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 | ||
71c811bf | 38 | #include "urcu/wfqueue.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" |
71c811bf | 43 | |
9f1621ca | 44 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
71c811bf | 45 | #undef _LGPL_SOURCE |
7ac06cef | 46 | #include "urcu-qsbr.h" |
71c811bf | 47 | #define _LGPL_SOURCE |
9f1621ca | 48 | |
f6d18c64 MD |
49 | void __attribute__((destructor)) rcu_exit(void); |
50 | ||
6abb4bd5 | 51 | static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; |
9f1621ca | 52 | |
6d841bc2 | 53 | int32_t gp_futex; |
bc6c15bb | 54 | |
9f1621ca MD |
55 | /* |
56 | * Global grace period counter. | |
57 | */ | |
02be5561 | 58 | unsigned long rcu_gp_ctr = RCU_GP_ONLINE; |
9f1621ca | 59 | |
408f6d92 PB |
60 | /* |
61 | * Active attempts to check for reader Q.S. before calling futex(). | |
62 | */ | |
63 | #define RCU_QS_ACTIVE_ATTEMPTS 100 | |
64 | ||
9f1621ca MD |
65 | /* |
66 | * Written to only by each individual reader. Read by both the reader and the | |
67 | * writers. | |
68 | */ | |
02be5561 | 69 | struct rcu_reader __thread rcu_reader; |
9f1621ca MD |
70 | |
71 | #ifdef DEBUG_YIELD | |
72 | unsigned int yield_active; | |
73 | unsigned int __thread rand_yield; | |
74 | #endif | |
75 | ||
16aa9ee8 | 76 | static CDS_LIST_HEAD(registry); |
9f1621ca | 77 | |
6abb4bd5 | 78 | static void mutex_lock(pthread_mutex_t *mutex) |
9f1621ca MD |
79 | { |
80 | int ret; | |
81 | ||
82 | #ifndef DISTRUST_SIGNALS_EXTREME | |
6abb4bd5 | 83 | ret = pthread_mutex_lock(mutex); |
9f1621ca MD |
84 | if (ret) { |
85 | perror("Error in pthread mutex lock"); | |
86 | exit(-1); | |
87 | } | |
88 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ | |
6abb4bd5 | 89 | while ((ret = pthread_mutex_trylock(mutex)) != 0) { |
9f1621ca MD |
90 | if (ret != EBUSY && ret != EINTR) { |
91 | printf("ret = %d, errno = %d\n", ret, errno); | |
92 | perror("Error in pthread mutex lock"); | |
93 | exit(-1); | |
94 | } | |
9f1621ca MD |
95 | poll(NULL,0,10); |
96 | } | |
97 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
98 | } | |
99 | ||
6abb4bd5 | 100 | static void mutex_unlock(pthread_mutex_t *mutex) |
9f1621ca MD |
101 | { |
102 | int ret; | |
103 | ||
6abb4bd5 | 104 | ret = pthread_mutex_unlock(mutex); |
9f1621ca MD |
105 | if (ret) { |
106 | perror("Error in pthread mutex unlock"); | |
107 | exit(-1); | |
108 | } | |
109 | } | |
110 | ||
bc6c15bb MD |
111 | /* |
112 | * synchronize_rcu() waiting. Single thread. | |
113 | */ | |
4d703340 | 114 | static void wait_gp(void) |
bc6c15bb | 115 | { |
4d703340 | 116 | /* Read reader_gp before read futex */ |
5481ddb3 | 117 | cmm_smp_rmb(); |
4d703340 | 118 | if (uatomic_read(&gp_futex) == -1) |
0854ccff | 119 | futex_noasync(&gp_futex, FUTEX_WAIT, -1, |
4d703340 | 120 | NULL, NULL, 0); |
bc6c15bb MD |
121 | } |
122 | ||
2dfb8b5e | 123 | static void update_counter_and_wait(void) |
9f1621ca | 124 | { |
16aa9ee8 | 125 | CDS_LIST_HEAD(qsreaders); |
4d703340 | 126 | int wait_loops = 0; |
02be5561 | 127 | struct rcu_reader *index, *tmp; |
9f1621ca | 128 | |
b39e1761 | 129 | #if (CAA_BITS_PER_LONG < 64) |
32c15e4e | 130 | /* Switch parity: 0 -> 1, 1 -> 0 */ |
6cf3827c | 131 | CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); |
b39e1761 | 132 | #else /* !(CAA_BITS_PER_LONG < 64) */ |
2dfb8b5e | 133 | /* Increment current G.P. */ |
6cf3827c | 134 | CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); |
b39e1761 | 135 | #endif /* !(CAA_BITS_PER_LONG < 64) */ |
2dfb8b5e | 136 | |
7a5a38f5 | 137 | /* |
5e77fc1f PM |
138 | * Must commit rcu_gp_ctr update to memory before waiting for |
139 | * quiescent state. Failure to do so could result in the writer | |
140 | * waiting forever while new readers are always accessing data | |
141 | * (no progress). Enforce compiler-order of store to rcu_gp_ctr | |
142 | * before load rcu_reader ctr. | |
