59ab333051bd9b1f624904280a52b344d26d25f4
[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)
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 URCU_ATTR_ALIAS(urcu_stringify(get_cpu_call_rcu_data))
466 struct call_rcu_data *alias_get_cpu_call_rcu_data();
467
468 /*
469 * Return the tid corresponding to the call_rcu thread whose
470 * call_rcu_data structure is specified.
471 */
472
473 pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
474 {
475 return crdp->tid;
476 }
477 URCU_ATTR_ALIAS(urcu_stringify(get_call_rcu_thread))
478 pthread_t alias_get_call_rcu_thread();
479
480 /*
481 * Create a call_rcu_data structure (with thread) and return a pointer.
482 */
483
484 static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
485 int cpu_affinity)
486 {
487 struct call_rcu_data *crdp;
488
489 call_rcu_data_init(&crdp, flags, cpu_affinity);
490 return crdp;
491 }
492
493 URCU_ATTR_ALIAS(urcu_stringify(create_call_rcu_data))
494 struct call_rcu_data *alias_create_call_rcu_data();
495 struct call_rcu_data *create_call_rcu_data(unsigned long flags,
496 int cpu_affinity)
497 {
498 struct call_rcu_data *crdp;
499
500 call_rcu_lock(&call_rcu_mutex);
501 crdp = __create_call_rcu_data(flags, cpu_affinity);
502 call_rcu_unlock(&call_rcu_mutex);
503 return crdp;
504 }
505
506 /*
507 * Set the specified CPU to use the specified call_rcu_data structure.
508 *
509 * Use NULL to remove a CPU's call_rcu_data structure, but it is
510 * the caller's responsibility to dispose of the removed structure.
511 * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
512 * (prior to NULLing it out, of course).
513 *
514 * The caller must wait for a grace-period to pass between return from
515 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
516 * previous call rcu data as argument.
517 */
518
519 int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
520 {
521 static int warned = 0;
522
523 call_rcu_lock(&call_rcu_mutex);
524 alloc_cpu_call_rcu_data();
525 if (cpu < 0 || maxcpus <= cpu) {
526 if (!warned) {
527 fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
528 warned = 1;
529 }
530 call_rcu_unlock(&call_rcu_mutex);
531 errno = EINVAL;
532 return -EINVAL;
533 }
534
535 if (per_cpu_call_rcu_data == NULL) {
536 call_rcu_unlock(&call_rcu_mutex);
537 errno = ENOMEM;
538 return -ENOMEM;
539 }
540
541 if (per_cpu_call_rcu_data[cpu] != NULL && crdp != NULL) {
542 call_rcu_unlock(&call_rcu_mutex);
543 errno = EEXIST;
544 return -EEXIST;
545 }
546
547 rcu_set_pointer(&per_cpu_call_rcu_data[cpu], crdp);
548 call_rcu_unlock(&call_rcu_mutex);
549 return 0;
550 }
551 URCU_ATTR_ALIAS(urcu_stringify(set_cpu_call_rcu_data))
552 int alias_set_cpu_call_rcu_data();
553
554 /*
555 * Return a pointer to the default call_rcu_data structure, creating
556 * one if need be. Because we never free call_rcu_data structures,
557 * we don't need to be in an RCU read-side critical section.
558 */
559
560 struct call_rcu_data *get_default_call_rcu_data(void)
561 {
562 if (default_call_rcu_data != NULL)
563 return rcu_dereference(default_call_rcu_data);
564 call_rcu_lock(&call_rcu_mutex);
565 if (default_call_rcu_data != NULL) {
566 call_rcu_unlock(&call_rcu_mutex);
567 return default_call_rcu_data;
568 }
569 call_rcu_data_init(&default_call_rcu_data, 0, -1);
570 call_rcu_unlock(&call_rcu_mutex);
571 return default_call_rcu_data;
572 }
573 URCU_ATTR_ALIAS(urcu_stringify(get_default_call_rcu_data))
574 struct call_rcu_data *alias_get_default_call_rcu_data();
575
576 /*
577 * Return the call_rcu_data structure that applies to the currently
578 * running thread. Any call_rcu_data structure assigned specifically
579 * to this thread has first priority, followed by any call_rcu_data
580 * structure assigned to the CPU on which the thread is running,
581 * followed by the default call_rcu_data structure. If there is not
582 * yet a default call_rcu_data structure, one will be created.
