fix: ifdef linux specific cpu count compat
[urcu.git] / src / urcu-qsbr.c
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CommitLineData
1/*
2 * urcu-qsbr.c
3 *
4 * Userspace RCU QSBR 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 _LGPL_SOURCE
28#include <stdio.h>
29#include <pthread.h>
30#include <signal.h>
31#include <stdlib.h>
32#include <stdint.h>
33#include <string.h>
34#include <errno.h>
35#include <poll.h>
36
37#include <urcu/assert.h>
38#include <urcu/wfcqueue.h>
39#include <urcu/map/urcu-qsbr.h>
40#define BUILD_QSBR_LIB
41#include <urcu/static/urcu-qsbr.h>
42#include <urcu/pointer.h>
43#include <urcu/tls-compat.h>
44
45#include "urcu-die.h"
46#include "urcu-wait.h"
47#include "urcu-utils.h"
48
49#define URCU_API_MAP
50/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
51#undef _LGPL_SOURCE
52#include <urcu/urcu-qsbr.h>
53#define _LGPL_SOURCE
54
55void __attribute__((destructor)) urcu_qsbr_exit(void);
56
57/*
58 * rcu_gp_lock ensures mutual exclusion between threads calling
59 * synchronize_rcu().
60 */
61static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
62/*
63 * rcu_registry_lock ensures mutual exclusion between threads
64 * registering and unregistering themselves to/from the registry, and
65 * with threads reading that registry from synchronize_rcu(). However,
66 * this lock is not held all the way through the completion of awaiting
67 * for the grace period. It is sporadically released between iterations
68 * on the registry.
69 * rcu_registry_lock may nest inside rcu_gp_lock.
70 */
71static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
72struct urcu_gp urcu_qsbr_gp = { .ctr = URCU_QSBR_GP_ONLINE };
73
74/*
75 * Active attempts to check for reader Q.S. before calling futex().
76 */
77#define RCU_QS_ACTIVE_ATTEMPTS 100
78
79/*
80 * Written to only by each individual reader. Read by both the reader and the
81 * writers.
82 */
83DEFINE_URCU_TLS(struct urcu_qsbr_reader, urcu_qsbr_reader);
84
85static CDS_LIST_HEAD(registry);
86
87/*
88 * Queue keeping threads awaiting to wait for a grace period. Contains
89 * struct gp_waiters_thread objects.
90 */
91static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
92
93static void mutex_lock(pthread_mutex_t *mutex)
94{
95 int ret;
96
97#ifndef DISTRUST_SIGNALS_EXTREME
98 ret = pthread_mutex_lock(mutex);
99 if (ret)
100 urcu_die(ret);
101#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
102 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
103 if (ret != EBUSY && ret != EINTR)
104 urcu_die(ret);
105 poll(NULL,0,10);
106 }
107#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
108}
109
110static void mutex_unlock(pthread_mutex_t *mutex)
111{
112 int ret;
113
114 ret = pthread_mutex_unlock(mutex);
115 if (ret)
116 urcu_die(ret);
117}
118
119/*
120 * synchronize_rcu() waiting. Single thread.
121 */
122static void wait_gp(void)
123{
124 /* Read reader_gp before read futex */
125 cmm_smp_rmb();
126 while (uatomic_read(&urcu_qsbr_gp.futex) == -1) {
127 if (!futex_noasync(&urcu_qsbr_gp.futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
128 /*
129 * Prior queued wakeups queued by unrelated code
130 * using the same address can cause futex wait to
131 * return 0 even through the futex value is still
132 * -1 (spurious wakeups). Check the value again
133 * in user-space to validate whether it really
134 * differs from -1.
135 */
136 continue;
137 }
138 switch (errno) {
139 case EAGAIN:
140 /* Value already changed. */
141 return;
142 case EINTR:
143 /* Retry if interrupted by signal. */
144 break; /* Get out of switch. Check again. */
145 default:
146 /* Unexpected error. */
147 urcu_die(errno);
148 }
149 }
150}
151
152/*
153 * Always called with rcu_registry lock held. Releases this lock between
154 * iterations and grabs it again. Holds the lock when it returns.
