Fix: x86 and s390: uatomic __hp() macro clang support
[urcu.git] / src / 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 _LGPL_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 "compat-getcpu.h"
38 #include <urcu/wfcqueue.h>
39 #include <urcu/call-rcu.h>
40 #include <urcu/pointer.h>
41 #include <urcu/list.h>
42 #include <urcu/futex.h>
43 #include <urcu/tls-compat.h>
44 #include <urcu/ref.h>
45 #include "urcu-die.h"
46 #include "urcu-utils.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 static struct urcu_atfork *registered_rculfhash_atfork;
104 static unsigned long registered_rculfhash_atfork_refcount;
105
106 /*
107 * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
108 * available, then we can have call_rcu threads assigned to individual
109 * CPUs rather than only to specific threads.
110 */
111
112 #if defined(HAVE_SYSCONF) && (defined(HAVE_SCHED_GETCPU) || defined(HAVE_GETCPUID))
113
114 /*
115 * Pointer to array of pointers to per-CPU call_rcu_data structures
116 * and # CPUs. per_cpu_call_rcu_data is a RCU-protected pointer to an
117 * array of RCU-protected pointers to call_rcu_data. call_rcu acts as a
118 * RCU read-side and reads per_cpu_call_rcu_data and the per-cpu pointer
119 * without mutex. The call_rcu_mutex protects updates.
120 */
121
122 static struct call_rcu_data **per_cpu_call_rcu_data;
123 static long maxcpus;
124
125 static void maxcpus_reset(void)
126 {
127 maxcpus = 0;
128 }
129
130 /* Allocate the array if it has not already been allocated. */
131
132 static void alloc_cpu_call_rcu_data(void)
133 {
134 struct call_rcu_data **p;
135 static int warned = 0;
136
137 if (maxcpus != 0)
138 return;
139 maxcpus = sysconf(_SC_NPROCESSORS_CONF);
140 if (maxcpus <= 0) {
141 return;
142 }
143 p = malloc(maxcpus * sizeof(*per_cpu_call_rcu_data));
144 if (p != NULL) {
145 memset(p, '\0', maxcpus * sizeof(*per_cpu_call_rcu_data));
146 rcu_set_pointer(&per_cpu_call_rcu_data, p);
147 } else {
148 if (!warned) {
149 fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
150 }
151 warned = 1;
152 }
153 }
154
155 #else /* #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
156
157 /*
158 * per_cpu_call_rcu_data should be constant, but some functions below, used both
159 * for cases where cpu number is available and not available, assume it it not
160 * constant.
161 */
162 static struct call_rcu_data **per_cpu_call_rcu_data = NULL;
163 static const long maxcpus = -1;
164
165 static void maxcpus_reset(void)
166 {
167 }
168
169 static void alloc_cpu_call_rcu_data(void)
170 {
171 }
172
173 #endif /* #else #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
174
175 /* Acquire the specified pthread mutex. */
176
177 static void call_rcu_lock(pthread_mutex_t *pmp)
178 {
179 int ret;
180
181 ret = pthread_mutex_lock(pmp);
182 if (ret)
183 urcu_die(ret);
184 }
185
186 /* Release the specified pthread mutex. */
187
188 static void call_rcu_unlock(pthread_mutex_t *pmp)
189 {
190 int ret;
191
192 ret = pthread_mutex_unlock(pmp);
193 if (ret)
194 urcu_die(ret);
195 }
196
197 /*
198 * Periodically retry setting CPU affinity if we migrate.
199 * Losing affinity can be caused by CPU hotunplug/hotplug, or by
200 * cpuset(7).
