_data();
 665
 666         /* Dispose of all of the rest of the call_rcu_data structures. */
 667         while (call_rcu_data_list.next != call_rcu_data_list.prev) {
 668                 crdp = cds_list_entry(call_rcu_data_list.prev,
 669                                       struct call_rcu_data, list);
 670                 if (crdp == default_call_rcu_data)
 671                         crdp = cds_list_entry(crdp->list.prev,
 672                                               struct call_rcu_data, list);
 673                 uatomic_set(&crdp->flags, URCU_CALL_RCU_STOPPED);
 674                 call_rcu_data_free(crdp);
 675         }
 676 }