Commit | Line | Data |
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9f1621ca | 1 | /* |
7ac06cef | 2 | * urcu-qsbr.c |
9f1621ca | 3 | * |
7ac06cef | 4 | * Userspace RCU QSBR library |
9f1621ca | 5 | * |
6982d6d7 | 6 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
9f1621ca MD |
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 | ||
c1d2c60b | 26 | #define _GNU_SOURCE |
71c811bf | 27 | #define _LGPL_SOURCE |
9f1621ca MD |
28 | #include <stdio.h> |
29 | #include <pthread.h> | |
30 | #include <signal.h> | |
31 | #include <assert.h> | |
32 | #include <stdlib.h> | |
6d841bc2 | 33 | #include <stdint.h> |
9f1621ca MD |
34 | #include <string.h> |
35 | #include <errno.h> | |
36 | #include <poll.h> | |
37 | ||
d73fb81f | 38 | #include "urcu/wfcqueue.h" |
57760d44 | 39 | #include "urcu/map/urcu-qsbr.h" |
727f819d | 40 | #define BUILD_QSBR_LIB |
af7c2dbe | 41 | #include "urcu/static/urcu-qsbr.h" |
618b2595 | 42 | #include "urcu-pointer.h" |
bd252a04 | 43 | #include "urcu/tls-compat.h" |
71c811bf | 44 | |
4a6d7378 | 45 | #include "urcu-die.h" |
cba82d7b | 46 | #include "urcu-wait.h" |
4a6d7378 | 47 | |
9f1621ca | 48 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
71c811bf | 49 | #undef _LGPL_SOURCE |
7ac06cef | 50 | #include "urcu-qsbr.h" |
71c811bf | 51 | #define _LGPL_SOURCE |
9f1621ca | 52 | |
f6d18c64 MD |
53 | void __attribute__((destructor)) rcu_exit(void); |
54 | ||
6abb4bd5 | 55 | static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; |
4de0cd31 | 56 | struct rcu_gp rcu_gp = { .ctr = RCU_GP_ONLINE }; |
9f1621ca | 57 | |
408f6d92 PB |
58 | /* |
59 | * Active attempts to check for reader Q.S. before calling futex(). | |
60 | */ | |
61 | #define RCU_QS_ACTIVE_ATTEMPTS 100 | |
62 | ||
9f1621ca MD |
63 | /* |
64 | * Written to only by each individual reader. Read by both the reader and the | |
65 | * writers. | |
66 | */ | |
bd252a04 | 67 | DEFINE_URCU_TLS(struct rcu_reader, rcu_reader); |
9f1621ca MD |
68 | |
69 | #ifdef DEBUG_YIELD | |
1de4df4b MD |
70 | unsigned int rcu_yield_active; |
71 | DEFINE_URCU_TLS(unsigned int, rcu_rand_yield); | |
9f1621ca MD |
72 | #endif |
73 | ||
16aa9ee8 | 74 | static CDS_LIST_HEAD(registry); |
9f1621ca | 75 | |
6362f68f | 76 | /* |
bf6822a6 | 77 | * Queue keeping threads awaiting to wait for a grace period. Contains |
6362f68f MD |
78 | * struct gp_waiters_thread objects. |
79 | */ | |
bf6822a6 | 80 | static DEFINE_URCU_WAIT_QUEUE(gp_waiters); |
6362f68f | 81 | |
6abb4bd5 | 82 | static void mutex_lock(pthread_mutex_t *mutex) |
9f1621ca MD |
83 | { |
84 | int ret; | |
85 | ||
86 | #ifndef DISTRUST_SIGNALS_EXTREME | |
6abb4bd5 | 87 | ret = pthread_mutex_lock(mutex); |
4a6d7378 MD |
88 | if (ret) |
89 | urcu_die(ret); | |
9f1621ca | 90 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ |
6abb4bd5 | 91 | while ((ret = pthread_mutex_trylock(mutex)) != 0) { |
4a6d7378 MD |
92 | if (ret != EBUSY && ret != EINTR) |
93 | urcu_die(ret); | |
9f1621ca MD |
94 | poll(NULL,0,10); |
95 | } | |
96 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
97 | } | |
98 | ||
6abb4bd5 | 99 | static void mutex_unlock(pthread_mutex_t *mutex) |
9f1621ca MD |
100 | { |
101 | int ret; | |
102 | ||
6abb4bd5 | 103 | ret = pthread_mutex_unlock(mutex); |
4a6d7378 MD |
104 | if (ret) |
105 | urcu_die(ret); | |
9f1621ca MD |
106 | } |
107 | ||
bc6c15bb MD |
