Fix: only define membarrier system call on Linux
[urcu.git] / 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 #define _LGPL_SOURCE
25 #include <stdio.h>
26 #include <pthread.h>
27 #include <signal.h>
28 #include <assert.h>
29 #include <stdlib.h>
30 #include <stdint.h>
31 #include <string.h>
32 #include <errno.h>
33 #include <poll.h>
34 #include <sys/time.h>
35 #include <unistd.h>
36 #include <sched.h>
37
38 #include "config.h"
39 #include "urcu/wfcqueue.h"
40 #include "urcu-call-rcu.h"
41 #include "urcu-pointer.h"
42 #include "urcu/list.h"
43 #include "urcu/futex.h"
44 #include "urcu/tls-compat.h"
45 #include "urcu/ref.h"
46 #include "urcu-die.h"
47
48 #define SET_AFFINITY_CHECK_PERIOD (1U << 8) /* 256 */
49 #define SET_AFFINITY_CHECK_PERIOD_MASK (SET_AFFINITY_CHECK_PERIOD - 1)
50
51 /* Data structure that identifies a call_rcu thread. */
52
53 struct call_rcu_data {
54 /*
55 * We do not align head on a different cache-line than tail
56 * mainly because call_rcu callback-invocation threads use
57 * batching ("splice") to get an entire list of callbacks, which
58 * effectively empties the queue, and requires to touch the tail
59 * anyway.
60 */
61 struct cds_wfcq_tail cbs_tail;
62 struct cds_wfcq_head cbs_head;
63 unsigned long flags;
64 int32_t futex;
65 unsigned long qlen; /* maintained for debugging. */
66 pthread_t tid;
67 int cpu_affinity;
68 unsigned long gp_count;
69 struct cds_list_head list;
70 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
71
72 struct call_rcu_completion {
73 int barrier_count;
74 int32_t futex;
75 struct urcu_ref ref;
76 };
77
78 struct call_rcu_completion_work {
79 struct rcu_head head;
80 struct call_rcu_completion *completion;
81 };
82
83 /*
84 * List of all call_rcu_data structures to keep valgrind happy.
85 * Protected by call_rcu_mutex.
86 */
87
88 static CDS_LIST_HEAD(call_rcu_data_list);
89
90 /* Link a thread using call_rcu() to its call_rcu thread. */
91
92 static DEFINE_URCU_TLS(struct call_rcu_data *, thread_call_rcu_data);
93
94 /*
95 * Guard call_rcu thread creation and atfork handlers.
96 */
97 static pthread_mutex_t call_rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
98
99 /* If a given thread does not have its own call_rcu thread, this is default. */
100
101 static struct call_rcu_data *default_call_rcu_data;
102
103 /*
104 * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
105 * available, then we can have call_rcu threads assigned to individual
106 * CPUs rather than only to specific threads.
107 */
108
109 #ifdef HAVE_SCHED_GETCPU
110
111 static int urcu_sched_getcpu(void)
112 {
113 return sched_getcpu();
114 }
115
116 #else /* #ifdef HAVE_SCHED_GETCPU */
117
118 static int urcu_sched_getcpu(void)
119 {
120 return -1;
121 }
122
123 #endif /* #else #ifdef HAVE_SCHED_GETCPU */
124
125 #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU)
126
127 /*
128 * Pointer to array of pointers to per-CPU call_rcu_data structures
129 * and # CPUs. per_cpu_call_rcu_data is a RCU-protected pointer to an
130 * array of RCU-protected pointers to call_rcu_data. call_rcu acts as a
131 * RCU read-side and reads per_cpu_call_rcu_data and the per-cpu pointer
132 * without mutex. The call_rcu_mutex protects updates.