155 */
156static void wait_for_readers(struct cds_list_head *input_readers,
157 struct cds_list_head *cur_snap_readers,
158 struct cds_list_head *qsreaders)
159{
160 unsigned int wait_loops = 0;
161 struct urcu_qsbr_reader *index, *tmp;
162
163 /*
164 * Wait for each thread URCU_TLS(urcu_qsbr_reader).ctr to either
165 * indicate quiescence (offline), or for them to observe the
166 * current urcu_qsbr_gp.ctr value.
167 */
168 for (;;) {
169 if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
170 wait_loops++;
171 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
172 uatomic_set(&urcu_qsbr_gp.futex, -1);
173 /*
174 * Write futex before write waiting (the other side
175 * reads them in the opposite order).
176 */
177 cmm_smp_wmb();
178 cds_list_for_each_entry(index, input_readers, node) {
179 _CMM_STORE_SHARED(index->waiting, 1);
180 }
181 /* Write futex before read reader_gp */
182 cmm_smp_mb();
183 }
184 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
185 switch (urcu_qsbr_reader_state(&index->ctr)) {
186 case URCU_READER_ACTIVE_CURRENT:
187 if (cur_snap_readers) {
188 cds_list_move(&index->node,
189 cur_snap_readers);
190 break;
191 }
192 /* Fall-through */
193 case URCU_READER_INACTIVE:
194 cds_list_move(&index->node, qsreaders);
195 break;
196 case URCU_READER_ACTIVE_OLD:
197 /*
198 * Old snapshot. Leaving node in
199 * input_readers will make us busy-loop
200 * until the snapshot becomes current or
201 * the reader becomes inactive.
202 */
203 break;
204 }
205 }
206
207 if (cds_list_empty(input_readers)) {
208 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
209 /* Read reader_gp before write futex */
210 cmm_smp_mb();
211 uatomic_set(&urcu_qsbr_gp.futex, 0);
212 }
213 break;
214 } else {
215 /* Temporarily unlock the registry lock. */
216 mutex_unlock(&rcu_registry_lock);
217 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
218 wait_gp();
219 } else {
220#ifndef HAS_INCOHERENT_CACHES
221 caa_cpu_relax();
222#else /* #ifndef HAS_INCOHERENT_CACHES */
223 cmm_smp_mb();
224#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
225 }
226 /* Re-lock the registry lock before the next loop. */
227 mutex_lock(&rcu_registry_lock);
228 }
229 }
230}
231
232/*
233 * Using a two-subphases algorithm for architectures with smaller than 64-bit
234 * long-size to ensure we do not encounter an overflow bug.
235 */
236
237#if (CAA_BITS_PER_LONG < 64)
238void urcu_qsbr_synchronize_rcu(void)
239{
240 CDS_LIST_HEAD(cur_snap_readers);
241 CDS_LIST_HEAD(qsreaders);
242 unsigned long was_online;
243 DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
244 struct urcu_waiters waiters;
245
246 was_online = urcu_qsbr_read_ongoing();
247
248 /* All threads should read qparity before accessing data structure
249 * where new ptr points to. In the "then" case, rcu_thread_offline
250 * includes a memory barrier.
251 *
252 * Mark the writer thread offline to make sure we don't wait for
253 * our own quiescent state. This allows using synchronize_rcu()
254 * in threads registered as readers.
255 */
256 if (was_online)
257 urcu_qsbr_thread_offline();
258 else
259 cmm_smp_mb();
260
261 /*
262 * Add ourself to gp_waiters queue of threads awaiting to wait
263 * for a grace period. Proceed to perform the grace period only
264 * if we are the first thread added into the queue.
265 */
266 if (urcu_wait_add(&gp_waiters, &wait) != 0) {
267 /* Not first in queue: will be awakened by another thread. */
268 urcu_adaptative_busy_wait(&wait);
269 goto gp_end;
270 }
271 /* We won't need to wake ourself up */
272 urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
273
274 mutex_lock(&rcu_gp_lock);
275
276 /*
277 * Move all waiters into our local queue.
