4 * Userspace RCU library - batch memory reclamation with kernel API
6 * Copyright (c) 2010 Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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.
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.
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
36 #include "compat-getcpu.h"
37 #include <urcu/assert.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>
46 #include "urcu-utils.h"
48 #define SET_AFFINITY_CHECK_PERIOD (1U << 8) /* 256 */
49 #define SET_AFFINITY_CHECK_PERIOD_MASK (SET_AFFINITY_CHECK_PERIOD - 1)
51 /* Data structure that identifies a call_rcu thread. */
53 struct call_rcu_data
{
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
61 struct cds_wfcq_tail cbs_tail
;
62 struct cds_wfcq_head cbs_head
;
65 unsigned long qlen
; /* maintained for debugging. */
68 unsigned long gp_count
;
69 struct cds_list_head list
;
70 } __attribute__((aligned(CAA_CACHE_LINE_SIZE
)));
72 struct call_rcu_completion
{
78 struct call_rcu_completion_work
{
80 struct call_rcu_completion
*completion
;
84 * List of all call_rcu_data structures to keep valgrind happy.
85 * Protected by call_rcu_mutex.
88 static CDS_LIST_HEAD(call_rcu_data_list
);
90 /* Link a thread using call_rcu() to its call_rcu thread. */
92 static DEFINE_URCU_TLS(struct call_rcu_data
*, thread_call_rcu_data
);
95 * Guard call_rcu thread creation and atfork handlers.
97 static pthread_mutex_t call_rcu_mutex
= PTHREAD_MUTEX_INITIALIZER
;
99 /* If a given thread does not have its own call_rcu thread, this is default. */
101 static struct call_rcu_data
*default_call_rcu_data
;
103 static struct urcu_atfork
*registered_rculfhash_atfork
;
104 static unsigned long registered_rculfhash_atfork_refcount
;
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.
112 #if defined(HAVE_SYSCONF) && (defined(HAVE_SCHED_GETCPU) || defined(HAVE_GETCPUID))
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.
122 static struct call_rcu_data
**per_cpu_call_rcu_data
;
125 static void maxcpus_reset(void)
130 /* Allocate the array if it has not already been allocated. */
132 static void alloc_cpu_call_rcu_data(void)
134 struct call_rcu_data
**p
;
135 static int warned
= 0;
139 maxcpus
= sysconf(_SC_NPROCESSORS_CONF
);
143 p
= malloc(maxcpus
* sizeof(*per_cpu_call_rcu_data
));
145 memset(p
, '\0', maxcpus
* sizeof(*per_cpu_call_rcu_data
));
146 rcu_set_pointer(&per_cpu_call_rcu_data
, p
);
149 fprintf(stderr
, "[error] liburcu: unable to allocate per-CPU pointer array\n");
155 #else /* #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
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
162 static struct call_rcu_data
**per_cpu_call_rcu_data
= NULL
;
163 static const long maxcpus
= -1;
165 static void maxcpus_reset(void)
169 static void alloc_cpu_call_rcu_data(void)
173 #endif /* #else #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
175 /* Acquire the specified pthread mutex. */
177 static void call_rcu_lock(pthread_mutex_t
*pmp
)
181 ret
= pthread_mutex_lock(pmp
);
186 /* Release the specified pthread mutex. */
188 static void call_rcu_unlock(pthread_mutex_t
*pmp
)
192 ret
= pthread_mutex_unlock(pmp
);
198 * Periodically retry setting CPU affinity if we migrate.