133 */
134
135 static struct call_rcu_data **per_cpu_call_rcu_data;
136 static long maxcpus;
137
138 static void maxcpus_reset(void)
139 {
140 maxcpus = 0;
141 }
142
143 /* Allocate the array if it has not already been allocated. */
144
145 static void alloc_cpu_call_rcu_data(void)
146 {
147 struct call_rcu_data **p;
148 static int warned = 0;
149
150 if (maxcpus != 0)
151 return;
152 maxcpus = sysconf(_SC_NPROCESSORS_CONF);
153 if (maxcpus <= 0) {
154 return;
155 }
156 p = malloc(maxcpus * sizeof(*per_cpu_call_rcu_data));
157 if (p != NULL) {
158 memset(p, '\0', maxcpus * sizeof(*per_cpu_call_rcu_data));
159 rcu_set_pointer(&per_cpu_call_rcu_data, p);
160 } else {
161 if (!warned) {
162 fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
163 }
164 warned = 1;
165 }
166 }
167
168 #else /* #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
169
170 /*
171 * per_cpu_call_rcu_data should be constant, but some functions below, used both
172 * for cases where cpu number is available and not available, assume it it not
173 * constant.
174 */
175 static struct call_rcu_data **per_cpu_call_rcu_data = NULL;
176 static const long maxcpus = -1;
177
178 static void maxcpus_reset(void)
179 {
180 }
181
182 static void alloc_cpu_call_rcu_data(void)
183 {
184 }
185
186 #endif /* #else #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
187
188 /* Acquire the specified pthread mutex. */
189
190 static void call_rcu_lock(pthread_mutex_t *pmp)
191 {
192 int ret;
193
194 ret = pthread_mutex_lock(pmp);
195 if (ret)
196 urcu_die(ret);
197 }
198
199 /* Release the specified pthread mutex. */
200
201 static void call_rcu_unlock(pthread_mutex_t *pmp)
202 {
203 int ret;
204
205 ret = pthread_mutex_unlock(pmp);
206 if (ret)
207 urcu_die(ret);
208 }
209
210 /*
211 * Periodically retry setting CPU affinity if we migrate.
212 * Losing affinity can be caused by CPU hotunplug/hotplug, or by
213 * cpuset(7).
214 */
215 #if HAVE_SCHED_SETAFFINITY
216 static
217 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
218 {
219 cpu_set_t mask;
220 int ret;
221
222 if (crdp->cpu_affinity < 0)
223 return 0;
224 if (++crdp->gp_count & SET_AFFINITY_CHECK_PERIOD_MASK)
225 return 0;
226 if (urcu_sched_getcpu() == crdp->cpu_affinity)
227 return 0;
228
229 CPU_ZERO(&mask);
230 CPU_SET(crdp->cpu_affinity, &mask);
231 #if SCHED_SETAFFINITY_ARGS == 2
232 ret = sched_setaffinity(0, &mask);
233 #else
234 ret = sched_setaffinity(0, sizeof(mask), &mask);
235 #endif
236 /*
237 * EINVAL is fine: can be caused by hotunplugged CPUs, or by
238 * cpuset(7). This is why we should always retry if we detect
239 * migration.
