cleanup: explicitly mark unused parameters (-Wunused-parameter)
[userspace-rcu.git] / src / urcu.c
... / ...
CommitLineData
1/*
2 * urcu.c
3 *
4 * Userspace RCU library
5 *
6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
7 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
8 *
9 * This library is free software; you can redistribute it and/or
10 * modify it under the terms of the GNU Lesser General Public
11 * License as published by the Free Software Foundation; either
12 * version 2.1 of the License, or (at your option) any later version.
13 *
14 * This library is distributed in the hope that it will be useful,
15 * but WITHOUT ANY WARRANTY; without even the implied warranty of
16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17 * Lesser General Public License for more details.
18 *
19 * You should have received a copy of the GNU Lesser General Public
20 * License along with this library; if not, write to the Free Software
21 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
22 *
23 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
24 */
25
26#define URCU_NO_COMPAT_IDENTIFIERS
27#define _BSD_SOURCE
28#define _LGPL_SOURCE
29#define _DEFAULT_SOURCE
30#include <stdio.h>
31#include <pthread.h>
32#include <signal.h>
33#include <assert.h>
34#include <stdlib.h>
35#include <stdint.h>
36#include <string.h>
37#include <errno.h>
38#include <stdbool.h>
39#include <poll.h>
40
41#include <urcu/config.h>
42#include <urcu/arch.h>
43#include <urcu/wfcqueue.h>
44#include <urcu/map/urcu.h>
45#include <urcu/static/urcu.h>
46#include <urcu/pointer.h>
47#include <urcu/tls-compat.h>
48
49#include "urcu-die.h"
50#include "urcu-wait.h"
51#include "urcu-utils.h"
52
53#define URCU_API_MAP
54/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
55#undef _LGPL_SOURCE
56#include <urcu/urcu.h>
57#define _LGPL_SOURCE
58
59/*
60 * If a reader is really non-cooperative and refuses to commit its
61 * rcu_active_readers count to memory (there is no barrier in the reader
62 * per-se), kick it after 10 loops waiting for it.
63 */
64#define KICK_READER_LOOPS 10
65
66/*
67 * Active attempts to check for reader Q.S. before calling futex().
68 */
69#define RCU_QS_ACTIVE_ATTEMPTS 100
70
71/* If the headers do not support membarrier system call, fall back on RCU_MB */
72#ifdef __NR_membarrier
73# define membarrier(...) syscall(__NR_membarrier, __VA_ARGS__)
74#else
75# define membarrier(...) -ENOSYS
76#endif
77
78enum membarrier_cmd {
79 MEMBARRIER_CMD_QUERY = 0,
80 MEMBARRIER_CMD_SHARED = (1 << 0),
81 /* reserved for MEMBARRIER_CMD_SHARED_EXPEDITED (1 << 1) */
82 /* reserved for MEMBARRIER_CMD_PRIVATE (1 << 2) */
83 MEMBARRIER_CMD_PRIVATE_EXPEDITED = (1 << 3),
84 MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED = (1 << 4),
85};
86
87#ifdef RCU_MEMBARRIER
88static int init_done;
89static int urcu_memb_has_sys_membarrier_private_expedited;
90
91#ifndef CONFIG_RCU_FORCE_SYS_MEMBARRIER
92/*
93 * Explicitly initialize to zero because we can't alias a non-static
94 * uninitialized variable.
95 */
96int urcu_memb_has_sys_membarrier = 0;
97URCU_ATTR_ALIAS("urcu_memb_has_sys_membarrier")
98extern int rcu_has_sys_membarrier_memb;
99#endif
100
101void __attribute__((constructor)) rcu_init(void);
102#endif
103
104#ifdef RCU_MB
105void rcu_init(void)
106{
107}
108URCU_ATTR_ALIAS(urcu_stringify(rcu_init))
109void alias_rcu_init(void);
110#endif
111
112#ifdef RCU_SIGNAL
113static int init_done;
114
115void __attribute__((constructor)) rcu_init(void);
116void __attribute__((destructor)) rcu_exit(void);
117#endif
118
119/*
120 * rcu_gp_lock ensures mutual exclusion between threads calling
121 * synchronize_rcu().
122 */
123static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
124/*
125 * rcu_registry_lock ensures mutual exclusion between threads
126 * registering and unregistering themselves to/from the registry, and
127 * with threads reading that registry from synchronize_rcu(). However,
128 * this lock is not held all the way through the completion of awaiting
129 * for the grace period. It is sporadically released between iterations
130 * on the registry.
