Commit | Line | Data |
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9f1621ca | 1 | /* |
7ac06cef | 2 | * urcu-qsbr.c |
9f1621ca | 3 | * |
7ac06cef | 4 | * Userspace RCU QSBR library |
9f1621ca MD |
5 | * |
6 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca> | |
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 | ||
26 | #include <stdio.h> | |
27 | #include <pthread.h> | |
28 | #include <signal.h> | |
29 | #include <assert.h> | |
30 | #include <stdlib.h> | |
31 | #include <string.h> | |
32 | #include <errno.h> | |
33 | #include <poll.h> | |
34 | ||
727f819d | 35 | #define BUILD_QSBR_LIB |
7ac06cef | 36 | #include "urcu-qsbr-static.h" |
9f1621ca | 37 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
7ac06cef | 38 | #include "urcu-qsbr.h" |
9f1621ca | 39 | |
f6d18c64 MD |
40 | void __attribute__((destructor)) rcu_exit(void); |
41 | ||
81d1f1f5 | 42 | static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER; |
9f1621ca | 43 | |
bc6c15bb MD |
44 | int gp_futex; |
45 | ||
9f1621ca MD |
46 | /* |
47 | * Global grace period counter. | |
48 | */ | |
ac258107 | 49 | unsigned long urcu_gp_ctr = RCU_GP_ONLINE; |
9f1621ca MD |
50 | |
51 | /* | |
52 | * Written to only by each individual reader. Read by both the reader and the | |
53 | * writers. | |
54 | */ | |
4f8e3380 | 55 | struct urcu_reader __thread urcu_reader; |
9f1621ca MD |
56 | |
57 | #ifdef DEBUG_YIELD | |
58 | unsigned int yield_active; | |
59 | unsigned int __thread rand_yield; | |
60 | #endif | |
61 | ||
4f8e3380 | 62 | static LIST_HEAD(registry); |
9f1621ca | 63 | |
90c1618a | 64 | static void internal_urcu_lock(void) |
9f1621ca MD |
65 | { |
66 | int ret; | |
67 | ||
68 | #ifndef DISTRUST_SIGNALS_EXTREME | |
69 | ret = pthread_mutex_lock(&urcu_mutex); | |
70 | if (ret) { | |
71 | perror("Error in pthread mutex lock"); | |
72 | exit(-1); | |
73 | } | |
74 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ | |
75 | while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) { | |
76 | if (ret != EBUSY && ret != EINTR) { | |
77 | printf("ret = %d, errno = %d\n", ret, errno); | |
78 | perror("Error in pthread mutex lock"); | |
79 | exit(-1); | |
80 | } | |
9f1621ca MD |
81 | poll(NULL,0,10); |
82 | } | |
83 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
84 | } | |
85 | ||
90c1618a | 86 | static void internal_urcu_unlock(void) |
9f1621ca MD |
87 | { |
88 | int ret; | |
89 | ||
90 | ret = pthread_mutex_unlock(&urcu_mutex); | |
91 | if (ret) { | |
92 | perror("Error in pthread mutex unlock"); | |
93 | exit(-1); | |
94 | } | |
95 | } | |
96 | ||
bc6c15bb MD |
97 | /* |
98 | * synchronize_rcu() waiting. Single thread. | |
99 | */ | |
4d703340 | 100 | static void wait_gp(void) |
bc6c15bb | 101 | { |
4d703340 MD |
102 | /* Read reader_gp before read futex */ |
103 | smp_rmb(); | |
104 | if (uatomic_read(&gp_futex) == -1) | |
0854ccff | 105 | futex_noasync(&gp_futex, FUTEX_WAIT, -1, |
4d703340 | 106 | NULL, NULL, 0); |
bc6c15bb MD |
107 | } |
108 | ||
90c1618a | 109 | static void wait_for_quiescent_state(void) |
9f1621ca | 110 | { |
4d703340 MD |
111 | LIST_HEAD(qsreaders); |
112 | int wait_loops = 0; | |
113 | struct urcu_reader *index, *tmp; | |
9f1621ca | 114 | |
4f8e3380 | 115 | if (list_empty(®istry)) |
9f1621ca MD |
116 | return; |
117 | /* | |
3395d46c | 118 | * Wait for each thread rcu_reader_qs_gp count to become 0. |
9f1621ca | 119 | */ |
4d703340 MD |
120 | for (;;) { |