201 */
202 #ifdef HAVE_SCHED_SETAFFINITY
203 static
204 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
205 {
206 cpu_set_t mask;
207 int ret;
208
209 if (crdp->cpu_affinity < 0)
210 return 0;
211 if (++crdp->gp_count & SET_AFFINITY_CHECK_PERIOD_MASK)
212 return 0;
213 if (urcu_sched_getcpu() == crdp->cpu_affinity)
214 return 0;
215
216 CPU_ZERO(&mask);
217 CPU_SET(crdp->cpu_affinity, &mask);
218 ret = sched_setaffinity(0, sizeof(mask), &mask);
219
220 /*
221 * EINVAL is fine: can be caused by hotunplugged CPUs, or by
222 * cpuset(7). This is why we should always retry if we detect
223 * migration.
224 */
225 if (ret && errno == EINVAL) {
226 ret = 0;
227 errno = 0;
228 }
229 return ret;
230 }
231 #else
232 static
233 int set_thread_cpu_affinity(struct call_rcu_data *crdp __attribute__((unused)))
234 {
235 return 0;
236 }
237 #endif
238
239 static void call_rcu_wait(struct call_rcu_data *crdp)
240 {
241 /* Read call_rcu list before read futex */
242 cmm_smp_mb();
243 if (uatomic_read(&crdp->futex) != -1)
244 return;
245 while (futex_async(&crdp->futex, FUTEX_WAIT, -1,
246 NULL, NULL, 0)) {
247 switch (errno) {
248 case EWOULDBLOCK:
249 /* Value already changed. */
250 return;
251 case EINTR:
252 /* Retry if interrupted by signal. */
253 break; /* Get out of switch. */
254 default:
255 /* Unexpected error. */
256 urcu_die(errno);
257 }
258 }
259 }
260
261 static void call_rcu_wake_up(struct call_rcu_data *crdp)
262 {
263 /* Write to call_rcu list before reading/writing futex */
264 cmm_smp_mb();
265 if (caa_unlikely(uatomic_read(&crdp->futex) == -1)) {
266 uatomic_set(&crdp->futex, 0);
267 if (futex_async(&crdp->futex, FUTEX_WAKE, 1,
268 NULL, NULL, 0) < 0)
269 urcu_die(errno);
270 }
271 }
272
273 static void call_rcu_completion_wait(struct call_rcu_completion *completion)
274 {
275 /* Read completion barrier count before read futex */
276 cmm_smp_mb();
277 if (uatomic_read(&completion->futex) != -1)
278 return;
279 while (futex_async(&completion->futex, FUTEX_WAIT, -1,
280 NULL, NULL, 0)) {
281 switch (errno) {
282 case EWOULDBLOCK:
283 /* Value already changed. */
284 return;
285 case EINTR:
286 /* Retry if interrupted by signal. */
287 break; /* Get out of switch. */
288 default:
289 /* Unexpected error. */
290 urcu_die(errno);
291 }
292 }
293 }
294
295 static void call_rcu_completion_wake_up(struct call_rcu_completion *completion)
296 {
297 /* Write to completion barrier count before reading/writing futex */
298 cmm_smp_mb();
299 if (caa_unlikely(uatomic_read(&completion->futex) == -1)) {
300 uatomic_set(&completion->futex, 0);
301 if (futex_async(&completion->futex, FUTEX_WAKE, 1,
302 NULL, NULL, 0) < 0)
303 urcu_die(errno);
304 }
305 }
306
307 /* This is the code run by each call_rcu thread. */
308
309 static void *call_rcu_thread(void *arg)
310 {
311 unsigned long cbcount;
312 struct call_rcu_data *crdp = (struct call_rcu_data *) arg;
313 int rt = !!(uatomic_read(&crdp->flags) & URCU_CALL_RCU_RT);
314
315 if (set_thread_cpu_affinity(crdp))
316 urcu_die(errno);
317
318 /*
319 * If callbacks take a read-side lock, we need to be registered.
