c4a78752b5c383e4ade261c85051e18793bafa87
[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 /* Data structure that identifies a call_rcu thread. */
49
50 struct call_rcu_data {
51 /*
52 * We do not align head on a different cache-line than tail
53 * mainly because call_rcu callback-invocation threads use
54 * batching ("splice") to get an entire list of callbacks, which
55 * effectively empties the queue, and requires to touch the tail
56 * anyway.
57 */
58 struct cds_wfcq_tail cbs_tail;
59 struct cds_wfcq_head cbs_head;
60 unsigned long flags;
61 int32_t futex;
62 unsigned long qlen; /* maintained for debugging. */
63 pthread_t tid;
64 int cpu_affinity;
65 struct cds_list_head list;
66 } __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
67
68 struct call_rcu_completion {
69 int barrier_count;
70 int32_t futex;
71 struct urcu_ref ref;
72 };
73
74 struct call_rcu_completion_work {
75 struct rcu_head head;
76 struct call_rcu_completion *completion;
77 };
78
79 /*
80 * List of all call_rcu_data structures to keep valgrind happy.
81 * Protected by call_rcu_mutex.
82 */
83
84 static CDS_LIST_HEAD(call_rcu_data_list);
85
86 /* Link a thread using call_rcu() to its call_rcu thread. */
87
88 static DEFINE_URCU_TLS(struct call_rcu_data *, thread_call_rcu_data);
89
90 /*
91 * Guard call_rcu thread creation and atfork handlers.
92 */
93 static pthread_mutex_t call_rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
94
95 /* If a given thread does not have its own call_rcu thread, this is default. */
96
97 static struct call_rcu_data *default_call_rcu_data;
98
99 /*
100 * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
101 * available, then we can have call_rcu threads assigned to individual
102 * CPUs rather than only to specific threads.
103 */
104
105 #ifdef HAVE_SCHED_GETCPU
106
107 static int urcu_sched_getcpu(void)
108 {
109 return sched_getcpu();
110 }
111
112 #else /* #ifdef HAVE_SCHED_GETCPU */
113
114 static int urcu_sched_getcpu(void)
115 {
116 return -1;
117 }
118
119 #endif /* #else #ifdef HAVE_SCHED_GETCPU */
120
121 #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU)
122
123 /*
124 * Pointer to array of pointers to per-CPU call_rcu_data structures
125 * and # CPUs. per_cpu_call_rcu_data is a RCU-protected pointer to an
126 * array of RCU-protected pointers to call_rcu_data. call_rcu acts as a
127 * RCU read-side and reads per_cpu_call_rcu_data and the per-cpu pointer
128 * without mutex. The call_rcu_mutex protects updates.
129 */
130
131 static struct call_rcu_data **per_cpu_call_rcu_data;
132 static long maxcpus;
133
134 static void maxcpus_reset(void)
135 {
136 maxcpus = 0;
137 }
138
139 /* Allocate the array if it has not already been allocated. */
140
141 static void alloc_cpu_call_rcu_data(void)
142 {
143 struct call_rcu_data **p;
144 static int warned = 0;
145
146 if (maxcpus != 0)
147 return;
148 maxcpus = sysconf(_SC_NPROCESSORS_CONF);
149 if (maxcpus <= 0) {
150 return;
151 }
152 p = malloc(maxcpus * sizeof(*per_cpu_call_rcu_data));
153 if (p != NULL) {
154 memset(p, '\0', maxcpus * sizeof(*per_cpu_call_rcu_data));
155 rcu_set_pointer(&per_cpu_call_rcu_data, p);
156 } else {
157 if (!warned) {
158 fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
159 }
160 warned = 1;
161 }
162 }
163
164 #else /* #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
165
166 /*
167 * per_cpu_call_rcu_data should be constant, but some functions below, used both
168 * for cases where cpu number is available and not available, assume it it not
169 * constant.