121 | wait_loops++; | |
122 | if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { | |
123 | uatomic_dec(&gp_futex); | |
124 | /* Write futex before read reader_gp */ | |
125 | smp_mb(); | |
126 | } | |
127 | ||
128 | list_for_each_entry_safe(index, tmp, ®istry, head) { | |
129 | if (!rcu_gp_ongoing(&index->ctr)) | |
130 | list_move(&index->head, &qsreaders); | |
131 | } | |
bc6c15bb | 132 | |
4d703340 MD |
133 | if (list_empty(®istry)) { |
134 | if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { | |
135 | /* Read reader_gp before write futex */ | |
136 | smp_mb(); | |
137 | uatomic_set(&gp_futex, 0); | |
138 | } | |
139 | break; | |
140 | } else { | |
141 | if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { | |
142 | wait_gp(); | |
bc6c15bb | 143 | } else { |
9f1621ca | 144 | #ifndef HAS_INCOHERENT_CACHES |
bc6c15bb | 145 | cpu_relax(); |
9f1621ca | 146 | #else /* #ifndef HAS_INCOHERENT_CACHES */ |
bc6c15bb | 147 | smp_mb(); |
9f1621ca | 148 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ |
bc6c15bb MD |
149 | } |
150 | } | |
9f1621ca | 151 | } |
4d703340 MD |
152 | /* put back the reader list in the registry */ |
153 | list_splice(&qsreaders, ®istry); | |
9f1621ca MD |
154 | } |
155 | ||
47d2f29e MD |
156 | /* |
157 | * Using a two-subphases algorithm for architectures with smaller than 64-bit | |
158 | * long-size to ensure we do not encounter an overflow bug. | |
159 | */ | |
160 | ||
161 | #if (BITS_PER_LONG < 64) | |
162 | /* | |
163 | * called with urcu_mutex held. | |
164 | */ | |
165 | static void switch_next_urcu_qparity(void) | |
166 | { | |
167 | STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR); | |
168 | } | |
169 | ||
170 | void synchronize_rcu(void) | |
171 | { | |
bc49c323 MD |
172 | unsigned long was_online; |
173 | ||
4f8e3380 | 174 | was_online = urcu_reader.ctr; |
bc49c323 | 175 | |
47d2f29e MD |
176 | /* All threads should read qparity before accessing data structure |
177 | * where new ptr points to. | |
178 | */ | |
179 | /* Write new ptr before changing the qparity */ | |
180 | smp_mb(); | |
181 | ||
bc49c323 MD |
182 | /* |
183 | * Mark the writer thread offline to make sure we don't wait for | |
184 | * our own quiescent state. This allows using synchronize_rcu() in | |
185 | * threads registered as readers. | |
186 | */ | |
187 | if (was_online) | |
4f8e3380 | 188 | STORE_SHARED(urcu_reader.ctr, 0); |
bc49c323 | 189 | |
47d2f29e MD |
190 | internal_urcu_lock(); |
191 | ||
192 | switch_next_urcu_qparity(); /* 0 -> 1 */ | |
193 | ||
194 | /* | |
195 | * Must commit qparity update to memory before waiting for parity | |
196 | * 0 quiescent state. Failure to do so could result in the writer | |
197 | * waiting forever while new readers are always accessing data (no | |
198 | * progress). | |
199 | * Ensured by STORE_SHARED and LOAD_SHARED. | |
200 | */ | |
201 | ||
202 | /* | |
203 | * Wait for previous parity to be empty of readers. | |
204 | */ | |
205 | wait_for_quiescent_state(); /* Wait readers in parity 0 */ | |
206 | ||
207 | /* | |
208 | * Must finish waiting for quiescent state for parity 0 before | |
209 | * committing qparity update to memory. Failure to do so could result in | |
210 | * the writer waiting forever while new readers are always accessing | |
211 | * data (no progress). | |
212 | * Ensured by STORE_SHARED and LOAD_SHARED. | |
213 | */ | |
214 | ||
215 | switch_next_urcu_qparity(); /* 1 -> 0 */ | |
