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 |
9f1621ca MD |
27 | #include <stdio.h> |
28 | #include <pthread.h> | |
29 | #include <signal.h> | |
30 | #include <assert.h> | |
31 | #include <stdlib.h> | |
6d841bc2 | 32 | #include <stdint.h> |
9f1621ca MD |
33 | #include <string.h> |
34 | #include <errno.h> | |
35 | #include <poll.h> | |
36 | ||
57760d44 | 37 | #include "urcu/map/urcu-qsbr.h" |
5e77fc1f | 38 | |
727f819d | 39 | #define BUILD_QSBR_LIB |
af7c2dbe | 40 | #include "urcu/static/urcu-qsbr.h" |
9f1621ca | 41 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
7ac06cef | 42 | #include "urcu-qsbr.h" |
9f1621ca | 43 | |
f6d18c64 MD |
44 | void __attribute__((destructor)) rcu_exit(void); |
45 | ||
6abb4bd5 | 46 | static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; |
9f1621ca | 47 | |
6d841bc2 | 48 | int32_t gp_futex; |
bc6c15bb | 49 | |
9f1621ca MD |
50 | /* |
51 | * Global grace period counter. | |
52 | */ | |
02be5561 | 53 | unsigned long rcu_gp_ctr = RCU_GP_ONLINE; |
9f1621ca | 54 | |
3df2c328 PB |
55 | /* |
56 | * Active attempts to check for reader Q.S. before calling futex(). | |
57 | */ | |
58 | #define RCU_QS_ACTIVE_ATTEMPTS 100 | |
59 | ||
9f1621ca MD |
60 | /* |
61 | * Written to only by each individual reader. Read by both the reader and the | |
62 | * writers. | |
63 | */ | |
02be5561 | 64 | struct rcu_reader __thread rcu_reader; |
9f1621ca MD |
65 | |
66 | #ifdef DEBUG_YIELD | |
67 | unsigned int yield_active; | |
68 | unsigned int __thread rand_yield; | |
69 | #endif | |
70 | ||
16aa9ee8 | 71 | static CDS_LIST_HEAD(registry); |
9f1621ca | 72 | |
6abb4bd5 | 73 | static void mutex_lock(pthread_mutex_t *mutex) |
9f1621ca MD |
74 | { |
75 | int ret; | |
76 | ||
77 | #ifndef DISTRUST_SIGNALS_EXTREME | |
6abb4bd5 | 78 | ret = pthread_mutex_lock(mutex); |
9f1621ca MD |
79 | if (ret) { |
80 | perror("Error in pthread mutex lock"); | |
81 | exit(-1); | |
82 | } | |
83 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ | |
6abb4bd5 | 84 | while ((ret = pthread_mutex_trylock(mutex)) != 0) { |
9f1621ca MD |
85 | if (ret != EBUSY && ret != EINTR) { |
86 | printf("ret = %d, errno = %d\n", ret, errno); | |
87 | perror("Error in pthread mutex lock"); | |
88 | exit(-1); | |
89 | } | |
9f1621ca MD |
90 | poll(NULL,0,10); |
91 | } | |
92 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
93 | } | |
94 | ||
6abb4bd5 | 95 | static void mutex_unlock(pthread_mutex_t *mutex) |
9f1621ca MD |
96 | { |
97 | int ret; | |
98 | ||
6abb4bd5 | 99 | ret = pthread_mutex_unlock(mutex); |
9f1621ca MD |
100 | if (ret) { |
101 | perror("Error in pthread mutex unlock"); | |
102 | exit(-1); | |
103 | } | |
104 | } | |
105 | ||
bc6c15bb MD |
106 | /* |
107 | * synchronize_rcu() waiting. Single thread. | |
108 | */ | |
4d703340 | 109 | static void wait_gp(void) |
bc6c15bb | 110 | { |
4d703340 | 111 | /* Read reader_gp before read futex */ |
5481ddb3 | 112 | cmm_smp_rmb(); |
4d703340 | 113 | if (uatomic_read(&gp_futex) == -1) |
0854ccff | 114 | futex_noasync(&gp_futex, FUTEX_WAIT, -1, |
4d703340 | 115 | NULL, NULL, 0); |
bc6c15bb MD |
116 | } |
117 | ||
2dfb8b5e | 118 | static void update_counter_and_wait(void) |
9f1621ca | 119 | { |
16aa9ee8 | 120 | CDS_LIST_HEAD(qsreaders); |
4d703340 | 121 | int wait_loops = 0; |
02be5561 | 122 | struct rcu_reader *index, *tmp; |
9f1621ca | 123 | |
b39e1761 | 124 | #if (CAA_BITS_PER_LONG < 64) |
32c15e4e | 125 | /* Switch parity: 0 -> 1, 1 -> 0 */ |
6cf3827c | 126 | CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); |
b39e1761 | 127 | #else /* !(CAA_BITS_PER_LONG < 64) */ |
2dfb8b5e | 128 | /* Increment current G.P. */ |
6cf3827c | 129 | CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); |
b39e1761 | 130 | #endif /* !(CAA_BITS_PER_LONG < 64) */ |
2dfb8b5e | 131 | |
