Document the new call_rcu() primitives.
[urcu.git] / urcu.c
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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
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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
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27#include <stdio.h>
28#include <pthread.h>
29#include <signal.h>
30#include <assert.h>
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31#include <stdlib.h>
32#include <string.h>
09a9f986 33#include <errno.h>
e8043c1b 34#include <poll.h>
27b012e2 35
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36#include "urcu-map.h"
37
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38#include "urcu-static.h"
39/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
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40#include "urcu.h"
41
fdf01eed 42#ifdef RCU_MEMBARRIER
834a45ba 43static int init_done;
fdf01eed 44int has_sys_membarrier;
834a45ba 45
02be5561 46void __attribute__((constructor)) rcu_init(void);
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47#endif
48
49#ifdef RCU_MB
02be5561 50void rcu_init(void)
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51{
52}
53#endif
8a5fb4c9 54
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55#ifdef RCU_SIGNAL
56static int init_done;
57
58void __attribute__((constructor)) rcu_init(void);
59void __attribute__((destructor)) rcu_exit(void);
60#endif
61
6abb4bd5 62static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
27b012e2 63
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64int gp_futex;
65
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66/*
67 * Global grace period counter.
02be5561 68 * Contains the current RCU_GP_CTR_PHASE.
afb8f2c9 69 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
b0d5e790 70 * Written to only by writer with mutex taken. Read by both writer and readers.
128166c9 71 */
27d65bc5 72unsigned long rcu_gp_ctr = RCU_GP_COUNT;
27b012e2 73
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74/*
75 * Written to only by each individual reader. Read by both the reader and the
76 * writers.
77 */
02be5561 78struct rcu_reader __thread rcu_reader;
27b012e2 79
cf380c2f 80#ifdef DEBUG_YIELD
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81unsigned int yield_active;
82unsigned int __thread rand_yield;
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83#endif
84
16aa9ee8 85static CDS_LIST_HEAD(registry);
27b012e2 86
6abb4bd5 87static void mutex_lock(pthread_mutex_t *mutex)
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88{
89 int ret;
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90
91#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5 92 ret = pthread_mutex_lock(mutex);
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93 if (ret) {
94 perror("Error in pthread mutex lock");
95 exit(-1);
96 }
09a9f986 97#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5 98 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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99 if (ret != EBUSY && ret != EINTR) {
100 printf("ret = %d, errno = %d\n", ret, errno);
101 perror("Error in pthread mutex lock");
102 exit(-1);
103 }
6cf3827c 104 if (CMM_LOAD_SHARED(rcu_reader.need_mb)) {
5481ddb3 105 cmm_smp_mb();
6cf3827c 106 _CMM_STORE_SHARED(rcu_reader.need_mb, 0);
5481ddb3 107 cmm_smp_mb();
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108 }
109 poll(NULL,0,10);
110 }
111#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
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112}
113
6abb4bd5 114static void mutex_unlock(pthread_mutex_t *mutex)
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115{
116 int ret;
117
6abb4bd5 118 ret = pthread_mutex_unlock(mutex);
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119 if (ret) {
120 perror("Error in pthread mutex unlock");
121 exit(-1);
122 }
123}
124
fdf01eed 125#ifdef RCU_MEMBARRIER
25cc6d18 126static void smp_mb_master(int group)
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127{
128 if (likely(has_sys_membarrier))
f0708810 129 membarrier(MEMBARRIER_EXPEDITED);
fdf01eed 130 else
5481ddb3 131 cmm_smp_mb();
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132}
133#endif
134
02be5561 135#ifdef RCU_MB
25cc6d18 136static void smp_mb_master(int group)
40e140c9 137{
5481ddb3 138 cmm_smp_mb();
40e140c9 139}
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140#endif
141
142#ifdef RCU_SIGNAL
78ff9419 143static void force_mb_all_readers(void)
27b012e2 144{
02be5561 145 struct rcu_reader *index;
e3b0cef0 146
27b012e2 147 /*
5481ddb3 148 * Ask for each threads to execute a cmm_smp_mb() so we can consider the
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149 * compiler barriers around rcu read lock as real memory barriers.
