Commit | Line | Data |
---|---|---|
b257a10b MD |
1 | /* |
2 | * urcu.c | |
3 | * | |
4 | * Userspace RCU library | |
5 | * | |
6982d6d7 | 6 | * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com> |
af02d47e | 7 | * Copyright (c) 2009 Paul E. McKenney, IBM Corporation. |
b257a10b | 8 | * |
af02d47e MD |
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 | |
54843abc PM |
22 | * |
23 | * IBM's contributions to this file may be relicensed under LGPLv2 or later. | |
b257a10b MD |
24 | */ |
25 | ||
fdf01eed | 26 | #define _BSD_SOURCE |
c1d2c60b | 27 | #define _GNU_SOURCE |
71c811bf | 28 | #define _LGPL_SOURCE |
27b012e2 MD |
29 | #include <stdio.h> |
30 | #include <pthread.h> | |
31 | #include <signal.h> | |
32 | #include <assert.h> | |
f69f195a | 33 | #include <stdlib.h> |
6d841bc2 | 34 | #include <stdint.h> |
f69f195a | 35 | #include <string.h> |
09a9f986 | 36 | #include <errno.h> |
e8043c1b | 37 | #include <poll.h> |
27b012e2 | 38 | |
71c811bf | 39 | #include "urcu/wfqueue.h" |
57760d44 | 40 | #include "urcu/map/urcu.h" |
af7c2dbe | 41 | #include "urcu/static/urcu.h" |
618b2595 | 42 | #include "urcu-pointer.h" |
bd252a04 | 43 | #include "urcu/tls-compat.h" |
71c811bf | 44 | |
4a6d7378 MD |
45 | #include "urcu-die.h" |
46 | ||
121a5d44 | 47 | /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */ |
71c811bf | 48 | #undef _LGPL_SOURCE |
27b012e2 | 49 | #include "urcu.h" |
71c811bf | 50 | #define _LGPL_SOURCE |
27b012e2 | 51 | |
3a71751e PB |
52 | /* |
53 | * If a reader is really non-cooperative and refuses to commit its | |
54 | * rcu_active_readers count to memory (there is no barrier in the reader | |
55 | * per-se), kick it after a few loops waiting for it. | |
56 | */ | |
57 | #define KICK_READER_LOOPS 10000 | |
58 | ||
59 | /* | |
60 | * Active attempts to check for reader Q.S. before calling futex(). | |
61 | */ | |
62 | #define RCU_QS_ACTIVE_ATTEMPTS 100 | |
63 | ||
fdf01eed | 64 | #ifdef RCU_MEMBARRIER |
834a45ba | 65 | static int init_done; |
fdf01eed | 66 | int has_sys_membarrier; |
834a45ba | 67 | |
02be5561 | 68 | void __attribute__((constructor)) rcu_init(void); |
fdf01eed MD |
69 | #endif |
70 | ||
71 | #ifdef RCU_MB | |
02be5561 | 72 | void rcu_init(void) |
e90a6e9c MD |
73 | { |
74 | } | |
75 | #endif | |
8a5fb4c9 | 76 | |
fdf01eed MD |
77 | #ifdef RCU_SIGNAL |
78 | static int init_done; | |
79 | ||
80 | void __attribute__((constructor)) rcu_init(void); | |
81 | void __attribute__((destructor)) rcu_exit(void); | |
82 | #endif | |
83 | ||
6abb4bd5 | 84 | static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; |
27b012e2 | 85 | |
6d841bc2 | 86 | int32_t gp_futex; |
bc6c15bb | 87 | |
128166c9 MD |
88 | /* |
89 | * Global grace period counter. | |
02be5561 | 90 | * Contains the current RCU_GP_CTR_PHASE. |
afb8f2c9 | 91 | * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path. |
b0d5e790 | 92 | * Written to only by writer with mutex taken. Read by both writer and readers. |
128166c9 | 93 | */ |
27d65bc5 | 94 | unsigned long rcu_gp_ctr = RCU_GP_COUNT; |
27b012e2 | 95 | |
b0d5e790 MD |
96 | /* |
97 | * Written to only by each individual reader. Read by both the reader and the | |
98 | * writers. | |
99 | */ | |
bd252a04 | 100 | DEFINE_URCU_TLS(struct rcu_reader, rcu_reader); |
27b012e2 | 101 | |
cf380c2f | 102 | #ifdef DEBUG_YIELD |
9d335088 | 103 | unsigned int yield_active; |
bd252a04 | 104 | DEFINE_URCU_TLS(unsigned int, rand_yield); |
cf380c2f MD |
105 | #endif |