199 * Losing affinity can be caused by CPU hotunplug/hotplug, or by
202 #ifdef HAVE_SCHED_SETAFFINITY
204 int set_thread_cpu_affinity(struct call_rcu_data
*crdp
)
209 if (crdp
->cpu_affinity
< 0)
211 if (++crdp
->gp_count
& SET_AFFINITY_CHECK_PERIOD_MASK
)
213 if (urcu_sched_getcpu() == crdp
->cpu_affinity
)
217 CPU_SET(crdp
->cpu_affinity
, &mask
);
218 ret
= sched_setaffinity(0, sizeof(mask
), &mask
);
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
225 if (ret
&& errno
== EINVAL
) {
233 int set_thread_cpu_affinity(struct call_rcu_data
*crdp
__attribute__((unused
)))
239 static void call_rcu_wait(struct call_rcu_data
*crdp
)
241 /* Read call_rcu list before read futex */
243 while (uatomic_read(&crdp
->futex
) == -1) {
244 if (!futex_async(&crdp
->futex
, FUTEX_WAIT
, -1, NULL
, NULL
, 0)) {
246 * Prior queued wakeups queued by unrelated code
247 * using the same address can cause futex wait to
248 * return 0 even through the futex value is still
249 * -1 (spurious wakeups). Check the value again
250 * in user-space to validate whether it really
257 /* Value already changed. */
260 /* Retry if interrupted by signal. */
261 break; /* Get out of switch. Check again. */
263 /* Unexpected error. */
269 static void call_rcu_wake_up(struct call_rcu_data
*crdp
)
271 /* Write to call_rcu list before reading/writing futex */
273 if (caa_unlikely(uatomic_read(&crdp
->futex
) == -1)) {
274 uatomic_set(&crdp
->futex
, 0);
275 if (futex_async(&crdp
->futex
, FUTEX_WAKE
, 1,
281 static void call_rcu_completion_wait(struct call_rcu_completion
*completion
)
283 /* Read completion barrier count before read futex */
285 while (uatomic_read(&completion
->futex
) == -1) {
286 if (!futex_async(&completion
->futex
, FUTEX_WAIT
, -1, NULL
, NULL
, 0)) {
288 * Prior queued wakeups queued by unrelated code
289 * using the same address can cause futex wait to
290 * return 0 even through the futex value is still
291 * -1 (spurious wakeups). Check the value again
292 * in user-space to validate whether it really
299 /* Value already changed. */
302 /* Retry if interrupted by signal. */
303 break; /* Get out of switch. Check again. */
305 /* Unexpected error. */
311 static void call_rcu_completion_wake_up(struct call_rcu_completion
*completion
)
313 /* Write to completion barrier count before reading/writing futex */
315 if (caa_unlikely(uatomic_read(&completion
->futex
) == -1)) {
316 uatomic_set(&completion
->futex
, 0);
317 if (futex_async(&completion
->futex
, FUTEX_WAKE
, 1,
323 /* This is the code run by each call_rcu thread. */
325 static void *call_rcu_thread(void *arg
)
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
);
331 if (set_thread_cpu_affinity(crdp
))
335 * If callbacks take a read-side lock, we need to be registered.
337 rcu_register_thread();
339 URCU_TLS(thread_call_rcu_data
) = crdp
;
341 uatomic_dec(&crdp
->futex
);
342 /* Decrement futex before reading call_rcu list */
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
;
351 if (set_thread_cpu_affinity(crdp
))
354 if (uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_PAUSE
) {
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.
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();
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 urcu_posix_assert(splice_ret
!= CDS_WFCQ_RET_WOULDBLOCK
);
375 urcu_posix_assert(splice_ret
!= CDS_WFCQ_RET_DEST_NON_EMPTY
);
376 if (splice_ret
!= CDS_WFCQ_RET_SRC_EMPTY
) {
379 __cds_wfcq_for_each_blocking_safe(&cbs_tmp_head
,
380 &cbs_tmp_tail
, cbs
, cbs_tmp_n
) {
381 struct rcu_head
*rhp
;
383 rhp
= caa_container_of(cbs
,
384 struct rcu_head
, next
);
388 uatomic_sub(&crdp
->qlen
, cbcount
);
390 if (uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_STOP
)
392 rcu_thread_offline();
394 if (cds_wfcq_empty(&crdp
->cbs_head
,
397 (void) poll(NULL
, 0, 10);
398 uatomic_dec(&crdp
->futex
);
400 * Decrement futex before reading
405 (void) poll(NULL
, 0, 10);
408 (void) poll(NULL
, 0, 10);
414 * Read call_rcu list before write futex.