131 * rcu_registry_lock may nest inside rcu_gp_lock.
132 */
133static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
134struct urcu_gp rcu_gp = { .ctr = URCU_GP_COUNT };
135URCU_ATTR_ALIAS(urcu_stringify(rcu_gp))
136extern struct urcu_gp alias_rcu_gp;
137
138/*
139 * Written to only by each individual reader. Read by both the reader and the
140 * writers.
141 */
142DEFINE_URCU_TLS(struct urcu_reader, rcu_reader);
143DEFINE_URCU_TLS_ALIAS(struct urcu_reader, rcu_reader, alias_rcu_reader);
144
145static CDS_LIST_HEAD(registry);
146
147/*
148 * Queue keeping threads awaiting to wait for a grace period. Contains
149 * struct gp_waiters_thread objects.
150 */
151static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
152
153static void mutex_lock(pthread_mutex_t *mutex)
154{
155 int ret;
156
157#ifndef DISTRUST_SIGNALS_EXTREME
158 ret = pthread_mutex_lock(mutex);
159 if (ret)
160 urcu_die(ret);
161#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
162 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
163 if (ret != EBUSY && ret != EINTR)
164 urcu_die(ret);
165 if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) {
166 cmm_smp_mb();
167 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
168 cmm_smp_mb();
169 }
170 (void) poll(NULL, 0, 10);
171 }
172#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
173}
174
175static void mutex_unlock(pthread_mutex_t *mutex)
176{
177 int ret;
178
179 ret = pthread_mutex_unlock(mutex);
180 if (ret)
181 urcu_die(ret);
182}
183
184#ifdef RCU_MEMBARRIER
185static void smp_mb_master(void)
186{
187 if (caa_likely(urcu_memb_has_sys_membarrier)) {
188 if (membarrier(urcu_memb_has_sys_membarrier_private_expedited ?
189 MEMBARRIER_CMD_PRIVATE_EXPEDITED :
190 MEMBARRIER_CMD_SHARED, 0))
191 urcu_die(errno);
192 } else {
193 cmm_smp_mb();
194 }
195}
196#endif
197
198#ifdef RCU_MB
199static void smp_mb_master(void)
200{
201 cmm_smp_mb();
202}
203#endif
204
205#ifdef RCU_SIGNAL
206static void force_mb_all_readers(void)
207{
208 struct urcu_reader *index;
209
210 /*
211 * Ask for each threads to execute a cmm_smp_mb() so we can consider the
212 * compiler barriers around rcu read lock as real memory barriers.
213 */
214 if (cds_list_empty(&registry))
215 return;
216 /*
217 * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
218 * a cache flush on architectures with non-coherent cache. Let's play
219 * safe and don't assume anything : we use cmm_smp_mc() to make sure the
220 * cache flush is enforced.
221 */
222 cds_list_for_each_entry(index, &registry, node) {
223 CMM_STORE_SHARED(index->need_mb, 1);
224 pthread_kill(index->tid, SIGRCU);
225 }
226 /*
227 * Wait for sighandler (and thus mb()) to execute on every thread.
228 *
229 * Note that the pthread_kill() will never be executed on systems
230 * that correctly deliver signals in a timely manner. However, it
231 * is not uncommon for kernels to have bugs that can result in
232 * lost or unduly delayed signals.
233 *
234 * If you are seeing the below pthread_kill() executing much at
235 * all, we suggest testing the underlying kernel and filing the
236 * relevant bug report. For Linux kernels, we recommend getting
237 * the Linux Test Project (LTP).
238 */
239 cds_list_for_each_entry(index, &registry, node) {
240 while (CMM_LOAD_SHARED(index->need_mb)) {
241 pthread_kill(index->tid, SIGRCU);
242 (void) poll(NULL, 0, 1);
243 }
244 }
245 cmm_smp_mb(); /* read ->need_mb before ending the barrier */
246}
247
248static void smp_mb_master(void)
249{
250 force_mb_all_readers();
251}
252#endif /* #ifdef RCU_SIGNAL */
253
254/*
255 * synchronize_rcu() waiting. Single thread.
256 * Always called with rcu_registry lock held. Releases this lock and
257 * grabs it again. Holds the lock when it returns.
258 */
259static void wait_gp(void)
260{
261 /*
262 * Read reader_gp before read futex. smp_mb_master() needs to
263 * be called with the rcu registry lock held in RCU_SIGNAL
264 * flavor.