240 */
241 if (ret && errno == EINVAL) {
242 ret = 0;
243 errno = 0;
244 }
245 return ret;
246 }
247 #else
248 static
249 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
250 {
251 return 0;
252 }
253 #endif
254
255 static void call_rcu_wait(struct call_rcu_data *crdp)
256 {
257 /* Read call_rcu list before read futex */
258 cmm_smp_mb();
259 if (uatomic_read(&crdp->futex) != -1)
260 return;
261 while (futex_async(&crdp->futex, FUTEX_WAIT, -1,
262 NULL, NULL, 0)) {
263 switch (errno) {
264 case EWOULDBLOCK:
265 /* Value already changed. */
266 return;
267 case EINTR:
268 /* Retry if interrupted by signal. */
269 break; /* Get out of switch. */
270 default:
271 /* Unexpected error. */
272 urcu_die(errno);
273 }
274 }
275 }
276
277 static void call_rcu_wake_up(struct call_rcu_data *crdp)
278 {
279 /* Write to call_rcu list before reading/writing futex */
280 cmm_smp_mb();
281 if (caa_unlikely(uatomic_read(&crdp->futex) == -1)) {
282 uatomic_set(&crdp->futex, 0);
283 if (futex_async(&crdp->futex, FUTEX_WAKE, 1,
284 NULL, NULL, 0) < 0)
285 urcu_die(errno);
286 }
287 }
288
289 static void call_rcu_completion_wait(struct call_rcu_completion *completion)
290 {
291 /* Read completion barrier count before read futex */
292 cmm_smp_mb();
293 if (uatomic_read(&completion->futex) != -1)
294 return;
295 while (futex_async(&completion->futex, FUTEX_WAIT, -1,
296 NULL, NULL, 0)) {
297 switch (errno) {
298 case EWOULDBLOCK:
299 /* Value already changed. */
300 return;
301 case EINTR:
302 /* Retry if interrupted by signal. */
303 break; /* Get out of switch. */
304 default:
305 /* Unexpected error. */
306 urcu_die(errno);
307 }
308 }
309 }
310
311 static void call_rcu_completion_wake_up(struct call_rcu_completion *completion)
312 {
313 /* Write to completion barrier count before reading/writing futex */
314 cmm_smp_mb();
315 if (caa_unlikely(uatomic_read(&completion->futex) == -1)) {
316 uatomic_set(&completion->futex, 0);
317 if (futex_async(&completion->futex, FUTEX_WAKE, 1,
318 NULL, NULL, 0) < 0)
319 urcu_die(errno);
320 }
321 }
322
323 /* This is the code run by each call_rcu thread. */
324
325 static void *call_rcu_thread(void *arg)
326 {
327 unsigned long cbcount;
328 struct call_rcu_data *crdp = (struct call_rcu_data *) arg;
329 int rt = !!(uatomic_read(&crdp->flags) & URCU_CALL_RCU_RT);
330
331 if (set_thread_cpu_affinity(crdp))
332 urcu_die(errno);
333
334 /*
335 * If callbacks take a read-side lock, we need to be registered.
336 */
337 rcu_register_thread();
338
339 URCU_TLS(thread_call_rcu_data) = crdp;
340 if (!rt) {
341 uatomic_dec(&crdp->futex);
342 /* Decrement futex before reading call_rcu list */
343 cmm_smp_mb();
344 }
345 for (;;) {
346 struct cds_wfcq_head cbs_tmp_head;
347 struct cds_wfcq_tail cbs_tmp_tail;
348 struct cds_wfcq_node *cbs, *cbs_tmp_n;
349 enum cds_wfcq_ret splice_ret;
350
351 if (set_thread_cpu_affinity(crdp))
352 urcu_die(errno);
353
354 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) {
355 /*
356 * Pause requested. Become quiescent: remove
357 * ourself from all global lists, and don't
358 * process any callback. The callback lists may
359 * still be non-empty though.
360 */
361 rcu_unregister_thread();
362 cmm_smp_mb__before_uatomic_or();
363 uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSED);
364 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) != 0)
365 (void) poll(NULL, 0, 1);
366 uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSED);
367 cmm_smp_mb__after_uatomic_and();
368 rcu_register_thread();
369 }
370
371 cds_wfcq_init(&cbs_tmp_head, &cbs_tmp_tail);
372 splice_ret = __cds_wfcq_splice_blocking(&cbs_tmp_head,
373 &cbs_tmp_tail, &crdp->cbs_head, &crdp->cbs_tail);
374 assert(splice_ret != CDS_WFCQ_RET_WOULDBLOCK);
375 assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
376 if (splice_ret != CDS_WFCQ_RET_SRC_EMPTY) {
377 synchronize_rcu();
378 cbcount = 0;
379 __cds_wfcq_for_each_blocking_safe(&cbs_tmp_head,
380 &cbs_tmp_tail, cbs, cbs_tmp_n) {
381 struct rcu_head *rhp;
382
383 rhp = caa_container_of(cbs,
384 struct rcu_head, next);
385 rhp->func(rhp);
386 cbcount++;
387 }
388 uatomic_sub(&crdp->qlen, cbcount);
389 }
390 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOP)
391 break;
392 rcu_thread_offline();
393 if (!rt) {
394 if (cds_wfcq_empty(&crdp->cbs_head,
395 &crdp->cbs_tail)) {
396 call_rcu_wait(crdp);
397 (void) poll(NULL, 0, 10);
398 uatomic_dec(&crdp->futex);
399 /*
400 * Decrement futex before reading
401 * call_rcu list.