417 uatomic_set(&crdp
->futex
, 0);
419 uatomic_or(&crdp
->flags
, URCU_CALL_RCU_STOPPED
);
420 rcu_unregister_thread();
425 * Create both a call_rcu thread and the corresponding call_rcu_data
426 * structure, linking the structure in as specified. Caller must hold
430 static void call_rcu_data_init(struct call_rcu_data
**crdpp
,
434 struct call_rcu_data
*crdp
;
437 crdp
= malloc(sizeof(*crdp
));
440 memset(crdp
, '\0', sizeof(*crdp
));
441 cds_wfcq_init(&crdp
->cbs_head
, &crdp
->cbs_tail
);
445 cds_list_add(&crdp
->list
, &call_rcu_data_list
);
446 crdp
->cpu_affinity
= cpu_affinity
;
448 cmm_smp_mb(); /* Structure initialized before pointer is planted. */
450 ret
= pthread_create(&crdp
->tid
, NULL
, call_rcu_thread
, crdp
);
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().
461 * The call to this function and use of the returned call_rcu_data
462 * should be protected by RCU read-side lock.
465 struct call_rcu_data
*get_cpu_call_rcu_data(int cpu
)
467 static int warned
= 0;
468 struct call_rcu_data
**pcpu_crdp
;
470 pcpu_crdp
= rcu_dereference(per_cpu_call_rcu_data
);
471 if (pcpu_crdp
== NULL
)
473 if (!warned
&& maxcpus
> 0 && (cpu
< 0 || maxcpus
<= cpu
)) {
474 fprintf(stderr
, "[error] liburcu: get CPU # out of range\n");
477 if (cpu
< 0 || maxcpus
<= cpu
)
479 return rcu_dereference(pcpu_crdp
[cpu
]);
483 * Return the tid corresponding to the call_rcu thread whose
484 * call_rcu_data structure is specified.
487 pthread_t
get_call_rcu_thread(struct call_rcu_data
*crdp
)
493 * Create a call_rcu_data structure (with thread) and return a pointer.
496 static struct call_rcu_data
*__create_call_rcu_data(unsigned long flags
,
499 struct call_rcu_data
*crdp
;
501 call_rcu_data_init(&crdp
, flags
, cpu_affinity
);
505 struct call_rcu_data
*create_call_rcu_data(unsigned long flags
,
508 struct call_rcu_data
*crdp
;
510 call_rcu_lock(&call_rcu_mutex
);
511 crdp
= __create_call_rcu_data(flags
, cpu_affinity
);
512 call_rcu_unlock(&call_rcu_mutex
);
517 * Set the specified CPU to use the specified call_rcu_data structure.
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).
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.
529 int set_cpu_call_rcu_data(int cpu
, struct call_rcu_data
*crdp
)
531 static int warned
= 0;
533 call_rcu_lock(&call_rcu_mutex
);
534 alloc_cpu_call_rcu_data();
535 if (cpu
< 0 || maxcpus
<= cpu
) {
537 fprintf(stderr
, "[error] liburcu: set CPU # out of range\n");
540 call_rcu_unlock(&call_rcu_mutex
);
545 if (per_cpu_call_rcu_data
== NULL
) {
546 call_rcu_unlock(&call_rcu_mutex
);
551 if (per_cpu_call_rcu_data
[cpu
] != NULL
&& crdp
!= NULL
) {
552 call_rcu_unlock(&call_rcu_mutex
);
557 rcu_set_pointer(&per_cpu_call_rcu_data
[cpu
], crdp
);
558 call_rcu_unlock(&call_rcu_mutex
);
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.
