Revert "Use initial-exec tls model"
[urcu.git] / src / urcu.c
CommitLineData
b257a10b
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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 *
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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
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22 *
23 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
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24 */
25
fdf01eed 26#define _BSD_SOURCE
71c811bf 27#define _LGPL_SOURCE
82d50e1a 28#define _DEFAULT_SOURCE
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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
999991c6 39#include "urcu/arch.h"
d73fb81f 40#include "urcu/wfcqueue.h"
57760d44 41#include "urcu/map/urcu.h"
af7c2dbe 42#include "urcu/static/urcu.h"
618b2595 43#include "urcu-pointer.h"
bd252a04 44#include "urcu/tls-compat.h"
71c811bf 45
4a6d7378 46#include "urcu-die.h"
5bffdd5d 47#include "urcu-wait.h"
4a6d7378 48
121a5d44 49/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
71c811bf 50#undef _LGPL_SOURCE
27b012e2 51#include "urcu.h"
71c811bf 52#define _LGPL_SOURCE
27b012e2 53
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54/*
55 * If a reader is really non-cooperative and refuses to commit its
56 * rcu_active_readers count to memory (there is no barrier in the reader
9340c38d 57 * per-se), kick it after 10 loops waiting for it.
3a71751e 58 */
9340c38d 59#define KICK_READER_LOOPS 10
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60
61/*
62 * Active attempts to check for reader Q.S. before calling futex().
63 */
64#define RCU_QS_ACTIVE_ATTEMPTS 100
65
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66/* If the headers do not support membarrier system call, fall back on RCU_MB */
67#ifdef __NR_membarrier
68# define membarrier(...) syscall(__NR_membarrier, __VA_ARGS__)
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69#else
70# define membarrier(...) -ENOSYS
71#endif
72
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73enum membarrier_cmd {
74 MEMBARRIER_CMD_QUERY = 0,
75 MEMBARRIER_CMD_SHARED = (1 << 0),
76};
553b7eb9 77
fdf01eed 78#ifdef RCU_MEMBARRIER
834a45ba 79static int init_done;
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80#ifndef CONFIG_RCU_FORCE_SYS_MEMBARRIER
81int rcu_has_sys_membarrier_memb;
82#endif
834a45ba 83
02be5561 84void __attribute__((constructor)) rcu_init(void);
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85#endif
86
87#ifdef RCU_MB
02be5561 88void rcu_init(void)
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89{
90}
91#endif
8a5fb4c9 92
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93#ifdef RCU_SIGNAL
94static int init_done;
95
96void __attribute__((constructor)) rcu_init(void);
97void __attribute__((destructor)) rcu_exit(void);
98#endif
99
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100/*
101 * rcu_gp_lock ensures mutual exclusion between threads calling
102 * synchronize_rcu().
103 */
6abb4bd5 104static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
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105/*
106 * rcu_registry_lock ensures mutual exclusion between threads
107 * registering and unregistering themselves to/from the registry, and
108 * with threads reading that registry from synchronize_rcu(). However,
109 * this lock is not held all the way through the completion of awaiting
110 * for the grace period. It is sporadically released between iterations
111 * on the registry.
112 * rcu_registry_lock may nest inside rcu_gp_lock.
113 */
114static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
4de0cd31 115struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
27b012e2 116
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117/*
118 * Written to only by each individual reader. Read by both the reader and the
119 * writers.
120 */
2f661865 121DEFINE_URCU_TLS(struct rcu_reader, rcu_reader);
27b012e2 122
16aa9ee8 123static CDS_LIST_HEAD(registry);
27b012e2 124
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125/*
126 * Queue keeping threads awaiting to wait for a grace period. Contains
127 * struct gp_waiters_thread objects.
