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 | 68 | |
16aa9ee8 | 69 | static CDS_LIST_HEAD(registry); |
9f1621ca | 70 | |
6362f68f | 71 | /* |
bf6822a6 | 72 | * Queue keeping threads awaiting to wait for a grace period. Contains |
6362f68f MD |
73 | * struct gp_waiters_thread objects. |
74 | */ | |
bf6822a6 | 75 | static DEFINE_URCU_WAIT_QUEUE(gp_waiters); |
6362f68f | 76 | |
6abb4bd5 | 77 | static void mutex_lock(pthread_mutex_t *mutex) |
9f1621ca MD |
78 | { |
79 | int ret; | |
80 | ||
81 | #ifndef DISTRUST_SIGNALS_EXTREME | |
6abb4bd5 | 82 | ret = pthread_mutex_lock(mutex); |
4a6d7378 MD |
83 | if (ret) |
84 | urcu_die(ret); | |
9f1621ca | 85 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ |
6abb4bd5 | 86 | while ((ret = pthread_mutex_trylock(mutex)) != 0) { |
4a6d7378 MD |
87 | if (ret != EBUSY && ret != EINTR) |
88 | urcu_die(ret); | |
9f1621ca MD |
89 | poll(NULL,0,10); |
90 | } | |
91 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
92 | } | |
93 | ||
6abb4bd5 | 94 | static void mutex_unlock(pthread_mutex_t *mutex) |
9f1621ca MD |
95 | { |
96 | int ret; | |
97 | ||
6abb4bd5 | 98 | ret = pthread_mutex_unlock(mutex); |
4a6d7378 MD |
99 | if (ret) |
100 | urcu_die(ret); | |
9f1621ca MD |
101 | } |
102 | ||
bc6c15bb MD |
103 | /* |
104 | * synchronize_rcu() waiting. Single thread. | |
105 | */ | |
4d703340 | 106 | static void wait_gp(void) |
bc6c15bb | 107 | { |
4d703340 | 108 | /* Read reader_gp before read futex */ |
5481ddb3 | 109 | cmm_smp_rmb(); |
15302e28 LJ |
110 | if (uatomic_read(&rcu_gp.futex) == -1) |
111 | futex_noasync(&rcu_gp.futex, FUTEX_WAIT, -1, | |
4d703340 | 112 | NULL, NULL, 0); |
bc6c15bb MD |
113 | } |
114 | ||
708d89f0 MD |
115 | static void wait_for_readers(struct cds_list_head *input_readers, |
116 | struct cds_list_head *cur_snap_readers, | |
117 | struct cds_list_head *qsreaders) | |
9f1621ca | 118 | { |
9340c38d | 119 | unsigned int wait_loops = 0; |
02be5561 | 120 | struct rcu_reader *index, *tmp; |
9f1621ca | 121 | |
9f1621ca | 122 | /* |
f6b42f9c MD |
123 | * Wait for each thread URCU_TLS(rcu_reader).ctr to either |
124 | * indicate quiescence (offline), or for them to observe the | |
15302e28 | 125 | * current rcu_gp.ctr value. |
9f1621ca | 126 | */ |
4d703340 | 127 | for (;;) { |
5e81fed7 MD |
128 | if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS) |
129 | wait_loops++; | |
83a2c421 | 130 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
15302e28 | 131 | uatomic_set(&rcu_gp.futex, -1); |
83a2c421 PB |
132 | /* |
133 | * Write futex before write waiting (the other side | |
134 | * reads them in the opposite order). | |
135 | */ | |
136 | cmm_smp_wmb(); | |
708d89f0 | 137 | cds_list_for_each_entry(index, input_readers, node) { |
83a2c421 PB |
138 | _CMM_STORE_SHARED(index->waiting, 1); |
139 | } | |
4d703340 | 140 | /* Write futex before read reader_gp */ |
5481ddb3 | 141 | cmm_smp_mb(); |
4d703340 | 142 | } |
708d89f0 MD |
143 | cds_list_for_each_entry_safe(index, tmp, input_readers, node) { |
144 | switch (rcu_reader_state(&index->ctr)) { | |
145 | case RCU_READER_ACTIVE_CURRENT: | |
146 | if (cur_snap_readers) { | |
147 | cds_list_move(&index->node, | |
148 | cur_snap_readers); | |
149 | break; | |
150 | } | |
151 | /* Fall-through */ | |
152 | case RCU_READER_INACTIVE: | |
153 | cds_list_move(&index->node, qsreaders); | |
154 | break; | |
155 | case RCU_READER_ACTIVE_OLD: | |
156 | /* | |
157 | * Old snapshot. Leaving node in | |
158 | * input_readers will make us busy-loop | |
159 | * until the snapshot becomes current or | |
160 | * the reader becomes inactive. | |
161 | */ | |
162 | break; | |
163 | } | |
4d703340 | 164 | } |
bc6c15bb | 165 | |