568 struct call_rcu_data
*get_default_call_rcu_data(void)
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
;
577 call_rcu_data_init(&default_call_rcu_data
, 0, -1);
578 call_rcu_unlock(&call_rcu_mutex
);
579 return default_call_rcu_data
;
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.
590 * Calls to this function and use of the returned call_rcu_data should
591 * be protected by RCU read-side lock.
593 struct call_rcu_data
*get_call_rcu_data(void)
595 struct call_rcu_data
*crd
;
597 if (URCU_TLS(thread_call_rcu_data
) != NULL
)
598 return URCU_TLS(thread_call_rcu_data
);
601 crd
= get_cpu_call_rcu_data(urcu_sched_getcpu());
606 return get_default_call_rcu_data();
610 * Return a pointer to this task's call_rcu_data if there is one.
613 struct call_rcu_data
*get_thread_call_rcu_data(void)
615 return URCU_TLS(thread_call_rcu_data
);
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.)
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).
629 void set_thread_call_rcu_data(struct call_rcu_data
*crdp
)
631 URCU_TLS(thread_call_rcu_data
) = crdp
;
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
642 int create_all_cpu_call_rcu_data(unsigned long flags
)
645 struct call_rcu_data
*crdp
;
648 call_rcu_lock(&call_rcu_mutex
);
649 alloc_cpu_call_rcu_data();
650 call_rcu_unlock(&call_rcu_mutex
);
655 if (per_cpu_call_rcu_data
== NULL
) {
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
);
665 crdp
= __create_call_rcu_data(flags
, i
);
667 call_rcu_unlock(&call_rcu_mutex
);
671 call_rcu_unlock(&call_rcu_mutex
);
672 if ((ret
= set_cpu_call_rcu_data(i
, crdp
)) != 0) {
673 call_rcu_data_free(crdp
);
675 /* it has been created by other thread */
686 * Wake up the call_rcu thread corresponding to the specified
687 * call_rcu_data structure.
689 static void wake_call_rcu_thread(struct call_rcu_data
*crdp
)
691 if (!(_CMM_LOAD_SHARED(crdp
->flags
) & URCU_CALL_RCU_RT
))
692 call_rcu_wake_up(crdp
);
695 static void _call_rcu(struct rcu_head
*head
,
696 void (*func
)(struct rcu_head
*head
),
697 struct call_rcu_data
*crdp
)
699 cds_wfcq_node_init(&head
->next
);
701 cds_wfcq_enqueue(&crdp
->cbs_head
, &crdp
->cbs_tail
, &head
->next
);
702 uatomic_inc(&crdp
->qlen
);
703 wake_call_rcu_thread(crdp
);
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.
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().
718 * call_rcu must be called by registered RCU read-side threads.
720 void call_rcu(struct rcu_head
*head
,
721 void (*func
)(struct rcu_head
*head
))
723 struct call_rcu_data
*crdp
;
725 /* Holding rcu read-side lock across use of per-cpu crdp */
727 crdp
= get_call_rcu_data();
728 _call_rcu(head
, func
, crdp
);
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.
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.
747 * We also silently refuse to free NULL pointers. This simplifies
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.
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.
758 void call_rcu_data_free(struct call_rcu_data
*crdp
)
760 if (crdp
== NULL
|| crdp
== default_call_rcu_data
) {
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);
769 call_rcu_lock(&call_rcu_mutex
);
770 if (!cds_wfcq_empty(&crdp
->cbs_head
, &crdp
->cbs_tail
)) {
771 call_rcu_unlock(&call_rcu_mutex
);
772 /* Create default call rcu data if need be. */
773 /* CBs queued here will be handed to the default list. */
774 (void) get_default_call_rcu_data();
775 call_rcu_lock(&call_rcu_mutex
);
776 __cds_wfcq_splice_blocking(&default_call_rcu_data
->cbs_head
,
777 &default_call_rcu_data
->cbs_tail
,
778 &crdp
->cbs_head
, &crdp
->cbs_tail
);
779 uatomic_add(&default_call_rcu_data
->qlen
,
780 uatomic_read(&crdp
->qlen
));
781 wake_call_rcu_thread(default_call_rcu_data
);
784 cds_list_del(&crdp
->list
);
785 call_rcu_unlock(&call_rcu_mutex
);
791 * Clean up all the per-CPU call_rcu threads.