106 | ||
16aa9ee8 | 107 | static CDS_LIST_HEAD(registry); |
27b012e2 | 108 | |
6abb4bd5 | 109 | static void mutex_lock(pthread_mutex_t *mutex) |
41718ff9 MD |
110 | { |
111 | int ret; | |
09a9f986 PM |
112 | |
113 | #ifndef DISTRUST_SIGNALS_EXTREME | |
6abb4bd5 | 114 | ret = pthread_mutex_lock(mutex); |
4a6d7378 MD |
115 | if (ret) |
116 | urcu_die(ret); | |
09a9f986 | 117 | #else /* #ifndef DISTRUST_SIGNALS_EXTREME */ |
6abb4bd5 | 118 | while ((ret = pthread_mutex_trylock(mutex)) != 0) { |
4a6d7378 MD |
119 | if (ret != EBUSY && ret != EINTR) |
120 | urcu_die(ret); | |
bd252a04 | 121 | if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) { |
5481ddb3 | 122 | cmm_smp_mb(); |
bd252a04 | 123 | _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0); |
5481ddb3 | 124 | cmm_smp_mb(); |
09a9f986 PM |
125 | } |
126 | poll(NULL,0,10); | |
127 | } | |
128 | #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */ | |
41718ff9 MD |
129 | } |
130 | ||
6abb4bd5 | 131 | static void mutex_unlock(pthread_mutex_t *mutex) |
41718ff9 MD |
132 | { |
133 | int ret; | |
134 | ||
6abb4bd5 | 135 | ret = pthread_mutex_unlock(mutex); |
4a6d7378 MD |
136 | if (ret) |
137 | urcu_die(ret); | |
41718ff9 MD |
138 | } |
139 | ||
fdf01eed | 140 | #ifdef RCU_MEMBARRIER |
25cc6d18 | 141 | static void smp_mb_master(int group) |
fdf01eed | 142 | { |
a0b7f7ea | 143 | if (caa_likely(has_sys_membarrier)) |
f0708810 | 144 | membarrier(MEMBARRIER_EXPEDITED); |
fdf01eed | 145 | else |
5481ddb3 | 146 | cmm_smp_mb(); |
fdf01eed MD |
147 | } |
148 | #endif | |
149 | ||
02be5561 | 150 | #ifdef RCU_MB |
25cc6d18 | 151 | static void smp_mb_master(int group) |
40e140c9 | 152 | { |
5481ddb3 | 153 | cmm_smp_mb(); |
40e140c9 | 154 | } |
fdf01eed MD |
155 | #endif |
156 | ||
157 | #ifdef RCU_SIGNAL | |
78ff9419 | 158 | static void force_mb_all_readers(void) |
27b012e2 | 159 | { |
02be5561 | 160 | struct rcu_reader *index; |
e3b0cef0 | 161 | |
27b012e2 | 162 | /* |
5481ddb3 | 163 | * Ask for each threads to execute a cmm_smp_mb() so we can consider the |
27b012e2 MD |
164 | * compiler barriers around rcu read lock as real memory barriers. |
165 | */ | |
16aa9ee8 | 166 | if (cds_list_empty(®istry)) |
27b012e2 | 167 | return; |
3a86deba | 168 | /* |
5481ddb3 | 169 | * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs |
157dca95 | 170 | * a cache flush on architectures with non-coherent cache. Let's play |
5481ddb3 | 171 | * safe and don't assume anything : we use cmm_smp_mc() to make sure the |
157dca95 | 172 | * cache flush is enforced. |
3a86deba | 173 | */ |
16aa9ee8 | 174 | cds_list_for_each_entry(index, ®istry, node) { |
6cf3827c | 175 | CMM_STORE_SHARED(index->need_mb, 1); |
02be5561 | 176 | pthread_kill(index->tid, SIGRCU); |
09a9f986 | 177 | } |
27b012e2 MD |
178 | /* |
179 | * Wait for sighandler (and thus mb()) to execute on every thread. | |
09a9f986 PM |
180 | * |
181 | * Note that the pthread_kill() will never be executed on systems | |
182 | * that correctly deliver signals in a timely manner. However, it | |
183 | * is not uncommon for kernels to have bugs that can result in | |
184 | * lost or unduly delayed signals. | |
185 | * | |
186 | * If you are seeing the below pthread_kill() executing much at | |
187 | * all, we suggest testing the underlying kernel and filing the | |
188 | * relevant bug report. For Linux kernels, we recommend getting | |
189 | * the Linux Test Project (LTP). | |
27b012e2 | 190 | */ |