320 */
321 rcu_register_thread();
322
323 URCU_TLS(thread_call_rcu_data) = crdp;
324 if (!rt) {
325 uatomic_dec(&crdp->futex);
326 /* Decrement futex before reading call_rcu list */
327 cmm_smp_mb();
328 }
329 for (;;) {
330 struct cds_wfcq_head cbs_tmp_head;
331 struct cds_wfcq_tail cbs_tmp_tail;
332 struct cds_wfcq_node *cbs, *cbs_tmp_n;
333 enum cds_wfcq_ret splice_ret;
334
335 if (set_thread_cpu_affinity(crdp))
336 urcu_die(errno);
337
338 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) {
339 /*
340 * Pause requested. Become quiescent: remove
341 * ourself from all global lists, and don't
342 * process any callback. The callback lists may
343 * still be non-empty though.
344 */
345 rcu_unregister_thread();
346 cmm_smp_mb__before_uatomic_or();
347 uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSED);
348 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) != 0)
349 (void) poll(NULL, 0, 1);
350 uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSED);
351 cmm_smp_mb__after_uatomic_and();
352 rcu_register_thread();
353 }
354
355 cds_wfcq_init(&cbs_tmp_head, &cbs_tmp_tail);
356 splice_ret = __cds_wfcq_splice_blocking(&cbs_tmp_head,
357 &cbs_tmp_tail, &crdp->cbs_head, &crdp->cbs_tail);
358 assert(splice_ret != CDS_WFCQ_RET_WOULDBLOCK);
359 assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
360 if (splice_ret != CDS_WFCQ_RET_SRC_EMPTY) {
361 synchronize_rcu();
362 cbcount = 0;
363 __cds_wfcq_for_each_blocking_safe(&cbs_tmp_head,
364 &cbs_tmp_tail, cbs, cbs_tmp_n) {
365 struct rcu_head *rhp;
366
367 rhp = caa_container_of(cbs,
368 struct rcu_head, next);
369 rhp->func(rhp);
370 cbcount++;
371 }
372 uatomic_sub(&crdp->qlen, cbcount);
373 }
374 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOP)
375 break;
376 rcu_thread_offline();
377 if (!rt) {
378 if (cds_wfcq_empty(&crdp->cbs_head,
379 &crdp->cbs_tail)) {
380 call_rcu_wait(crdp);
381 (void) poll(NULL, 0, 10);
382 uatomic_dec(&crdp->futex);
383 /*
384 * Decrement futex before reading
385 * call_rcu list.
386 */
387 cmm_smp_mb();
388 } else {
389 (void) poll(NULL, 0, 10);
390 }
391 } else {
392 (void) poll(NULL, 0, 10);
393 }
394 rcu_thread_online();
395 }
396 if (!rt) {
397 /*
398 * Read call_rcu list before write futex.
399 */
400 cmm_smp_mb();
401 uatomic_set(&crdp->futex, 0);
402 }
403 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOPPED);
404 rcu_unregister_thread();
405 return NULL;
406 }
407
408 /*
409 * Create both a call_rcu thread and the corresponding call_rcu_data
410 * structure, linking the structure in as specified. Caller must hold
411 * call_rcu_mutex.
412 */
413
414 static void call_rcu_data_init(struct call_rcu_data **crdpp,
415 unsigned long flags,
416 int cpu_affinity)
417 {
418 struct call_rcu_data *crdp;
419 int ret;
420
421 crdp = malloc(sizeof(*crdp));
422 if (crdp == NULL)
423 urcu_die(errno);
424 memset(crdp, '\0', sizeof(*crdp));
425 cds_wfcq_init(&crdp->cbs_head, &crdp->cbs_tail);
426 crdp->qlen = 0;
427 crdp->futex = 0;
428 crdp->flags = flags;
429 cds_list_add(&crdp->list, &call_rcu_data_list);
430 crdp->cpu_affinity = cpu_affinity;
431 crdp->gp_count = 0;
432 cmm_smp_mb(); /* Structure initialized before pointer is planted. */
433 *crdpp = crdp;
434 ret = pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp);
435 if (ret)
436 urcu_die(ret);
437 }
438
439 /*
440 * Return a pointer to the call_rcu_data structure for the specified
441 * CPU, returning NULL if there is none. We cannot automatically
442 * created it because the platform we are running on might not define
443 * urcu_sched_getcpu().