402 */
403 cmm_smp_mb();
404 } else {
405 (void) poll(NULL, 0, 10);
406 }
407 } else {
408 (void) poll(NULL, 0, 10);
409 }
410 rcu_thread_online();
411 }
412 if (!rt) {
413 /*
414 * Read call_rcu list before write futex.
415 */
416 cmm_smp_mb();
417 uatomic_set(&crdp->futex, 0);
418 }
419 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOPPED);
420 rcu_unregister_thread();
421 return NULL;
422 }
423
424 /*
425 * Create both a call_rcu thread and the corresponding call_rcu_data
426 * structure, linking the structure in as specified. Caller must hold
427 * call_rcu_mutex.
428 */
429
430 static void call_rcu_data_init(struct call_rcu_data **crdpp,
431 unsigned long flags,
432 int cpu_affinity)
433 {
434 struct call_rcu_data *crdp;
435 int ret;
436
437 crdp = malloc(sizeof(*crdp));
438 if (crdp == NULL)
439 urcu_die(errno);
440 memset(crdp, '\0', sizeof(*crdp));
441 cds_wfcq_init(&crdp->cbs_head, &crdp->cbs_tail);
442 crdp->qlen = 0;
443 crdp->futex = 0;
444 crdp->flags = flags;
445 cds_list_add(&crdp->list, &call_rcu_data_list);
446 crdp->cpu_affinity = cpu_affinity;
447 crdp->gp_count = 0;
448 cmm_smp_mb(); /* Structure initialized before pointer is planted. */
449 *crdpp = crdp;
450 ret = pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp);
451 if (ret)
452 urcu_die(ret);
453 }
454
455 /*
456 * Return a pointer to the call_rcu_data structure for the specified
457 * CPU, returning NULL if there is none. We cannot automatically
458 * created it because the platform we are running on might not define
459 * urcu_sched_getcpu().
460 *
461 * The call to this function and use of the returned call_rcu_data
462 * should be protected by RCU read-side lock.
463 */
464
465 struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
466 {
467 static int warned = 0;
468 struct call_rcu_data **pcpu_crdp;
469
470 pcpu_crdp = rcu_dereference(per_cpu_call_rcu_data);
471 if (pcpu_crdp == NULL)
472 return NULL;
473 if (!warned && maxcpus > 0 && (cpu < 0 || maxcpus <= cpu)) {
474 fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
475 warned = 1;
476 }
477 if (cpu < 0 || maxcpus <= cpu)
478 return NULL;
479 return rcu_dereference(pcpu_crdp[cpu]);
480 }
481
482 /*
483 * Return the tid corresponding to the call_rcu thread whose
484 * call_rcu_data structure is specified.
485 */
486
487 pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
488 {
489 return crdp->tid;
490 }
491
492 /*
493 * Create a call_rcu_data structure (with thread) and return a pointer.
494 */
495
496 static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
497 int cpu_affinity)
498 {
499 struct call_rcu_data *crdp;
500
501 call_rcu_data_init(&crdp, flags, cpu_affinity);
502 return crdp;
503 }
504
505 struct call_rcu_data *create_call_rcu_data(unsigned long flags,
506 int cpu_affinity)
507 {
508 struct call_rcu_data *crdp;
509
510 call_rcu_lock(&call_rcu_mutex);
511 crdp = __create_call_rcu_data(flags, cpu_affinity);
512 call_rcu_unlock(&call_rcu_mutex);
513 return crdp;
514 }
515
516 /*
517 * Set the specified CPU to use the specified call_rcu_data structure.