16aa9ee8 | 191 | cds_list_for_each_entry(index, ®istry, node) { |
6cf3827c | 192 | while (CMM_LOAD_SHARED(index->need_mb)) { |
02be5561 | 193 | pthread_kill(index->tid, SIGRCU); |
09a9f986 PM |
194 | poll(NULL, 0, 1); |
195 | } | |
196 | } | |
5481ddb3 | 197 | cmm_smp_mb(); /* read ->need_mb before ending the barrier */ |
27b012e2 | 198 | } |
9d7e3f89 | 199 | |
25cc6d18 | 200 | static void smp_mb_master(int group) |
9d7e3f89 MD |
201 | { |
202 | force_mb_all_readers(); | |
203 | } | |
fdf01eed | 204 | #endif /* #ifdef RCU_SIGNAL */ |
27b012e2 | 205 | |
bc6c15bb MD |
206 | /* |
207 | * synchronize_rcu() waiting. Single thread. | |
208 | */ | |
cfe78e25 | 209 | static void wait_gp(void) |
bc6c15bb | 210 | { |
cfe78e25 | 211 | /* Read reader_gp before read futex */ |
25cc6d18 | 212 | smp_mb_master(RCU_MB_GROUP); |
cfe78e25 | 213 | if (uatomic_read(&gp_futex) == -1) |
0854ccff | 214 | futex_async(&gp_futex, FUTEX_WAIT, -1, |
cfe78e25 | 215 | NULL, NULL, 0); |
bc6c15bb MD |
216 | } |
217 | ||
2dfb8b5e | 218 | void update_counter_and_wait(void) |
27b012e2 | 219 | { |
16aa9ee8 | 220 | CDS_LIST_HEAD(qsreaders); |
cfe78e25 | 221 | int wait_loops = 0; |
02be5561 | 222 | struct rcu_reader *index, *tmp; |
27b012e2 | 223 | |
32c15e4e | 224 | /* Switch parity: 0 -> 1, 1 -> 0 */ |
6cf3827c | 225 | CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE); |
2dfb8b5e MD |
226 | |
227 | /* | |
d40fde2c MD |
228 | * Must commit rcu_gp_ctr update to memory before waiting for quiescent |
229 | * state. Failure to do so could result in the writer waiting forever | |
230 | * while new readers are always accessing data (no progress). Enforce | |
231 | * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr. | |
2dfb8b5e | 232 | */ |
5481ddb3 | 233 | cmm_barrier(); |
2dfb8b5e MD |
234 | |
235 | /* | |
935b11ff | 236 | * |
5481ddb3 | 237 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
2dfb8b5e MD |
238 | * model easier to understand. It does not have a big performance impact |
239 | * anyway, given this is the write-side. | |
240 | */ | |
5481ddb3 | 241 | cmm_smp_mb(); |
2dfb8b5e | 242 | |
40e140c9 | 243 | /* |
bd252a04 | 244 | * Wait for each thread URCU_TLS(rcu_reader).ctr count to become 0. |
27b012e2 | 245 | */ |
cfe78e25 MD |
246 | for (;;) { |
247 | wait_loops++; | |
248 | if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { | |
249 | uatomic_dec(&gp_futex); | |
250 | /* Write futex before read reader_gp */ | |
25cc6d18 | 251 | smp_mb_master(RCU_MB_GROUP); |
cfe78e25 MD |
252 | } |
253 | ||
16aa9ee8 | 254 | cds_list_for_each_entry_safe(index, tmp, ®istry, node) { |
b95a001f | 255 | if (!rcu_gp_ongoing(&index->ctr)) |
16aa9ee8 | 256 | cds_list_move(&index->node, &qsreaders); |
cfe78e25 MD |
257 | } |
258 | ||
e8043c1b | 259 | #ifndef HAS_INCOHERENT_CACHES |
16aa9ee8 | 260 | if (cds_list_empty(®istry)) { |
cfe78e25 MD |
261 | if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { |
262 | /* Read reader_gp before write futex */ | |
25cc6d18 | 263 | smp_mb_master(RCU_MB_GROUP); |
cfe78e25 | 264 | uatomic_set(&gp_futex, 0); |
bc6c15bb | 265 | } |
cfe78e25 MD |
266 | break; |
267 | } else { | |
268 | if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) | |
269 | wait_gp(); | |
270 | else | |
06f22bdb | 271 | caa_cpu_relax(); |
bc6c15bb | 272 | } |
e8043c1b | 273 | #else /* #ifndef HAS_INCOHERENT_CACHES */ |
27b012e2 | 274 | /* |
40e140c9 | 275 | * BUSY-LOOP. Force the reader thread to commit its |
bd252a04 MD |