278 */
279 urcu_move_waiters(&waiters, &gp_waiters);
280
281 mutex_lock(&rcu_registry_lock);
282
283 if (cds_list_empty(&registry))
284 goto out;
285
286 /*
287 * Wait for readers to observe original parity or be quiescent.
288 * wait_for_readers() can release and grab again rcu_registry_lock
289 * internally.
290 */
291 wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
292
293 /*
294 * Must finish waiting for quiescent state for original parity
295 * before committing next urcu_qsbr_gp.ctr update to memory. Failure
296 * to do so could result in the writer waiting forever while new
297 * readers are always accessing data (no progress). Enforce
298 * compiler-order of load URCU_TLS(urcu_qsbr_reader).ctr before store
299 * to urcu_qsbr_gp.ctr.
300 */
301 cmm_barrier();
302
303 /*
304 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
305 * model easier to understand. It does not have a big performance impact
306 * anyway, given this is the write-side.
307 */
308 cmm_smp_mb();
309
310 /* Switch parity: 0 -> 1, 1 -> 0 */
311 CMM_STORE_SHARED(urcu_qsbr_gp.ctr, urcu_qsbr_gp.ctr ^ URCU_QSBR_GP_CTR);
312
313 /*
314 * Must commit urcu_qsbr_gp.ctr update to memory before waiting for
315 * quiescent state. Failure to do so could result in the writer
316 * waiting forever while new readers are always accessing data
317 * (no progress). Enforce compiler-order of store to urcu_qsbr_gp.ctr
318 * before load URCU_TLS(urcu_qsbr_reader).ctr.
319 */
320 cmm_barrier();
321
322 /*
323 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
324 * model easier to understand. It does not have a big performance impact
325 * anyway, given this is the write-side.
326 */
327 cmm_smp_mb();
328
329 /*
330 * Wait for readers to observe new parity or be quiescent.
331 * wait_for_readers() can release and grab again rcu_registry_lock
332 * internally.
333 */
334 wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
335
336 /*
337 * Put quiescent reader list back into registry.
338 */
339 cds_list_splice(&qsreaders, &registry);
340out:
341 mutex_unlock(&rcu_registry_lock);
342 mutex_unlock(&rcu_gp_lock);
343 urcu_wake_all_waiters(&waiters);
344gp_end:
345 /*
346 * Finish waiting for reader threads before letting the old ptr being
347 * freed.
348 */
349 if (was_online)
350 urcu_qsbr_thread_online();
351 else
352 cmm_smp_mb();
353}
354#else /* !(CAA_BITS_PER_LONG < 64) */
355void urcu_qsbr_synchronize_rcu(void)
356{
357 CDS_LIST_HEAD(qsreaders);
358 unsigned long was_online;
359 DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
360 struct urcu_waiters waiters;
361
362 was_online = urcu_qsbr_read_ongoing();
363
364 /*
365 * Mark the writer thread offline to make sure we don't wait for
366 * our own quiescent state. This allows using synchronize_rcu()
367 * in threads registered as readers.
368 */
369 if (was_online)
370 urcu_qsbr_thread_offline();
371 else
372 cmm_smp_mb();
373
374 /*
375 * Add ourself to gp_waiters queue of threads awaiting to wait
376 * for a grace period. Proceed to perform the grace period only
377 * if we are the first thread added into the queue.
378 */
379 if (urcu_wait_add(&gp_waiters, &wait) != 0) {
380 /* Not first in queue: will be awakened by another thread. */
381 urcu_adaptative_busy_wait(&wait);
382 goto gp_end;
383 }
384 /* We won't need to wake ourself up */
385 urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
386
387 mutex_lock(&rcu_gp_lock);
388
389 /*
390 * Move all waiters into our local queue.