444 *
445 * The call to this function and use of the returned call_rcu_data
446 * should be protected by RCU read-side lock.
447 */
448
449 struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
450 {
451 static int warned = 0;
452 struct call_rcu_data **pcpu_crdp;
453
454 pcpu_crdp = rcu_dereference(per_cpu_call_rcu_data);
455 if (pcpu_crdp == NULL)
456 return NULL;
457 if (!warned && maxcpus > 0 && (cpu < 0 || maxcpus <= cpu)) {
458 fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
459 warned = 1;
460 }
461 if (cpu < 0 || maxcpus <= cpu)
462 return NULL;
463 return rcu_dereference(pcpu_crdp[cpu]);
464 }
465
466 /*
467 * Return the tid corresponding to the call_rcu thread whose
468 * call_rcu_data structure is specified.
469 */
470
471 pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
472 {
473 return crdp->tid;
474 }
475
476 /*
477 * Create a call_rcu_data structure (with thread) and return a pointer.
478 */
479
480 static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
481 int cpu_affinity)
482 {
483 struct call_rcu_data *crdp;
484
485 call_rcu_data_init(&crdp, flags, cpu_affinity);
486 return crdp;
487 }
488
489 struct call_rcu_data *create_call_rcu_data(unsigned long flags,
490 int cpu_affinity)
491 {
492 struct call_rcu_data *crdp;
493
494 call_rcu_lock(&call_rcu_mutex);
495 crdp = __create_call_rcu_data(flags, cpu_affinity);
496 call_rcu_unlock(&call_rcu_mutex);
497 return crdp;
498 }
499
500 /*
501 * Set the specified CPU to use the specified call_rcu_data structure.
502 *
503 * Use NULL to remove a CPU's call_rcu_data structure, but it is
504 * the caller's responsibility to dispose of the removed structure.
505 * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
506 * (prior to NULLing it out, of course).
507 *
508 * The caller must wait for a grace-period to pass between return from
509 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
510 * previous call rcu data as argument.
511 */
512
513 int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
514 {
515 static int warned = 0;
516
517 call_rcu_lock(&call_rcu_mutex);
518 alloc_cpu_call_rcu_data();
519 if (cpu < 0 || maxcpus <= cpu) {
520 if (!warned) {
521 fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
522 warned = 1;
523 }
524 call_rcu_unlock(&call_rcu_mutex);
525 errno = EINVAL;
526 return -EINVAL;
527 }
528
529 if (per_cpu_call_rcu_data == NULL) {
530 call_rcu_unlock(&call_rcu_mutex);
531 errno = ENOMEM;
532 return -ENOMEM;
533 }
534
535 if (per_cpu_call_rcu_data[cpu] != NULL && crdp != NULL) {
536 call_rcu_unlock(&call_rcu_mutex);
537 errno = EEXIST;
538 return -EEXIST;
539 }
540
541 rcu_set_pointer(&per_cpu_call_rcu_data[cpu], crdp);
542 call_rcu_unlock(&call_rcu_mutex);
543 return 0;
544 }
545
546 /*
547 * Return a pointer to the default call_rcu_data structure, creating
548 * one if need be. Because we never free call_rcu_data structures,
549 * we don't need to be in an RCU read-side critical section.