276 | * URCU_TLS(rcu_reader).ctr update to memory if we wait |
277 | * for too long. | |
27b012e2 | 278 | */ |
16aa9ee8 | 279 | if (cds_list_empty(®istry)) { |
cfe78e25 MD |
280 | if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) { |
281 | /* Read reader_gp before write futex */ | |
25cc6d18 | 282 | smp_mb_master(RCU_MB_GROUP); |
cfe78e25 MD |
283 | uatomic_set(&gp_futex, 0); |
284 | } | |
285 | break; | |
286 | } else { | |
287 | switch (wait_loops) { | |
bc6c15bb | 288 | case RCU_QS_ACTIVE_ATTEMPTS: |
cfe78e25 MD |
289 | wait_gp(); |
290 | break; /* only escape switch */ | |
bc6c15bb | 291 | case KICK_READER_LOOPS: |
25cc6d18 | 292 | smp_mb_master(RCU_MB_GROUP); |
40e140c9 | 293 | wait_loops = 0; |
cfe78e25 | 294 | break; /* only escape switch */ |
bc6c15bb | 295 | default: |
06f22bdb | 296 | caa_cpu_relax(); |
40e140c9 MD |
297 | } |
298 | } | |
e8043c1b | 299 | #endif /* #else #ifndef HAS_INCOHERENT_CACHES */ |
27b012e2 | 300 | } |
cfe78e25 | 301 | /* put back the reader list in the registry */ |
16aa9ee8 | 302 | cds_list_splice(&qsreaders, ®istry); |
27b012e2 MD |
303 | } |
304 | ||
9598a481 | 305 | void synchronize_rcu(void) |
2bc59bd7 | 306 | { |
6abb4bd5 | 307 | mutex_lock(&rcu_gp_lock); |
135530fd | 308 | |
16aa9ee8 | 309 | if (cds_list_empty(®istry)) |
2dfb8b5e MD |
310 | goto out; |
311 | ||
9598a481 | 312 | /* All threads should read qparity before accessing data structure |
6abb4bd5 MD |
313 | * where new ptr points to. Must be done within rcu_gp_lock because it |
314 | * iterates on reader threads.*/ | |
9598a481 | 315 | /* Write new ptr before changing the qparity */ |
25cc6d18 | 316 | smp_mb_master(RCU_MB_GROUP); |
9598a481 | 317 | |
9598a481 MD |
318 | /* |
319 | * Wait for previous parity to be empty of readers. | |
320 | */ | |
2dfb8b5e | 321 | update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ |
9598a481 MD |
322 | |
323 | /* | |
324 | * Must finish waiting for quiescent state for parity 0 before | |
d40fde2c MD |
325 | * committing next rcu_gp_ctr update to memory. Failure to do so could |
326 | * result in the writer waiting forever while new readers are always | |
327 | * accessing data (no progress). Enforce compiler-order of load | |
bd252a04 | 328 | * URCU_TLS(rcu_reader).ctr before store to rcu_gp_ctr. |
9598a481 | 329 | */ |
5481ddb3 | 330 | cmm_barrier(); |
9598a481 | 331 | |
5dba80f9 | 332 | /* |
5481ddb3 | 333 | * Adding a cmm_smp_mb() which is _not_ formally required, but makes the |
5dba80f9 MD |
334 | * model easier to understand. It does not have a big performance impact |
335 | * anyway, given this is the write-side. | |
336 | */ | |
5481ddb3 | 337 | cmm_smp_mb(); |
67c2d80b | 338 | |
9598a481 MD |
339 | /* |
340 | * Wait for previous parity to be empty of readers. | |
341 | */ | |
2dfb8b5e | 342 | update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ |
9598a481 | 343 | |
9598a481 | 344 | /* Finish waiting for reader threads before letting the old ptr being |
6abb4bd5 MD |
345 | * freed. Must be done within rcu_gp_lock because it iterates on reader |
346 | * threads. */ | |
25cc6d18 | 347 | smp_mb_master(RCU_MB_GROUP); |
2dfb8b5e | 348 | out: |
6abb4bd5 | 349 | mutex_unlock(&rcu_gp_lock); |
2bc59bd7 PM |
350 | } |
351 | ||
121a5d44 MD |
352 | /* |
353 | * library wrappers to be used by non-LGPL compatible source code. | |
354 | */ | |
355 | ||
356 | void rcu_read_lock(void) | |
357 | { | |
358 | _rcu_read_lock(); | |
359 | } | |
360 | ||
