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
38 #include "urcu/wfqueue.h"
39 #include "urcu-call-rcu.h"
40 #include "urcu-pointer.h"
41 #include "urcu/list.h"
42 #include "urcu/futex.h"
44 /* Data structure that identifies a call_rcu thread. */
46 struct call_rcu_data
{
47 struct cds_wfq_queue cbs
;
50 unsigned long qlen
; /* maintained for debugging. */
53 struct cds_list_head list
;
54 } __attribute__((aligned(CAA_CACHE_LINE_SIZE
)));
57 * List of all call_rcu_data structures to keep valgrind happy.
58 * Protected by call_rcu_mutex.
61 CDS_LIST_HEAD(call_rcu_data_list
);
63 /* Link a thread using call_rcu() to its call_rcu thread. */
65 static __thread
struct call_rcu_data
*thread_call_rcu_data
;
67 /* Guard call_rcu thread creation. */
69 static pthread_mutex_t call_rcu_mutex
= PTHREAD_MUTEX_INITIALIZER
;
71 /* If a given thread does not have its own call_rcu thread, this is default. */
73 static struct call_rcu_data
*default_call_rcu_data
;
76 * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
77 * available, then we can have call_rcu threads assigned to individual
78 * CPUs rather than only to specific threads.
81 #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
84 * Pointer to array of pointers to per-CPU call_rcu_data structures
85 * and # CPUs. per_cpu_call_rcu_data is a RCU-protected pointer to an
86 * array of RCU-protected pointers to call_rcu_data. call_rcu acts as a
87 * RCU read-side and reads per_cpu_call_rcu_data and the per-cpu pointer
88 * without mutex. The call_rcu_mutex protects updates.
91 static struct call_rcu_data
**per_cpu_call_rcu_data
;
94 static void maxcpus_reset(void)
99 /* Allocate the array if it has not already been allocated. */
101 static void alloc_cpu_call_rcu_data(void)
103 struct call_rcu_data
**p
;
104 static int warned
= 0;
108 maxcpus
= sysconf(_SC_NPROCESSORS_CONF
);
112 p
= malloc(maxcpus
* sizeof(*per_cpu_call_rcu_data
));
114 memset(p
, '\0', maxcpus
* sizeof(*per_cpu_call_rcu_data
));
115 rcu_set_pointer(&per_cpu_call_rcu_data
, p
);
118 fprintf(stderr
, "[error] liburcu: unable to allocate per-CPU pointer array\n");
124 #else /* #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
127 * per_cpu_call_rcu_data should be constant, but some functions below, used both
128 * for cases where cpu number is available and not available, assume it it not
131 static struct call_rcu_data
**per_cpu_call_rcu_data
= NULL
;
132 static const long maxcpus
= -1;
134 static void maxcpus_reset(void)
138 static void alloc_cpu_call_rcu_data(void)
142 static int sched_getcpu(void)
147 #endif /* #else #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
149 /* Acquire the specified pthread mutex. */
151 static void call_rcu_lock(pthread_mutex_t
*pmp
)
153 if (pthread_mutex_lock(pmp
) != 0) {
154 perror("pthread_mutex_lock");
159 /* Release the specified pthread mutex. */
161 static void call_rcu_unlock(pthread_mutex_t
*pmp
)
163 if (pthread_mutex_unlock(pmp
) != 0) {
164 perror("pthread_mutex_unlock");
169 #if HAVE_SCHED_SETAFFINITY
171 int set_thread_cpu_affinity(struct call_rcu_data
*crdp
)
175 if (crdp
->cpu_affinity
< 0)
179 CPU_SET(crdp
->cpu_affinity
, &mask
);
180 #if SCHED_SETAFFINITY_ARGS == 2
181 return sched_setaffinity(0, &mask
);
183 return sched_setaffinity(0, sizeof(mask
), &mask
);
188 int set_thread_cpu_affinity(struct call_rcu_data
*crdp
)
194 static void call_rcu_wait(struct call_rcu_data
*crdp
)
196 /* Read call_rcu list before read futex */
198 if (uatomic_read(&crdp
->futex
) == -1)
199 futex_async(&crdp
->futex
, FUTEX_WAIT
, -1,
203 static void call_rcu_wake_up(struct call_rcu_data
*crdp
)
205 /* Write to call_rcu list before reading/writing futex */
207 if (caa_unlikely(uatomic_read(&crdp
->futex
) == -1)) {
208 uatomic_set(&crdp
->futex
, 0);
209 futex_async(&crdp
->futex
, FUTEX_WAKE
, 1,
214 /* This is the code run by each call_rcu thread. */
216 static void *call_rcu_thread(void *arg
)
218 unsigned long cbcount
;
219 struct cds_wfq_node
*cbs
;
220 struct cds_wfq_node
**cbs_tail
;
221 struct call_rcu_data
*crdp
= (struct call_rcu_data
*)arg
;
222 struct rcu_head
*rhp
;
223 int rt
= !!(uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_RT
);
225 if (set_thread_cpu_affinity(crdp
) != 0) {
226 perror("pthread_setaffinity_np");
231 * If callbacks take a read-side lock, we need to be registered.