d40fde2c | 143 | */ |
5481ddb3 | 144 | cmm_barrier(); |
d40fde2c MD |
145 | |
146 | /* | |
5481ddb3 | 147 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
935b11ff MD |
148 | * model easier to understand. It does not have a big performance impact |
149 | * anyway, given this is the write-side. | |
7a5a38f5 | 150 | */ |
5481ddb3 | 151 | cmm_smp_mb(); |
7a5a38f5 | 152 | |
9f1621ca | 153 | /* |
3395d46c | 154 | * Wait for each thread rcu_reader_qs_gp count to become 0. |
9f1621ca | 155 | */ |
4d703340 MD |
156 | for (;;) { |
157 | wait_loops++; | |
83a2c421 PB |
158 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
159 | uatomic_set(&gp_futex, -1); | |
160 | /* | |
161 | * Write futex before write waiting (the other side | |
162 | * reads them in the opposite order). | |
163 | */ | |
164 | cmm_smp_wmb(); | |
165 | cds_list_for_each_entry(index, ®istry, node) { | |
166 | _CMM_STORE_SHARED(index->waiting, 1); | |
167 | } | |
4d703340 | 168 | /* Write futex before read reader_gp */ |
5481ddb3 | 169 | cmm_smp_mb(); |
4d703340 | 170 | } |
16aa9ee8 | 171 | cds_list_for_each_entry_safe(index, tmp, ®istry, node) { |
4d703340 | 172 | if (!rcu_gp_ongoing(&index->ctr)) |
16aa9ee8 | 173 | cds_list_move(&index->node, &qsreaders); |
4d703340 | 174 | } |
bc6c15bb | 175 | |
16aa9ee8 | 176 | if (cds_list_empty(®istry)) { |
83a2c421 | 177 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 178 | /* Read reader_gp before write futex */ |
5481ddb3 | 179 | cmm_smp_mb(); |
4d703340 MD |
180 | uatomic_set(&gp_futex, 0); |
181 | } | |
182 | break; | |
183 | } else { | |
83a2c421 | 184 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 185 | wait_gp(); |
bc6c15bb | 186 | } else { |
9f1621ca | 187 | #ifndef HAS_INCOHERENT_CACHES |
06f22bdb | 188 | caa_cpu_relax(); |
9f1621ca | 189 | #else /* #ifndef HAS_INCOHERENT_CACHES */ |
5481ddb3 | 190 | cmm_smp_mb(); |
9f1621ca | 191 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ |
bc6c15bb MD |
192 | } |
193 | } | |
9f1621ca | 194 | } |
4d703340 | 195 | /* put back the reader list in the registry */ |
16aa9ee8 | 196 | cds_list_splice(&qsreaders, ®istry); |
9f1621ca MD |
197 | } |
198 | ||
47d2f29e MD |
199 | /* |
200 | * Using a two-subphases algorithm for architectures with smaller than 64-bit | |
201 | * long-size to ensure we do not encounter an overflow bug. | |
202 | */ | |
203 | ||
b39e1761 | 204 | #if (CAA_BITS_PER_LONG < 64) |
47d2f29e MD |
205 | void synchronize_rcu(void) |
206 | { | |
bc49c323 MD |
207 | unsigned long was_online; |
208 | ||
02be5561 | 209 | was_online = rcu_reader.ctr; |
bc49c323 | 210 | |
47d2f29e | 211 | /* All threads should read qparity before accessing data structure |
27b940e7 PB |
212 | * where new ptr points to. In the "then" case, rcu_thread_offline |
213 | * includes a memory barrier. | |
214 | * | |
bc49c323 | 215 | * Mark the writer thread offline to make sure we don't wait for |
5e77fc1f PM |
216 | * our own quiescent state. This allows using synchronize_rcu() |
217 | * in threads registered as readers. | |
bc49c323 | 218 | */ |
27b940e7 PB |
219 | if (was_online) |
220 | rcu_thread_offline(); | |
221 | else | |
222 | cmm_smp_mb(); | |
bc49c323 | 223 | |
6abb4bd5 | 224 | mutex_lock(&rcu_gp_lock); |
47d2f29e | 225 | |
16aa9ee8 | 226 | if (cds_list_empty(®istry)) |
2dfb8b5e | 227 | goto out; |
47d2f29e MD |
228 | |
229 | /* | |
230 | * Wait for previous parity to be empty of readers. | |
231 | */ | |
2dfb8b5e | 232 | update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ |
47d2f29e MD |
233 | |
234 | /* | |
235 | * Must finish waiting for quiescent state for parity 0 before | |
5e77fc1f PM |
236 | * committing next rcu_gp_ctr update to memory. Failure to |
237 | * do so could result in the writer waiting forever while new | |
238 | * readers are always accessing data (no progress). Enforce | |
239 | * compiler-order of load rcu_reader ctr before store to | |