793 void free_all_cpu_call_rcu_data(void)
796 struct call_rcu_data
**crdp
;
797 static int warned
= 0;
802 crdp
= malloc(sizeof(*crdp
) * maxcpus
);
805 fprintf(stderr
, "[error] liburcu: unable to allocate per-CPU pointer array\n");
811 for (cpu
= 0; cpu
< maxcpus
; cpu
++) {
812 crdp
[cpu
] = get_cpu_call_rcu_data(cpu
);
813 if (crdp
[cpu
] == NULL
)
815 set_cpu_call_rcu_data(cpu
, NULL
);
818 * Wait for call_rcu sites acting as RCU readers of the
819 * call_rcu_data to become quiescent.
822 for (cpu
= 0; cpu
< maxcpus
; cpu
++) {
823 if (crdp
[cpu
] == NULL
)
825 call_rcu_data_free(crdp
[cpu
]);
831 void free_completion(struct urcu_ref
*ref
)
833 struct call_rcu_completion
*completion
;
835 completion
= caa_container_of(ref
, struct call_rcu_completion
, ref
);
840 void _rcu_barrier_complete(struct rcu_head
*head
)
842 struct call_rcu_completion_work
*work
;
843 struct call_rcu_completion
*completion
;
845 work
= caa_container_of(head
, struct call_rcu_completion_work
, head
);
846 completion
= work
->completion
;
847 if (!uatomic_sub_return(&completion
->barrier_count
, 1))
848 call_rcu_completion_wake_up(completion
);
849 urcu_ref_put(&completion
->ref
, free_completion
);
854 * Wait for all in-flight call_rcu callbacks to complete execution.
856 void rcu_barrier(void)
858 struct call_rcu_data
*crdp
;
859 struct call_rcu_completion
*completion
;
863 /* Put in offline state in QSBR. */
864 was_online
= _rcu_read_ongoing();
866 rcu_thread_offline();
868 * Calling a rcu_barrier() within a RCU read-side critical
869 * section is an error.
871 if (_rcu_read_ongoing()) {
872 static int warned
= 0;
875 fprintf(stderr
, "[error] liburcu: rcu_barrier() called from within RCU read-side critical section.\n");
881 completion
= calloc(sizeof(*completion
), 1);
885 call_rcu_lock(&call_rcu_mutex
);
886 cds_list_for_each_entry(crdp
, &call_rcu_data_list
, list
)
889 /* Referenced by rcu_barrier() and each call_rcu thread. */
890 urcu_ref_set(&completion
->ref
, count
+ 1);
891 completion
->barrier_count
= count
;
893 cds_list_for_each_entry(crdp
, &call_rcu_data_list
, list
) {
894 struct call_rcu_completion_work
*work
;
896 work
= calloc(sizeof(*work
), 1);
899 work
->completion
= completion
;
900 _call_rcu(&work
->head
, _rcu_barrier_complete
, crdp
);
902 call_rcu_unlock(&call_rcu_mutex
);
906 uatomic_dec(&completion
->futex
);
907 /* Decrement futex before reading barrier_count */
909 if (!uatomic_read(&completion
->barrier_count
))
911 call_rcu_completion_wait(completion
);
914 urcu_ref_put(&completion
->ref
, free_completion
);
922 * Acquire the call_rcu_mutex in order to ensure that the child sees
923 * all of the call_rcu() data structures in a consistent state. Ensure
924 * that all call_rcu threads are in a quiescent state across fork.
925 * Suitable for pthread_atfork() and friends.