108 | /* |
109 | * synchronize_rcu() waiting. Single thread. | |
110 | */ | |
4d703340 | 111 | static void wait_gp(void) |
bc6c15bb | 112 | { |
4d703340 | 113 | /* Read reader_gp before read futex */ |
5481ddb3 | 114 | cmm_smp_rmb(); |
15302e28 LJ |
115 | if (uatomic_read(&rcu_gp.futex) == -1) |
116 | futex_noasync(&rcu_gp.futex, FUTEX_WAIT, -1, | |
4d703340 | 117 | NULL, NULL, 0); |
bc6c15bb MD |
118 | } |
119 | ||
708d89f0 MD |
120 | static void wait_for_readers(struct cds_list_head *input_readers, |
121 | struct cds_list_head *cur_snap_readers, | |
122 | struct cds_list_head *qsreaders) | |
9f1621ca | 123 | { |
4d703340 | 124 | int wait_loops = 0; |
02be5561 | 125 | struct rcu_reader *index, *tmp; |
9f1621ca | 126 | |
9f1621ca | 127 | /* |
f6b42f9c MD |
128 | * Wait for each thread URCU_TLS(rcu_reader).ctr to either |
129 | * indicate quiescence (offline), or for them to observe the | |
15302e28 | 130 | * current rcu_gp.ctr value. |
9f1621ca | 131 | */ |
4d703340 MD |
132 | for (;;) { |
133 | wait_loops++; | |
83a2c421 | 134 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
15302e28 | 135 | uatomic_set(&rcu_gp.futex, -1); |
83a2c421 PB |
136 | /* |
137 | * Write futex before write waiting (the other side | |
138 | * reads them in the opposite order). | |
139 | */ | |
140 | cmm_smp_wmb(); | |
708d89f0 | 141 | cds_list_for_each_entry(index, input_readers, node) { |
83a2c421 PB |
142 | _CMM_STORE_SHARED(index->waiting, 1); |
143 | } | |
4d703340 | 144 | /* Write futex before read reader_gp */ |
5481ddb3 | 145 | cmm_smp_mb(); |
4d703340 | 146 | } |
708d89f0 MD |
147 | cds_list_for_each_entry_safe(index, tmp, input_readers, node) { |
148 | switch (rcu_reader_state(&index->ctr)) { | |
149 | case RCU_READER_ACTIVE_CURRENT: | |
150 | if (cur_snap_readers) { | |
151 | cds_list_move(&index->node, | |
152 | cur_snap_readers); | |
153 | break; | |
154 | } | |
155 | /* Fall-through */ | |
156 | case RCU_READER_INACTIVE: | |
157 | cds_list_move(&index->node, qsreaders); | |
158 | break; | |
159 | case RCU_READER_ACTIVE_OLD: | |
160 | /* | |
161 | * Old snapshot. Leaving node in | |
162 | * input_readers will make us busy-loop | |
163 | * until the snapshot becomes current or | |
164 | * the reader becomes inactive. | |
165 | */ | |
166 | break; | |
167 | } | |
4d703340 | 168 | } |
bc6c15bb | 169 | |
708d89f0 | 170 | if (cds_list_empty(input_readers)) { |
83a2c421 | 171 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 172 | /* Read reader_gp before write futex */ |
5481ddb3 | 173 | cmm_smp_mb(); |
15302e28 | 174 | uatomic_set(&rcu_gp.futex, 0); |
4d703340 MD |
175 | } |
176 | break; | |
177 | } else { | |
83a2c421 | 178 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 179 | wait_gp(); |
bc6c15bb | 180 | } else { |
9f1621ca | 181 | #ifndef HAS_INCOHERENT_CACHES |
06f22bdb | 182 | caa_cpu_relax(); |
9f1621ca | 183 | #else /* #ifndef HAS_INCOHERENT_CACHES */ |
5481ddb3 | 184 | cmm_smp_mb(); |
9f1621ca | 185 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ |
bc6c15bb MD |
186 | } |
187 | } | |
9f1621ca MD |
188 | } |
189 | } | |
190 | ||
47d2f29e MD |
191 | /* |
192 | * Using a two-subphases algorithm for architectures with smaller than 64-bit | |
193 | * long-size to ensure we do not encounter an overflow bug. | |
194 | */ | |
195 | ||
b39e1761 | 196 | #if (CAA_BITS_PER_LONG < 64) |