128 */
129static DEFINE_URCU_WAIT_QUEUE(gp_waiters);
130
6abb4bd5 131static void mutex_lock(pthread_mutex_t *mutex)
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132{
133 int ret;
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134
135#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5 136 ret = pthread_mutex_lock(mutex);
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137 if (ret)
138 urcu_die(ret);
09a9f986 139#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5 140 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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141 if (ret != EBUSY && ret != EINTR)
142 urcu_die(ret);
bd252a04 143 if (CMM_LOAD_SHARED(URCU_TLS(rcu_reader).need_mb)) {
5481ddb3 144 cmm_smp_mb();
bd252a04 145 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
5481ddb3 146 cmm_smp_mb();
09a9f986 147 }
8999a9ee 148 (void) poll(NULL, 0, 10);
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149 }
150#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
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151}
152
6abb4bd5 153static void mutex_unlock(pthread_mutex_t *mutex)
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154{
155 int ret;
156
6abb4bd5 157 ret = pthread_mutex_unlock(mutex);
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158 if (ret)
159 urcu_die(ret);
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160}
161
fdf01eed 162#ifdef RCU_MEMBARRIER
a4922ed9 163static void smp_mb_master(void)
fdf01eed 164{
d8d9a340 165 if (caa_likely(rcu_has_sys_membarrier_memb))
64f469e6 166 (void) membarrier(MEMBARRIER_CMD_SHARED, 0);
fdf01eed 167 else
5481ddb3 168 cmm_smp_mb();
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169}
170#endif
171
02be5561 172#ifdef RCU_MB
a4922ed9 173static void smp_mb_master(void)
40e140c9 174{
5481ddb3 175 cmm_smp_mb();
40e140c9 176}
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177#endif
178
179#ifdef RCU_SIGNAL
78ff9419 180static void force_mb_all_readers(void)
27b012e2 181{
02be5561 182 struct rcu_reader *index;
e3b0cef0 183
27b012e2 184 /*
5481ddb3 185 * Ask for each threads to execute a cmm_smp_mb() so we can consider the
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186 * compiler barriers around rcu read lock as real memory barriers.
187 */
16aa9ee8 188 if (cds_list_empty(&registry))
27b012e2 189 return;
3a86deba 190 /*
5481ddb3 191 * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
157dca95 192 * a cache flush on architectures with non-coherent cache. Let's play
5481ddb3 193 * safe and don't assume anything : we use cmm_smp_mc() to make sure the
157dca95 194 * cache flush is enforced.
3a86deba 195 */
16aa9ee8 196 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 197 CMM_STORE_SHARED(index->need_mb, 1);
02be5561 198 pthread_kill(index->tid, SIGRCU);
09a9f986 199 }
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200 /*
201 * Wait for sighandler (and thus mb()) to execute on every thread.
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202 *
203 * Note that the pthread_kill() will never be executed on systems
204 * that correctly deliver signals in a timely manner. However, it
205 * is not uncommon for kernels to have bugs that can result in
206 * lost or unduly delayed signals.
207 *
208 * If you are seeing the below pthread_kill() executing much at
209 * all, we suggest testing the underlying kernel and filing the
210 * relevant bug report. For Linux kernels, we recommend getting
211 * the Linux Test Project (LTP).
27b012e2 212 */
16aa9ee8 213 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 214 while (CMM_LOAD_SHARED(index->need_mb)) {
02be5561 215 pthread_kill(index->tid, SIGRCU);
8999a9ee 216 (void) poll(NULL, 0, 1);
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217 }
218 }
5481ddb3 219 cmm_smp_mb(); /* read ->need_mb before ending the barrier */
27b012e2 220}
9d7e3f89 221
a4922ed9 222static void smp_mb_master(void)
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223{
224 force_mb_all_readers();
225}
fdf01eed 226#endif /* #ifdef RCU_SIGNAL */
27b012e2 227
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228/*
229 * synchronize_rcu() waiting. Single thread.
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230 * Always called with rcu_registry lock held. Releases this lock and
231 * grabs it again. Holds the lock when it returns.
bc6c15bb 232 */
cfe78e25 233static void wait_gp(void)
bc6c15bb 234{
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235 /*
236 * Read reader_gp before read futex. smp_mb_master() needs to
237 * be called with the rcu registry lock held in RCU_SIGNAL
238 * flavor.
239 */
a4922ed9 240 smp_mb_master();
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241 /* Temporarily unlock the registry lock. */
242 mutex_unlock(&rcu_registry_lock);
b0a841b4 243 if (uatomic_read(&rcu_gp.futex) != -1)
fca9fb96 244 goto end;
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245 while (futex_async(&rcu_gp.futex, FUTEX_WAIT, -1,
246 NULL, NULL, 0)) {
247 switch (errno) {
248 case EWOULDBLOCK:
249 /* Value already changed. */
fca9fb96 250 goto end;
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251 case EINTR:
252 /* Retry if interrupted by signal. */
253 break; /* Get out of switch. */
254 default:
255 /* Unexpected error. */
256 urcu_die(errno);
257 }
258 }
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259end:
260 /*
261 * Re-lock the registry lock before the next loop.