233 rcu_register_thread();
235 thread_call_rcu_data
= crdp
;
237 uatomic_dec(&crdp
->futex
);
238 /* Decrement futex before reading call_rcu list */
242 if (&crdp
->cbs
.head
!= _CMM_LOAD_SHARED(crdp
->cbs
.tail
)) {
243 while ((cbs
= _CMM_LOAD_SHARED(crdp
->cbs
.head
)) == NULL
)
245 _CMM_STORE_SHARED(crdp
->cbs
.head
, NULL
);
246 cbs_tail
= (struct cds_wfq_node
**)
247 uatomic_xchg(&crdp
->cbs
.tail
, &crdp
->cbs
.head
);
251 while (cbs
->next
== NULL
&&
252 &cbs
->next
!= cbs_tail
)
254 if (cbs
== &crdp
->cbs
.dummy
) {
258 rhp
= (struct rcu_head
*)cbs
;
262 } while (cbs
!= NULL
);
263 uatomic_sub(&crdp
->qlen
, cbcount
);
265 if (uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_STOP
)
267 rcu_thread_offline();
270 == _CMM_LOAD_SHARED(crdp
->cbs
.tail
)) {
273 uatomic_dec(&crdp
->futex
);
275 * Decrement futex before reading
289 * Read call_rcu list before write futex.
292 uatomic_set(&crdp
->futex
, 0);
294 uatomic_or(&crdp
->flags
, URCU_CALL_RCU_STOPPED
);
295 rcu_unregister_thread();
300 * Create both a call_rcu thread and the corresponding call_rcu_data
301 * structure, linking the structure in as specified. Caller must hold
305 static void call_rcu_data_init(struct call_rcu_data
**crdpp
,
309 struct call_rcu_data
*crdp
;
311 crdp
= malloc(sizeof(*crdp
));
313 fprintf(stderr
, "Out of memory.\n");
316 memset(crdp
, '\0', sizeof(*crdp
));
317 cds_wfq_init(&crdp
->cbs
);
321 cds_list_add(&crdp
->list
, &call_rcu_data_list
);
322 crdp
->cpu_affinity
= cpu_affinity
;
323 cmm_smp_mb(); /* Structure initialized before pointer is planted. */
325 if (pthread_create(&crdp
->tid
, NULL
, call_rcu_thread
, crdp
) != 0) {
326 perror("pthread_create");
332 * Return a pointer to the call_rcu_data structure for the specified
333 * CPU, returning NULL if there is none. We cannot automatically
334 * created it because the platform we are running on might not define
337 * The call to this function and use of the returned call_rcu_data
338 * should be protected by RCU read-side lock.
341 struct call_rcu_data
*get_cpu_call_rcu_data(int cpu
)
343 static int warned
= 0;
344 struct call_rcu_data
**pcpu_crdp
;
346 pcpu_crdp
= rcu_dereference(per_cpu_call_rcu_data
);
347 if (pcpu_crdp
== NULL
)
349 if (!warned
&& maxcpus
> 0 && (cpu
< 0 || maxcpus
<= cpu
)) {
350 fprintf(stderr
, "[error] liburcu: get CPU # out of range\n");
353 if (cpu
< 0 || maxcpus
<= cpu
)
355 return rcu_dereference(pcpu_crdp
[cpu
]);
359 * Return the tid corresponding to the call_rcu thread whose
360 * call_rcu_data structure is specified.
