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" |
71c811bf | 42 | |
9f1621ca | 43 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
71c811bf | 44 | #undef _LGPL_SOURCE |
7ac06cef | 45 | #include "urcu-qsbr.h" |
71c811bf | 46 | #define _LGPL_SOURCE |
9f1621ca | 47 | |
f6d18c64 MD |
48 | void __attribute__((destructor)) rcu_exit(void); |
49 | ||
6abb4bd5 | 50 | static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; |
9f1621ca | 51 | |
6d841bc2 | 52 | int32_t gp_futex; |
bc6c15bb | 53 | |
9f1621ca MD |
54 | /* |
55 | * Global grace period counter. | |
56 | */ | |
02be5561 | 57 | unsigned long rcu_gp_ctr = RCU_GP_ONLINE; |
9f1621ca | 58 | |
408f6d92 PB |
59 | /* |
60 | * Active attempts to check for reader Q.S. before calling futex(). | |
61 | */ | |
62 | #define RCU_QS_ACTIVE_ATTEMPTS 100 | |
63 | ||
9f1621ca MD |
64 | /* |
65 | * Written to only by each individual reader. Read by both the reader and the | |
66 | * writers. | |
67 | */ | |
02be5561 | 68 | struct rcu_reader __thread rcu_reader; |
9f1621ca MD |
69 | |
70 | #ifdef DEBUG_YIELD | |
71 | unsigned int yield_active; | |
72 | unsigned int __thread rand_yield; | |
73 | #endif | |
74 | ||
16aa9ee8 | 75 | static CDS_LIST_HEAD(registry); |
9f1621ca | 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); |
9f1621ca MD |
83 | if (ret) { |
84 | perror("Error in pthread mutex lock"); | |
85 | exit(-1); | |
86 | } | |
87 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ | |
6abb4bd5 | 88 | while ((ret = pthread_mutex_trylock(mutex)) != 0) { |
9f1621ca MD |
89 | if (ret != EBUSY && ret != EINTR) { |
90 | printf("ret = %d, errno = %d\n", ret, errno); | |
91 | perror("Error in pthread mutex lock"); | |
92 | exit(-1); | |
93 | } | |
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); |
9f1621ca MD |
104 | if (ret) { |
105 | perror("Error in pthread mutex unlock"); | |
106 | exit(-1); | |
107 | } | |
108 | } | |
109 | ||
bc6c15bb MD |
110 | /* |
111 | * synchronize_rcu() waiting. Single thread. | |
112 | */ | |
4d703340 | 113 | static void wait_gp(void) |
bc6c15bb | 114 | { |
4d703340 | 115 | /* Read reader_gp before read futex */ |
5481ddb3 | 116 | cmm_smp_rmb(); |
4d703340 | 117 | if (uatomic_read(&gp_futex) == -1) |
0854ccff | 118 | futex_noasync(&gp_futex, FUTEX_WAIT, -1, |
4d703340 | 119 | NULL, NULL, 0); |
bc6c15bb MD |
120 | } |
121 | ||
2dfb8b5e | 122 | static void update_counter_and_wait(void) |
9f1621ca | 123 | { |
16aa9ee8 | 124 | CDS_LIST_HEAD(qsreaders); |
4d703340 | 125 | int wait_loops = 0; |
02be5561 | 126 | struct rcu_reader *index, *tmp; |
9f1621ca | 127 | |
b39e1761 | 128 | #if (CAA_BITS_PER_LONG < 64) |
32c15e4e | 129 | /* Switch parity: 0 -> 1, 1 -> 0 */ |
6cf3827c | 130 | CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); |
b39e1761 | 131 | #else /* !(CAA_BITS_PER_LONG < 64) */ |
2dfb8b5e | 132 | /* Increment current G.P. */ |
6cf3827c | 133 | CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); |
b39e1761 | 134 | #endif /* !(CAA_BITS_PER_LONG < 64) */ |
2dfb8b5e | 135 | |
7a5a38f5 | 136 | /* |