262 */
263 mutex_lock(&rcu_registry_lock);
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264}
265
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266/*
267 * Always called with rcu_registry lock held. Releases this lock between
268 * iterations and grabs it again. Holds the lock when it returns.
269 */
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270static void wait_for_readers(struct cds_list_head *input_readers,
271 struct cds_list_head *cur_snap_readers,
272 struct cds_list_head *qsreaders)
27b012e2 273{
9340c38d 274 unsigned int wait_loops = 0;
02be5561 275 struct rcu_reader *index, *tmp;
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276#ifdef HAS_INCOHERENT_CACHES
277 unsigned int wait_gp_loops = 0;
278#endif /* HAS_INCOHERENT_CACHES */
27b012e2 279
40e140c9 280 /*
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281 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
282 * indicate quiescence (not nested), or observe the current
ed1b099e 283 * rcu_gp.ctr value.
27b012e2 284 */
cfe78e25 285 for (;;) {
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286 if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
287 wait_loops++;
9340c38d 288 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
ed1b099e 289 uatomic_dec(&rcu_gp.futex);
cfe78e25 290 /* Write futex before read reader_gp */
a4922ed9 291 smp_mb_master();
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292 }
293
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294 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
295 switch (rcu_reader_state(&index->ctr)) {
296 case RCU_READER_ACTIVE_CURRENT:
297 if (cur_snap_readers) {
298 cds_list_move(&index->node,
299 cur_snap_readers);
300 break;
301 }
302 /* Fall-through */
303 case RCU_READER_INACTIVE:
304 cds_list_move(&index->node, qsreaders);
305 break;
306 case RCU_READER_ACTIVE_OLD:
307 /*
308 * Old snapshot. Leaving node in
309 * input_readers will make us busy-loop
310 * until the snapshot becomes current or
311 * the reader becomes inactive.
312 */
313 break;
314 }
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315 }
316
e8043c1b 317#ifndef HAS_INCOHERENT_CACHES
fd189fa5 318 if (cds_list_empty(input_readers)) {
9340c38d 319 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
cfe78e25 320 /* Read reader_gp before write futex */
a4922ed9 321 smp_mb_master();
ed1b099e 322 uatomic_set(&rcu_gp.futex, 0);
bc6c15bb 323 }
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324 break;
325 } else {
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326 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
327 /* wait_gp unlocks/locks registry lock. */
cfe78e25 328 wait_gp();
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329 } else {
330 /* Temporarily unlock the registry lock. */
331 mutex_unlock(&rcu_registry_lock);
06f22bdb 332 caa_cpu_relax();
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333 /*
334 * Re-lock the registry lock before the
335 * next loop.
336 */
337 mutex_lock(&rcu_registry_lock);
338 }
bc6c15bb 339 }
e8043c1b 340#else /* #ifndef HAS_INCOHERENT_CACHES */
27b012e2 341 /*
40e140c9 342 * BUSY-LOOP. Force the reader thread to commit its
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343 * URCU_TLS(rcu_reader).ctr update to memory if we wait
344 * for too long.
27b012e2 345 */
fd189fa5 346 if (cds_list_empty(input_readers)) {
9340c38d 347 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
cfe78e25 348 /* Read reader_gp before write futex */
a4922ed9 349 smp_mb_master();
ed1b099e 350 uatomic_set(&rcu_gp.futex, 0);
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351 }
352 break;
353 } else {
9340c38d 354 if (wait_gp_loops == KICK_READER_LOOPS) {
a4922ed9 355 smp_mb_master();
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356 wait_gp_loops = 0;
357 }
358 if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) {
fca9fb96 359 /* wait_gp unlocks/locks registry lock. */
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360 wait_gp();
361 wait_gp_loops++;
362 } else {
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363 /* Temporarily unlock the registry lock. */
364 mutex_unlock(&rcu_registry_lock);
06f22bdb 365 caa_cpu_relax();
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366 /*
367 * Re-lock the registry lock before the
368 * next loop.
369 */
370 mutex_lock(&rcu_registry_lock);
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371 }
372 }
e8043c1b 373#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
27b012e2 374 }
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375}
376
9598a481 377void synchronize_rcu(void)
2bc59bd7 378{
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379 CDS_LIST_HEAD(cur_snap_readers);
380 CDS_LIST_HEAD(qsreaders);
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381 DEFINE_URCU_WAIT_NODE(wait, URCU_WAIT_WAITING);
382 struct urcu_waiters waiters;
383
384 /*
385 * Add ourself to gp_waiters queue of threads awaiting to wait
386 * for a grace period. Proceed to perform the grace period only
387 * if we are the first thread added into the queue.