170 */
171 static struct call_rcu_data **per_cpu_call_rcu_data = NULL;
172 static const long maxcpus = -1;
173
174 static void maxcpus_reset(void)
175 {
176 }
177
178 static void alloc_cpu_call_rcu_data(void)
179 {
180 }
181
182 #endif /* #else #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
183
184 /* Acquire the specified pthread mutex. */
185
186 static void call_rcu_lock(pthread_mutex_t *pmp)
187 {
188 int ret;
189
190 ret = pthread_mutex_lock(pmp);
191 if (ret)
192 urcu_die(ret);
193 }
194
195 /* Release the specified pthread mutex. */
196
197 static void call_rcu_unlock(pthread_mutex_t *pmp)
198 {
199 int ret;
200
201 ret = pthread_mutex_unlock(pmp);
202 if (ret)
203 urcu_die(ret);
204 }
205
206 #if HAVE_SCHED_SETAFFINITY
207 static
208 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
209 {
210 cpu_set_t mask;
211
212 if (crdp->cpu_affinity < 0)
213 return 0;
214
215 CPU_ZERO(&mask);
216 CPU_SET(crdp->cpu_affinity, &mask);
217 #if SCHED_SETAFFINITY_ARGS == 2
218 return sched_setaffinity(0, &mask);
219 #else
220 return sched_setaffinity(0, sizeof(mask), &mask);
221 #endif
222 }
223 #else
224 static
225 int set_thread_cpu_affinity(struct call_rcu_data *crdp)
226 {
227 return 0;
228 }
229 #endif
230
231 static void call_rcu_wait(struct call_rcu_data *crdp)
232 {
233 /* Read call_rcu list before read futex */
234 cmm_smp_mb();
235 if (uatomic_read(&crdp->futex) == -1)
236 futex_async(&crdp->futex, FUTEX_WAIT, -1,
237 NULL, NULL, 0);
238 }
239
240 static void call_rcu_wake_up(struct call_rcu_data *crdp)
241 {
242 /* Write to call_rcu list before reading/writing futex */
243 cmm_smp_mb();
244 if (caa_unlikely(uatomic_read(&crdp->futex) == -1)) {
245 uatomic_set(&crdp->futex, 0);
246 futex_async(&crdp->futex, FUTEX_WAKE, 1,
247 NULL, NULL, 0);
248 }
249 }
250
251 static void call_rcu_completion_wait(struct call_rcu_completion *completion)
252 {
253 /* Read completion barrier count before read futex */
254 cmm_smp_mb();
255 if (uatomic_read(&completion->futex) == -1)
256 futex_async(&completion->futex, FUTEX_WAIT, -1,
257 NULL, NULL, 0);
258 }
259
260 static void call_rcu_completion_wake_up(struct call_rcu_completion *completion)
261 {
262 /* Write to completion barrier count before reading/writing futex */
263 cmm_smp_mb();
264 if (caa_unlikely(uatomic_read(&completion->futex) == -1)) {
265 uatomic_set(&completion->futex, 0);
266 futex_async(&completion->futex, FUTEX_WAKE, 1,
267 NULL, NULL, 0);
268 }
269 }
270
271 /* This is the code run by each call_rcu thread. */
272
273 static void *call_rcu_thread(void *arg)
274 {
275 unsigned long cbcount;
276 struct call_rcu_data *crdp = (struct call_rcu_data *) arg;
277 int rt = !!(uatomic_read(&crdp->flags) & URCU_CALL_RCU_RT);
278 int ret;
279
280 ret = set_thread_cpu_affinity(crdp);
281 if (ret)
282 urcu_die(errno);
283
284 /*
285 * If callbacks take a read-side lock, we need to be registered.
286 */
287 rcu_register_thread();
288
289 URCU_TLS(thread_call_rcu_data) = crdp;
290 if (!rt) {
291 uatomic_dec(&crdp->futex);
292 /* Decrement futex before reading call_rcu list */
293 cmm_smp_mb();
294 }
295 for (;;) {
296 struct cds_wfcq_head cbs_tmp_head;
297 struct cds_wfcq_tail cbs_tmp_tail;
298 struct cds_wfcq_node *cbs, *cbs_tmp_n;
299 enum cds_wfcq_ret splice_ret;
300
301 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) {
302 /*
303 * Pause requested. Become quiescent: remove
304 * ourself from all global lists, and don't
305 * process any callback. The callback lists may
306 * still be non-empty though.
