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" |
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 | ||
66bc4dcd MD |
54 | /* |
55 | * rcu_gp_lock ensures mutual exclusion between threads calling | |
56 | * synchronize_rcu(). | |
57 | */ | |
6abb4bd5 | 58 | static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; |
66bc4dcd MD |
59 | /* |
60 | * rcu_registry_lock ensures mutual exclusion between threads | |
61 | * registering and unregistering themselves to/from the registry, and | |
62 | * with threads reading that registry from synchronize_rcu(). However, | |
63 | * this lock is not held all the way through the completion of awaiting | |
64 | * for the grace period. It is sporadically released between iterations | |
65 | * on the registry. | |
66 | * rcu_registry_lock may nest inside rcu_gp_lock. | |
67 | */ | |
68 | static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER; | |
9f1621ca | 69 | |
6d841bc2 | 70 | int32_t gp_futex; |
bc6c15bb | 71 | |
9f1621ca MD |
72 | /* |
73 | * Global grace period counter. | |
74 | */ | |
02be5561 | 75 | unsigned long rcu_gp_ctr = RCU_GP_ONLINE; |
9f1621ca | 76 | |
408f6d92 PB |
77 | /* |
78 | * Active attempts to check for reader Q.S. before calling futex(). | |
79 | */ | |
80 | #define RCU_QS_ACTIVE_ATTEMPTS 100 | |
81 | ||
9f1621ca MD |
82 | /* |
83 | * Written to only by each individual reader. Read by both the reader and the | |
84 | * writers. | |
85 | */ | |
1745be1a | 86 | __DEFINE_URCU_TLS_GLOBAL(struct rcu_reader, rcu_reader); |
9f1621ca MD |
87 | |
88 | #ifdef DEBUG_YIELD | |
89 | unsigned int yield_active; | |
1745be1a | 90 | __DEFINE_URCU_TLS_GLOBAL(unsigned int, rand_yield); |
9f1621ca MD |
91 | #endif |
92 | ||
16aa9ee8 | 93 | static CDS_LIST_HEAD(registry); |
9f1621ca | 94 | |
6abb4bd5 | 95 | static void mutex_lock(pthread_mutex_t *mutex) |
9f1621ca MD |
96 | { |
97 | int ret; | |
98 | ||
99 | #ifndef DISTRUST_SIGNALS_EXTREME | |
6abb4bd5 | 100 | ret = pthread_mutex_lock(mutex); |
4a6d7378 MD |
101 | if (ret) |
102 | urcu_die(ret); | |
9f1621ca | 103 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ |
6abb4bd5 | 104 | while ((ret = pthread_mutex_trylock(mutex)) != 0) { |
4a6d7378 MD |
105 | if (ret != EBUSY && ret != EINTR) |
106 | urcu_die(ret); | |
9f1621ca MD |
107 | poll(NULL,0,10); |
108 | } | |
109 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
110 | } | |
111 | ||
6abb4bd5 | 112 | static void mutex_unlock(pthread_mutex_t *mutex) |
9f1621ca MD |
113 | { |
114 | int ret; | |
115 | ||
6abb4bd5 | 116 | ret = pthread_mutex_unlock(mutex); |
4a6d7378 MD |
117 | if (ret) |
118 | urcu_die(ret); | |
9f1621ca MD |
119 | } |
120 | ||
bc6c15bb MD |
121 | /* |
122 | * synchronize_rcu() waiting. Single thread. | |
123 | */ | |
4d703340 | 124 | static void wait_gp(void) |
bc6c15bb | 125 | { |
4d703340 | 126 | /* Read reader_gp before read futex */ |
5481ddb3 | 127 | cmm_smp_rmb(); |
4d703340 | 128 | if (uatomic_read(&gp_futex) == -1) |
0854ccff | 129 | futex_noasync(&gp_futex, FUTEX_WAIT, -1, |
4d703340 | 130 | NULL, NULL, 0); |
bc6c15bb MD |
131 | } |
132 | ||
66bc4dcd MD |
133 | /* |
134 | * Always called with rcu_registry lock held. Releases this lock between | |
135 | * iterations and grabs it again. Holds the lock when it returns. | |
136 | */ | |
