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