927 void call_rcu_before_fork(void)
929 struct call_rcu_data
*crdp
;
930 struct urcu_atfork
*atfork
;
932 call_rcu_lock(&call_rcu_mutex
);
934 atfork
= registered_rculfhash_atfork
;
936 atfork
->before_fork(atfork
->priv
);
938 cds_list_for_each_entry(crdp
, &call_rcu_data_list
, list
) {
939 uatomic_or(&crdp
->flags
, URCU_CALL_RCU_PAUSE
);
940 cmm_smp_mb__after_uatomic_or();
941 wake_call_rcu_thread(crdp
);
943 cds_list_for_each_entry(crdp
, &call_rcu_data_list
, list
) {
944 while ((uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_PAUSED
) == 0)
945 (void) poll(NULL
, 0, 1);
950 * Clean up call_rcu data structures in the parent of a successful fork()
951 * that is not followed by exec() in the child. Suitable for
952 * pthread_atfork() and friends.
954 void call_rcu_after_fork_parent(void)
956 struct call_rcu_data
*crdp
;
957 struct urcu_atfork
*atfork
;
959 cds_list_for_each_entry(crdp
, &call_rcu_data_list
, list
)
960 uatomic_and(&crdp
->flags
, ~URCU_CALL_RCU_PAUSE
);
961 cds_list_for_each_entry(crdp
, &call_rcu_data_list
, list
) {
962 while ((uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_PAUSED
) != 0)
963 (void) poll(NULL
, 0, 1);
965 atfork
= registered_rculfhash_atfork
;
967 atfork
->after_fork_parent(atfork
->priv
);
968 call_rcu_unlock(&call_rcu_mutex
);
972 * Clean up call_rcu data structures in the child of a successful fork()
973 * that is not followed by exec(). Suitable for pthread_atfork() and
976 void call_rcu_after_fork_child(void)
978 struct call_rcu_data
*crdp
, *next
;
979 struct urcu_atfork
*atfork
;
981 /* Release the mutex. */
982 call_rcu_unlock(&call_rcu_mutex
);
984 atfork
= registered_rculfhash_atfork
;
986 atfork
->after_fork_child(atfork
->priv
);
988 /* Do nothing when call_rcu() has not been used */
989 if (cds_list_empty(&call_rcu_data_list
))
993 * Allocate a new default call_rcu_data structure in order
994 * to get a working call_rcu thread to go with it.
996 default_call_rcu_data
= NULL
;
997 (void)get_default_call_rcu_data();
999 /* Cleanup call_rcu_data pointers before use */
1001 free(per_cpu_call_rcu_data
);
1002 rcu_set_pointer(&per_cpu_call_rcu_data
, NULL
);
1003 URCU_TLS(thread_call_rcu_data
) = NULL
;
1006 * Dispose of all of the rest of the call_rcu_data structures.
1007 * Leftover call_rcu callbacks will be merged into the new
1008 * default call_rcu thread queue.
1010 cds_list_for_each_entry_safe(crdp
, next
, &call_rcu_data_list
, list
) {
1011 if (crdp
== default_call_rcu_data
)
1013 uatomic_set(&crdp
->flags
, URCU_CALL_RCU_STOPPED
);
1014 call_rcu_data_free(crdp
);
1018 void urcu_register_rculfhash_atfork(struct urcu_atfork
*atfork
)
1020 call_rcu_lock(&call_rcu_mutex
);
1021 if (registered_rculfhash_atfork_refcount
++)
1023 registered_rculfhash_atfork
= atfork
;
1025 call_rcu_unlock(&call_rcu_mutex
);
1028 void urcu_unregister_rculfhash_atfork(struct urcu_atfork
*atfork
__attribute__((unused
)))
1030 call_rcu_lock(&call_rcu_mutex
);
1031 if (--registered_rculfhash_atfork_refcount
)
1033 registered_rculfhash_atfork
= NULL
;
1035 call_rcu_unlock(&call_rcu_mutex
);