2dfb8b5e | 137 | static void update_counter_and_wait(void) |
9f1621ca | 138 | { |
16aa9ee8 | 139 | CDS_LIST_HEAD(qsreaders); |
6b702fa4 | 140 | unsigned int wait_loops = 0; |
02be5561 | 141 | struct rcu_reader *index, *tmp; |
9f1621ca | 142 | |
b39e1761 | 143 | #if (CAA_BITS_PER_LONG < 64) |
32c15e4e | 144 | /* Switch parity: 0 -> 1, 1 -> 0 */ |
6cf3827c | 145 | CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); |
b39e1761 | 146 | #else /* !(CAA_BITS_PER_LONG < 64) */ |
2dfb8b5e | 147 | /* Increment current G.P. */ |
6cf3827c | 148 | CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); |
b39e1761 | 149 | #endif /* !(CAA_BITS_PER_LONG < 64) */ |
2dfb8b5e | 150 | |
7a5a38f5 | 151 | /* |
5e77fc1f PM |
152 | * Must commit rcu_gp_ctr update to memory before waiting for |
153 | * quiescent state. Failure to do so could result in the writer | |
154 | * waiting forever while new readers are always accessing data | |
155 | * (no progress). Enforce compiler-order of store to rcu_gp_ctr | |
bd252a04 | 156 | * before load URCU_TLS(rcu_reader).ctr. |
d40fde2c | 157 | */ |
5481ddb3 | 158 | cmm_barrier(); |
d40fde2c MD |
159 | |
160 | /* | |
5481ddb3 | 161 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
935b11ff MD |
162 | * model easier to understand. It does not have a big performance impact |
163 | * anyway, given this is the write-side. | |
7a5a38f5 | 164 | */ |
5481ddb3 | 165 | cmm_smp_mb(); |
7a5a38f5 | 166 | |
9f1621ca | 167 | /* |
3395d46c | 168 | * Wait for each thread rcu_reader_qs_gp count to become 0. |
9f1621ca | 169 | */ |
4d703340 | 170 | for (;;) { |
cca4c8dc MD |
171 | if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS) |
172 | wait_loops++; | |
83a2c421 PB |
173 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
174 | uatomic_set(&gp_futex, -1); | |
175 | /* | |
176 | * Write futex before write waiting (the other side | |
177 | * reads them in the opposite order). | |
178 | */ | |
179 | cmm_smp_wmb(); | |
180 | cds_list_for_each_entry(index, ®istry, node) { | |
181 | _CMM_STORE_SHARED(index->waiting, 1); | |
182 | } | |
4d703340 | 183 | /* Write futex before read reader_gp */ |
5481ddb3 | 184 | cmm_smp_mb(); |
4d703340 | 185 | } |
16aa9ee8 | 186 | cds_list_for_each_entry_safe(index, tmp, ®istry, node) { |
4d703340 | 187 | if (!rcu_gp_ongoing(&index->ctr)) |
16aa9ee8 | 188 | cds_list_move(&index->node, &qsreaders); |
4d703340 | 189 | } |
bc6c15bb | 190 | |
16aa9ee8 | 191 | if (cds_list_empty(®istry)) { |
83a2c421 | 192 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 193 | /* Read reader_gp before write futex */ |
5481ddb3 | 194 | cmm_smp_mb(); |
4d703340 MD |
195 | uatomic_set(&gp_futex, 0); |
196 | } | |
197 | break; | |
198 | } else { | |
66bc4dcd MD |
199 | /* Temporarily unlock the registry lock. */ |
200 | mutex_unlock(&rcu_registry_lock); | |
83a2c421 | 201 | if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { |
4d703340 | 202 | wait_gp(); |
bc6c15bb | 203 | } else { |
9f1621ca | 204 | #ifndef HAS_INCOHERENT_CACHES |
06f22bdb | 205 | caa_cpu_relax(); |
9f1621ca | 206 | #else /* #ifndef HAS_INCOHERENT_CACHES */ |
5481ddb3 | 207 | cmm_smp_mb(); |
9f1621ca | 208 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ |
bc6c15bb | 209 | } |
66bc4dcd MD |
210 | /* Re-lock the registry lock before the next loop. */ |
211 | mutex_lock(&rcu_registry_lock); | |