307 */
308 rcu_unregister_thread();
309 cmm_smp_mb__before_uatomic_or();
310 uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSED);
311 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) != 0)
312 poll(NULL, 0, 1);
313 uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSED);
314 cmm_smp_mb__after_uatomic_and();
315 rcu_register_thread();
316 }
317
318 cds_wfcq_init(&cbs_tmp_head, &cbs_tmp_tail);
319 splice_ret = __cds_wfcq_splice_blocking(&cbs_tmp_head,
320 &cbs_tmp_tail, &crdp->cbs_head, &crdp->cbs_tail);
321 assert(splice_ret != CDS_WFCQ_RET_WOULDBLOCK);
322 assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
323 if (splice_ret != CDS_WFCQ_RET_SRC_EMPTY) {
324 synchronize_rcu();
325 cbcount = 0;
326 __cds_wfcq_for_each_blocking_safe(&cbs_tmp_head,
327 &cbs_tmp_tail, cbs, cbs_tmp_n) {
328 struct rcu_head *rhp;
329
330 rhp = caa_container_of(cbs,
331 struct rcu_head, next);
332 rhp->func(rhp);
333 cbcount++;
334 }
335 uatomic_sub(&crdp->qlen, cbcount);
336 }
337 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOP)
338 break;
339 rcu_thread_offline();
340 if (!rt) {
341 if (cds_wfcq_empty(&crdp->cbs_head,
342 &crdp->cbs_tail)) {
343 call_rcu_wait(crdp);
344 poll(NULL, 0, 10);
345 uatomic_dec(&crdp->futex);
346 /*
347 * Decrement futex before reading
348 * call_rcu list.
349 */
350 cmm_smp_mb();
351 } else {
352 poll(NULL, 0, 10);
353 }
354 } else {
355 poll(NULL, 0, 10);
356 }
357 rcu_thread_online();
358 }
359 if (!rt) {
360 /*
361 * Read call_rcu list before write futex.
362 */
363 cmm_smp_mb();
364 uatomic_set(&crdp->futex, 0);
365 }
366 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOPPED);
367 rcu_unregister_thread();
368 return NULL;
369 }
370
371 /*
372 * Create both a call_rcu thread and the corresponding call_rcu_data
373 * structure, linking the structure in as specified. Caller must hold
374 * call_rcu_mutex.
375 */
376
377 static void call_rcu_data_init(struct call_rcu_data **crdpp,
378 unsigned long flags,
379 int cpu_affinity)
380 {
381 struct call_rcu_data *crdp;
382 int ret;
383
384 crdp = malloc(sizeof(*crdp));
385 if (crdp == NULL)
386 urcu_die(errno);
387 memset(crdp, '\0', sizeof(*crdp));
388 cds_wfcq_init(&crdp->cbs_head, &crdp->cbs_tail);
389 crdp->qlen = 0;
390 crdp->futex = 0;
391 crdp->flags = flags;
392 cds_list_add(&crdp->list, &call_rcu_data_list);
393 crdp->cpu_affinity = cpu_affinity;
394 cmm_smp_mb(); /* Structure initialized before pointer is planted. */
395 *crdpp = crdp;
396 ret = pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp);
397 if (ret)
398 urcu_die(ret);
399 }
400
401 /*
402 * Return a pointer to the call_rcu_data structure for the specified
403 * CPU, returning NULL if there is none. We cannot automatically
404 * created it because the platform we are running on might not define
405 * urcu_sched_getcpu().
406 *
407 * The call to this function and use of the returned call_rcu_data
408 * should be protected by RCU read-side lock.
409 */
410
411 struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
412 {
413 static int warned = 0;
414 struct call_rcu_data **pcpu_crdp;
415
416 pcpu_crdp = rcu_dereference(per_cpu_call_rcu_data);
417 if (pcpu_crdp == NULL)
418 return NULL;
419 if (!warned && maxcpus > 0 && (cpu < 0 || maxcpus <= cpu)) {
420 fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
421 warned = 1;
422 }
423 if (cpu < 0 || maxcpus <= cpu)
424 return NULL;
425 return rcu_dereference(pcpu_crdp[cpu]);
426 }
427
428 /*
429 * Return the tid corresponding to the call_rcu thread whose
430 * call_rcu_data structure is specified.