583 *
584 * Calls to this function and use of the returned call_rcu_data should
585 * be protected by RCU read-side lock.
586 */
587 struct call_rcu_data *get_call_rcu_data(void)
588 {
589 struct call_rcu_data *crd;
590
591 if (URCU_TLS(thread_call_rcu_data) != NULL)
592 return URCU_TLS(thread_call_rcu_data);
593
594 if (maxcpus > 0) {
595 crd = get_cpu_call_rcu_data(urcu_sched_getcpu());
596 if (crd)
597 return crd;
598 }
599
600 return get_default_call_rcu_data();
601 }
602 URCU_ATTR_ALIAS(urcu_stringify(get_call_rcu_data))
603 struct call_rcu_data *alias_get_call_rcu_data();
604
605 /*
606 * Return a pointer to this task's call_rcu_data if there is one.
607 */
608
609 struct call_rcu_data *get_thread_call_rcu_data(void)
610 {
611 return URCU_TLS(thread_call_rcu_data);
612 }
613 URCU_ATTR_ALIAS(urcu_stringify(get_thread_call_rcu_data))
614 struct call_rcu_data *alias_get_thread_call_rcu_data();
615
616 /*
617 * Set this task's call_rcu_data structure as specified, regardless
618 * of whether or not this task already had one. (This allows switching
619 * to and from real-time call_rcu threads, for example.)
620 *
621 * Use NULL to remove a thread's call_rcu_data structure, but it is
622 * the caller's responsibility to dispose of the removed structure.
623 * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
624 * (prior to NULLing it out, of course).
625 */
626
627 void set_thread_call_rcu_data(struct call_rcu_data *crdp)
628 {
629 URCU_TLS(thread_call_rcu_data) = crdp;
630 }
631 URCU_ATTR_ALIAS(urcu_stringify(set_thread_call_rcu_data))
632 void alias_set_thread_call_rcu_data();
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 URCU_ATTR_ALIAS(urcu_stringify(create_all_cpu_call_rcu_data))
685 int alias_create_all_cpu_call_rcu_data();
686
687 /*
688 * Wake up the call_rcu thread corresponding to the specified
689 * call_rcu_data structure.
690 */
691 static void wake_call_rcu_thread(struct call_rcu_data *crdp)
692 {
693 if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT))
694 call_rcu_wake_up(crdp);
695 }
696
697 static void _call_rcu(struct rcu_head *head,
698 void (*func)(struct rcu_head *head),
699 struct call_rcu_data *crdp)
700 {
701 cds_wfcq_node_init(&head->next);
702 head->func = func;
703 cds_wfcq_enqueue(&crdp->cbs_head, &crdp->cbs_tail, &head->next);
704 uatomic_inc(&crdp->qlen);
705 wake_call_rcu_thread(crdp);
706 }
707
708 /*
709 * Schedule a function to be invoked after a following grace period.
710 * This is the only function that must be called -- the others are
711 * only present to allow applications to tune their use of RCU for
712 * maximum performance.
713 *
714 * Note that unless a call_rcu thread has not already been created,
715 * the first invocation of call_rcu() will create one. So, if you
716 * need the first invocation of call_rcu() to be fast, make sure
717 * to create a call_rcu thread first. One way to accomplish this is
718 * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
719 *
720 * call_rcu must be called by registered RCU read-side threads.
721 */
722 void call_rcu(struct rcu_head *head,
723 void (*func)(struct rcu_head *head))
724 {
725 struct call_rcu_data *crdp;
726
727 /* Holding rcu read-side lock across use of per-cpu crdp */
728 _rcu_read_lock();
729 crdp = get_call_rcu_data();
730 _call_rcu(head, func, crdp);
731 _rcu_read_unlock();
732 }
733 URCU_ATTR_ALIAS(urcu_stringify(call_rcu)) void alias_call_rcu();
734
735 /*
736 * Free up the specified call_rcu_data structure, terminating the
737 * associated call_rcu thread. The caller must have previously
738 * removed the call_rcu_data structure from per-thread or per-CPU
739 * usage. For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
740 * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
741 * per-thread call_rcu_data structures.