708d89f0 | 166 | if (cds_list_empty(input_readers)) { |
83a2c421 | 167 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 168 | /* Read reader_gp before write futex */ |
5481ddb3 | 169 | cmm_smp_mb(); |
15302e28 | 170 | uatomic_set(&rcu_gp.futex, 0); |
4d703340 MD |
171 | } |
172 | break; | |
173 | } else { | |
83a2c421 | 174 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 175 | wait_gp(); |
bc6c15bb | 176 | } else { |
9f1621ca | 177 | #ifndef HAS_INCOHERENT_CACHES |
06f22bdb | 178 | caa_cpu_relax(); |
9f1621ca | 179 | #else /* #ifndef HAS_INCOHERENT_CACHES */ |
5481ddb3 | 180 | cmm_smp_mb(); |
9f1621ca | 181 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ |
bc6c15bb MD |
182 | } |
183 | } | |
9f1621ca MD |
184 | } |
185 | } | |
186 | ||
47d2f29e MD |
187 | /* |
188 | * Using a two-subphases algorithm for architectures with smaller than 64-bit | |
189 | * long-size to ensure we do not encounter an overflow bug. | |
190 | */ | |
191 | ||
b39e1761 | 192 | #if (CAA_BITS_PER_LONG < 64) |
47d2f29e MD |
193 | void synchronize_rcu(void) |
194 | { | |
708d89f0 MD |
195 | CDS_LIST_HEAD(cur_snap_readers); |
196 | CDS_LIST_HEAD(qsreaders); | |
bc49c323 | 197 | unsigned long was_online; |
bf6822a6 MD |
198 | DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); |
199 | struct urcu_waiters waiters; | |
bc49c323 | 200 | |
882f3357 | 201 | was_online = rcu_read_ongoing(); |
bc49c323 | 202 | |
47d2f29e | 203 | /* All threads should read qparity before accessing data structure |
27b940e7 PB |
204 | * where new ptr points to. In the "then" case, rcu_thread_offline |
205 | * includes a memory barrier. | |
206 | * | |
bc49c323 | 207 | * Mark the writer thread offline to make sure we don't wait for |
5e77fc1f PM |
208 | * our own quiescent state. This allows using synchronize_rcu() |
209 | * in threads registered as readers. | |
bc49c323 | 210 | */ |
27b940e7 PB |
211 | if (was_online) |
212 | rcu_thread_offline(); | |
213 | else | |
214 | cmm_smp_mb(); | |
bc49c323 | 215 | |
6362f68f | 216 | /* |
bf6822a6 | 217 | * Add ourself to gp_waiters queue of threads awaiting to wait |
6362f68f | 218 | * for a grace period. Proceed to perform the grace period only |
bf6822a6 | 219 | * if we are the first thread added into the queue. |
6362f68f | 220 | */ |
bf6822a6 MD |
221 | if (urcu_wait_add(&gp_waiters, &wait) != 0) { |
222 | /* Not first in queue: will be awakened by another thread. */ | |
223 | urcu_adaptative_busy_wait(&wait); | |
6362f68f MD |
224 | goto gp_end; |
225 | } | |
bf6822a6 MD |
226 | /* We won't need to wake ourself up */ |
227 | urcu_wait_set_state(&wait, URCU_WAIT_RUNNING); | |
6362f68f | 228 | |
6abb4bd5 | 229 | mutex_lock(&rcu_gp_lock); |
47d2f29e | 230 | |
6362f68f | 231 | /* |
bf6822a6 | 232 | * Move all waiters into our local queue. |
6362f68f | 233 | */ |
bf6822a6 | 234 | urcu_move_waiters(&waiters, &gp_waiters); |
6362f68f | 235 | |
16aa9ee8 | 236 | if (cds_list_empty(®istry)) |
2dfb8b5e | 237 | goto out; |
47d2f29e MD |
238 | |
239 | /* | |
f6b42f9c | 240 | * Wait for readers to observe original parity or be quiescent. |
47d2f29e | 241 | */ |
708d89f0 | 242 | wait_for_readers(®istry, &cur_snap_readers, &qsreaders); |
47d2f29e MD |
243 | |
244 | /* | |
f6b42f9c | 245 | * Must finish waiting for quiescent state for original parity |
15302e28 | 246 | * before committing next rcu_gp.ctr update to memory. Failure |
f6b42f9c | 247 | * to do so could result in the writer waiting forever while new |
5e77fc1f | 248 | * readers are always accessing data (no progress). Enforce |
f6b42f9c | 249 | * compiler-order of load URCU_TLS(rcu_reader).ctr before store |
15302e28 | 250 | * to rcu_gp.ctr. |
47d2f29e | 251 | */ |