363 pthread_t
get_call_rcu_thread(struct call_rcu_data
*crdp
)
369 * Create a call_rcu_data structure (with thread) and return a pointer.
372 static struct call_rcu_data
*__create_call_rcu_data(unsigned long flags
,
375 struct call_rcu_data
*crdp
;
377 call_rcu_data_init(&crdp
, flags
, cpu_affinity
);
381 struct call_rcu_data
*create_call_rcu_data(unsigned long flags
,
384 struct call_rcu_data
*crdp
;
386 call_rcu_lock(&call_rcu_mutex
);
387 crdp
= __create_call_rcu_data(flags
, cpu_affinity
);
388 call_rcu_unlock(&call_rcu_mutex
);
393 * Set the specified CPU to use the specified call_rcu_data structure.
395 * Use NULL to remove a CPU's call_rcu_data structure, but it is
396 * the caller's responsibility to dispose of the removed structure.
397 * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
398 * (prior to NULLing it out, of course).
400 * The caller must wait for a grace-period to pass between return from
401 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
402 * previous call rcu data as argument.
405 int set_cpu_call_rcu_data(int cpu
, struct call_rcu_data
*crdp
)
407 static int warned
= 0;
409 call_rcu_lock(&call_rcu_mutex
);
410 alloc_cpu_call_rcu_data();
411 if (cpu
< 0 || maxcpus
<= cpu
) {
413 fprintf(stderr
, "[error] liburcu: set CPU # out of range\n");
416 call_rcu_unlock(&call_rcu_mutex
);
421 if (per_cpu_call_rcu_data
== NULL
) {
422 call_rcu_unlock(&call_rcu_mutex
);
427 if (per_cpu_call_rcu_data
[cpu
] != NULL
&& crdp
!= NULL
) {
428 call_rcu_unlock(&call_rcu_mutex
);
433 rcu_set_pointer(&per_cpu_call_rcu_data
[cpu
], crdp
);
434 call_rcu_unlock(&call_rcu_mutex
);
439 * Return a pointer to the default call_rcu_data structure, creating
440 * one if need be. Because we never free call_rcu_data structures,
441 * we don't need to be in an RCU read-side critical section.
444 struct call_rcu_data
*get_default_call_rcu_data(void)
446 if (default_call_rcu_data
!= NULL
)
447 return rcu_dereference(default_call_rcu_data
);
448 call_rcu_lock(&call_rcu_mutex
);
449 if (default_call_rcu_data
!= NULL
) {
450 call_rcu_unlock(&call_rcu_mutex
);
451 return default_call_rcu_data
;
453 call_rcu_data_init(&default_call_rcu_data
, 0, -1);
454 call_rcu_unlock(&call_rcu_mutex
);
455 return default_call_rcu_data
;
459 * Return the call_rcu_data structure that applies to the currently
460 * running thread. Any call_rcu_data structure assigned specifically
461 * to this thread has first priority, followed by any call_rcu_data
462 * structure assigned to the CPU on which the thread is running,
463 * followed by the default call_rcu_data structure. If there is not
464 * yet a default call_rcu_data structure, one will be created.
466 * Calls to this function and use of the returned call_rcu_data should
467 * be protected by RCU read-side lock.
469 struct call_rcu_data
*get_call_rcu_data(void)
471 struct call_rcu_data
*crd
;
473 if (thread_call_rcu_data
!= NULL
)
474 return thread_call_rcu_data
;
477 crd
= get_cpu_call_rcu_data(sched_getcpu());
482 return get_default_call_rcu_data();
486 * Return a pointer to this task's call_rcu_data if there is one.
489 struct call_rcu_data
*get_thread_call_rcu_data(void)
491 return thread_call_rcu_data
;
495 * Set this task's call_rcu_data structure as specified, regardless
496 * of whether or not this task already had one. (This allows switching
497 * to and from real-time call_rcu threads, for example.)