7a5a38f5 | 132 | /* |
5e77fc1f PM |
133 | * Must commit rcu_gp_ctr update to memory before waiting for |
134 | * quiescent state. Failure to do so could result in the writer | |
135 | * waiting forever while new readers are always accessing data | |
136 | * (no progress). Enforce compiler-order of store to rcu_gp_ctr | |
137 | * before load rcu_reader ctr. | |
d40fde2c | 138 | */ |
5481ddb3 | 139 | cmm_barrier(); |
d40fde2c MD |
140 | |
141 | /* | |
5481ddb3 | 142 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
935b11ff MD |
143 | * model easier to understand. It does not have a big performance impact |
144 | * anyway, given this is the write-side. | |
7a5a38f5 | 145 | */ |
5481ddb3 | 146 | cmm_smp_mb(); |
7a5a38f5 | 147 | |
9f1621ca | 148 | /* |
3395d46c | 149 | * Wait for each thread rcu_reader_qs_gp count to become 0. |
9f1621ca | 150 | */ |
4d703340 MD |
151 | for (;;) { |
152 | wait_loops++; | |
153 | if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { | |
154 | uatomic_dec(&gp_futex); | |
155 | /* Write futex before read reader_gp */ | |
5481ddb3 | 156 | cmm_smp_mb(); |
4d703340 MD |
157 | } |
158 | ||
16aa9ee8 | 159 | cds_list_for_each_entry_safe(index, tmp, ®istry, node) { |
4d703340 | 160 | if (!rcu_gp_ongoing(&index->ctr)) |
16aa9ee8 | 161 | cds_list_move(&index->node, &qsreaders); |
4d703340 | 162 | } |
bc6c15bb | 163 | |
16aa9ee8 | 164 | if (cds_list_empty(®istry)) { |
4d703340 MD |
165 | if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { |
166 | /* Read reader_gp before write futex */ | |
5481ddb3 | 167 | cmm_smp_mb(); |
4d703340 MD |
168 | uatomic_set(&gp_futex, 0); |
169 | } | |
170 | break; | |
171 | } else { | |
172 | if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { | |
173 | wait_gp(); | |
bc6c15bb | 174 | } else { |
9f1621ca | 175 | #ifndef HAS_INCOHERENT_CACHES |
06f22bdb | 176 | caa_cpu_relax(); |
9f1621ca | 177 | #else /* #ifndef HAS_INCOHERENT_CACHES */ |
5481ddb3 | 178 | cmm_smp_mb(); |
9f1621ca | 179 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ |
bc6c15bb MD |
180 | } |
181 | } | |
9f1621ca | 182 | } |
4d703340 | 183 | /* put back the reader list in the registry */ |
16aa9ee8 | 184 | cds_list_splice(&qsreaders, ®istry); |
9f1621ca MD |
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 | { | |
bc49c323 MD |
195 | unsigned long was_online; |
196 | ||
02be5561 | 197 | was_online = rcu_reader.ctr; |
bc49c323 | 198 | |
47d2f29e MD |
199 | /* All threads should read qparity before accessing data structure |
200 | * where new ptr points to. | |
201 | */ | |
202 | /* Write new ptr before changing the qparity */ | |
5481ddb3 | 203 | cmm_smp_mb(); |
47d2f29e | 204 | |
bc49c323 MD |
205 | /* |
206 | * Mark the writer thread offline to make sure we don't wait for | |
5e77fc1f PM |
207 | * our own quiescent state. This allows using synchronize_rcu() |
208 | * in threads registered as readers. | |
bc49c323 MD |
209 | */ |
210 | if (was_online) | |
6cf3827c | 211 | CMM_STORE_SHARED(rcu_reader.ctr, 0); |
bc49c323 | 212 | |
6abb4bd5 | 213 | mutex_lock(&rcu_gp_lock); |
47d2f29e | 214 | |
16aa9ee8 | 215 | if (cds_list_empty(®istry)) |
2dfb8b5e | 216 | goto out; |
47d2f29e MD |
217 | |
218 | /* | |
219 | * Wait for previous parity to be empty of readers. | |
220 | */ | |
2dfb8b5e | 221 | update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ |
47d2f29e MD |
222 | |
223 | /* | |
224 | * Must finish waiting for quiescent state for parity 0 before | |
5e77fc1f PM |
225 | * committing next rcu_gp_ctr update to memory. Failure to |
226 | * do so could result in the writer waiting forever while new | |
227 | * readers are always accessing data (no progress). Enforce | |
228 | * compiler-order of load rcu_reader ctr before store to | |
229 | * rcu_gp_ctr. | |
47d2f29e | 230 | */ |