550 */
551
552 struct call_rcu_data *get_default_call_rcu_data(void)
553 {
554 if (default_call_rcu_data != NULL)
555 return rcu_dereference(default_call_rcu_data);
556 call_rcu_lock(&call_rcu_mutex);
557 if (default_call_rcu_data != NULL) {
558 call_rcu_unlock(&call_rcu_mutex);
559 return default_call_rcu_data;
560 }
561 call_rcu_data_init(&default_call_rcu_data, 0, -1);
562 call_rcu_unlock(&call_rcu_mutex);
563 return default_call_rcu_data;
564 }
565
566 /*
567 * Return the call_rcu_data structure that applies to the currently
568 * running thread. Any call_rcu_data structure assigned specifically
569 * to this thread has first priority, followed by any call_rcu_data
570 * structure assigned to the CPU on which the thread is running,
571 * followed by the default call_rcu_data structure. If there is not
572 * yet a default call_rcu_data structure, one will be created.
573 *
574 * Calls to this function and use of the returned call_rcu_data should
575 * be protected by RCU read-side lock.
576 */
577 struct call_rcu_data *get_call_rcu_data(void)
578 {
579 struct call_rcu_data *crd;
580
581 if (URCU_TLS(thread_call_rcu_data) != NULL)
582 return URCU_TLS(thread_call_rcu_data);
583
584 if (maxcpus > 0) {
585 crd = get_cpu_call_rcu_data(urcu_sched_getcpu());
586 if (crd)
587 return crd;
588 }
589
590 return get_default_call_rcu_data();
591 }
592
593 /*
594 * Return a pointer to this task's call_rcu_data if there is one.
595 */
596
597 struct call_rcu_data *get_thread_call_rcu_data(void)
598 {
599 return URCU_TLS(thread_call_rcu_data);
600 }
601
602 /*
603 * Set this task's call_rcu_data structure as specified, regardless
604 * of whether or not this task already had one. (This allows switching
605 * to and from real-time call_rcu threads, for example.)
606 *
607 * Use NULL to remove a thread's call_rcu_data structure, but it is
608 * the caller's responsibility to dispose of the removed structure.
609 * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
610 * (prior to NULLing it out, of course).
611 */
612
613 void set_thread_call_rcu_data(struct call_rcu_data *crdp)
614 {
615 URCU_TLS(thread_call_rcu_data) = crdp;
616 }
617
618 /*
619 * Create a separate call_rcu thread for each CPU. This does not
620 * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
621 * function if you want that behavior. Should be paired with
622 * free_all_cpu_call_rcu_data() to teardown these call_rcu worker
623 * threads.
624 */
625
626 int create_all_cpu_call_rcu_data(unsigned long flags)
627 {
628 int i;
629 struct call_rcu_data *crdp;
630 int ret;
631
632 call_rcu_lock(&call_rcu_mutex);
633 alloc_cpu_call_rcu_data();
634 call_rcu_unlock(&call_rcu_mutex);
635 if (maxcpus <= 0) {
636 errno = EINVAL;
637 return -EINVAL;
638 }
639 if (per_cpu_call_rcu_data == NULL) {
640 errno = ENOMEM;
641 return -ENOMEM;
642 }
643 for (i = 0; i < maxcpus; i++) {
644 call_rcu_lock(&call_rcu_mutex);
645 if (get_cpu_call_rcu_data(i)) {
646 call_rcu_unlock(&call_rcu_mutex);
647 continue;
648 }
649 crdp = __create_call_rcu_data(flags, i);
650 if (crdp == NULL) {
651 call_rcu_unlock(&call_rcu_mutex);
652 errno = ENOMEM;
653 return -ENOMEM;
654 }
655 call_rcu_unlock(&call_rcu_mutex);
656 if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
657 call_rcu_data_free(crdp);
658
659 /* it has been created by other thread */
660 if (ret == -EEXIST)
661 continue;
662
663 return ret;
664 }
665 }
666 return 0;
667 }
668
669 /*
670 * Wake up the call_rcu thread corresponding to the specified
671 * call_rcu_data structure.