499 * Use NULL to remove a thread's call_rcu_data structure, but it is
500 * the caller's responsibility to dispose of the removed structure.
501 * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
502 * (prior to NULLing it out, of course).
505 void set_thread_call_rcu_data(struct call_rcu_data
*crdp
)
507 thread_call_rcu_data
= crdp
;
511 * Create a separate call_rcu thread for each CPU. This does not
512 * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
513 * function if you want that behavior. Should be paired with
514 * free_all_cpu_call_rcu_data() to teardown these call_rcu worker
518 int create_all_cpu_call_rcu_data(unsigned long flags
)
521 struct call_rcu_data
*crdp
;
524 call_rcu_lock(&call_rcu_mutex
);
525 alloc_cpu_call_rcu_data();
526 call_rcu_unlock(&call_rcu_mutex
);
531 if (per_cpu_call_rcu_data
== NULL
) {
535 for (i
= 0; i
< maxcpus
; i
++) {
536 call_rcu_lock(&call_rcu_mutex
);
537 if (get_cpu_call_rcu_data(i
)) {
538 call_rcu_unlock(&call_rcu_mutex
);
541 crdp
= __create_call_rcu_data(flags
, i
);
543 call_rcu_unlock(&call_rcu_mutex
);
547 call_rcu_unlock(&call_rcu_mutex
);
548 if ((ret
= set_cpu_call_rcu_data(i
, crdp
)) != 0) {
549 call_rcu_data_free(crdp
);
551 /* it has been created by other thread */
562 * Wake up the call_rcu thread corresponding to the specified
563 * call_rcu_data structure.
565 static void wake_call_rcu_thread(struct call_rcu_data
*crdp
)
567 if (!(_CMM_LOAD_SHARED(crdp
->flags
) & URCU_CALL_RCU_RT
))
568 call_rcu_wake_up(crdp
);
572 * Schedule a function to be invoked after a following grace period.
573 * This is the only function that must be called -- the others are
574 * only present to allow applications to tune their use of RCU for
575 * maximum performance.
577 * Note that unless a call_rcu thread has not already been created,
578 * the first invocation of call_rcu() will create one. So, if you
579 * need the first invocation of call_rcu() to be fast, make sure
580 * to create a call_rcu thread first. One way to accomplish this is
581 * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
583 * call_rcu must be called by registered RCU read-side threads.
586 void call_rcu(struct rcu_head
*head
,
587 void (*func
)(struct rcu_head
*head
))
589 struct call_rcu_data
*crdp
;
591 cds_wfq_node_init(&head
->next
);
593 /* Holding rcu read-side lock across use of per-cpu crdp */
595 crdp
= get_call_rcu_data();
596 cds_wfq_enqueue(&crdp
->cbs
, &head
->next
);
597 uatomic_inc(&crdp
->qlen
);
598 wake_call_rcu_thread(crdp
);
603 * Free up the specified call_rcu_data structure, terminating the
604 * associated call_rcu thread. The caller must have previously
605 * removed the call_rcu_data structure from per-thread or per-CPU
606 * usage. For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
607 * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
608 * per-thread call_rcu_data structures.
610 * We silently refuse to free up the default call_rcu_data structure
611 * because that is where we put any leftover callbacks. Note that
612 * the possibility of self-spawning callbacks makes it impossible
613 * to execute all the callbacks in finite time without putting any
614 * newly spawned callbacks somewhere else. The "somewhere else" of
615 * last resort is the default call_rcu_data structure.
617 * We also silently refuse to free NULL pointers. This simplifies
620 * The caller must wait for a grace-period to pass between return from
621 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
622 * previous call rcu data as argument.
