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 MD |
45 | #include "urcu-die.h" |
46 | ||
9f1621ca | 47 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
71c811bf | 48 | #undef _LGPL_SOURCE |
7ac06cef | 49 | #include "urcu-qsbr.h" |
71c811bf | 50 | #define _LGPL_SOURCE |
9f1621ca | 51 | |
f6d18c64 MD |
52 | void __attribute__((destructor)) rcu_exit(void); |
53 | ||
6abb4bd5 | 54 | static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; |
9f1621ca | 55 | |
1de4df4b | 56 | int32_t rcu_gp_futex; |
bc6c15bb | 57 | |
9f1621ca MD |
58 | /* |
59 | * Global grace period counter. | |
60 | */ | |
02be5561 | 61 | unsigned long rcu_gp_ctr = RCU_GP_ONLINE; |
9f1621ca | 62 | |
408f6d92 PB |
63 | /* |
64 | * Active attempts to check for reader Q.S. before calling futex(). | |
65 | */ | |
66 | #define RCU_QS_ACTIVE_ATTEMPTS 100 | |
67 | ||
9f1621ca MD |
68 | /* |
69 | * Written to only by each individual reader. Read by both the reader and the | |
70 | * writers. | |
71 | */ | |
bd252a04 | 72 | DEFINE_URCU_TLS(struct rcu_reader, rcu_reader); |
9f1621ca MD |
73 | |
74 | #ifdef DEBUG_YIELD | |
1de4df4b MD |
75 | unsigned int rcu_yield_active; |
76 | DEFINE_URCU_TLS(unsigned int, rcu_rand_yield); | |
9f1621ca MD |
77 | #endif |
78 | ||
16aa9ee8 | 79 | static CDS_LIST_HEAD(registry); |
9f1621ca | 80 | |
6abb4bd5 | 81 | static void mutex_lock(pthread_mutex_t *mutex) |
9f1621ca MD |
82 | { |
83 | int ret; | |
84 | ||
85 | #ifndef DISTRUST_SIGNALS_EXTREME | |
6abb4bd5 | 86 | ret = pthread_mutex_lock(mutex); |
4a6d7378 MD |
87 | if (ret) |
88 | urcu_die(ret); | |
9f1621ca | 89 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ |
6abb4bd5 | 90 | while ((ret = pthread_mutex_trylock(mutex)) != 0) { |
4a6d7378 MD |
91 | if (ret != EBUSY && ret != EINTR) |
92 | urcu_die(ret); | |
9f1621ca MD |
93 | poll(NULL,0,10); |
94 | } | |
95 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
96 | } | |
97 | ||
6abb4bd5 | 98 | static void mutex_unlock(pthread_mutex_t *mutex) |
9f1621ca MD |
99 | { |
100 | int ret; | |
101 | ||
6abb4bd5 | 102 | ret = pthread_mutex_unlock(mutex); |
4a6d7378 MD |
103 | if (ret) |
104 | urcu_die(ret); | |
9f1621ca MD |
105 | } |
106 | ||
bc6c15bb MD |
107 | /* |
108 | * synchronize_rcu() waiting. Single thread. | |
109 | */ | |
4d703340 | 110 | static void wait_gp(void) |
bc6c15bb | 111 | { |
4d703340 | 112 | /* Read reader_gp before read futex */ |
5481ddb3 | 113 | cmm_smp_rmb(); |
1de4df4b MD |
114 | if (uatomic_read(&rcu_gp_futex) == -1) |
115 | futex_noasync(&rcu_gp_futex, FUTEX_WAIT, -1, | |
4d703340 | 116 | NULL, NULL, 0); |
bc6c15bb MD |
117 | } |
118 | ||
708d89f0 MD |
119 | static void wait_for_readers(struct cds_list_head *input_readers, |
120 | struct cds_list_head *cur_snap_readers, | |
121 | struct cds_list_head *qsreaders) | |
9f1621ca | 122 | { |
4d703340 | 123 | int wait_loops = 0; |
02be5561 | 124 | struct rcu_reader *index, *tmp; |
9f1621ca | 125 | |
9f1621ca | 126 | /* |
f6b42f9c MD |
127 | * Wait for each thread URCU_TLS(rcu_reader).ctr to either |
128 | * indicate quiescence (offline), or for them to observe the | |
129 | * current rcu_gp_ctr value. | |
9f1621ca | 130 | */ |
4d703340 MD |
131 | for (;;) { |
132 | wait_loops++; | |
83a2c421 | 133 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
1de4df4b | 134 | uatomic_set(&rcu_gp_futex, -1); |