672 */
673 static void wake_call_rcu_thread(struct call_rcu_data *crdp)
674 {
675 if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT))
676 call_rcu_wake_up(crdp);
677 }
678
679 static void _call_rcu(struct rcu_head *head,
680 void (*func)(struct rcu_head *head),
681 struct call_rcu_data *crdp)
682 {
683 cds_wfcq_node_init(&head->next);
684 head->func = func;
685 cds_wfcq_enqueue(&crdp->cbs_head, &crdp->cbs_tail, &head->next);
686 uatomic_inc(&crdp->qlen);
687 wake_call_rcu_thread(crdp);
688 }
689
690 /*
691 * Schedule a function to be invoked after a following grace period.
692 * This is the only function that must be called -- the others are
693 * only present to allow applications to tune their use of RCU for
694 * maximum performance.
695 *
696 * Note that unless a call_rcu thread has not already been created,
697 * the first invocation of call_rcu() will create one. So, if you
698 * need the first invocation of call_rcu() to be fast, make sure
699 * to create a call_rcu thread first. One way to accomplish this is
700 * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
701 *
702 * call_rcu must be called by registered RCU read-side threads.
703 */
704 void call_rcu(struct rcu_head *head,
705 void (*func)(struct rcu_head *head))
706 {
707 struct call_rcu_data *crdp;
708
709 /* Holding rcu read-side lock across use of per-cpu crdp */
710 _rcu_read_lock();
711 crdp = get_call_rcu_data();
712 _call_rcu(head, func, crdp);
713 _rcu_read_unlock();
714 }
715
716 /*
717 * Free up the specified call_rcu_data structure, terminating the
718 * associated call_rcu thread. The caller must have previously
719 * removed the call_rcu_data structure from per-thread or per-CPU
720 * usage. For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
721 * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
722 * per-thread call_rcu_data structures.
723 *
724 * We silently refuse to free up the default call_rcu_data structure
725 * because that is where we put any leftover callbacks. Note that
726 * the possibility of self-spawning callbacks makes it impossible
727 * to execute all the callbacks in finite time without putting any
728 * newly spawned callbacks somewhere else. The "somewhere else" of
729 * last resort is the default call_rcu_data structure.
730 *
731 * We also silently refuse to free NULL pointers. This simplifies
732 * the calling code.
733 *
734 * The caller must wait for a grace-period to pass between return from
735 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
736 * previous call rcu data as argument.
737 *
738 * Note: introducing __cds_wfcq_splice_blocking() in this function fixed
739 * a list corruption bug in the 0.7.x series. The equivalent fix
740 * appeared in 0.6.8 for the stable-0.6 branch.
741 */
742 void call_rcu_data_free(struct call_rcu_data *crdp)
743 {
744 if (crdp == NULL || crdp == default_call_rcu_data) {
745 return;
746 }
747 if ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0) {
748 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOP);
749 wake_call_rcu_thread(crdp);
750 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
751 (void) poll(NULL, 0, 1);
752 }
753 call_rcu_lock(&call_rcu_mutex);
754 if (!cds_wfcq_empty(&crdp->cbs_head, &crdp->cbs_tail)) {
755 call_rcu_unlock(&call_rcu_mutex);
756 /* Create default call rcu data if need be. */
757 /* CBs queued here will be handed to the default list. */
758 (void) get_default_call_rcu_data();
759 call_rcu_lock(&call_rcu_mutex);
760 __cds_wfcq_splice_blocking(&default_call_rcu_data->cbs_head,
761 &default_call_rcu_data->cbs_tail,
762 &crdp->cbs_head, &crdp->cbs_tail);
763 uatomic_add(&default_call_rcu_data->qlen,
764 uatomic_read(&crdp->qlen));
765 wake_call_rcu_thread(default_call_rcu_data);
766 }
767
768 cds_list_del(&crdp->list);
769 call_rcu_unlock(&call_rcu_mutex);
770
771 free(crdp);
772 }
773
774 /*
775 * Clean up all the per-CPU call_rcu threads.