240 | * rcu_gp_ctr. | |
47d2f29e | 241 | */ |
5481ddb3 | 242 | cmm_barrier(); |
47d2f29e | 243 | |
47d2f29e | 244 | /* |
5481ddb3 | 245 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
2dfb8b5e MD |
246 | * model easier to understand. It does not have a big performance impact |
247 | * anyway, given this is the write-side. | |
47d2f29e | 248 | */ |
5481ddb3 | 249 | cmm_smp_mb(); |
47d2f29e MD |
250 | |
251 | /* | |
252 | * Wait for previous parity to be empty of readers. | |
253 | */ | |
2dfb8b5e MD |
254 | update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ |
255 | out: | |
6abb4bd5 | 256 | mutex_unlock(&rcu_gp_lock); |
47d2f29e | 257 | |
bc49c323 MD |
258 | /* |
259 | * Finish waiting for reader threads before letting the old ptr being | |
47d2f29e MD |
260 | * freed. |
261 | */ | |
bc49c323 | 262 | if (was_online) |
27b940e7 PB |
263 | rcu_thread_online(); |
264 | else | |
265 | cmm_smp_mb(); | |
47d2f29e | 266 | } |
b39e1761 | 267 | #else /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
268 | void synchronize_rcu(void) |
269 | { | |
f0f7dbdd | 270 | unsigned long was_online; |
ff2f67a0 | 271 | |
02be5561 | 272 | was_online = rcu_reader.ctr; |
ff2f67a0 MD |
273 | |
274 | /* | |
275 | * Mark the writer thread offline to make sure we don't wait for | |
5e77fc1f PM |
276 | * our own quiescent state. This allows using synchronize_rcu() |
277 | * in threads registered as readers. | |
ff2f67a0 | 278 | */ |
27b940e7 PB |
279 | if (was_online) |
280 | rcu_thread_offline(); | |
281 | else | |
282 | cmm_smp_mb(); | |
ff2f67a0 | 283 | |
6abb4bd5 | 284 | mutex_lock(&rcu_gp_lock); |
16aa9ee8 | 285 | if (cds_list_empty(®istry)) |
2dfb8b5e MD |
286 | goto out; |
287 | update_counter_and_wait(); | |
288 | out: | |
6abb4bd5 | 289 | mutex_unlock(&rcu_gp_lock); |
ff2f67a0 MD |
290 | |
291 | if (was_online) | |
27b940e7 PB |
292 | rcu_thread_online(); |
293 | else | |
294 | cmm_smp_mb(); | |
9f1621ca | 295 | } |
b39e1761 | 296 | #endif /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
297 | |
298 | /* | |
299 | * library wrappers to be used by non-LGPL compatible source code. | |
300 | */ | |
301 | ||
302 | void rcu_read_lock(void) | |
303 | { | |
304 | _rcu_read_lock(); | |
305 | } | |
306 | ||
307 | void rcu_read_unlock(void) | |
308 | { | |
309 | _rcu_read_unlock(); | |
310 | } | |
311 | ||
7ac06cef MD |
312 | void rcu_quiescent_state(void) |
313 | { | |
314 | _rcu_quiescent_state(); | |
315 | } | |
316 | ||
317 | void rcu_thread_offline(void) | |
318 | { | |
319 | _rcu_thread_offline(); | |
320 | } | |
321 | ||
322 | void rcu_thread_online(void) | |
323 | { | |
324 | _rcu_thread_online(); | |
325 | } | |
326 | ||
9f1621ca MD |
327 | void rcu_register_thread(void) |
328 | { | |
02be5561 MD |
329 | rcu_reader.tid = pthread_self(); |
330 | assert(rcu_reader.ctr == 0); | |
4f8e3380 | 331 | |
6abb4bd5 | 332 | mutex_lock(&rcu_gp_lock); |
16aa9ee8 | 333 | cds_list_add(&rcu_reader.node, ®istry); |
6abb4bd5 | 334 | mutex_unlock(&rcu_gp_lock); |
5f373c84 | 335 | _rcu_thread_online(); |
9f1621ca MD |
336 | } |
337 | ||
338 | void rcu_unregister_thread(void) | |
339 | { | |
76f3022f MD |
340 | /* |
341 | * We have to make the thread offline otherwise we end up dealocking | |
342 | * with a waiting writer. | |
343 | */ | |
344 | _rcu_thread_offline(); | |
6abb4bd5 | 345 | mutex_lock(&rcu_gp_lock); |
16aa9ee8 | 346 | cds_list_del(&rcu_reader.node); |
6abb4bd5 | 347 | mutex_unlock(&rcu_gp_lock); |
9f1621ca | 348 | } |
f6d18c64 MD |
349 | |
350 | void rcu_exit(void) | |
351 | { | |
01cadde4 MD |
352 | /* |
353 | * Assertion disabled because call_rcu threads are now rcu | |
354 | * readers, and left running at exit. | |
355 | * assert(cds_list_empty(®istry)); | |
356 | */ | |
f6d18c64 | 357 | } |
5e77fc1f PM |
358 | |
359 | #include "urcu-call-rcu-impl.h" | |
0376e7b2 | 360 | #include "urcu-defer-impl.h" |