47d2f29e MD |
197 | void synchronize_rcu(void) |
198 | { | |
708d89f0 MD |
199 | CDS_LIST_HEAD(cur_snap_readers); |
200 | CDS_LIST_HEAD(qsreaders); | |
bc49c323 | 201 | unsigned long was_online; |
bf6822a6 MD |
202 | DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); |
203 | struct urcu_waiters waiters; | |
bc49c323 | 204 | |
882f3357 | 205 | was_online = rcu_read_ongoing(); |
bc49c323 | 206 | |
47d2f29e | 207 | /* All threads should read qparity before accessing data structure |
27b940e7 PB |
208 | * where new ptr points to. In the "then" case, rcu_thread_offline |
209 | * includes a memory barrier. | |
210 | * | |
bc49c323 | 211 | * Mark the writer thread offline to make sure we don't wait for |
5e77fc1f PM |
212 | * our own quiescent state. This allows using synchronize_rcu() |
213 | * in threads registered as readers. | |
bc49c323 | 214 | */ |
27b940e7 PB |
215 | if (was_online) |
216 | rcu_thread_offline(); | |
217 | else | |
218 | cmm_smp_mb(); | |
bc49c323 | 219 | |
6362f68f | 220 | /* |
bf6822a6 | 221 | * Add ourself to gp_waiters queue of threads awaiting to wait |
6362f68f | 222 | * for a grace period. Proceed to perform the grace period only |
bf6822a6 | 223 | * if we are the first thread added into the queue. |
6362f68f | 224 | */ |
bf6822a6 MD |
225 | if (urcu_wait_add(&gp_waiters, &wait) != 0) { |
226 | /* Not first in queue: will be awakened by another thread. */ | |
227 | urcu_adaptative_busy_wait(&wait); | |
6362f68f MD |
228 | goto gp_end; |
229 | } | |
bf6822a6 MD |
230 | /* We won't need to wake ourself up */ |
231 | urcu_wait_set_state(&wait, URCU_WAIT_RUNNING); | |
6362f68f | 232 | |
6abb4bd5 | 233 | mutex_lock(&rcu_gp_lock); |
47d2f29e | 234 | |
6362f68f | 235 | /* |
bf6822a6 | 236 | * Move all waiters into our local queue. |
6362f68f | 237 | */ |
bf6822a6 | 238 | urcu_move_waiters(&waiters, &gp_waiters); |
6362f68f | 239 | |
16aa9ee8 | 240 | if (cds_list_empty(®istry)) |
2dfb8b5e | 241 | goto out; |
47d2f29e MD |
242 | |
243 | /* | |
f6b42f9c | 244 | * Wait for readers to observe original parity or be quiescent. |
47d2f29e | 245 | */ |
708d89f0 | 246 | wait_for_readers(®istry, &cur_snap_readers, &qsreaders); |
47d2f29e MD |
247 | |
248 | /* | |
f6b42f9c | 249 | * Must finish waiting for quiescent state for original parity |
15302e28 | 250 | * before committing next rcu_gp.ctr update to memory. Failure |
f6b42f9c | 251 | * to do so could result in the writer waiting forever while new |
5e77fc1f | 252 | * readers are always accessing data (no progress). Enforce |
f6b42f9c | 253 | * compiler-order of load URCU_TLS(rcu_reader).ctr before store |
15302e28 | 254 | * to rcu_gp.ctr. |
47d2f29e | 255 | */ |
5481ddb3 | 256 | cmm_barrier(); |
47d2f29e | 257 | |
47d2f29e | 258 | /* |
5481ddb3 | 259 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
2dfb8b5e MD |
260 | * model easier to understand. It does not have a big performance impact |
261 | * anyway, given this is the write-side. | |
47d2f29e | 262 | */ |
5481ddb3 | 263 | cmm_smp_mb(); |
47d2f29e | 264 | |
f6b42f9c | 265 | /* Switch parity: 0 -> 1, 1 -> 0 */ |
15302e28 | 266 | CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR); |
f6b42f9c | 267 | |
47d2f29e | 268 | /* |
15302e28 | 269 | * Must commit rcu_gp.ctr update to memory before waiting for |
f6b42f9c MD |
270 | * quiescent state. Failure to do so could result in the writer |