bc6c15bb | 212 | } |
9f1621ca | 213 | } |
4d703340 | 214 | /* put back the reader list in the registry */ |
16aa9ee8 | 215 | cds_list_splice(&qsreaders, ®istry); |
9f1621ca MD |
216 | } |
217 | ||
47d2f29e MD |
218 | /* |
219 | * Using a two-subphases algorithm for architectures with smaller than 64-bit | |
220 | * long-size to ensure we do not encounter an overflow bug. | |
221 | */ | |
222 | ||
b39e1761 | 223 | #if (CAA_BITS_PER_LONG < 64) |
47d2f29e MD |
224 | void synchronize_rcu(void) |
225 | { | |
bc49c323 MD |
226 | unsigned long was_online; |
227 | ||
bd252a04 | 228 | was_online = URCU_TLS(rcu_reader).ctr; |
bc49c323 | 229 | |
47d2f29e | 230 | /* All threads should read qparity before accessing data structure |
27b940e7 PB |
231 | * where new ptr points to. In the "then" case, rcu_thread_offline |
232 | * includes a memory barrier. | |
233 | * | |
bc49c323 | 234 | * Mark the writer thread offline to make sure we don't wait for |
5e77fc1f PM |
235 | * our own quiescent state. This allows using synchronize_rcu() |
236 | * in threads registered as readers. | |
bc49c323 | 237 | */ |
27b940e7 PB |
238 | if (was_online) |
239 | rcu_thread_offline(); | |
240 | else | |
241 | cmm_smp_mb(); | |
bc49c323 | 242 | |
6abb4bd5 | 243 | mutex_lock(&rcu_gp_lock); |
66bc4dcd | 244 | mutex_lock(&rcu_registry_lock); |
47d2f29e | 245 | |
16aa9ee8 | 246 | if (cds_list_empty(®istry)) |
2dfb8b5e | 247 | goto out; |
47d2f29e MD |
248 | |
249 | /* | |
250 | * Wait for previous parity to be empty of readers. | |
66bc4dcd MD |
251 | * update_counter_and_wait() can release and grab again |
252 | * rcu_registry_lock interally. | |
47d2f29e | 253 | */ |
2dfb8b5e | 254 | update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ |
47d2f29e MD |
255 | |
256 | /* | |
257 | * Must finish waiting for quiescent state for parity 0 before | |
5e77fc1f PM |
258 | * committing next rcu_gp_ctr update to memory. Failure to |
259 | * do so could result in the writer waiting forever while new | |
260 | * readers are always accessing data (no progress). Enforce | |
bd252a04 | 261 | * compiler-order of load URCU_TLS(rcu_reader).ctr before store to |
5e77fc1f | 262 | * rcu_gp_ctr. |
47d2f29e | 263 | */ |
5481ddb3 | 264 | cmm_barrier(); |
47d2f29e | 265 | |
47d2f29e | 266 | /* |
5481ddb3 | 267 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
2dfb8b5e MD |
268 | * model easier to understand. It does not have a big performance impact |
269 | * anyway, given this is the write-side. | |
47d2f29e | 270 | */ |
5481ddb3 | 271 | cmm_smp_mb(); |
47d2f29e MD |
272 | |
273 | /* | |
274 | * Wait for previous parity to be empty of readers. | |
66bc4dcd MD |
275 | * update_counter_and_wait() can release and grab again |
276 | * rcu_registry_lock interally. | |
47d2f29e | 277 | */ |
2dfb8b5e MD |
278 | update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ |
279 | out: | |
66bc4dcd | 280 | mutex_unlock(&rcu_registry_lock); |
6abb4bd5 | 281 | mutex_unlock(&rcu_gp_lock); |
47d2f29e | 282 | |
bc49c323 MD |
283 | /* |
284 | * Finish waiting for reader threads before letting the old ptr being | |
47d2f29e MD |
285 | * freed. |
286 | */ | |
bc49c323 | 287 | if (was_online) |
27b940e7 PB |
288 | rcu_thread_online(); |
289 | else | |
290 | cmm_smp_mb(); | |
47d2f29e | 291 | } |