742 *
743 * We silently refuse to free up the default call_rcu_data structure
744 * because that is where we put any leftover callbacks. Note that
745 * the possibility of self-spawning callbacks makes it impossible
746 * to execute all the callbacks in finite time without putting any
747 * newly spawned callbacks somewhere else. The "somewhere else" of
748 * last resort is the default call_rcu_data structure.
749 *
750 * We also silently refuse to free NULL pointers. This simplifies
751 * the calling code.
752 *
753 * The caller must wait for a grace-period to pass between return from
754 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
755 * previous call rcu data as argument.
756 *
757 * Note: introducing __cds_wfcq_splice_blocking() in this function fixed
758 * a list corruption bug in the 0.7.x series. The equivalent fix
759 * appeared in 0.6.8 for the stable-0.6 branch.
760 */
761 void call_rcu_data_free(struct call_rcu_data *crdp)
762 {
763 if (crdp == NULL || crdp == default_call_rcu_data) {
764 return;
765 }
766 if ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0) {
767 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOP);
768 wake_call_rcu_thread(crdp);
769 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
770 (void) poll(NULL, 0, 1);
771 }
772 call_rcu_lock(&call_rcu_mutex);
773 if (!cds_wfcq_empty(&crdp->cbs_head, &crdp->cbs_tail)) {
774 call_rcu_unlock(&call_rcu_mutex);
775 /* Create default call rcu data if need be. */
776 /* CBs queued here will be handed to the default list. */
777 (void) get_default_call_rcu_data();
778 call_rcu_lock(&call_rcu_mutex);
779 __cds_wfcq_splice_blocking(&default_call_rcu_data->cbs_head,
780 &default_call_rcu_data->cbs_tail,
781 &crdp->cbs_head, &crdp->cbs_tail);
782 uatomic_add(&default_call_rcu_data->qlen,
783 uatomic_read(&crdp->qlen));
784 wake_call_rcu_thread(default_call_rcu_data);
785 }
786
787 cds_list_del(&crdp->list);
788 call_rcu_unlock(&call_rcu_mutex);
789
790 free(crdp);
791 }
792 URCU_ATTR_ALIAS(urcu_stringify(call_rcu_data_free))
793 void alias_call_rcu_data_free();
794
795 /*
796 * Clean up all the per-CPU call_rcu threads.
797 */
798 void free_all_cpu_call_rcu_data(void)
799 {
800 int cpu;
801 struct call_rcu_data **crdp;
802 static int warned = 0;
803
804 if (maxcpus <= 0)
805 return;
806
807 crdp = malloc(sizeof(*crdp) * maxcpus);
808 if (!crdp) {
809 if (!warned) {
810 fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
811 }
812 warned = 1;
813 return;
814 }
815
816 for (cpu = 0; cpu < maxcpus; cpu++) {
817 crdp[cpu] = get_cpu_call_rcu_data(cpu);
818 if (crdp[cpu] == NULL)
819 continue;
820 set_cpu_call_rcu_data(cpu, NULL);
821 }
822 /*
823 * Wait for call_rcu sites acting as RCU readers of the
824 * call_rcu_data to become quiescent.