271 | * waiting forever while new readers are always accessing data | |
15302e28 | 272 | * (no progress). Enforce compiler-order of store to rcu_gp.ctr |
f6b42f9c | 273 | * before load URCU_TLS(rcu_reader).ctr. |
47d2f29e | 274 | */ |
f6b42f9c MD |
275 | cmm_barrier(); |
276 | ||
277 | /* | |
278 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the | |
279 | * model easier to understand. It does not have a big performance impact | |
280 | * anyway, given this is the write-side. | |
281 | */ | |
282 | cmm_smp_mb(); | |
283 | ||
284 | /* | |
285 | * Wait for readers to observe new parity or be quiescent. | |
286 | */ | |
708d89f0 MD |
287 | wait_for_readers(&cur_snap_readers, NULL, &qsreaders); |
288 | ||
289 | /* | |
290 | * Put quiescent reader list back into registry. | |
291 | */ | |
292 | cds_list_splice(&qsreaders, ®istry); | |
2dfb8b5e | 293 | out: |
6abb4bd5 | 294 | mutex_unlock(&rcu_gp_lock); |
bf6822a6 | 295 | urcu_wake_all_waiters(&waiters); |
6362f68f | 296 | gp_end: |
bc49c323 MD |
297 | /* |
298 | * Finish waiting for reader threads before letting the old ptr being | |
47d2f29e MD |
299 | * freed. |
300 | */ | |
bc49c323 | 301 | if (was_online) |
27b940e7 PB |
302 | rcu_thread_online(); |
303 | else | |
304 | cmm_smp_mb(); | |
47d2f29e | 305 | } |
b39e1761 | 306 | #else /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
307 | void synchronize_rcu(void) |
308 | { | |
708d89f0 | 309 | CDS_LIST_HEAD(qsreaders); |
f0f7dbdd | 310 | unsigned long was_online; |
bf6822a6 MD |
311 | DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); |
312 | struct urcu_waiters waiters; | |
ff2f67a0 | 313 | |
882f3357 | 314 | was_online = rcu_read_ongoing(); |
ff2f67a0 MD |
315 | |
316 | /* | |
317 | * Mark the writer thread offline to make sure we don't wait for | |
5e77fc1f PM |
318 | * our own quiescent state. This allows using synchronize_rcu() |
319 | * in threads registered as readers. | |
ff2f67a0 | 320 | */ |
27b940e7 PB |
321 | if (was_online) |
322 | rcu_thread_offline(); | |
323 | else | |
324 | cmm_smp_mb(); | |
ff2f67a0 | 325 | |
6362f68f | 326 | /* |
bf6822a6 | 327 | * Add ourself to gp_waiters queue of threads awaiting to wait |
6362f68f | 328 | * for a grace period. Proceed to perform the grace period only |
bf6822a6 | 329 | * if we are the first thread added into the queue. |
6362f68f | 330 | */ |
bf6822a6 MD |
331 | if (urcu_wait_add(&gp_waiters, &wait) != 0) { |
332 | /* Not first in queue: will be awakened by another thread. */ | |
333 | urcu_adaptative_busy_wait(&wait); | |
6362f68f MD |
334 | goto gp_end; |
335 | } | |
bf6822a6 MD |
336 | /* We won't need to wake ourself up */ |
337 | urcu_wait_set_state(&wait, URCU_WAIT_RUNNING); | |
6362f68f | 338 | |
6abb4bd5 | 339 | mutex_lock(&rcu_gp_lock); |
6362f68f MD |
340 | |
341 | /* | |
bf6822a6 | 342 | * Move all waiters into our local queue. |
6362f68f | 343 | */ |
bf6822a6 | 344 | urcu_move_waiters(&waiters, &gp_waiters); |
6362f68f | 345 | |
16aa9ee8 | 346 | if (cds_list_empty(®istry)) |
2dfb8b5e | 347 | goto out; |
f6b42f9c MD |
348 | |
349 | /* Increment current G.P. */ | |
15302e28 | 350 | CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr + RCU_GP_CTR); |
f6b42f9c MD |
351 | |
352 | /* | |
15302e28 | 353 | * Must commit rcu_gp.ctr update to memory before waiting for |
f6b42f9c MD |