5481ddb3 | 252 | cmm_barrier(); |
47d2f29e | 253 | |
47d2f29e | 254 | /* |
5481ddb3 | 255 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
2dfb8b5e MD |
256 | * model easier to understand. It does not have a big performance impact |
257 | * anyway, given this is the write-side. | |
47d2f29e | 258 | */ |
5481ddb3 | 259 | cmm_smp_mb(); |
47d2f29e | 260 | |
f6b42f9c | 261 | /* Switch parity: 0 -> 1, 1 -> 0 */ |
15302e28 | 262 | CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR); |
f6b42f9c | 263 | |
47d2f29e | 264 | /* |
15302e28 | 265 | * Must commit rcu_gp.ctr update to memory before waiting for |
f6b42f9c MD |
266 | * quiescent state. Failure to do so could result in the writer |
267 | * waiting forever while new readers are always accessing data | |
15302e28 | 268 | * (no progress). Enforce compiler-order of store to rcu_gp.ctr |
f6b42f9c | 269 | * before load URCU_TLS(rcu_reader).ctr. |
47d2f29e | 270 | */ |
f6b42f9c MD |
271 | cmm_barrier(); |
272 | ||
273 | /* | |
274 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the | |
275 | * model easier to understand. It does not have a big performance impact | |
276 | * anyway, given this is the write-side. | |
277 | */ | |
278 | cmm_smp_mb(); | |
279 | ||
280 | /* | |
281 | * Wait for readers to observe new parity or be quiescent. | |
282 | */ | |
708d89f0 MD |
283 | wait_for_readers(&cur_snap_readers, NULL, &qsreaders); |
284 | ||
285 | /* | |
286 | * Put quiescent reader list back into registry. | |
287 | */ | |
288 | cds_list_splice(&qsreaders, ®istry); | |
2dfb8b5e | 289 | out: |
6abb4bd5 | 290 | mutex_unlock(&rcu_gp_lock); |
bf6822a6 | 291 | urcu_wake_all_waiters(&waiters); |
6362f68f | 292 | gp_end: |
bc49c323 MD |
293 | /* |
294 | * Finish waiting for reader threads before letting the old ptr being | |
47d2f29e MD |
295 | * freed. |
296 | */ | |
bc49c323 | 297 | if (was_online) |
27b940e7 PB |
298 | rcu_thread_online(); |
299 | else | |
300 | cmm_smp_mb(); | |
47d2f29e | 301 | } |
b39e1761 | 302 | #else /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
303 | void synchronize_rcu(void) |
304 | { | |
708d89f0 | 305 | CDS_LIST_HEAD(qsreaders); |
f0f7dbdd | 306 | unsigned long was_online; |
bf6822a6 MD |
307 | DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING); |
308 | struct urcu_waiters waiters; | |
ff2f67a0 | 309 | |
882f3357 | 310 | was_online = rcu_read_ongoing(); |
ff2f67a0 MD |
311 | |
312 | /* | |
313 | * Mark the writer thread offline to make sure we don't wait for | |
5e77fc1f PM |
314 | * our own quiescent state. This allows using synchronize_rcu() |
315 | * in threads registered as readers. | |
ff2f67a0 | 316 | */ |
27b940e7 PB |
317 | if (was_online) |
318 | rcu_thread_offline(); | |
319 | else | |
320 | cmm_smp_mb(); | |
ff2f67a0 | 321 | |
6362f68f | 322 | /* |
bf6822a6 | 323 | * Add ourself to gp_waiters queue of threads awaiting to wait |
6362f68f | 324 | * for a grace period. Proceed to perform the grace period only |
bf6822a6 | 325 | * if we are the first thread added into the queue. |
6362f68f | 326 | */ |
bf6822a6 MD |
327 | if (urcu_wait_add(&gp_waiters, &wait) != 0) { |
328 | /* Not first in queue: will be awakened by another thread. */ | |
329 | urcu_adaptative_busy_wait(&wait); | |
6362f68f MD |
330 | goto gp_end; |
331 | } | |
bf6822a6 MD |
332 | /* We won't need to wake ourself up */ |
333 | urcu_wait_set_state(&wait, URCU_WAIT_RUNNING); | |
6362f68f | 334 | |
6abb4bd5 | 335 | mutex_lock(&rcu_gp_lock); |
6362f68f MD |
336 | |
337 | /* | |
bf6822a6 | 338 | * Move all waiters into our local queue. |
6362f68f | 339 | */ |
bf6822a6 | 340 | urcu_move_waiters(&waiters, &gp_waiters); |
6362f68f | 341 | |