265 */
266 smp_mb_master();
267 /* Temporarily unlock the registry lock. */
268 mutex_unlock(&rcu_registry_lock);
269 if (uatomic_read(&rcu_gp.futex) != -1)
270 goto end;
271 while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
272 NULL, NULL, 0)) {
273 switch (errno) {
274 case EWOULDBLOCK:
275 /* Value already changed. */
276 goto end;
277 case EINTR:
278 /* Retry if interrupted by signal. */
279 break; /* Get out of switch. */
280 default:
281 /* Unexpected error. */
282 urcu_die(errno);
283 }
284 }
285end:
286 /*
287 * Re-lock the registry lock before the next loop.
288 */
289 mutex_lock(&rcu_registry_lock);
290}
291
292/*
293 * Always called with rcu_registry lock held. Releases this lock between
294 * iterations and grabs it again. Holds the lock when it returns.
295 */
296static void wait_for_readers(struct cds_list_head *input_readers,
297 struct cds_list_head *cur_snap_readers,
298 struct cds_list_head *qsreaders)
299{
300 unsigned int wait_loops = 0;
301 struct urcu_reader *index, *tmp;
302#ifdef HAS_INCOHERENT_CACHES
303 unsigned int wait_gp_loops = 0;
304#endif /* HAS_INCOHERENT_CACHES */
305
306 /*
307 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
308 * indicate quiescence (not nested), or observe the current
309 * rcu_gp.ctr value.
310 */
311 for (;;) {
312 if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
313 wait_loops++;
314 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
315 uatomic_dec(&rcu_gp.futex);
316 /* Write futex before read reader_gp */
317 smp_mb_master();
318 }
319
320 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
321 switch (urcu_common_reader_state(&rcu_gp, &index->ctr)) {
322 case URCU_READER_ACTIVE_CURRENT:
323 if (cur_snap_readers) {
324 cds_list_move(&index->node,
325 cur_snap_readers);
326 break;
327 }
328 /* Fall-through */
329 case URCU_READER_INACTIVE:
330 cds_list_move(&index->node, qsreaders);
331 break;
332 case URCU_READER_ACTIVE_OLD:
333 /*
334 * Old snapshot. Leaving node in
335 * input_readers will make us busy-loop
336 * until the snapshot becomes current or
337 * the reader becomes inactive.
338 */
339 break;
340 }
341 }
342
343#ifndef HAS_INCOHERENT_CACHES
344 if (cds_list_empty(input_readers)) {
345 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
346 /* Read reader_gp before write futex */
347 smp_mb_master();
348 uatomic_set(&rcu_gp.futex, 0);
349 }
350 break;
351 } else {
352 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
353 /* wait_gp unlocks/locks registry lock. */
354 wait_gp();
355 } else {
356 /* Temporarily unlock the registry lock. */
357 mutex_unlock(&rcu_registry_lock);
358 caa_cpu_relax();
359 /*
360 * Re-lock the registry lock before the
361 * next loop.
362 */
363 mutex_lock(&rcu_registry_lock);
364 }
365 }
366#else /* #ifndef HAS_INCOHERENT_CACHES */
367 /*
368 * BUSY-LOOP. Force the reader thread to commit its
369 * URCU_TLS(rcu_reader).ctr update to memory if we wait
370 * for too long.
371 */
372 if (cds_list_empty(input_readers)) {
373 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
374 /* Read reader_gp before write futex */
375 smp_mb_master();
376 uatomic_set(&rcu_gp.futex, 0);
377 }
378 break;
379 } else {
380 if (wait_gp_loops == KICK_READER_LOOPS) {
381 smp_mb_master();
382 wait_gp_loops = 0;
383 }
384 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
385 /* wait_gp unlocks/locks registry lock. */
386 wait_gp();
387 wait_gp_loops++;
388 } else {
389 /* Temporarily unlock the registry lock. */
390 mutex_unlock(&rcu_registry_lock);
391 caa_cpu_relax();
392 /*
393 * Re-lock the registry lock before the
394 * next loop.
395 */
396 mutex_lock(&rcu_registry_lock);
397 }
398 }
399#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
400 }
401}
402
403void synchronize_rcu(void)
404{
405 CDS_LIST_HEAD(cur_snap_readers);
406 CDS_LIST_HEAD(qsreaders);
407 DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
408 struct urcu_waiters waiters;
409
410 /*
411 * Add ourself to gp_waiters queue of threads awaiting to wait
412 * for a grace period. Proceed to perform the grace period only
413 * if we are the first thread added into the queue.