776 */
777 void free_all_cpu_call_rcu_data(void)
778 {
779 int cpu;
780 struct call_rcu_data **crdp;
781 static int warned = 0;
782
783 if (maxcpus <= 0)
784 return;
785
786 crdp = malloc(sizeof(*crdp) * maxcpus);
787 if (!crdp) {
788 if (!warned) {
789 fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
790 }
791 warned = 1;
792 return;
793 }
794
795 for (cpu = 0; cpu < maxcpus; cpu++) {
796 crdp[cpu] = get_cpu_call_rcu_data(cpu);
797 if (crdp[cpu] == NULL)
798 continue;
799 set_cpu_call_rcu_data(cpu, NULL);
800 }
801 /*
802 * Wait for call_rcu sites acting as RCU readers of the
803 * call_rcu_data to become quiescent.
804 */
805 synchronize_rcu();
806 for (cpu = 0; cpu < maxcpus; cpu++) {
807 if (crdp[cpu] == NULL)
808 continue;
809 call_rcu_data_free(crdp[cpu]);
810 }
811 free(crdp);
812 }
813
814 static
815 void free_completion(struct urcu_ref *ref)
816 {
817 struct call_rcu_completion *completion;
818
819 completion = caa_container_of(ref, struct call_rcu_completion, ref);
820 free(completion);
821 }
822
823 static
824 void _rcu_barrier_complete(struct rcu_head *head)
825 {
826 struct call_rcu_completion_work *work;
827 struct call_rcu_completion *completion;
828
829 work = caa_container_of(head, struct call_rcu_completion_work, head);
830 completion = work->completion;
831 if (!uatomic_sub_return(&completion->barrier_count, 1))
832 call_rcu_completion_wake_up(completion);
833 urcu_ref_put(&completion->ref, free_completion);
834 free(work);
835 }
836
837 /*
838 * Wait for all in-flight call_rcu callbacks to complete execution.
839 */
840 void rcu_barrier(void)
841 {
842 struct call_rcu_data *crdp;
843 struct call_rcu_completion *completion;
844 int count = 0;
845 int was_online;
846
847 /* Put in offline state in QSBR. */
848 was_online = _rcu_read_ongoing();
849 if (was_online)
850 rcu_thread_offline();
851 /*
852 * Calling a rcu_barrier() within a RCU read-side critical
853 * section is an error.
854 */
855 if (_rcu_read_ongoing()) {
856 static int warned = 0;
857
858 if (!warned) {
859 fprintf(stderr, "[error] liburcu: rcu_barrier() called from within RCU read-side critical section.\n");
860 }
861 warned = 1;
862 goto online;
863 }
864
865 completion = calloc(sizeof(*completion), 1);
866 if (!completion)
867 urcu_die(errno);
868
869 call_rcu_lock(&call_rcu_mutex);
870 cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
871 count++;
872
873 /* Referenced by rcu_barrier() and each call_rcu thread. */
874 urcu_ref_set(&completion->ref, count + 1);
875 completion->barrier_count = count;
876
877 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
878 struct call_rcu_completion_work *work;
879
880 work = calloc(sizeof(*work), 1);
881 if (!work)
882 urcu_die(errno);
883 work->completion = completion;
884 _call_rcu(&work->head, _rcu_barrier_complete, crdp);
885 }
886 call_rcu_unlock(&call_rcu_mutex);
887
888 /* Wait for them */
889 for (;;) {
890 uatomic_dec(&completion->futex);
891 /* Decrement futex before reading barrier_count */
892 cmm_smp_mb();
893 if (!uatomic_read(&completion->barrier_count))
894 break;
895 call_rcu_completion_wait(completion);
896 }
897
898 urcu_ref_put(&completion->ref, free_completion);
899
900 online:
901 if (was_online)
902 rcu_thread_online();
903 }
904
905 /*
906 * Acquire the call_rcu_mutex in order to ensure that the child sees
907 * all of the call_rcu() data structures in a consistent state. Ensure
908 * that all call_rcu threads are in a quiescent state across fork.