624 void call_rcu_data_free(struct call_rcu_data
*crdp
)
626 struct cds_wfq_node
*cbs
;
627 struct cds_wfq_node
**cbs_tail
;
628 struct cds_wfq_node
**cbs_endprev
;
630 if (crdp
== NULL
|| crdp
== default_call_rcu_data
) {
633 if ((uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_STOPPED
) == 0) {
634 uatomic_or(&crdp
->flags
, URCU_CALL_RCU_STOP
);
635 wake_call_rcu_thread(crdp
);
636 while ((uatomic_read(&crdp
->flags
) & URCU_CALL_RCU_STOPPED
) == 0)
639 if (&crdp
->cbs
.head
!= _CMM_LOAD_SHARED(crdp
->cbs
.tail
)) {
640 while ((cbs
= _CMM_LOAD_SHARED(crdp
->cbs
.head
)) == NULL
)
642 _CMM_STORE_SHARED(crdp
->cbs
.head
, NULL
);
643 cbs_tail
= (struct cds_wfq_node
**)
644 uatomic_xchg(&crdp
->cbs
.tail
, &crdp
->cbs
.head
);
645 /* Create default call rcu data if need be */
646 (void) get_default_call_rcu_data();
647 cbs_endprev
= (struct cds_wfq_node
**)
648 uatomic_xchg(&default_call_rcu_data
, cbs_tail
);
650 uatomic_add(&default_call_rcu_data
->qlen
,
651 uatomic_read(&crdp
->qlen
));
652 wake_call_rcu_thread(default_call_rcu_data
);
655 call_rcu_lock(&call_rcu_mutex
);
656 cds_list_del(&crdp
->list
);
657 call_rcu_unlock(&call_rcu_mutex
);
663 * Clean up all the per-CPU call_rcu threads.
665 void free_all_cpu_call_rcu_data(void)
668 struct call_rcu_data
**crdp
;
669 static int warned
= 0;
674 crdp
= malloc(sizeof(*crdp
) * maxcpus
);
677 fprintf(stderr
, "[error] liburcu: unable to allocate per-CPU pointer array\n");
683 for (cpu
= 0; cpu
< maxcpus
; cpu
++) {
684 crdp
[cpu
] = get_cpu_call_rcu_data(cpu
);
685 if (crdp
[cpu
] == NULL
)
687 set_cpu_call_rcu_data(cpu
, NULL
);
690 * Wait for call_rcu sites acting as RCU readers of the
691 * call_rcu_data to become quiescent.
694 for (cpu
= 0; cpu
< maxcpus
; cpu
++) {
695 if (crdp
[cpu
] == NULL
)
697 call_rcu_data_free(crdp
[cpu
]);
703 * Acquire the call_rcu_mutex in order to ensure that the child sees
704 * all of the call_rcu() data structures in a consistent state.
705 * Suitable for pthread_atfork() and friends.
707 void call_rcu_before_fork(void)
709 call_rcu_lock(&call_rcu_mutex
);
713 * Clean up call_rcu data structures in the parent of a successful fork()
714 * that is not followed by exec() in the child. Suitable for
715 * pthread_atfork() and friends.
717 void call_rcu_after_fork_parent(void)
719 call_rcu_unlock(&call_rcu_mutex
);
723 * Clean up call_rcu data structures in the child of a successful fork()
724 * that is not followed by exec(). Suitable for pthread_atfork() and
727 void call_rcu_after_fork_child(void)
729 struct call_rcu_data
*crdp
, *next
;
731 /* Release the mutex. */
732 call_rcu_unlock(&call_rcu_mutex
);
734 /* Do nothing when call_rcu() has not been used */
735 if (cds_list_empty(&call_rcu_data_list
))
739 * Allocate a new default call_rcu_data structure in order
740 * to get a working call_rcu thread to go with it.
742 default_call_rcu_data
= NULL
;
743 (void)get_default_call_rcu_data();
745 /* Cleanup call_rcu_data pointers before use */
747 free(per_cpu_call_rcu_data
);
748 rcu_set_pointer(&per_cpu_call_rcu_data
, NULL
);
749 thread_call_rcu_data
= NULL
;
751 /* Dispose of all of the rest of the call_rcu_data structures. */
752 cds_list_for_each_entry_safe(crdp
, next
, &call_rcu_data_list
, list
) {
753 if (crdp
== default_call_rcu_data
)
755 uatomic_set(&crdp
->flags
, URCU_CALL_RCU_STOPPED
);
756 call_rcu_data_free(crdp
);