431 */
432
433 pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
434 {
435 return crdp->tid;
436 }
437
438 /*
439 * Create a call_rcu_data structure (with thread) and return a pointer.
440 */
441
442 static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
443 int cpu_affinity)
444 {
445 struct call_rcu_data *crdp;
446
447 call_rcu_data_init(&crdp, flags, cpu_affinity);
448 return crdp;
449 }
450
451 struct call_rcu_data *create_call_rcu_data(unsigned long flags,
452 int cpu_affinity)
453 {
454 struct call_rcu_data *crdp;
455
456 call_rcu_lock(&call_rcu_mutex);
457 crdp = __create_call_rcu_data(flags, cpu_affinity);
458 call_rcu_unlock(&call_rcu_mutex);
459 return crdp;
460 }
461
462 /*
463 * Set the specified CPU to use the specified call_rcu_data structure.
464 *
465 * Use NULL to remove a CPU's call_rcu_data structure, but it is
466 * the caller's responsibility to dispose of the removed structure.
467 * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
468 * (prior to NULLing it out, of course).
469 *
470 * The caller must wait for a grace-period to pass between return from
471 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
472 * previous call rcu data as argument.
473 */
474
475 int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
476 {
477 static int warned = 0;
478
479 call_rcu_lock(&call_rcu_mutex);
480 alloc_cpu_call_rcu_data();
481 if (cpu < 0 || maxcpus <= cpu) {
482 if (!warned) {
483 fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
484 warned = 1;
485 }
486 call_rcu_unlock(&call_rcu_mutex);
487 errno = EINVAL;
488 return -EINVAL;
489 }
490
491 if (per_cpu_call_rcu_data == NULL) {
492 call_rcu_unlock(&call_rcu_mutex);
493 errno = ENOMEM;
494 return -ENOMEM;
495 }
496
497 if (per_cpu_call_rcu_data[cpu] != NULL && crdp != NULL) {
498 call_rcu_unlock(&call_rcu_mutex);
499 errno = EEXIST;
500 return -EEXIST;
501 }
502
503 rcu_set_pointer(&per_cpu_call_rcu_data[cpu], crdp);
504 call_rcu_unlock(&call_rcu_mutex);
505 return 0;
506 }
507
508 /*
509 * Return a pointer to the default call_rcu_data structure, creating
510 * one if need be. Because we never free call_rcu_data structures,
511 * we don't need to be in an RCU read-side critical section.
512 */
513
514 struct call_rcu_data *get_default_call_rcu_data(void)
515 {
516 if (default_call_rcu_data != NULL)
517 return rcu_dereference(default_call_rcu_data);
518 call_rcu_lock(&call_rcu_mutex);
519 if (default_call_rcu_data != NULL) {
520 call_rcu_unlock(&call_rcu_mutex);
521 return default_call_rcu_data;
522 }
523 call_rcu_data_init(&default_call_rcu_data, 0, -1);
524 call_rcu_unlock(&call_rcu_mutex);
525 return default_call_rcu_data;
526 }
527
528 /*
529 * Return the call_rcu_data structure that applies to the currently
530 * running thread. Any call_rcu_data structure assigned specifically
531 * to this thread has first priority, followed by any call_rcu_data
532 * structure assigned to the CPU on which the thread is running,
533 * followed by the default call_rcu_data structure. If there is not
534 * yet a default call_rcu_data structure, one will be created.
535 *
536 * Calls to this function and use of the returned call_rcu_data should
537 * be protected by RCU read-side lock.
538 */
539 struct call_rcu_data *get_call_rcu_data(void)
540 {
541 struct call_rcu_data *crd;
542
543 if (URCU_TLS(thread_call_rcu_data) != NULL)
544 return URCU_TLS(thread_call_rcu_data);
545
546 if (maxcpus > 0) {
547 crd = get_cpu_call_rcu_data(urcu_sched_getcpu());
548 if (crd)
549 return crd;
550 }
551
552 return get_default_call_rcu_data();
553 }
554
555 /*
556 * Return a pointer to this task's call_rcu_data if there is one.