16aa9ee8 | 342 | if (cds_list_empty(®istry)) |
2dfb8b5e | 343 | goto out; |
f6b42f9c MD |
344 | |
345 | /* Increment current G.P. */ | |
15302e28 | 346 | CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr + RCU_GP_CTR); |
f6b42f9c MD |
347 | |
348 | /* | |
15302e28 | 349 | * Must commit rcu_gp.ctr update to memory before waiting for |
f6b42f9c MD |
350 | * quiescent state. Failure to do so could result in the writer |
351 | * waiting forever while new readers are always accessing data | |
15302e28 | 352 | * (no progress). Enforce compiler-order of store to rcu_gp.ctr |
f6b42f9c MD |
353 | * before load URCU_TLS(rcu_reader).ctr. |
354 | */ | |
355 | cmm_barrier(); | |
356 | ||
357 | /* | |
358 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the | |
359 | * model easier to understand. It does not have a big performance impact | |
360 | * anyway, given this is the write-side. | |
361 | */ | |
362 | cmm_smp_mb(); | |
363 | ||
364 | /* | |
365 | * Wait for readers to observe new count of be quiescent. | |
366 | */ | |
708d89f0 MD |
367 | wait_for_readers(®istry, NULL, &qsreaders); |
368 | ||
369 | /* | |
370 | * Put quiescent reader list back into registry. | |
371 | */ | |
372 | cds_list_splice(&qsreaders, ®istry); | |
2dfb8b5e | 373 | out: |
6abb4bd5 | 374 | mutex_unlock(&rcu_gp_lock); |
bf6822a6 | 375 | urcu_wake_all_waiters(&waiters); |
6362f68f | 376 | gp_end: |
ff2f67a0 | 377 | if (was_online) |
27b940e7 PB |
378 | rcu_thread_online(); |
379 | else | |
380 | cmm_smp_mb(); | |
9f1621ca | 381 | } |
b39e1761 | 382 | #endif /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
383 | |
384 | /* | |
385 | * library wrappers to be used by non-LGPL compatible source code. | |
386 | */ | |
387 | ||
388 | void rcu_read_lock(void) | |
389 | { | |
390 | _rcu_read_lock(); | |
391 | } | |
392 | ||
393 | void rcu_read_unlock(void) | |
394 | { | |
395 | _rcu_read_unlock(); | |
396 | } | |
397 | ||
882f3357 MD |
398 | int rcu_read_ongoing(void) |
399 | { | |
400 | return _rcu_read_ongoing(); | |
401 | } | |
402 | ||
7ac06cef MD |
403 | void rcu_quiescent_state(void) |
404 | { | |
405 | _rcu_quiescent_state(); | |
406 | } | |
407 | ||
408 | void rcu_thread_offline(void) | |
409 | { | |
410 | _rcu_thread_offline(); | |
411 | } | |
412 | ||
413 | void rcu_thread_online(void) | |
414 | { | |
415 | _rcu_thread_online(); | |
416 | } | |
417 | ||
9f1621ca MD |
418 | void rcu_register_thread(void) |
419 | { | |
bd252a04 MD |
420 | URCU_TLS(rcu_reader).tid = pthread_self(); |
421 | assert(URCU_TLS(rcu_reader).ctr == 0); | |
4f8e3380 | 422 | |
6abb4bd5 | 423 | mutex_lock(&rcu_gp_lock); |
bd252a04 | 424 | cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); |
6abb4bd5 | 425 | mutex_unlock(&rcu_gp_lock); |
5f373c84 | 426 | _rcu_thread_online(); |
9f1621ca MD |
427 | } |
428 | ||
429 | void rcu_unregister_thread(void) | |
430 | { | |
76f3022f MD |
431 | /* |
432 | * We have to make the thread offline otherwise we end up dealocking | |
433 | * with a waiting writer. | |
434 | */ | |
435 | _rcu_thread_offline(); | |
6abb4bd5 | 436 | mutex_lock(&rcu_gp_lock); |
bd252a04 | 437 | cds_list_del(&URCU_TLS(rcu_reader).node); |
6abb4bd5 | 438 | mutex_unlock(&rcu_gp_lock); |
9f1621ca | 439 | } |
f6d18c64 MD |
440 | |
441 | void rcu_exit(void) | |
442 | { | |
01cadde4 MD |
443 | /* |
444 | * Assertion disabled because call_rcu threads are now rcu | |
445 | * readers, and left running at exit. | |
446 | * assert(cds_list_empty(®istry)); | |
447 | */ | |
f6d18c64 | 448 | } |
5e77fc1f | 449 | |
5e6b23a6 | 450 | DEFINE_RCU_FLAVOR(rcu_flavor); |
541d828d | 451 | |
5e77fc1f | 452 | #include "urcu-call-rcu-impl.h" |
0376e7b2 | 453 | #include "urcu-defer-impl.h" |