150 */
16aa9ee8 151 if (cds_list_empty(&registry))
27b012e2 152 return;
3a86deba 153 /*
5481ddb3 154 * pthread_kill has a cmm_smp_mb(). But beware, we assume it performs
157dca95 155 * a cache flush on architectures with non-coherent cache. Let's play
5481ddb3 156 * safe and don't assume anything : we use cmm_smp_mc() to make sure the
157dca95 157 * cache flush is enforced.
3a86deba 158 */
16aa9ee8 159 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 160 CMM_STORE_SHARED(index->need_mb, 1);
02be5561 161 pthread_kill(index->tid, SIGRCU);
09a9f986 162 }
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163 /*
164 * Wait for sighandler (and thus mb()) to execute on every thread.
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165 *
166 * Note that the pthread_kill() will never be executed on systems
167 * that correctly deliver signals in a timely manner. However, it
168 * is not uncommon for kernels to have bugs that can result in
169 * lost or unduly delayed signals.
170 *
171 * If you are seeing the below pthread_kill() executing much at
172 * all, we suggest testing the underlying kernel and filing the
173 * relevant bug report. For Linux kernels, we recommend getting
174 * the Linux Test Project (LTP).
27b012e2 175 */
16aa9ee8 176 cds_list_for_each_entry(index, &registry, node) {
6cf3827c 177 while (CMM_LOAD_SHARED(index->need_mb)) {
02be5561 178 pthread_kill(index->tid, SIGRCU);
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179 poll(NULL, 0, 1);
180 }
181 }
5481ddb3 182 cmm_smp_mb(); /* read ->need_mb before ending the barrier */
27b012e2 183}
9d7e3f89 184
25cc6d18 185static void smp_mb_master(int group)
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186{
187 force_mb_all_readers();
188}
fdf01eed 189#endif /* #ifdef RCU_SIGNAL */
27b012e2 190
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191/*
192 * synchronize_rcu() waiting. Single thread.
193 */
cfe78e25 194static void wait_gp(void)
bc6c15bb 195{
cfe78e25 196 /* Read reader_gp before read futex */
25cc6d18 197 smp_mb_master(RCU_MB_GROUP);
cfe78e25 198 if (uatomic_read(&gp_futex) == -1)
0854ccff 199 futex_async(&gp_futex, FUTEX_WAIT, -1,
cfe78e25 200 NULL, NULL, 0);
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201}
202
2dfb8b5e 203void update_counter_and_wait(void)
27b012e2 204{
16aa9ee8 205 CDS_LIST_HEAD(qsreaders);
cfe78e25 206 int wait_loops = 0;
02be5561 207 struct rcu_reader *index, *tmp;
27b012e2 208
32c15e4e 209 /* Switch parity: 0 -> 1, 1 -> 0 */
6cf3827c 210 CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
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211
212 /*
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213 * Must commit rcu_gp_ctr update to memory before waiting for quiescent
214 * state. Failure to do so could result in the writer waiting forever
215 * while new readers are always accessing data (no progress). Enforce
216 * compiler-order of store to rcu_gp_ctr before load rcu_reader ctr.
2dfb8b5e 217 */
5481ddb3 218 cmm_barrier();
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219
220 /*
935b11ff 221 *
5481ddb3 222 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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223 * model easier to understand. It does not have a big performance impact
224 * anyway, given this is the write-side.
225 */
5481ddb3 226 cmm_smp_mb();
2dfb8b5e 227
40e140c9 228 /*
02be5561 229 * Wait for each thread rcu_reader.ctr count to become 0.
27b012e2 230 */
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231 for (;;) {
232 wait_loops++;
233 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
234 uatomic_dec(&gp_futex);
235 /* Write futex before read reader_gp */
25cc6d18 236 smp_mb_master(RCU_MB_GROUP);
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237 }
238
16aa9ee8 239 cds_list_for_each_entry_safe(index, tmp, &registry, node) {
b95a001f 240 if (!rcu_gp_ongoing(&index->ctr))
16aa9ee8 241 cds_list_move(&index->node, &qsreaders);
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242 }
243
e8043c1b 244#ifndef HAS_INCOHERENT_CACHES
16aa9ee8 245 if (cds_list_empty(&registry)) {
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246 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
247 /* Read reader_gp before write futex */
25cc6d18 248 smp_mb_master(RCU_MB_GROUP);
cfe78e25 249 uatomic_set(&gp_futex, 0);
bc6c15bb 250 }
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251 break;
252 } else {
253 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
254 wait_gp();
255 else
06f22bdb 256 caa_cpu_relax();
bc6c15bb 257 }
e8043c1b 258#else /* #ifndef HAS_INCOHERENT_CACHES */
27b012e2 259 /*
40e140c9 260 * BUSY-LOOP. Force the reader thread to commit its
02be5561 261 * rcu_reader.ctr update to memory if we wait for too long.