825 */
826 synchronize_rcu();
827 for (cpu = 0; cpu < maxcpus; cpu++) {
828 if (crdp[cpu] == NULL)
829 continue;
830 call_rcu_data_free(crdp[cpu]);
831 }
832 free(crdp);
833 }
834 #ifdef RCU_QSBR
835 /* ABI6 has a non-namespaced free_all_cpu_call_rcu_data for qsbr */
836 #undef free_all_cpu_call_rcu_data
837 URCU_ATTR_ALIAS("urcu_qsbr_free_all_cpu_call_rcu_data")
838 void free_all_cpu_call_rcu_data();
839 #define free_all_cpu_call_rcu_data urcu_qsbr_free_all_cpu_call_rcu_data
840 #else
841 URCU_ATTR_ALIAS(urcu_stringify(free_all_cpu_call_rcu_data))
842 void alias_free_all_cpu_call_rcu_data();
843 #endif
844
845 static
846 void free_completion(struct urcu_ref *ref)
847 {
848 struct call_rcu_completion *completion;
849
850 completion = caa_container_of(ref, struct call_rcu_completion, ref);
851 free(completion);
852 }
853
854 static
855 void _rcu_barrier_complete(struct rcu_head *head)
856 {
857 struct call_rcu_completion_work *work;
858 struct call_rcu_completion *completion;
859
860 work = caa_container_of(head, struct call_rcu_completion_work, head);
861 completion = work->completion;
862 if (!uatomic_sub_return(&completion->barrier_count, 1))
863 call_rcu_completion_wake_up(completion);
864 urcu_ref_put(&completion->ref, free_completion);
865 free(work);
866 }
867
868 /*
869 * Wait for all in-flight call_rcu callbacks to complete execution.
870 */
871 void rcu_barrier(void)
872 {
873 struct call_rcu_data *crdp;
874 struct call_rcu_completion *completion;
875 int count = 0;
876 int was_online;
877
878 /* Put in offline state in QSBR. */
879 was_online = _rcu_read_ongoing();
880 if (was_online)
881 rcu_thread_offline();
882 /*
883 * Calling a rcu_barrier() within a RCU read-side critical
884 * section is an error.
885 */
886 if (_rcu_read_ongoing()) {
887 static int warned = 0;
888
889 if (!warned) {
890 fprintf(stderr, "[error] liburcu: rcu_barrier() called from within RCU read-side critical section.\n");
891 }
892 warned = 1;
893 goto online;
894 }
895
896 completion = calloc(sizeof(*completion), 1);
897 if (!completion)
898 urcu_die(errno);
899
900 call_rcu_lock(&call_rcu_mutex);
901 cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
902 count++;
903
904 /* Referenced by rcu_barrier() and each call_rcu thread. */
905 urcu_ref_set(&completion->ref, count + 1);
906 completion->barrier_count = count;
907
908 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
909 struct call_rcu_completion_work *work;
910
911 work = calloc(sizeof(*work), 1);
912 if (!work)
913 urcu_die(errno);
914 work->completion = completion;
915 _call_rcu(&work->head, _rcu_barrier_complete, crdp);
916 }
917 call_rcu_unlock(&call_rcu_mutex);
918
919 /* Wait for them */
920 for (;;) {
921 uatomic_dec(&completion->futex);
922 /* Decrement futex before reading barrier_count */
923 cmm_smp_mb();
924 if (!uatomic_read(&completion->barrier_count))
925 break;
926 call_rcu_completion_wait(completion);
927 }
928
929 urcu_ref_put(&completion->ref, free_completion);
930
931 online:
932 if (was_online)
933 rcu_thread_online();
934 }
935 URCU_ATTR_ALIAS(urcu_stringify(rcu_barrier))
936 void alias_rcu_barrier();
937
938 /*
939 * Acquire the call_rcu_mutex in order to ensure that the child sees
940 * all of the call_rcu() data structures in a consistent state. Ensure
941 * that all call_rcu threads are in a quiescent state across fork.
942 * Suitable for pthread_atfork() and friends.
943 */
944 void call_rcu_before_fork(void)
945 {
946 struct call_rcu_data *crdp;
947 struct urcu_atfork *atfork;
948
949 call_rcu_lock(&call_rcu_mutex);
950
951 atfork = registered_rculfhash_atfork;
952 if (atfork)
953 atfork->before_fork(atfork->priv);
954
955 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
956 uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSE);
957 cmm_smp_mb__after_uatomic_or();
958 wake_call_rcu_thread(crdp);
959 }
960 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
961 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) == 0)
962 (void) poll(NULL, 0, 1);
963 }
964 }
965 URCU_ATTR_ALIAS(urcu_stringify(call_rcu_before_fork))
966 void alias_call_rcu_before_fork();
967
968 /*
969 * Clean up call_rcu data structures in the parent of a successful fork()
970 * that is not followed by exec() in the child. Suitable for
971 * pthread_atfork() and friends.