83a2c421 PB |
135 | /* |
136 | * Write futex before write waiting (the other side | |
137 | * reads them in the opposite order). | |
138 | */ | |
139 | cmm_smp_wmb(); | |
708d89f0 | 140 | cds_list_for_each_entry(index, input_readers, node) { |
83a2c421 PB |
141 | _CMM_STORE_SHARED(index->waiting, 1); |
142 | } | |
4d703340 | 143 | /* Write futex before read reader_gp */ |
5481ddb3 | 144 | cmm_smp_mb(); |
4d703340 | 145 | } |
708d89f0 MD |
146 | cds_list_for_each_entry_safe(index, tmp, input_readers, node) { |
147 | switch (rcu_reader_state(&index->ctr)) { | |
148 | case RCU_READER_ACTIVE_CURRENT: | |
149 | if (cur_snap_readers) { | |
150 | cds_list_move(&index->node, | |
151 | cur_snap_readers); | |
152 | break; | |
153 | } | |
154 | /* Fall-through */ | |
155 | case RCU_READER_INACTIVE: | |
156 | cds_list_move(&index->node, qsreaders); | |
157 | break; | |
158 | case RCU_READER_ACTIVE_OLD: | |
159 | /* | |
160 | * Old snapshot. Leaving node in | |
161 | * input_readers will make us busy-loop | |
162 | * until the snapshot becomes current or | |
163 | * the reader becomes inactive. | |
164 | */ | |
165 | break; | |
166 | } | |
4d703340 | 167 | } |
bc6c15bb | 168 | |
708d89f0 | 169 | if (cds_list_empty(input_readers)) { |
83a2c421 | 170 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 171 | /* Read reader_gp before write futex */ |
5481ddb3 | 172 | cmm_smp_mb(); |
1de4df4b | 173 | uatomic_set(&rcu_gp_futex, 0); |
4d703340 MD |
174 | } |
175 | break; | |
176 | } else { | |
83a2c421 | 177 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 178 | wait_gp(); |
bc6c15bb | 179 | } else { |
9f1621ca | 180 | #ifndef HAS_INCOHERENT_CACHES |
06f22bdb | 181 | caa_cpu_relax(); |
9f1621ca | 182 | #else /* #ifndef HAS_INCOHERENT_CACHES */ |
5481ddb3 | 183 | cmm_smp_mb(); |
9f1621ca | 184 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ |
bc6c15bb MD |
185 | } |
186 | } | |
9f1621ca MD |
187 | } |
188 | } | |
189 | ||
47d2f29e MD |
190 | /* |
191 | * Using a two-subphases algorithm for architectures with smaller than 64-bit | |
192 | * long-size to ensure we do not encounter an overflow bug. | |
193 | */ | |
194 | ||
b39e1761 | 195 | #if (CAA_BITS_PER_LONG < 64) |
47d2f29e MD |
196 | void synchronize_rcu(void) |
197 | { | |
708d89f0 MD |
198 | CDS_LIST_HEAD(cur_snap_readers); |
199 | CDS_LIST_HEAD(qsreaders); | |
bc49c323 MD |
200 | unsigned long was_online; |
201 | ||
bd252a04 | 202 | was_online = URCU_TLS(rcu_reader).ctr; |
bc49c323 | 203 | |
47d2f29e | 204 | /* All threads should read qparity before accessing data structure |
27b940e7 PB |
205 | * where new ptr points to. In the "then" case, rcu_thread_offline |
206 | * includes a memory barrier. | |
207 | * | |
bc49c323 | 208 | * Mark the writer thread offline to make sure we don't wait for |
5e77fc1f PM |
209 | * our own quiescent state. This allows using synchronize_rcu() |
210 | * in threads registered as readers. | |
bc49c323 | 211 | */ |
27b940e7 PB |
212 | if (was_online) |
213 | rcu_thread_offline(); | |
214 | else | |
215 | cmm_smp_mb(); | |
bc49c323 | 216 | |
6abb4bd5 | 217 | mutex_lock(&rcu_gp_lock); |
47d2f29e | 218 | |
16aa9ee8 | 219 | if (cds_list_empty(®istry)) |
2dfb8b5e | 220 | goto out; |
47d2f29e MD |
221 | |
222 | /* | |
f6b42f9c | 223 | * Wait for readers to observe original parity or be quiescent. |