5481ddb3 | 231 | cmm_barrier(); |
47d2f29e | 232 | |
47d2f29e | 233 | /* |
5481ddb3 | 234 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
2dfb8b5e MD |
235 | * model easier to understand. It does not have a big performance impact |
236 | * anyway, given this is the write-side. | |
47d2f29e | 237 | */ |
5481ddb3 | 238 | cmm_smp_mb(); |
47d2f29e MD |
239 | |
240 | /* | |
241 | * Wait for previous parity to be empty of readers. | |
242 | */ | |
2dfb8b5e MD |
243 | update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ |
244 | out: | |
6abb4bd5 | 245 | mutex_unlock(&rcu_gp_lock); |
47d2f29e | 246 | |
bc49c323 MD |
247 | /* |
248 | * Finish waiting for reader threads before letting the old ptr being | |
47d2f29e MD |
249 | * freed. |
250 | */ | |
bc49c323 | 251 | if (was_online) |
5e77fc1f PM |
252 | _CMM_STORE_SHARED(rcu_reader.ctr, |
253 | CMM_LOAD_SHARED(rcu_gp_ctr)); | |
5481ddb3 | 254 | cmm_smp_mb(); |
47d2f29e | 255 | } |
b39e1761 | 256 | #else /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
257 | void synchronize_rcu(void) |
258 | { | |
f0f7dbdd | 259 | unsigned long was_online; |
ff2f67a0 | 260 | |
02be5561 | 261 | was_online = rcu_reader.ctr; |
ff2f67a0 MD |
262 | |
263 | /* | |
264 | * Mark the writer thread offline to make sure we don't wait for | |
5e77fc1f PM |
265 | * our own quiescent state. This allows using synchronize_rcu() |
266 | * in threads registered as readers. | |
ff2f67a0 | 267 | */ |
5481ddb3 | 268 | cmm_smp_mb(); |
ff2f67a0 | 269 | if (was_online) |
6cf3827c | 270 | CMM_STORE_SHARED(rcu_reader.ctr, 0); |
ff2f67a0 | 271 | |
6abb4bd5 | 272 | mutex_lock(&rcu_gp_lock); |
16aa9ee8 | 273 | if (cds_list_empty(®istry)) |
2dfb8b5e MD |
274 | goto out; |
275 | update_counter_and_wait(); | |
276 | out: | |
6abb4bd5 | 277 | mutex_unlock(&rcu_gp_lock); |
ff2f67a0 MD |
278 | |
279 | if (was_online) | |
5e77fc1f PM |
280 | _CMM_STORE_SHARED(rcu_reader.ctr, |
281 | CMM_LOAD_SHARED(rcu_gp_ctr)); | |
5481ddb3 | 282 | cmm_smp_mb(); |
9f1621ca | 283 | } |
b39e1761 | 284 | #endif /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
285 | |
286 | /* | |
287 | * library wrappers to be used by non-LGPL compatible source code. | |
288 | */ | |
289 | ||
290 | void rcu_read_lock(void) | |
291 | { | |
292 | _rcu_read_lock(); | |
293 | } | |
294 | ||
295 | void rcu_read_unlock(void) | |
296 | { | |
297 | _rcu_read_unlock(); | |
298 | } | |
299 | ||
7ac06cef MD |
300 | void rcu_quiescent_state(void) |
301 | { | |
302 | _rcu_quiescent_state(); | |
303 | } | |
304 | ||
305 | void rcu_thread_offline(void) | |
306 | { | |
307 | _rcu_thread_offline(); | |
308 | } | |
309 | ||
310 | void rcu_thread_online(void) | |
311 | { | |
312 | _rcu_thread_online(); | |
313 | } | |
314 | ||
9f1621ca MD |
315 | void rcu_register_thread(void) |
316 | { | |
02be5561 MD |
317 | rcu_reader.tid = pthread_self(); |
318 | assert(rcu_reader.ctr == 0); | |
4f8e3380 | 319 | |
6abb4bd5 | 320 | mutex_lock(&rcu_gp_lock); |
16aa9ee8 | 321 | cds_list_add(&rcu_reader.node, ®istry); |
6abb4bd5 | 322 | mutex_unlock(&rcu_gp_lock); |
5f373c84 | 323 | _rcu_thread_online(); |
9f1621ca MD |
324 | } |
325 | ||
326 | void rcu_unregister_thread(void) | |
327 | { | |
76f3022f MD |
328 | /* |
329 | * We have to make the thread offline otherwise we end up dealocking | |
330 | * with a waiting writer. | |
331 | */ | |
332 | _rcu_thread_offline(); | |
6abb4bd5 | 333 | mutex_lock(&rcu_gp_lock); |
16aa9ee8 | 334 | cds_list_del(&rcu_reader.node); |
6abb4bd5 | 335 | mutex_unlock(&rcu_gp_lock); |
9f1621ca | 336 | } |
f6d18c64 MD |
337 | |
338 | void rcu_exit(void) | |
339 | { | |
16aa9ee8 | 340 | assert(cds_list_empty(®istry)); |
f6d18c64 | 341 | } |
5e77fc1f PM |
342 | |
343 | #include "urcu-call-rcu-impl.h" | |
0376e7b2 | 344 | #include "urcu-defer-impl.h" |