361 | void rcu_read_unlock(void) | |
362 | { | |
363 | _rcu_read_unlock(); | |
364 | } | |
365 | ||
121a5d44 | 366 | void rcu_register_thread(void) |
27b012e2 | 367 | { |
bd252a04 MD |
368 | URCU_TLS(rcu_reader).tid = pthread_self(); |
369 | assert(URCU_TLS(rcu_reader).need_mb == 0); | |
370 | assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK)); | |
02be5561 | 371 | |
6abb4bd5 | 372 | mutex_lock(&rcu_gp_lock); |
02be5561 | 373 | rcu_init(); /* In case gcc does not support constructor attribute */ |
bd252a04 | 374 | cds_list_add(&URCU_TLS(rcu_reader).node, ®istry); |
6abb4bd5 | 375 | mutex_unlock(&rcu_gp_lock); |
27b012e2 MD |
376 | } |
377 | ||
121a5d44 | 378 | void rcu_unregister_thread(void) |
27b012e2 | 379 | { |
6abb4bd5 | 380 | mutex_lock(&rcu_gp_lock); |
bd252a04 | 381 | cds_list_del(&URCU_TLS(rcu_reader).node); |
6abb4bd5 | 382 | mutex_unlock(&rcu_gp_lock); |
27b012e2 MD |
383 | } |
384 | ||
fdf01eed MD |
385 | #ifdef RCU_MEMBARRIER |
386 | void rcu_init(void) | |
387 | { | |
388 | if (init_done) | |
389 | return; | |
390 | init_done = 1; | |
cf5271ee | 391 | if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY)) |
fdf01eed MD |
392 | has_sys_membarrier = 1; |
393 | } | |
394 | #endif | |
395 | ||
396 | #ifdef RCU_SIGNAL | |
02be5561 | 397 | static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context) |
27b012e2 | 398 | { |
40e140c9 | 399 | /* |
5481ddb3 DG |
400 | * Executing this cmm_smp_mb() is the only purpose of this signal handler. |
401 | * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is | |
40e140c9 MD |
402 | * executed on. |
403 | */ | |
5481ddb3 | 404 | cmm_smp_mb(); |
bd252a04 | 405 | _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0); |
5481ddb3 | 406 | cmm_smp_mb(); |
27b012e2 MD |
407 | } |
408 | ||
8a5fb4c9 | 409 | /* |
02be5561 | 410 | * rcu_init constructor. Called when the library is linked, but also when |
8a5fb4c9 MD |
411 | * reader threads are calling rcu_register_thread(). |
412 | * Should only be called by a single thread at a given time. This is ensured by | |
6abb4bd5 MD |
413 | * holing the rcu_gp_lock from rcu_register_thread() or by running at library |
414 | * load time, which should not be executed by multiple threads nor concurrently | |
415 | * with rcu_register_thread() anyway. | |
8a5fb4c9 | 416 | */ |
02be5561 | 417 | void rcu_init(void) |
27b012e2 MD |
418 | { |
419 | struct sigaction act; | |
420 | int ret; | |
421 | ||
8a5fb4c9 MD |
422 | if (init_done) |
423 | return; | |
424 | init_done = 1; | |
425 | ||
02be5561 | 426 | act.sa_sigaction = sigrcu_handler; |
dd052bd3 | 427 | act.sa_flags = SA_SIGINFO | SA_RESTART; |
c297c21c | 428 | sigemptyset(&act.sa_mask); |
02be5561 | 429 | ret = sigaction(SIGRCU, &act, NULL); |
4a6d7378 MD |
430 | if (ret) |
431 | urcu_die(errno); | |
27b012e2 MD |
432 | } |
433 | ||
02be5561 | 434 | void rcu_exit(void) |
27b012e2 MD |
435 | { |
436 | struct sigaction act; | |
437 | int ret; | |
438 | ||
02be5561 | 439 | ret = sigaction(SIGRCU, NULL, &act); |
4a6d7378 MD |
440 | if (ret) |
441 | urcu_die(errno); | |
02be5561 | 442 | assert(act.sa_sigaction == sigrcu_handler); |
16aa9ee8 | 443 | assert(cds_list_empty(®istry)); |
27b012e2 | 444 | } |
5e77fc1f | 445 | |
fdf01eed | 446 | #endif /* #ifdef RCU_SIGNAL */ |
5e77fc1f | 447 | |
5e6b23a6 | 448 | DEFINE_RCU_FLAVOR(rcu_flavor); |
541d828d | 449 | |
5e77fc1f | 450 | #include "urcu-call-rcu-impl.h" |
0376e7b2 | 451 | #include "urcu-defer-impl.h" |