518 *
519 * Use NULL to remove a CPU's call_rcu_data structure, but it is
520 * the caller's responsibility to dispose of the removed structure.
521 * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
522 * (prior to NULLing it out, of course).
523 *
524 * The caller must wait for a grace-period to pass between return from
525 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
526 * previous call rcu data as argument.
527 */
528
529 int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
530 {
531 static int warned = 0;
532
533 call_rcu_lock(&call_rcu_mutex);
534 alloc_cpu_call_rcu_data();
535 if (cpu < 0 || maxcpus <= cpu) {
536 if (!warned) {
537 fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
538 warned = 1;
539 }
540 call_rcu_unlock(&call_rcu_mutex);
541 errno = EINVAL;
542 return -EINVAL;
543 }
544
545 if (per_cpu_call_rcu_data == NULL) {
546 call_rcu_unlock(&call_rcu_mutex);
547 errno = ENOMEM;
548 return -ENOMEM;
549 }
550
551 if (per_cpu_call_rcu_data[cpu] != NULL && crdp != NULL) {
552 call_rcu_unlock(&call_rcu_mutex);
553 errno = EEXIST;
554 return -EEXIST;
555 }
556
557 rcu_set_pointer(&per_cpu_call_rcu_data[cpu], crdp);
558 call_rcu_unlock(&call_rcu_mutex);
559 return 0;
560 }
561
562 /*
563 * Return a pointer to the default call_rcu_data structure, creating
564 * one if need be. Because we never free call_rcu_data structures,
565 * we don't need to be in an RCU read-side critical section.
566 */
567
568 struct call_rcu_data *get_default_call_rcu_data(void)
569 {
570 if (default_call_rcu_data != NULL)
571 return rcu_dereference(default_call_rcu_data);
572 call_rcu_lock(&call_rcu_mutex);
573 if (default_call_rcu_data != NULL) {
574 call_rcu_unlock(&call_rcu_mutex);
575 return default_call_rcu_data;
576 }
577 call_rcu_data_init(&default_call_rcu_data, 0, -1);
578 call_rcu_unlock(&call_rcu_mutex);
579 return default_call_rcu_data;
580 }
581
582 /*
583 * Return the call_rcu_data structure that applies to the currently
584 * running thread. Any call_rcu_data structure assigned specifically
585 * to this thread has first priority, followed by any call_rcu_data
586 * structure assigned to the CPU on which the thread is running,
587 * followed by the default call_rcu_data structure. If there is not
588 * yet a default call_rcu_data structure, one will be created.
589 *
590 * Calls to this function and use of the returned call_rcu_data should
591 * be protected by RCU read-side lock.
592 */
593 struct call_rcu_data *get_call_rcu_data(void)
594 {
595 struct call_rcu_data *crd;
596
597 if (URCU_TLS(thread_call_rcu_data) != NULL)
598 return URCU_TLS(thread_call_rcu_data);
599
600 if (maxcpus > 0) {
601 crd = get_cpu_call_rcu_data(urcu_sched_getcpu());
602 if (crd)
603 return crd;
604 }
605
606 return get_default_call_rcu_data();
607 }
608
609 /*
610 * Return a pointer to this task's call_rcu_data if there is one.
611 */
612
613 struct call_rcu_data *get_thread_call_rcu_data(void)
614 {
615 return URCU_TLS(thread_call_rcu_data);
616 }
617
618 /*
619 * Set this task's call_rcu_data structure as specified, regardless
620 * of whether or not this task already had one. (This allows switching
621 * to and from real-time call_rcu threads, for example.)
622 *
623 * Use NULL to remove a thread's call_rcu_data structure, but it is
624 * the caller's responsibility to dispose of the removed structure.
625 * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
626 * (prior to NULLing it out, of course).
627 */
628
629 void set_thread_call_rcu_data(struct call_rcu_data *crdp)
630 {
631 URCU_TLS(thread_call_rcu_data) = crdp;
632 }
633
634 /*
635 * Create a separate call_rcu thread for each CPU. This does not
636 * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
637 * function if you want that behavior. Should be paired with
638 * free_all_cpu_call_rcu_data() to teardown these call_rcu worker
639 * threads.