5e77fc1f PM |
137 | * Must commit rcu_gp_ctr update to memory before waiting for |
138 | * quiescent state. Failure to do so could result in the writer | |
139 | * waiting forever while new readers are always accessing data | |
140 | * (no progress). Enforce compiler-order of store to rcu_gp_ctr | |
141 | * before load rcu_reader ctr. | |
d40fde2c | 142 | */ |
5481ddb3 | 143 | cmm_barrier(); |
d40fde2c MD |
144 | |
145 | /* | |
5481ddb3 | 146 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
935b11ff MD |
147 | * model easier to understand. It does not have a big performance impact |
148 | * anyway, given this is the write-side. | |
7a5a38f5 | 149 | */ |
5481ddb3 | 150 | cmm_smp_mb(); |
7a5a38f5 | 151 | |
9f1621ca | 152 | /* |
3395d46c | 153 | * Wait for each thread rcu_reader_qs_gp count to become 0. |
9f1621ca | 154 | */ |
4d703340 MD |
155 | for (;;) { |
156 | wait_loops++; | |
83a2c421 PB |
157 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
158 | uatomic_set(&gp_futex, -1); | |
159 | /* | |
160 | * Write futex before write waiting (the other side | |
161 | * reads them in the opposite order). | |
162 | */ | |
163 | cmm_smp_wmb(); | |
164 | cds_list_for_each_entry(index, ®istry, node) { | |
165 | _CMM_STORE_SHARED(index->waiting, 1); | |
166 | } | |
4d703340 | 167 | /* Write futex before read reader_gp */ |
5481ddb3 | 168 | cmm_smp_mb(); |
4d703340 | 169 | } |
16aa9ee8 | 170 | cds_list_for_each_entry_safe(index, tmp, ®istry, node) { |
4d703340 | 171 | if (!rcu_gp_ongoing(&index->ctr)) |
16aa9ee8 | 172 | cds_list_move(&index->node, &qsreaders); |
4d703340 | 173 | } |
bc6c15bb | 174 | |
16aa9ee8 | 175 | if (cds_list_empty(®istry)) { |
83a2c421 | 176 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 177 | /* Read reader_gp before write futex */ |
5481ddb3 | 178 | cmm_smp_mb(); |
4d703340 MD |
179 | uatomic_set(&gp_futex, 0); |
180 | } | |
181 | break; | |
182 | } else { | |
83a2c421 | 183 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 184 | wait_gp(); |
bc6c15bb | 185 | } else { |
9f1621ca | 186 | #ifndef HAS_INCOHERENT_CACHES |
06f22bdb | 187 | caa_cpu_relax(); |
9f1621ca | 188 | #else /* #ifndef HAS_INCOHERENT_CACHES */ |
5481ddb3 | 189 | cmm_smp_mb(); |
9f1621ca | 190 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ |
bc6c15bb MD |
191 | } |
192 | } | |
9f1621ca | 193 | } |
4d703340 | 194 | /* put back the reader list in the registry */ |
16aa9ee8 | 195 | cds_list_splice(&qsreaders, ®istry); |
9f1621ca MD |
196 | } |
197 | ||
47d2f29e MD |
198 | /* |
199 | * Using a two-subphases algorithm for architectures with smaller than 64-bit | |
200 | * long-size to ensure we do not encounter an overflow bug. | |
201 | */ | |
202 | ||
b39e1761 | 203 | #if (CAA_BITS_PER_LONG < 64) |
47d2f29e MD |
204 | void synchronize_rcu(void) |
205 | { | |
bc49c323 MD |
206 | unsigned long was_online; |
207 | ||
02be5561 | 208 | was_online = rcu_reader.ctr; |
bc49c323 | 209 | |
47d2f29e MD |
210 | /* All threads should read qparity before accessing data structure |