557 */
558
559 struct call_rcu_data *get_thread_call_rcu_data(void)
560 {
561 return URCU_TLS(thread_call_rcu_data);
562 }
563
564 /*
565 * Set this task's call_rcu_data structure as specified, regardless
566 * of whether or not this task already had one. (This allows switching
567 * to and from real-time call_rcu threads, for example.)
568 *
569 * Use NULL to remove a thread's call_rcu_data structure, but it is
570 * the caller's responsibility to dispose of the removed structure.
571 * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
572 * (prior to NULLing it out, of course).
573 */
574
575 void set_thread_call_rcu_data(struct call_rcu_data *crdp)
576 {
577 URCU_TLS(thread_call_rcu_data) = crdp;
578 }
579
580 /*
581 * Create a separate call_rcu thread for each CPU. This does not
582 * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
583 * function if you want that behavior. Should be paired with
584 * free_all_cpu_call_rcu_data() to teardown these call_rcu worker
585 * threads.
586 */
587
588 int create_all_cpu_call_rcu_data(unsigned long flags)
589 {
590 int i;
591 struct call_rcu_data *crdp;
592 int ret;
593
594 call_rcu_lock(&call_rcu_mutex);
595 alloc_cpu_call_rcu_data();
596 call_rcu_unlock(&call_rcu_mutex);
597 if (maxcpus <= 0) {
598 errno = EINVAL;
599 return -EINVAL;
600 }
601 if (per_cpu_call_rcu_data == NULL) {
602 errno = ENOMEM;
603 return -ENOMEM;
604 }
605 for (i = 0; i < maxcpus; i++) {
606 call_rcu_lock(&call_rcu_mutex);
607 if (get_cpu_call_rcu_data(i)) {
608 call_rcu_unlock(&call_rcu_mutex);
609 continue;
610 }
611 crdp = __create_call_rcu_data(flags, i);
612 if (crdp == NULL) {
613 call_rcu_unlock(&call_rcu_mutex);
614 errno = ENOMEM;
615 return -ENOMEM;
616 }
617 call_rcu_unlock(&call_rcu_mutex);
618 if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
619 call_rcu_data_free(crdp);
620
621 /* it has been created by other thread */
622 if (ret == -EEXIST)
623 continue;
624
625 return ret;
626 }
627 }
628 return 0;
629 }
630
631 /*
632 * Wake up the call_rcu thread corresponding to the specified
633 * call_rcu_data structure.
634 */
635 static void wake_call_rcu_thread(struct call_rcu_data *crdp)
636 {
637 if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT))
638 call_rcu_wake_up(crdp);
639 }
640
641 static void _call_rcu(struct rcu_head *head,
642 void (*func)(struct rcu_head *head),
643 struct call_rcu_data *crdp)
644 {
645 cds_wfcq_node_init(&head->next);
646 head->func = func;
647 cds_wfcq_enqueue(&crdp->cbs_head, &crdp->cbs_tail, &head->next);
648 uatomic_inc(&crdp->qlen);
649 wake_call_rcu_thread(crdp);
650 }
651
652 /*
653 * Schedule a function to be invoked after a following grace period.
654 * This is the only function that must be called -- the others are
655 * only present to allow applications to tune their use of RCU for
656 * maximum performance.
657 *
658 * Note that unless a call_rcu thread has not already been created,
659 * the first invocation of call_rcu() will create one. So, if you
660 * need the first invocation of call_rcu() to be fast, make sure
661 * to create a call_rcu thread first. One way to accomplish this is
662 * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
663 *
664 * call_rcu must be called by registered RCU read-side threads.
665 */
666 void call_rcu(struct rcu_head *head,
667 void (*func)(struct rcu_head *head))
668 {
669 struct call_rcu_data *crdp;
670
671 /* Holding rcu read-side lock across use of per-cpu crdp */
672 _rcu_read_lock();
673 crdp = get_call_rcu_data();
674 _call_rcu(head, func, crdp);
675 _rcu_read_unlock();
676 }
677
678 /*
679 * Free up the specified call_rcu_data structure, terminating the
680 * associated call_rcu thread. The caller must have previously
681 * removed the call_rcu_data structure from per-thread or per-CPU
682 * usage. For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
683 * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
684 * per-thread call_rcu_data structures.