b39e1761 | 292 | #else /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
293 | void synchronize_rcu(void) |
294 | { | |
f0f7dbdd | 295 | unsigned long was_online; |
ff2f67a0 | 296 | |
bd252a04 | 297 | was_online = URCU_TLS(rcu_reader).ctr; |
ff2f67a0 MD |
298 | |
299 | /* | |
300 | * Mark the writer thread offline to make sure we don't wait for | |
5e77fc1f PM |
301 | * our own quiescent state. This allows using synchronize_rcu() |
302 | * in threads registered as readers. | |
ff2f67a0 | 303 | */ |
27b940e7 PB |
304 | if (was_online) |
305 | rcu_thread_offline(); | |
306 | else | |
307 | cmm_smp_mb(); | |
ff2f67a0 | 308 | |
6abb4bd5 | 309 | mutex_lock(&rcu_gp_lock); |
66bc4dcd | 310 | mutex_lock(&rcu_registry_lock); |
16aa9ee8 | 311 | if (cds_list_empty(®istry)) |
2dfb8b5e | 312 | goto out; |
66bc4dcd MD |
313 | /* |
314 | * update_counter_and_wait() can release and grab again | |
315 | * rcu_registry_lock interally. | |
316 | */ | |
2dfb8b5e MD |
317 | update_counter_and_wait(); |
318 | out: | |
66bc4dcd | 319 | mutex_unlock(&rcu_registry_lock); |
6abb4bd5 | 320 | mutex_unlock(&rcu_gp_lock); |
ff2f67a0 MD |
321 | |
322 | if (was_online) | |
27b940e7 PB |
323 | rcu_thread_online(); |
324 | else | |
325 | cmm_smp_mb(); | |
9f1621ca | 326 | } |
b39e1761 | 327 | #endif /* !(CAA_BITS_PER_LONG < 64) */ |
9f1621ca MD |
328 | |
329 | /* | |
330 | * library wrappers to be used by non-LGPL compatible source code. | |
331 | */ | |
332 | ||
333 | void rcu_read_lock(void) | |
334 | { | |
335 | _rcu_read_lock(); | |
336 | } | |
337 | ||
338 | void rcu_read_unlock(void) | |
339 | { | |
340 | _rcu_read_unlock(); | |
341 | } | |
342 | ||
7ac06cef MD |
343 | void rcu_quiescent_state(void) |
344 | { | |
345 | _rcu_quiescent_state(); | |
346 | } | |
347 | ||
348 | void rcu_thread_offline(void) | |
349 | { | |
350 | _rcu_thread_offline(); | |
351 | } | |
352 | ||
353 | void rcu_thread_online(void) | |
354 | { | |
355 | _rcu_thread_online(); | |
356 | } | |
357 | ||
9f1621ca MD |
358 | void rcu_register_thread(void) |
359 | { | |
bd252a04 MD |
360 | URCU_TLS(rcu_reader).tid = pthread_self(); |
361 | assert(URCU_TLS(rcu_reader).ctr == 0); | |
4f8e3380 | 362 | |
66bc4dcd | 363 | mutex_lock(&rcu_registry_lock); |
bd252a04 | 364 | cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); |
66bc4dcd | 365 | mutex_unlock(&rcu_registry_lock); |
5f373c84 | 366 | _rcu_thread_online(); |
9f1621ca MD |
367 | } |
368 | ||
369 | void rcu_unregister_thread(void) | |
370 | { | |
76f3022f MD |
371 | /* |
372 | * We have to make the thread offline otherwise we end up dealocking | |
373 | * with a waiting writer. | |
374 | */ | |
375 | _rcu_thread_offline(); | |
66bc4dcd | 376 | mutex_lock(&rcu_registry_lock); |
bd252a04 | 377 | cds_list_del(&URCU_TLS(rcu_reader).node); |
66bc4dcd | 378 | mutex_unlock(&rcu_registry_lock); |
9f1621ca | 379 | } |
f6d18c64 MD |
380 | |
381 | void rcu_exit(void) | |
382 | { | |
01cadde4 MD |
383 | /* |
384 | * Assertion disabled because call_rcu threads are now rcu | |
385 | * readers, and left running at exit. | |
386 | * assert(cds_list_empty(®istry)); | |
387 | */ | |
f6d18c64 | 388 | } |
5e77fc1f | 389 | |
5e6b23a6 | 390 | DEFINE_RCU_FLAVOR(rcu_flavor); |
541d828d | 391 | |
5e77fc1f | 392 | #include "urcu-call-rcu-impl.h" |
0376e7b2 | 393 | #include "urcu-defer-impl.h" |