388 * The implicit memory barrier before urcu_wait_add()
389 * orders prior memory accesses of threads put into the wait
390 * queue before their insertion into the wait queue.
391 */
392 if (urcu_wait_add(&gp_waiters, &wait) != 0) {
393 /* Not first in queue: will be awakened by another thread. */
394 urcu_adaptative_busy_wait(&wait);
395 /* Order following memory accesses after grace period. */
396 cmm_smp_mb();
397 return;
398 }
399 /* We won't need to wake ourself up */
400 urcu_wait_set_state(&wait, URCU_WAIT_RUNNING);
fd189fa5 401
6abb4bd5 402 mutex_lock(&rcu_gp_lock);
135530fd 403
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404 /*
405 * Move all waiters into our local queue.
406 */
407 urcu_move_waiters(&waiters, &gp_waiters);
408
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409 mutex_lock(&rcu_registry_lock);
410
16aa9ee8 411 if (cds_list_empty(&registry))
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412 goto out;
413
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414 /*
415 * All threads should read qparity before accessing data structure
416 * where new ptr points to. Must be done within rcu_registry_lock
417 * because it iterates on reader threads.
418 */
9598a481 419 /* Write new ptr before changing the qparity */
a4922ed9 420 smp_mb_master();
9598a481 421
9598a481 422 /*
c9488684 423 * Wait for readers to observe original parity or be quiescent.
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424 * wait_for_readers() can release and grab again rcu_registry_lock
425 * interally.
9598a481 426 */
fd189fa5 427 wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
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428
429 /*
c9488684 430 * Must finish waiting for quiescent state for original parity before
ed1b099e 431 * committing next rcu_gp.ctr update to memory. Failure to do so could
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432 * result in the writer waiting forever while new readers are always
433 * accessing data (no progress). Enforce compiler-order of load
ed1b099e 434 * URCU_TLS(rcu_reader).ctr before store to rcu_gp.ctr.
9598a481 435 */
5481ddb3 436 cmm_barrier();
9598a481 437
5dba80f9 438 /*
5481ddb3 439 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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440 * model easier to understand. It does not have a big performance impact
441 * anyway, given this is the write-side.
442 */
5481ddb3 443 cmm_smp_mb();
67c2d80b 444
c9488684 445 /* Switch parity: 0 -> 1, 1 -> 0 */
ed1b099e 446 CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE);
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447
448 /*
ed1b099e 449 * Must commit rcu_gp.ctr update to memory before waiting for quiescent
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450 * state. Failure to do so could result in the writer waiting forever
451 * while new readers are always accessing data (no progress). Enforce
ed1b099e 452 * compiler-order of store to rcu_gp.ctr before load rcu_reader ctr.
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453 */
454 cmm_barrier();
455
456 /*
457 *
458 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
459 * model easier to understand. It does not have a big performance impact
460 * anyway, given this is the write-side.
461 */
462 cmm_smp_mb();
463
9598a481 464 /*
c9488684 465 * Wait for readers to observe new parity or be quiescent.
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466 * wait_for_readers() can release and grab again rcu_registry_lock
467 * interally.
9598a481 468 */
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469 wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
470
471 /*
472 * Put quiescent reader list back into registry.
473 */
474 cds_list_splice(&qsreaders, &registry);
9598a481 475
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476 /*
477 * Finish waiting for reader threads before letting the old ptr
478 * being freed. Must be done within rcu_registry_lock because it
479 * iterates on reader threads.
480 */
a4922ed9 481 smp_mb_master();
2dfb8b5e 482out:
731ccb96 483 mutex_unlock(&rcu_registry_lock);
6abb4bd5 484 mutex_unlock(&rcu_gp_lock);
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485
486 /*
487 * Wakeup waiters only after we have completed the grace period
488 * and have ensured the memory barriers at the end of the grace
489 * period have been issued.
490 */
491 urcu_wake_all_waiters(&waiters);
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492}
493
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494/*
495 * library wrappers to be used by non-LGPL compatible source code.