354 | * quiescent state. Failure to do so could result in the writer |
355 | * waiting forever while new readers are always accessing data | |
15302e28 | 356 | * (no progress). Enforce compiler-order of store to rcu_gp.ctr |
f6b42f9c MD |
357 | * before load URCU_TLS(rcu_reader).ctr. |
358 | */ | |
359 | cmm_barrier(); | |
360 | ||
361 | /* | |
362 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the | |
363 | * model easier to understand. It does not have a big performance impact | |
364 | * anyway, given this is the write-side. | |
365 | */ | |
366 | cmm_smp_mb(); | |
367 | ||
368 | /* | |
369 | * Wait for readers to observe new count of be quiescent. | |
370 | */ | |
708d89f0 MD |
371 | wait_for_readers(®istry, NULL, &qsreaders); |
372 | ||
373 | /* | |
374 | * Put quiescent reader list back into registry. | |
375 | */ | |
376 | cds_list_splice(&qsreaders, ®istry); | |
2dfb8b5e | 377 | out: |
6abb4bd5 | 378 | mutex_unlock(&rcu_gp_lock); |
bf6822a6 | 379 | urcu_wake_all_waiters(&waiters); |
6362f68f | 380 | gp_end: |
ff2f67a0 | 381 | if (was_online) |
27b940e7 PB |
382 | rcu_thread_online(); |
383 | else | |
384 | cmm_smp_mb(); | |
9f1621ca | 385 | } |
b39e1761 | 386 | #endif /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
387 | |
388 | /* | |
389 | * library wrappers to be used by non-LGPL compatible source code. | |
390 | */ | |
391 | ||
392 | void rcu_read_lock(void) | |
393 | { | |
394 | _rcu_read_lock(); | |
395 | } | |
396 | ||
397 | void rcu_read_unlock(void) | |
398 | { | |
399 | _rcu_read_unlock(); | |
400 | } | |
401 | ||
882f3357 MD |
402 | int rcu_read_ongoing(void) |
403 | { | |
404 | return _rcu_read_ongoing(); | |
405 | } | |
406 | ||
7ac06cef MD |
407 | void rcu_quiescent_state(void) |
408 | { | |
409 | _rcu_quiescent_state(); | |
410 | } | |
411 | ||
412 | void rcu_thread_offline(void) | |
413 | { | |
414 | _rcu_thread_offline(); | |
415 | } | |
416 | ||
417 | void rcu_thread_online(void) | |
418 | { | |
419 | _rcu_thread_online(); | |
420 | } | |
421 | ||
9f1621ca MD |
422 | void rcu_register_thread(void) |
423 | { | |
bd252a04 MD |
424 | URCU_TLS(rcu_reader).tid = pthread_self(); |
425 | assert(URCU_TLS(rcu_reader).ctr == 0); | |
4f8e3380 | 426 | |
6abb4bd5 | 427 | mutex_lock(&rcu_gp_lock); |
bd252a04 | 428 | cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); |
6abb4bd5 | 429 | mutex_unlock(&rcu_gp_lock); |
5f373c84 | 430 | _rcu_thread_online(); |
9f1621ca MD |
431 | } |
432 | ||
433 | void rcu_unregister_thread(void) | |
434 | { | |
76f3022f MD |
435 | /* |
436 | * We have to make the thread offline otherwise we end up dealocking | |
437 | * with a waiting writer. | |
438 | */ | |
439 | _rcu_thread_offline(); | |
6abb4bd5 | 440 | mutex_lock(&rcu_gp_lock); |
bd252a04 | 441 | cds_list_del(&URCU_TLS(rcu_reader).node); |
6abb4bd5 | 442 | mutex_unlock(&rcu_gp_lock); |
9f1621ca | 443 | } |
f6d18c64 MD |
444 | |
445 | void rcu_exit(void) | |
446 | { | |
01cadde4 MD |
447 | /* |
448 | * Assertion disabled because call_rcu threads are now rcu | |
449 | * readers, and left running at exit. | |
450 | * assert(cds_list_empty(®istry)); | |
451 | */ | |
f6d18c64 | 452 | } |
5e77fc1f | 453 | |
5e6b23a6 | 454 | DEFINE_RCU_FLAVOR(rcu_flavor); |
541d828d | 455 | |
5e77fc1f | 456 | #include "urcu-call-rcu-impl.h" |
0376e7b2 | 457 | #include "urcu-defer-impl.h" |