216 | ||
217 | /* | |
218 | * Must commit qparity update to memory before waiting for parity | |
219 | * 1 quiescent state. Failure to do so could result in the writer | |
220 | * waiting forever while new readers are always accessing data (no | |
221 | * progress). | |
222 | * Ensured by STORE_SHARED and LOAD_SHARED. | |
223 | */ | |
224 | ||
225 | /* | |
226 | * Wait for previous parity to be empty of readers. | |
227 | */ | |
228 | wait_for_quiescent_state(); /* Wait readers in parity 1 */ | |
229 | ||
230 | internal_urcu_unlock(); | |
231 | ||
bc49c323 MD |
232 | /* |
233 | * Finish waiting for reader threads before letting the old ptr being | |
47d2f29e MD |
234 | * freed. |
235 | */ | |
bc49c323 | 236 | if (was_online) |
4f8e3380 | 237 | _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr)); |
47d2f29e MD |
238 | smp_mb(); |
239 | } | |
240 | #else /* !(BITS_PER_LONG < 64) */ | |
9f1621ca MD |
241 | void synchronize_rcu(void) |
242 | { | |
f0f7dbdd | 243 | unsigned long was_online; |
ff2f67a0 | 244 | |
4f8e3380 | 245 | was_online = urcu_reader.ctr; |
ff2f67a0 MD |
246 | |
247 | /* | |
248 | * Mark the writer thread offline to make sure we don't wait for | |
249 | * our own quiescent state. This allows using synchronize_rcu() in | |
250 | * threads registered as readers. | |
251 | */ | |
8f50d1ce | 252 | smp_mb(); |
ff2f67a0 | 253 | if (was_online) |
4f8e3380 | 254 | STORE_SHARED(urcu_reader.ctr, 0); |
ff2f67a0 | 255 | |
4e27f058 | 256 | internal_urcu_lock(); |
55570466 | 257 | STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR); |
9f1621ca | 258 | wait_for_quiescent_state(); |
9f1621ca | 259 | internal_urcu_unlock(); |
ff2f67a0 MD |
260 | |
261 | if (was_online) | |
4f8e3380 | 262 | _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr)); |
8f50d1ce | 263 | smp_mb(); |
9f1621ca | 264 | } |
47d2f29e | 265 | #endif /* !(BITS_PER_LONG < 64) */ |
9f1621ca MD |
266 | |
267 | /* | |
268 | * library wrappers to be used by non-LGPL compatible source code. | |
269 | */ | |
270 | ||
271 | void rcu_read_lock(void) | |
272 | { | |
273 | _rcu_read_lock(); | |
274 | } | |
275 | ||
276 | void rcu_read_unlock(void) | |
277 | { | |
278 | _rcu_read_unlock(); | |
279 | } | |
280 | ||
7ac06cef MD |
281 | void rcu_quiescent_state(void) |
282 | { | |
283 | _rcu_quiescent_state(); | |
284 | } | |
285 | ||
286 | void rcu_thread_offline(void) | |
287 | { | |
288 | _rcu_thread_offline(); | |
289 | } | |
290 | ||
291 | void rcu_thread_online(void) | |
292 | { | |
293 | _rcu_thread_online(); | |
294 | } | |
295 | ||
9f1621ca MD |
296 | void rcu_register_thread(void) |
297 | { | |
4f8e3380 MD |
298 | urcu_reader.tid = pthread_self(); |
299 | assert(urcu_reader.ctr == 0); | |
300 | ||
9f1621ca | 301 | internal_urcu_lock(); |
4f8e3380 | 302 | list_add(&urcu_reader.head, ®istry); |
9f1621ca | 303 | internal_urcu_unlock(); |
5f373c84 | 304 | _rcu_thread_online(); |
9f1621ca MD |
305 | } |
306 | ||
307 | void rcu_unregister_thread(void) | |
308 | { | |
76f3022f MD |
309 | /* |
310 | * We have to make the thread offline otherwise we end up dealocking | |
311 | * with a waiting writer. | |
312 | */ | |
313 | _rcu_thread_offline(); | |
9f1621ca | 314 | internal_urcu_lock(); |
4f8e3380 | 315 | list_del(&urcu_reader.head); |
9f1621ca MD |
316 | internal_urcu_unlock(); |
317 | } | |
f6d18c64 MD |
318 | |
319 | void rcu_exit(void) | |
320 | { | |
321 | assert(list_empty(®istry)); | |
322 | } |