414 * The implicit memory barrier before urcu_wait_add()
415 * orders prior memory accesses of threads put into the wait
416 * queue before their insertion into the wait queue.
417 */
418 if (urcu_wait_add(&gp_waiters, &wait) != 0) {
419 /* Not first in queue: will be awakened by another thread. */
420 urcu_adaptative_busy_wait(&wait);
421 /* Order following memory accesses after grace period. */
422 cmm_smp_mb();
423 return;
424 }
425 /* We won't need to wake ourself up */
426 urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
427
428 mutex_lock(&rcu_gp_lock);
429
430 /*
431 * Move all waiters into our local queue.
432 */
433 urcu_move_waiters(&waiters, &gp_waiters);
434
435 mutex_lock(&rcu_registry_lock);
436
437 if (cds_list_empty(&registry))
438 goto out;
439
440 /*
441 * All threads should read qparity before accessing data structure
442 * where new ptr points to. Must be done within rcu_registry_lock
443 * because it iterates on reader threads.
444 */
445 /* Write new ptr before changing the qparity */
446 smp_mb_master();
447
448 /*
449 * Wait for readers to observe original parity or be quiescent.
450 * wait_for_readers() can release and grab again rcu_registry_lock
451 * interally.
452 */
453 wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
454
455 /*
456 * Must finish waiting for quiescent state for original parity before
457 * committing next rcu_gp.ctr update to memory. Failure to do so could
458 * result in the writer waiting forever while new readers are always
459 * accessing data (no progress). Enforce compiler-order of load
460 * URCU_TLS(rcu_reader).ctr before store to rcu_gp.ctr.
461 */
462 cmm_barrier();
463
464 /*
465 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
466 * model easier to understand. It does not have a big performance impact
467 * anyway, given this is the write-side.
468 */
469 cmm_smp_mb();
470
471 /* Switch parity: 0 -> 1, 1 -> 0 */
472 CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ URCU_GP_CTR_PHASE);
473
474 /*
475 * Must commit rcu_gp.ctr update to memory before waiting for quiescent
476 * state. Failure to do so could result in the writer waiting forever
477 * while new readers are always accessing data (no progress). Enforce
478 * compiler-order of store to rcu_gp.ctr before load rcu_reader ctr.
479 */
480 cmm_barrier();
481
482 /*
483 *
484 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
485 * model easier to understand. It does not have a big performance impact
486 * anyway, given this is the write-side.
487 */
488 cmm_smp_mb();
489
490 /*
491 * Wait for readers to observe new parity or be quiescent.
492 * wait_for_readers() can release and grab again rcu_registry_lock
493 * interally.
494 */
495 wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
496
497 /*
498 * Put quiescent reader list back into registry.
499 */
500 cds_list_splice(&qsreaders, &registry);
501
502 /*
503 * Finish waiting for reader threads before letting the old ptr
504 * being freed. Must be done within rcu_registry_lock because it
505 * iterates on reader threads.
506 */
507 smp_mb_master();
508out:
509 mutex_unlock(&rcu_registry_lock);
510 mutex_unlock(&rcu_gp_lock);
511
512 /*
513 * Wakeup waiters only after we have completed the grace period
514 * and have ensured the memory barriers at the end of the grace
515 * period have been issued.
516 */
517 urcu_wake_all_waiters(&waiters);
518}
519URCU_ATTR_ALIAS(urcu_stringify(synchronize_rcu))
520void alias_synchronize_rcu();
521
522/*
523 * library wrappers to be used by non-LGPL compatible source code.