685 *
686 * We silently refuse to free up the default call_rcu_data structure
687 * because that is where we put any leftover callbacks. Note that
688 * the possibility of self-spawning callbacks makes it impossible
689 * to execute all the callbacks in finite time without putting any
690 * newly spawned callbacks somewhere else. The "somewhere else" of
691 * last resort is the default call_rcu_data structure.
692 *
693 * We also silently refuse to free NULL pointers. This simplifies
694 * the calling code.
695 *
696 * The caller must wait for a grace-period to pass between return from
697 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
698 * previous call rcu data as argument.
699 *
700 * Note: introducing __cds_wfcq_splice_blocking() in this function fixed
701 * a list corruption bug in the 0.7.x series. The equivalent fix
702 * appeared in 0.6.8 for the stable-0.6 branch.
703 */
704 void call_rcu_data_free(struct call_rcu_data *crdp)
705 {
706 if (crdp == NULL || crdp == default_call_rcu_data) {
707 return;
708 }
709 if ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0) {
710 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOP);
711 wake_call_rcu_thread(crdp);
712 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
713 poll(NULL, 0, 1);
714 }
715 if (!cds_wfcq_empty(&crdp->cbs_head, &crdp->cbs_tail)) {
716 /* Create default call rcu data if need be */
717 (void) get_default_call_rcu_data();
718 __cds_wfcq_splice_blocking(&default_call_rcu_data->cbs_head,
719 &default_call_rcu_data->cbs_tail,
720 &crdp->cbs_head, &crdp->cbs_tail);
721 uatomic_add(&default_call_rcu_data->qlen,
722 uatomic_read(&crdp->qlen));
723 wake_call_rcu_thread(default_call_rcu_data);
724 }
725
726 call_rcu_lock(&call_rcu_mutex);
727 cds_list_del(&crdp->list);
728 call_rcu_unlock(&call_rcu_mutex);
729
730 free(crdp);
731 }
732
733 /*
734 * Clean up all the per-CPU call_rcu threads.
735 */
736 void free_all_cpu_call_rcu_data(void)
737 {
738 int cpu;
739 struct call_rcu_data **crdp;
740 static int warned = 0;
741
742 if (maxcpus <= 0)
743 return;
744
745 crdp = malloc(sizeof(*crdp) * maxcpus);
746 if (!crdp) {
747 if (!warned) {
748 fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
749 }
750 warned = 1;
751 return;
752 }
753
754 for (cpu = 0; cpu < maxcpus; cpu++) {
755 crdp[cpu] = get_cpu_call_rcu_data(cpu);
756 if (crdp[cpu] == NULL)
757 continue;
758 set_cpu_call_rcu_data(cpu, NULL);
759 }
760 /*
761 * Wait for call_rcu sites acting as RCU readers of the
762 * call_rcu_data to become quiescent.
763 */
764 synchronize_rcu();
765 for (cpu = 0; cpu < maxcpus; cpu++) {
766 if (crdp[cpu] == NULL)
767 continue;
768 call_rcu_data_free(crdp[cpu]);
769 }
770 free(crdp);
771 }
772
773 static
774 void free_completion(struct urcu_ref *ref)
775 {
776 struct call_rcu_completion *completion;
777
778 completion = caa_container_of(ref, struct call_rcu_completion, ref);
779 free(completion);
780 }
781
782 static
783 void _rcu_barrier_complete(struct rcu_head *head)
784 {
785 struct call_rcu_completion_work *work;
786 struct call_rcu_completion *completion;
787
788 work = caa_container_of(head, struct call_rcu_completion_work, head);
789 completion = work->completion;
790 if (!uatomic_sub_return(&completion->barrier_count, 1))
791 call_rcu_completion_wake_up(completion);
792 urcu_ref_put(&completion->ref, free_completion);
793 free(work);
794 }
795
796 /*
797 * Wait for all in-flight call_rcu callbacks to complete execution.
798 */
799 void rcu_barrier(void)
800 {
801 struct call_rcu_data *crdp;
802 struct call_rcu_completion *completion;
803 int count = 0;
804 int was_online;
805
806 /* Put in offline state in QSBR. */
807 was_online = _rcu_read_ongoing();
808 if (was_online)
809 rcu_thread_offline();
810 /*
811 * Calling a rcu_barrier() within a RCU read-side critical
812 * section is an error.