640 */
641
642 int create_all_cpu_call_rcu_data(unsigned long flags)
643 {
644 int i;
645 struct call_rcu_data *crdp;
646 int ret;
647
648 call_rcu_lock(&call_rcu_mutex);
649 alloc_cpu_call_rcu_data();
650 call_rcu_unlock(&call_rcu_mutex);
651 if (maxcpus <= 0) {
652 errno = EINVAL;
653 return -EINVAL;
654 }
655 if (per_cpu_call_rcu_data == NULL) {
656 errno = ENOMEM;
657 return -ENOMEM;
658 }
659 for (i = 0; i < maxcpus; i++) {
660 call_rcu_lock(&call_rcu_mutex);
661 if (get_cpu_call_rcu_data(i)) {
662 call_rcu_unlock(&call_rcu_mutex);
663 continue;
664 }
665 crdp = __create_call_rcu_data(flags, i);
666 if (crdp == NULL) {
667 call_rcu_unlock(&call_rcu_mutex);
668 errno = ENOMEM;
669 return -ENOMEM;
670 }
671 call_rcu_unlock(&call_rcu_mutex);
672 if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
673 call_rcu_data_free(crdp);
674
675 /* it has been created by other thread */
676 if (ret == -EEXIST)
677 continue;
678
679 return ret;
680 }
681 }
682 return 0;
683 }
684
685 /*
686 * Wake up the call_rcu thread corresponding to the specified
687 * call_rcu_data structure.
688 */
689 static void wake_call_rcu_thread(struct call_rcu_data *crdp)
690 {
691 if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT))
692 call_rcu_wake_up(crdp);
693 }
694
695 static void _call_rcu(struct rcu_head *head,
696 void (*func)(struct rcu_head *head),
697 struct call_rcu_data *crdp)
698 {
699 cds_wfcq_node_init(&head->next);
700 head->func = func;
701 cds_wfcq_enqueue(&crdp->cbs_head, &crdp->cbs_tail, &head->next);
702 uatomic_inc(&crdp->qlen);
703 wake_call_rcu_thread(crdp);
704 }
705
706 /*
707 * Schedule a function to be invoked after a following grace period.
708 * This is the only function that must be called -- the others are
709 * only present to allow applications to tune their use of RCU for
710 * maximum performance.
711 *
712 * Note that unless a call_rcu thread has not already been created,
713 * the first invocation of call_rcu() will create one. So, if you
714 * need the first invocation of call_rcu() to be fast, make sure
715 * to create a call_rcu thread first. One way to accomplish this is
716 * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
717 *
718 * call_rcu must be called by registered RCU read-side threads.
719 */
720 void call_rcu(struct rcu_head *head,
721 void (*func)(struct rcu_head *head))
722 {
723 struct call_rcu_data *crdp;
724
725 /* Holding rcu read-side lock across use of per-cpu crdp */
726 _rcu_read_lock();
727 crdp = get_call_rcu_data();
728 _call_rcu(head, func, crdp);
729 _rcu_read_unlock();
730 }
731
732 /*
733 * Free up the specified call_rcu_data structure, terminating the
734 * associated call_rcu thread. The caller must have previously
735 * removed the call_rcu_data structure from per-thread or per-CPU
736 * usage. For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
737 * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
738 * per-thread call_rcu_data structures.
739 *
740 * We silently refuse to free up the default call_rcu_data structure
741 * because that is where we put any leftover callbacks. Note that
742 * the possibility of self-spawning callbacks makes it impossible
743 * to execute all the callbacks in finite time without putting any
744 * newly spawned callbacks somewhere else. The "somewhere else" of
745 * last resort is the default call_rcu_data structure.
746 *
747 * We also silently refuse to free NULL pointers. This simplifies
748 * the calling code.
749 *
750 * The caller must wait for a grace-period to pass between return from
751 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
752 * previous call rcu data as argument.