211 | * where new ptr points to. | |
212 | */ | |
213 | /* Write new ptr before changing the qparity */ | |
5481ddb3 | 214 | cmm_smp_mb(); |
47d2f29e | 215 | |
bc49c323 MD |
216 | /* |
217 | * Mark the writer thread offline to make sure we don't wait for | |
5e77fc1f PM |
218 | * our own quiescent state. This allows using synchronize_rcu() |
219 | * in threads registered as readers. | |
bc49c323 MD |
220 | */ |
221 | if (was_online) | |
6cf3827c | 222 | CMM_STORE_SHARED(rcu_reader.ctr, 0); |
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) |
5e77fc1f PM |
263 | _CMM_STORE_SHARED(rcu_reader.ctr, |
264 | CMM_LOAD_SHARED(rcu_gp_ctr)); | |
5481ddb3 | 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 | */ |
5481ddb3 | 279 | cmm_smp_mb(); |
ff2f67a0 | 280 | if (was_online) |
6cf3827c | 281 | CMM_STORE_SHARED(rcu_reader.ctr, 0); |
ff2f67a0 | 282 | |
6abb4bd5 | 283 | mutex_lock(&rcu_gp_lock); |
16aa9ee8 | 284 | if (cds_list_empty(®istry)) |
2dfb8b5e MD |
285 | goto out; |
286 | update_counter_and_wait(); | |
287 | out: | |
6abb4bd5 | 288 | mutex_unlock(&rcu_gp_lock); |
ff2f67a0 MD |
289 | |
290 | if (was_online) | |
5e77fc1f PM |
291 | _CMM_STORE_SHARED(rcu_reader.ctr, |
292 | CMM_LOAD_SHARED(rcu_gp_ctr)); | |
5481ddb3 | 293 | cmm_smp_mb(); |
9f1621ca | 294 | } |
b39e1761 | 295 | #endif /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
296 | |
297 | /* | |
298 | * library wrappers to be used by non-LGPL compatible source code. | |
299 | */ | |
300 | ||
301 | void rcu_read_lock(void) | |
302 | { | |
303 | _rcu_read_lock(); | |
304 | } | |
305 | ||
306 | void rcu_read_unlock(void) | |
307 | { | |
308 | _rcu_read_unlock(); | |
309 | } | |
310 | ||
7ac06cef MD |
311 | void rcu_quiescent_state(void) |
312 | { | |
313 | _rcu_quiescent_state(); | |
314 | } | |
315 | ||
316 | void rcu_thread_offline(void) | |
317 | { | |
318 | _rcu_thread_offline(); | |
319 | } | |
320 | ||
321 | void rcu_thread_online(void) | |
322 | { | |
323 | _rcu_thread_online(); | |
324 | } | |
325 | ||
9f1621ca MD |
326 | void rcu_register_thread(void) |
327 | { | |
02be5561 MD |
328 | rcu_reader.tid = pthread_self(); |
329 | assert(rcu_reader.ctr == 0); | |
4f8e3380 | 330 | |
6abb4bd5 | 331 | mutex_lock(&rcu_gp_lock); |
16aa9ee8 | 332 | cds_list_add(&rcu_reader.node, ®istry); |
6abb4bd5 | 333 | mutex_unlock(&rcu_gp_lock); |
5f373c84 | 334 | _rcu_thread_online(); |
9f1621ca MD |
335 | } |
336 | ||
337 | void rcu_unregister_thread(void) | |
338 | { | |
76f3022f MD |
339 | /* |
340 | * We have to make the thread offline otherwise we end up dealocking | |
341 | * with a waiting writer. | |
342 | */ | |
343 | _rcu_thread_offline(); | |
6abb4bd5 | 344 | mutex_lock(&rcu_gp_lock); |
16aa9ee8 | 345 | cds_list_del(&rcu_reader.node); |
6abb4bd5 | 346 | mutex_unlock(&rcu_gp_lock); |
9f1621ca | 347 | } |
f6d18c64 MD |
348 | |
349 | void rcu_exit(void) | |
350 | { | |
16aa9ee8 | 351 | assert(cds_list_empty(®istry)); |
f6d18c64 | 352 | } |
5e77fc1f PM |
353 | |
354 | #include "urcu-call-rcu-impl.h" | |
0376e7b2 | 355 | #include "urcu-defer-impl.h" |