496 */
497
498void rcu_read_lock(void)
499{
500 _rcu_read_lock();
501}
502
503void rcu_read_unlock(void)
504{
505 _rcu_read_unlock();
506}
507
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508int rcu_read_ongoing(void)
509{
510 return _rcu_read_ongoing();
511}
512
121a5d44 513void rcu_register_thread(void)
27b012e2 514{
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515 URCU_TLS(rcu_reader).tid = pthread_self();
516 assert(URCU_TLS(rcu_reader).need_mb == 0);
517 assert(!(URCU_TLS(rcu_reader).ctr & RCU_GP_CTR_NEST_MASK));
02be5561 518
731ccb96 519 mutex_lock(&rcu_registry_lock);
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520 assert(!URCU_TLS(rcu_reader).registered);
521 URCU_TLS(rcu_reader).registered = 1;
02be5561 522 rcu_init(); /* In case gcc does not support constructor attribute */
bd252a04 523 cds_list_add(&URCU_TLS(rcu_reader).node, &registry);
731ccb96 524 mutex_unlock(&rcu_registry_lock);
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525}
526
121a5d44 527void rcu_unregister_thread(void)
27b012e2 528{
731ccb96 529 mutex_lock(&rcu_registry_lock);
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530 assert(URCU_TLS(rcu_reader).registered);
531 URCU_TLS(rcu_reader).registered = 0;
bd252a04 532 cds_list_del(&URCU_TLS(rcu_reader).node);
731ccb96 533 mutex_unlock(&rcu_registry_lock);
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534}
535
fdf01eed 536#ifdef RCU_MEMBARRIER
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537
538#ifdef CONFIG_RCU_FORCE_SYS_MEMBARRIER
539static
540void rcu_sys_membarrier_status(int available)
541{
542 if (!available)
543 abort();
544}
545#else
546static
547void rcu_sys_membarrier_status(int available)
548{
549 if (available)
550 rcu_has_sys_membarrier_memb = 1;
551}
552#endif
553
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554void rcu_init(void)
555{
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556 int ret;
557
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558 if (init_done)
559 return;
560 init_done = 1;
64f469e6 561 ret = membarrier(MEMBARRIER_CMD_QUERY, 0);
d8d9a340 562 rcu_sys_membarrier_status(ret >= 0 && (ret & MEMBARRIER_CMD_SHARED));
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563}
564#endif
565
566#ifdef RCU_SIGNAL
02be5561 567static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 568{
40e140c9 569 /*
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570 * Executing this cmm_smp_mb() is the only purpose of this signal handler.
571 * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
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572 * executed on.
573 */
5481ddb3 574 cmm_smp_mb();
bd252a04 575 _CMM_STORE_SHARED(URCU_TLS(rcu_reader).need_mb, 0);
5481ddb3 576 cmm_smp_mb();
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577}
578
8a5fb4c9 579/*
02be5561 580 * rcu_init constructor. Called when the library is linked, but also when
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581 * reader threads are calling rcu_register_thread().
582 * Should only be called by a single thread at a given time. This is ensured by
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583 * holing the rcu_registry_lock from rcu_register_thread() or by running
584 * at library load time, which should not be executed by multiple
585 * threads nor concurrently with rcu_register_thread() anyway.
8a5fb4c9 586 */
02be5561 587void rcu_init(void)
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588{
589 struct sigaction act;
590 int ret;
591
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592 if (init_done)
593 return;
594 init_done = 1;
595
02be5561 596 act.sa_sigaction = sigrcu_handler;
dd052bd3 597 act.sa_flags = SA_SIGINFO | SA_RESTART;
c297c21c 598 sigemptyset(&act.sa_mask);
02be5561 599 ret = sigaction(SIGRCU, &act, NULL);
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600 if (ret)
601 urcu_die(errno);
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602}
603
02be5561 604void rcu_exit(void)
27b012e2 605{
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606 /*
607 * Don't unregister the SIGRCU signal handler anymore, because
608 * call_rcu threads could still be using it shortly before the
609 * application exits.
610 * Assertion disabled because call_rcu threads are now rcu
611 * readers, and left running at exit.
612 * assert(cds_list_empty(&registry));
613 */
27b012e2 614}
5e77fc1f 615
fdf01eed 616#endif /* #ifdef RCU_SIGNAL */
5e77fc1f 617
5e6b23a6 618DEFINE_RCU_FLAVOR(rcu_flavor);
541d828d 619
5e77fc1f 620#include "urcu-call-rcu-impl.h"
0376e7b2 621#include "urcu-defer-impl.h"
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