972 */
973 void call_rcu_after_fork_parent(void)
974 {
975 struct call_rcu_data *crdp;
976 struct urcu_atfork *atfork;
977
978 cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
979 uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSE);
980 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
981 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) != 0)
982 (void) poll(NULL, 0, 1);
983 }
984 atfork = registered_rculfhash_atfork;
985 if (atfork)
986 atfork->after_fork_parent(atfork->priv);
987 call_rcu_unlock(&call_rcu_mutex);
988 }
989 URCU_ATTR_ALIAS(urcu_stringify(call_rcu_after_fork_parent))
990 void alias_call_rcu_after_fork_parent();
991
992 /*
993 * Clean up call_rcu data structures in the child of a successful fork()
994 * that is not followed by exec(). Suitable for pthread_atfork() and
995 * friends.
996 */
997 void call_rcu_after_fork_child(void)
998 {
999 struct call_rcu_data *crdp, *next;
1000 struct urcu_atfork *atfork;
1001
1002 /* Release the mutex. */
1003 call_rcu_unlock(&call_rcu_mutex);
1004
1005 atfork = registered_rculfhash_atfork;
1006 if (atfork)
1007 atfork->after_fork_child(atfork->priv);
1008
1009 /* Do nothing when call_rcu() has not been used */
1010 if (cds_list_empty(&call_rcu_data_list))
1011 return;
1012
1013 /*
1014 * Allocate a new default call_rcu_data structure in order
1015 * to get a working call_rcu thread to go with it.
1016 */
1017 default_call_rcu_data = NULL;
1018 (void)get_default_call_rcu_data();
1019
1020 /* Cleanup call_rcu_data pointers before use */
1021 maxcpus_reset();
1022 free(per_cpu_call_rcu_data);
1023 rcu_set_pointer(&per_cpu_call_rcu_data, NULL);
1024 URCU_TLS(thread_call_rcu_data) = NULL;
1025
1026 /*
1027 * Dispose of all of the rest of the call_rcu_data structures.
1028 * Leftover call_rcu callbacks will be merged into the new
1029 * default call_rcu thread queue.
1030 */
1031 cds_list_for_each_entry_safe(crdp, next, &call_rcu_data_list, list) {
1032 if (crdp == default_call_rcu_data)
1033 continue;
1034 uatomic_set(&crdp->flags, URCU_CALL_RCU_STOPPED);
1035 call_rcu_data_free(crdp);
1036 }
1037 }
1038 URCU_ATTR_ALIAS(urcu_stringify(call_rcu_after_fork_child))
1039 void alias_call_rcu_after_fork_child();
1040
1041 void urcu_register_rculfhash_atfork(struct urcu_atfork *atfork)
1042 {
1043 call_rcu_lock(&call_rcu_mutex);
1044 if (registered_rculfhash_atfork_refcount++)
1045 goto end;
1046 registered_rculfhash_atfork = atfork;
1047 end:
1048 call_rcu_unlock(&call_rcu_mutex);
1049 }
1050 URCU_ATTR_ALIAS(urcu_stringify(urcu_register_rculfhash_atfork))
1051 void alias_urcu_register_rculfhash_atfork();
1052
1053 void urcu_unregister_rculfhash_atfork(struct urcu_atfork *atfork __attribute__((unused)))
1054 {
1055 call_rcu_lock(&call_rcu_mutex);
1056 if (--registered_rculfhash_atfork_refcount)
1057 goto end;
1058 registered_rculfhash_atfork = NULL;
1059 end:
1060 call_rcu_unlock(&call_rcu_mutex);
1061 }
1062 URCU_ATTR_ALIAS(urcu_stringify(urcu_unregister_rculfhash_atfork))
1063 void alias_urcu_unregister_rculfhash_atfork();
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