47d2f29e | 224 | */ |
708d89f0 | 225 | wait_for_readers(®istry, &cur_snap_readers, &qsreaders); |
47d2f29e MD |
226 | |
227 | /* | |
f6b42f9c MD |
228 | * Must finish waiting for quiescent state for original parity |
229 | * before committing next rcu_gp_ctr update to memory. Failure | |
230 | * to do so could result in the writer waiting forever while new | |
5e77fc1f | 231 | * readers are always accessing data (no progress). Enforce |
f6b42f9c MD |
232 | * compiler-order of load URCU_TLS(rcu_reader).ctr before store |
233 | * to rcu_gp_ctr. | |
47d2f29e | 234 | */ |
5481ddb3 | 235 | cmm_barrier(); |
47d2f29e | 236 | |
47d2f29e | 237 | /* |
5481ddb3 | 238 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
2dfb8b5e MD |
239 | * model easier to understand. It does not have a big performance impact |
240 | * anyway, given this is the write-side. | |
47d2f29e | 241 | */ |
5481ddb3 | 242 | cmm_smp_mb(); |
47d2f29e | 243 | |
f6b42f9c MD |
244 | /* Switch parity: 0 -> 1, 1 -> 0 */ |
245 | CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); | |
246 | ||
47d2f29e | 247 | /* |
f6b42f9c MD |
248 | * Must commit rcu_gp_ctr update to memory before waiting for |
249 | * quiescent state. Failure to do so could result in the writer | |
250 | * waiting forever while new readers are always accessing data | |
251 | * (no progress). Enforce compiler-order of store to rcu_gp_ctr | |
252 | * before load URCU_TLS(rcu_reader).ctr. | |
47d2f29e | 253 | */ |
f6b42f9c MD |
254 | cmm_barrier(); |
255 | ||
256 | /* | |
257 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the | |
258 | * model easier to understand. It does not have a big performance impact | |
259 | * anyway, given this is the write-side. | |
260 | */ | |
261 | cmm_smp_mb(); | |
262 | ||
263 | /* | |
264 | * Wait for readers to observe new parity or be quiescent. | |
265 | */ | |
708d89f0 MD |
266 | wait_for_readers(&cur_snap_readers, NULL, &qsreaders); |
267 | ||
268 | /* | |
269 | * Put quiescent reader list back into registry. | |
270 | */ | |
271 | cds_list_splice(&qsreaders, ®istry); | |
2dfb8b5e | 272 | out: |
6abb4bd5 | 273 | mutex_unlock(&rcu_gp_lock); |
47d2f29e | 274 | |
bc49c323 MD |
275 | /* |
276 | * Finish waiting for reader threads before letting the old ptr being | |
47d2f29e MD |
277 | * freed. |
278 | */ | |
bc49c323 | 279 | if (was_online) |
27b940e7 PB |
280 | rcu_thread_online(); |
281 | else | |
282 | cmm_smp_mb(); | |
47d2f29e | 283 | } |
b39e1761 | 284 | #else /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
285 | void synchronize_rcu(void) |
286 | { | |
708d89f0 | 287 | CDS_LIST_HEAD(qsreaders); |
f0f7dbdd | 288 | unsigned long was_online; |
ff2f67a0 | 289 | |
bd252a04 | 290 | was_online = URCU_TLS(rcu_reader).ctr; |
ff2f67a0 MD |
291 | |
292 | /* | |
293 | * Mark the writer thread offline to make sure we don't wait for | |
5e77fc1f PM |
294 | * our own quiescent state. This allows using synchronize_rcu() |
295 | * in threads registered as readers. | |
ff2f67a0 | 296 | */ |
27b940e7 PB |
297 | if (was_online) |
298 | rcu_thread_offline(); | |
299 | else | |
300 | cmm_smp_mb(); | |
ff2f67a0 | 301 | |
6abb4bd5 | 302 | mutex_lock(&rcu_gp_lock); |
16aa9ee8 | 303 | if (cds_list_empty(®istry)) |
2dfb8b5e | 304 | goto out; |
f6b42f9c MD |
305 | |