909 * Suitable for pthread_atfork() and friends.
910 */
911 void call_rcu_before_fork(void)
912 {
913 struct call_rcu_data *crdp;
914 struct urcu_atfork *atfork;
915
916 call_rcu_lock(&call_rcu_mutex);
917
918 atfork = registered_rculfhash_atfork;
919 if (atfork)
920 atfork->before_fork(atfork->priv);
921
922 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
923 uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSE);
924 cmm_smp_mb__after_uatomic_or();
925 wake_call_rcu_thread(crdp);
926 }
927 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
928 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) == 0)
929 (void) poll(NULL, 0, 1);
930 }
931 }
932
933 /*
934 * Clean up call_rcu data structures in the parent of a successful fork()
935 * that is not followed by exec() in the child. Suitable for
936 * pthread_atfork() and friends.
937 */
938 void call_rcu_after_fork_parent(void)
939 {
940 struct call_rcu_data *crdp;
941 struct urcu_atfork *atfork;
942
943 cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
944 uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSE);
945 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
946 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) != 0)
947 (void) poll(NULL, 0, 1);
948 }
949 atfork = registered_rculfhash_atfork;
950 if (atfork)
951 atfork->after_fork_parent(atfork->priv);
952 call_rcu_unlock(&call_rcu_mutex);
953 }
954
955 /*
956 * Clean up call_rcu data structures in the child of a successful fork()
957 * that is not followed by exec(). Suitable for pthread_atfork() and
958 * friends.
959 */
960 void call_rcu_after_fork_child(void)
961 {
962 struct call_rcu_data *crdp, *next;
963 struct urcu_atfork *atfork;
964
965 /* Release the mutex. */
966 call_rcu_unlock(&call_rcu_mutex);
967
968 atfork = registered_rculfhash_atfork;
969 if (atfork)
970 atfork->after_fork_child(atfork->priv);
971
972 /* Do nothing when call_rcu() has not been used */
973 if (cds_list_empty(&call_rcu_data_list))
974 return;
975
976 /*
977 * Allocate a new default call_rcu_data structure in order
978 * to get a working call_rcu thread to go with it.
979 */
980 default_call_rcu_data = NULL;
981 (void)get_default_call_rcu_data();
982
983 /* Cleanup call_rcu_data pointers before use */
984 maxcpus_reset();
985 free(per_cpu_call_rcu_data);
986 rcu_set_pointer(&per_cpu_call_rcu_data, NULL);
987 URCU_TLS(thread_call_rcu_data) = NULL;
988
989 /*
990 * Dispose of all of the rest of the call_rcu_data structures.
991 * Leftover call_rcu callbacks will be merged into the new
992 * default call_rcu thread queue.
993 */
994 cds_list_for_each_entry_safe(crdp, next, &call_rcu_data_list, list) {
995 if (crdp == default_call_rcu_data)
996 continue;
997 uatomic_set(&crdp->flags, URCU_CALL_RCU_STOPPED);
998 call_rcu_data_free(crdp);
999 }
1000 }
1001
1002 void urcu_register_rculfhash_atfork(struct urcu_atfork *atfork)
1003 {
1004 call_rcu_lock(&call_rcu_mutex);
1005 if (registered_rculfhash_atfork_refcount++)
1006 goto end;
1007 registered_rculfhash_atfork = atfork;
1008 end:
1009 call_rcu_unlock(&call_rcu_mutex);
1010 }
1011
1012 void urcu_unregister_rculfhash_atfork(struct urcu_atfork *atfork __attribute__((unused)))
1013 {
1014 call_rcu_lock(&call_rcu_mutex);
1015 if (--registered_rculfhash_atfork_refcount)
1016 goto end;
1017 registered_rculfhash_atfork = NULL;
1018 end:
1019 call_rcu_unlock(&call_rcu_mutex);
1020 }
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