524 */
525
526void rcu_read_lock(void)
527{
528 _rcu_read_lock();
529}
530URCU_ATTR_ALIAS(urcu_stringify(rcu_read_lock))
531void alias_rcu_read_lock();
532
533void rcu_read_unlock(void)
534{
535 _rcu_read_unlock();
536}
537URCU_ATTR_ALIAS(urcu_stringify(rcu_read_unlock))
538void alias_rcu_read_unlock();
539
540int rcu_read_ongoing(void)
541{
542 return _rcu_read_ongoing();
543}
544URCU_ATTR_ALIAS(urcu_stringify(rcu_read_ongoing))
545void alias_rcu_read_ongoing();
546
547void rcu_register_thread(void)
548{
549 URCU_TLS(rcu_reader).tid = pthread_self();
550 assert(URCU_TLS(rcu_reader).need_mb == 0);
551 assert(!(URCU_TLS(rcu_reader).ctr & URCU_GP_CTR_NEST_MASK));
552
553 mutex_lock(&rcu_registry_lock);
554 assert(!URCU_TLS(rcu_reader).registered);
555 URCU_TLS(rcu_reader).registered = 1;
556 rcu_init(); /* In case gcc does not support constructor attribute */
557 cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
558 mutex_unlock(&rcu_registry_lock);
559}
560URCU_ATTR_ALIAS(urcu_stringify(rcu_register_thread))
561void alias_rcu_register_thread();
562
563void rcu_unregister_thread(void)
564{
565 mutex_lock(&rcu_registry_lock);
566 assert(URCU_TLS(rcu_reader).registered);
567 URCU_TLS(rcu_reader).registered = 0;
568 cds_list_del(&URCU_TLS(rcu_reader).node);
569 mutex_unlock(&rcu_registry_lock);
570}
571URCU_ATTR_ALIAS(urcu_stringify(rcu_unregister_thread))
572void alias_rcu_unregister_thread();
573
574#ifdef RCU_MEMBARRIER
575
576#ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
577static
578void rcu_sys_membarrier_status(bool available)
579{
580 if (!available)
581 abort();
582}
583#else
584static
585void rcu_sys_membarrier_status(bool available)
586{
587 if (!available)
588 return;
589 urcu_memb_has_sys_membarrier = 1;
590}
591#endif
592
593static
594void rcu_sys_membarrier_init(void)
595{
596 bool available = false;
597 int mask;
598
599 mask = membarrier(MEMBARRIER_CMD_QUERY, 0);
600 if (mask >= 0) {
601 if (mask & MEMBARRIER_CMD_PRIVATE_EXPEDITED) {
602 if (membarrier(MEMBARRIER_CMD_REGISTER_PRIVATE_EXPEDITED, 0))
603 urcu_die(errno);
604 urcu_memb_has_sys_membarrier_private_expedited = 1;
605 available = true;
606 } else if (mask & MEMBARRIER_CMD_SHARED) {
607 available = true;
608 }
609 }
610 rcu_sys_membarrier_status(available);
611}
612
613void rcu_init(void)
614{
615 if (init_done)
616 return;
617 init_done = 1;
618 rcu_sys_membarrier_init();
619}
620URCU_ATTR_ALIAS(urcu_stringify(rcu_init))
621void alias_rcu_init(void);
622#endif
623
624#ifdef RCU_SIGNAL
625static void sigrcu_handler(int signo __attribute__((unused)),
626 siginfo_t *siginfo __attribute__((unused)),
627 void *context __attribute__((unused)))
628{
629 /*
630 * Executing this cmm_smp_mb() is the only purpose of this signal handler.
631 * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
632 * executed on.
633 */
634 cmm_smp_mb();
635 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
636 cmm_smp_mb();
637}
638
639/*
640 * rcu_init constructor. Called when the library is linked, but also when
641 * reader threads are calling rcu_register_thread().
642 * Should only be called by a single thread at a given time. This is ensured by
643 * holing the rcu_registry_lock from rcu_register_thread() or by running
644 * at library load time, which should not be executed by multiple
645 * threads nor concurrently with rcu_register_thread() anyway.
646 */
647void rcu_init(void)
648{
649 struct sigaction act;
650 int ret;
651
652 if (init_done)
653 return;
654 init_done = 1;
655
656 act.sa_sigaction = sigrcu_handler;
657 act.sa_flags = SA_SIGINFO | SA_RESTART;
658 sigemptyset(&act.sa_mask);
659 ret = sigaction(SIGRCU, &act, NULL);
660 if (ret)
661 urcu_die(errno);
662}
663URCU_ATTR_ALIAS(urcu_stringify(rcu_init))
664void alias_rcu_init(void);
665
666void rcu_exit(void)
667{
668 /*
669 * Don't unregister the SIGRCU signal handler anymore, because
670 * call_rcu threads could still be using it shortly before the
671 * application exits.
672 * Assertion disabled because call_rcu threads are now rcu
673 * readers, and left running at exit.
674 * assert(cds_list_empty(&registry));
675 */
676}
677URCU_ATTR_ALIAS(urcu_stringify(rcu_exit))
678void alias_rcu_exit(void);
679
680#endif /* #ifdef RCU_SIGNAL */
681
682DEFINE_RCU_FLAVOR(rcu_flavor);
683DEFINE_RCU_FLAVOR_ALIAS(rcu_flavor, alias_rcu_flavor);
684
685#include "urcu-call-rcu-impl.h"
686#include "urcu-defer-impl.h"
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