306 | /* Increment current G.P. */ | |
307 | CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); | |
308 | ||
309 | /* | |
310 | * Must commit rcu_gp_ctr update to memory before waiting for | |
311 | * quiescent state. Failure to do so could result in the writer | |
312 | * waiting forever while new readers are always accessing data | |
313 | * (no progress). Enforce compiler-order of store to rcu_gp_ctr | |
314 | * before load URCU_TLS(rcu_reader).ctr. | |
315 | */ | |
316 | cmm_barrier(); | |
317 | ||
318 | /* | |
319 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the | |
320 | * model easier to understand. It does not have a big performance impact | |
321 | * anyway, given this is the write-side. | |
322 | */ | |
323 | cmm_smp_mb(); | |
324 | ||
325 | /* | |
326 | * Wait for readers to observe new count of be quiescent. | |
327 | */ | |
708d89f0 MD |
328 | wait_for_readers(®istry, NULL, &qsreaders); |
329 | ||
330 | /* | |
331 | * Put quiescent reader list back into registry. | |
332 | */ | |
333 | cds_list_splice(&qsreaders, ®istry); | |
2dfb8b5e | 334 | out: |
6abb4bd5 | 335 | mutex_unlock(&rcu_gp_lock); |
ff2f67a0 MD |
336 | |
337 | if (was_online) | |
27b940e7 PB |
338 | rcu_thread_online(); |
339 | else | |
340 | cmm_smp_mb(); | |
9f1621ca | 341 | } |
b39e1761 | 342 | #endif /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
343 | |
344 | /* | |
345 | * library wrappers to be used by non-LGPL compatible source code. | |
346 | */ | |
347 | ||
348 | void rcu_read_lock(void) | |
349 | { | |
350 | _rcu_read_lock(); | |
351 | } | |
352 | ||
353 | void rcu_read_unlock(void) | |
354 | { | |
355 | _rcu_read_unlock(); | |
356 | } | |
357 | ||
7ac06cef MD |
358 | void rcu_quiescent_state(void) |
359 | { | |
360 | _rcu_quiescent_state(); | |
361 | } | |
362 | ||
363 | void rcu_thread_offline(void) | |
364 | { | |
365 | _rcu_thread_offline(); | |
366 | } | |
367 | ||
368 | void rcu_thread_online(void) | |
369 | { | |
370 | _rcu_thread_online(); | |
371 | } | |
372 | ||
9f1621ca MD |
373 | void rcu_register_thread(void) |
374 | { | |
bd252a04 MD |
375 | URCU_TLS(rcu_reader).tid = pthread_self(); |
376 | assert(URCU_TLS(rcu_reader).ctr == 0); | |
4f8e3380 | 377 | |
6abb4bd5 | 378 | mutex_lock(&rcu_gp_lock); |
bd252a04 | 379 | cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); |
6abb4bd5 | 380 | mutex_unlock(&rcu_gp_lock); |
5f373c84 | 381 | _rcu_thread_online(); |
9f1621ca MD |
382 | } |
383 | ||
384 | void rcu_unregister_thread(void) | |
385 | { | |
76f3022f MD |
386 | /* |
387 | * We have to make the thread offline otherwise we end up dealocking | |
388 | * with a waiting writer. | |
389 | */ | |
390 | _rcu_thread_offline(); | |
6abb4bd5 | 391 | mutex_lock(&rcu_gp_lock); |
bd252a04 | 392 | cds_list_del(&URCU_TLS(rcu_reader).node); |
6abb4bd5 | 393 | mutex_unlock(&rcu_gp_lock); |
9f1621ca | 394 | } |
f6d18c64 MD |
395 | |
396 | void rcu_exit(void) | |
397 | { | |
01cadde4 MD |
398 | /* |
399 | * Assertion disabled because call_rcu threads are now rcu | |
400 | * readers, and left running at exit. | |
401 | * assert(cds_list_empty(®istry)); | |
402 | */ | |
f6d18c64 | 403 | } |
5e77fc1f | 404 | |
5e6b23a6 | 405 | DEFINE_RCU_FLAVOR(rcu_flavor); |
541d828d | 406 | |
5e77fc1f | 407 | #include "urcu-call-rcu-impl.h" |
0376e7b2 | 408 | #include "urcu-defer-impl.h" |