753 *
754 * Note: introducing __cds_wfcq_splice_blocking() in this function fixed
755 * a list corruption bug in the 0.7.x series. The equivalent fix
756 * appeared in 0.6.8 for the stable-0.6 branch.
757 */
758 void call_rcu_data_free(struct call_rcu_data *crdp)
759 {
760 if (crdp == NULL || crdp == default_call_rcu_data) {
761 return;
762 }
763 if ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0) {
764 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOP);
765 wake_call_rcu_thread(crdp);
766 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
767 (void) poll(NULL, 0, 1);
768 }
769 if (!cds_wfcq_empty(&crdp->cbs_head, &crdp->cbs_tail)) {
770 /* Create default call rcu data if need be */
771 (void) get_default_call_rcu_data();
772 __cds_wfcq_splice_blocking(&default_call_rcu_data->cbs_head,
773 &default_call_rcu_data->cbs_tail,
774 &crdp->cbs_head, &crdp->cbs_tail);
775 uatomic_add(&default_call_rcu_data->qlen,
776 uatomic_read(&crdp->qlen));
777 wake_call_rcu_thread(default_call_rcu_data);
778 }
779
780 call_rcu_lock(&call_rcu_mutex);
781 cds_list_del(&crdp->list);
782 call_rcu_unlock(&call_rcu_mutex);
783
784 free(crdp);
785 }
786
787 /*
788 * Clean up all the per-CPU call_rcu threads.
789 */
790 void free_all_cpu_call_rcu_data(void)
791 {
792 int cpu;
793 struct call_rcu_data **crdp;
794 static int warned = 0;
795
796 if (maxcpus <= 0)
797 return;
798
799 crdp = malloc(sizeof(*crdp) * maxcpus);
800 if (!crdp) {
801 if (!warned) {
802 fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
803 }
804 warned = 1;
805 return;
806 }
807
808 for (cpu = 0; cpu < maxcpus; cpu++) {
809 crdp[cpu] = get_cpu_call_rcu_data(cpu);
810 if (crdp[cpu] == NULL)
811 continue;
812 set_cpu_call_rcu_data(cpu, NULL);
813 }
814 /*
815 * Wait for call_rcu sites acting as RCU readers of the
816 * call_rcu_data to become quiescent.
817 */
818 synchronize_rcu();
819 for (cpu = 0; cpu < maxcpus; cpu++) {
820 if (crdp[cpu] == NULL)
821 continue;
822 call_rcu_data_free(crdp[cpu]);
823 }
824 free(crdp);
825 }
826
827 static
828 void free_completion(struct urcu_ref *ref)
829 {
830 struct call_rcu_completion *completion;
831
832 completion = caa_container_of(ref, struct call_rcu_completion, ref);
833 free(completion);
834 }
835
836 static
837 void _rcu_barrier_complete(struct rcu_head *head)
838 {
839 struct call_rcu_completion_work *work;
840 struct call_rcu_completion *completion;
841
842 work = caa_container_of(head, struct call_rcu_completion_work, head);
843 completion = work->completion;
844 if (!uatomic_sub_return(&completion->barrier_count, 1))
845 call_rcu_completion_wake_up(completion);
846 urcu_ref_put(&completion->ref, free_completion);
847 free(work);
848 }
849
850 /*
851 * Wait for all in-flight call_rcu callbacks to complete execution.
852 */
853 void rcu_barrier(void)
854 {
855 struct call_rcu_data *crdp;
856 struct call_rcu_completion *completion;
857 int count = 0;
858 int was_online;
859
860 /* Put in offline state in QSBR. */
861 was_online = _rcu_read_ongoing();
862 if (was_online)
863 rcu_thread_offline();
864 /*
865 * Calling a rcu_barrier() within a RCU read-side critical
866 * section is an error.