813 */
814 if (_rcu_read_ongoing()) {
815 static int warned = 0;
816
817 if (!warned) {
818 fprintf(stderr, "[error] liburcu: rcu_barrier() called from within RCU read-side critical section.\n");
819 }
820 warned = 1;
821 goto online;
822 }
823
824 completion = calloc(sizeof(*completion), 1);
825 if (!completion)
826 urcu_die(errno);
827
828 call_rcu_lock(&call_rcu_mutex);
829 cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
830 count++;
831
832 /* Referenced by rcu_barrier() and each call_rcu thread. */
833 urcu_ref_set(&completion->ref, count + 1);
834 completion->barrier_count = count;
835
836 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
837 struct call_rcu_completion_work *work;
838
839 work = calloc(sizeof(*work), 1);
840 if (!work)
841 urcu_die(errno);
842 work->completion = completion;
843 _call_rcu(&work->head, _rcu_barrier_complete, crdp);
844 }
845 call_rcu_unlock(&call_rcu_mutex);
846
847 /* Wait for them */
848 for (;;) {
849 uatomic_dec(&completion->futex);
850 /* Decrement futex before reading barrier_count */
851 cmm_smp_mb();
852 if (!uatomic_read(&completion->barrier_count))
853 break;
854 call_rcu_completion_wait(completion);
855 }
856
857 urcu_ref_put(&completion->ref, free_completion);
858
859 online:
860 if (was_online)
861 rcu_thread_online();
862 }
863
864 /*
865 * Acquire the call_rcu_mutex in order to ensure that the child sees
866 * all of the call_rcu() data structures in a consistent state. Ensure
867 * that all call_rcu threads are in a quiescent state across fork.
868 * Suitable for pthread_atfork() and friends.
869 */
870 void call_rcu_before_fork(void)
871 {
872 struct call_rcu_data *crdp;
873
874 call_rcu_lock(&call_rcu_mutex);
875
876 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
877 uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSE);
878 cmm_smp_mb__after_uatomic_or();
879 wake_call_rcu_thread(crdp);
880 }
881 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
882 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) == 0)
883 poll(NULL, 0, 1);
884 }
885 }
886
887 /*
888 * Clean up call_rcu data structures in the parent of a successful fork()
889 * that is not followed by exec() in the child. Suitable for
890 * pthread_atfork() and friends.
891 */
892 void call_rcu_after_fork_parent(void)
893 {
894 struct call_rcu_data *crdp;
895
896 cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
897 uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSE);
898 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
899 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) != 0)
900 poll(NULL, 0, 1);
901 }
902 call_rcu_unlock(&call_rcu_mutex);
903 }
904
905 /*
906 * Clean up call_rcu data structures in the child of a successful fork()
907 * that is not followed by exec(). Suitable for pthread_atfork() and
908 * friends.
909 */
910 void call_rcu_after_fork_child(void)
911 {
912 struct call_rcu_data *crdp, *next;
913
914 /* Release the mutex. */
915 call_rcu_unlock(&call_rcu_mutex);
916
917 /* Do nothing when call_rcu() has not been used */
918 if (cds_list_empty(&call_rcu_data_list))
919 return;
920
921 /*
922 * Allocate a new default call_rcu_data structure in order
923 * to get a working call_rcu thread to go with it.
924 */
925 default_call_rcu_data = NULL;
926 (void)get_default_call_rcu_data();
927
928 /* Cleanup call_rcu_data pointers before use */
929 maxcpus_reset();
930 free(per_cpu_call_rcu_data);
931 rcu_set_pointer(&per_cpu_call_rcu_data, NULL);
932 URCU_TLS(thread_call_rcu_data) = NULL;
933
934 /*
935 * Dispose of all of the rest of the call_rcu_data structures.
936 * Leftover call_rcu callbacks will be merged into the new
937 * default call_rcu thread queue.
938 */
939 cds_list_for_each_entry_safe(crdp, next, &call_rcu_data_list, list) {
940 if (crdp == default_call_rcu_data)
941 continue;
942 uatomic_set(&crdp->flags, URCU_CALL_RCU_STOPPED);
943 call_rcu_data_free(crdp);
944 }
945 }
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