391 */
392 urcu_move_waiters(&waiters, &gp_waiters);
393
394 mutex_lock(&rcu_registry_lock);
395
396 if (cds_list_empty(&registry))
397 goto out;
398
399 /* Increment current G.P. */
400 CMM_STORE_SHARED(urcu_qsbr_gp.ctr, urcu_qsbr_gp.ctr + URCU_QSBR_GP_CTR);
401
402 /*
403 * Must commit urcu_qsbr_gp.ctr update to memory before waiting for
404 * quiescent state. Failure to do so could result in the writer
405 * waiting forever while new readers are always accessing data
406 * (no progress). Enforce compiler-order of store to urcu_qsbr_gp.ctr
407 * before load URCU_TLS(urcu_qsbr_reader).ctr.
408 */
409 cmm_barrier();
410
411 /*
412 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
413 * model easier to understand. It does not have a big performance impact
414 * anyway, given this is the write-side.
415 */
416 cmm_smp_mb();
417
418 /*
419 * Wait for readers to observe new count of be quiescent.
420 * wait_for_readers() can release and grab again rcu_registry_lock
421 * internally.
422 */
423 wait_for_readers(&registry, NULL, &qsreaders);
424
425 /*
426 * Put quiescent reader list back into registry.
427 */
428 cds_list_splice(&qsreaders, &registry);
429out:
430 mutex_unlock(&rcu_registry_lock);
431 mutex_unlock(&rcu_gp_lock);
432 urcu_wake_all_waiters(&waiters);
433gp_end:
434 if (was_online)
435 urcu_qsbr_thread_online();
436 else
437 cmm_smp_mb();
438}
439#endif /* !(CAA_BITS_PER_LONG < 64) */
440
441/*
442 * library wrappers to be used by non-LGPL compatible source code.
443 */
444
445void urcu_qsbr_read_lock(void)
446{
447 _urcu_qsbr_read_lock();
448}
449
450void urcu_qsbr_read_unlock(void)
451{
452 _urcu_qsbr_read_unlock();
453}
454
455int urcu_qsbr_read_ongoing(void)
456{
457 return _urcu_qsbr_read_ongoing();
458}
459void rcu_read_ongoing_qsbr();
460
461void urcu_qsbr_quiescent_state(void)
462{
463 _urcu_qsbr_quiescent_state();
464}
465void rcu_quiescent_state_qsbr();
466
467void urcu_qsbr_thread_offline(void)
468{
469 _urcu_qsbr_thread_offline();
470}
471void rcu_thread_offline_qsbr();
472
473void urcu_qsbr_thread_online(void)
474{
475 _urcu_qsbr_thread_online();
476}
477
478void urcu_qsbr_register_thread(void)
479{
480 URCU_TLS(urcu_qsbr_reader).tid = pthread_self();
481 urcu_posix_assert(URCU_TLS(urcu_qsbr_reader).ctr == 0);
482
483 mutex_lock(&rcu_registry_lock);
484 urcu_posix_assert(!URCU_TLS(urcu_qsbr_reader).registered);
485 URCU_TLS(urcu_qsbr_reader).registered = 1;
486 cds_list_add(&URCU_TLS(urcu_qsbr_reader).node, &registry);
487 mutex_unlock(&rcu_registry_lock);
488 _urcu_qsbr_thread_online();
489}
490
491void urcu_qsbr_unregister_thread(void)
492{
493 /*
494 * We have to make the thread offline otherwise we end up dealocking
495 * with a waiting writer.
496 */
497 _urcu_qsbr_thread_offline();
498 urcu_posix_assert(URCU_TLS(urcu_qsbr_reader).registered);
499 URCU_TLS(urcu_qsbr_reader).registered = 0;
500 mutex_lock(&rcu_registry_lock);
501 cds_list_del(&URCU_TLS(urcu_qsbr_reader).node);
502 mutex_unlock(&rcu_registry_lock);
503}
504
505void urcu_qsbr_exit(void)
506{
507 /*
508 * Assertion disabled because call_rcu threads are now rcu
509 * readers, and left running at exit.
510 * urcu_posix_assert(cds_list_empty(&registry));
511 */
512}
513
514DEFINE_RCU_FLAVOR(rcu_flavor);
515
516#include "urcu-call-rcu-impl.h"
517#include "urcu-defer-impl.h"
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