867 */
868 if (_rcu_read_ongoing()) {
869 static int warned = 0;
870
871 if (!warned) {
872 fprintf(stderr, "[error] liburcu: rcu_barrier() called from within RCU read-side critical section.\n");
873 }
874 warned = 1;
875 goto online;
876 }
877
878 completion = calloc(sizeof(*completion), 1);
879 if (!completion)
880 urcu_die(errno);
881
882 call_rcu_lock(&call_rcu_mutex);
883 cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
884 count++;
885
886 /* Referenced by rcu_barrier() and each call_rcu thread. */
887 urcu_ref_set(&completion->ref, count + 1);
888 completion->barrier_count = count;
889
890 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
891 struct call_rcu_completion_work *work;
892
893 work = calloc(sizeof(*work), 1);
894 if (!work)
895 urcu_die(errno);
896 work->completion = completion;
897 _call_rcu(&work->head, _rcu_barrier_complete, crdp);
898 }
899 call_rcu_unlock(&call_rcu_mutex);
900
901 /* Wait for them */
902 for (;;) {
903 uatomic_dec(&completion->futex);
904 /* Decrement futex before reading barrier_count */
905 cmm_smp_mb();
906 if (!uatomic_read(&completion->barrier_count))
907 break;
908 call_rcu_completion_wait(completion);
909 }
910
911 urcu_ref_put(&completion->ref, free_completion);
912
913 online:
914 if (was_online)
915 rcu_thread_online();
916 }
917
918 /*
919 * Acquire the call_rcu_mutex in order to ensure that the child sees
920 * all of the call_rcu() data structures in a consistent state. Ensure
921 * that all call_rcu threads are in a quiescent state across fork.
922 * Suitable for pthread_atfork() and friends.
923 */
924 void call_rcu_before_fork(void)
925 {
926 struct call_rcu_data *crdp;
927
928 call_rcu_lock(&call_rcu_mutex);
929
930 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
931 uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSE);
932 cmm_smp_mb__after_uatomic_or();
933 wake_call_rcu_thread(crdp);
934 }
935 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
936 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) == 0)
937 (void) poll(NULL, 0, 1);
938 }
939 }
940
941 /*
942 * Clean up call_rcu data structures in the parent of a successful fork()
943 * that is not followed by exec() in the child. Suitable for
944 * pthread_atfork() and friends.
945 */
946 void call_rcu_after_fork_parent(void)
947 {
948 struct call_rcu_data *crdp;
949
950 cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
951 uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSE);
952 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
953 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) != 0)
954 (void) poll(NULL, 0, 1);
955 }
956 call_rcu_unlock(&call_rcu_mutex);
957 }
958
959 /*
960 * Clean up call_rcu data structures in the child of a successful fork()
961 * that is not followed by exec(). Suitable for pthread_atfork() and
962 * friends.
963 */
964 void call_rcu_after_fork_child(void)
965 {
966 struct call_rcu_data *crdp, *next;
967
968 /* Release the mutex. */
969 call_rcu_unlock(&call_rcu_mutex);
970
971 /* Do nothing when call_rcu() has not been used */
972 if (cds_list_empty(&call_rcu_data_list))
973 return;
974
975 /*
976 * Allocate a new default call_rcu_data structure in order
977 * to get a working call_rcu thread to go with it.
978 */
979 default_call_rcu_data = NULL;
980 (void)get_default_call_rcu_data();
981
982 /* Cleanup call_rcu_data pointers before use */
983 maxcpus_reset();
984 free(per_cpu_call_rcu_data);
985 rcu_set_pointer(&per_cpu_call_rcu_data, NULL);
986 URCU_TLS(thread_call_rcu_data) = NULL;
987
988 /*
989 * Dispose of all of the rest of the call_rcu_data structures.
990 * Leftover call_rcu callbacks will be merged into the new
991 * default call_rcu thread queue.
992 */
993 cds_list_for_each_entry_safe(crdp, next, &call_rcu_data_list, list) {
994 if (crdp == default_call_rcu_data)
995 continue;
996 uatomic_set(&crdp->flags, URCU_CALL_RCU_STOPPED);
997 call_rcu_data_free(crdp);
998 }
999 }
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