27b012e2 262 */
16aa9ee8 263 if (cds_list_empty(&registry)) {
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264 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
265 /* Read reader_gp before write futex */
25cc6d18 266 smp_mb_master(RCU_MB_GROUP);
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267 uatomic_set(&gp_futex, 0);
268 }
269 break;
270 } else {
271 switch (wait_loops) {
bc6c15bb 272 case RCU_QS_ACTIVE_ATTEMPTS:
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273 wait_gp();
274 break; /* only escape switch */
bc6c15bb 275 case KICK_READER_LOOPS:
25cc6d18 276 smp_mb_master(RCU_MB_GROUP);
40e140c9 277 wait_loops = 0;
cfe78e25 278 break; /* only escape switch */
bc6c15bb 279 default:
06f22bdb 280 caa_cpu_relax();
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281 }
282 }
e8043c1b 283#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
27b012e2 284 }
cfe78e25 285 /* put back the reader list in the registry */
16aa9ee8 286 cds_list_splice(&qsreaders, &registry);
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287}
288
9598a481 289void synchronize_rcu(void)
2bc59bd7 290{
6abb4bd5 291 mutex_lock(&rcu_gp_lock);
135530fd 292
16aa9ee8 293 if (cds_list_empty(&registry))
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294 goto out;
295
9598a481 296 /* All threads should read qparity before accessing data structure
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297 * where new ptr points to. Must be done within rcu_gp_lock because it
298 * iterates on reader threads.*/
9598a481 299 /* Write new ptr before changing the qparity */
25cc6d18 300 smp_mb_master(RCU_MB_GROUP);
9598a481 301
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302 /*
303 * Wait for previous parity to be empty of readers.
304 */
2dfb8b5e 305 update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
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306
307 /*
308 * Must finish waiting for quiescent state for parity 0 before
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309 * committing next rcu_gp_ctr update to memory. Failure to do so could
310 * result in the writer waiting forever while new readers are always
311 * accessing data (no progress). Enforce compiler-order of load
312 * rcu_reader ctr before store to rcu_gp_ctr.
9598a481 313 */
5481ddb3 314 cmm_barrier();
9598a481 315
5dba80f9 316 /*
5481ddb3 317 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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318 * model easier to understand. It does not have a big performance impact
319 * anyway, given this is the write-side.
320 */
5481ddb3 321 cmm_smp_mb();
67c2d80b 322
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323 /*
324 * Wait for previous parity to be empty of readers.
325 */
2dfb8b5e 326 update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
9598a481 327
9598a481 328 /* Finish waiting for reader threads before letting the old ptr being
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329 * freed. Must be done within rcu_gp_lock because it iterates on reader
330 * threads. */
25cc6d18 331 smp_mb_master(RCU_MB_GROUP);
2dfb8b5e 332out:
6abb4bd5 333 mutex_unlock(&rcu_gp_lock);
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334}
335
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336/*
337 * library wrappers to be used by non-LGPL compatible source code.
338 */
339
340void rcu_read_lock(void)
341{
342 _rcu_read_lock();
343}
344
345void rcu_read_unlock(void)
346{
347 _rcu_read_unlock();
348}
349
121a5d44 350void rcu_register_thread(void)
27b012e2 351{
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352 rcu_reader.tid = pthread_self();
353 assert(rcu_reader.need_mb == 0);
4b5be3be 354 assert(!(rcu_reader.ctr & RCU_GP_CTR_NEST_MASK));
02be5561 355
6abb4bd5 356 mutex_lock(&rcu_gp_lock);
02be5561 357 rcu_init(); /* In case gcc does not support constructor attribute */
16aa9ee8 358 cds_list_add(&rcu_reader.node, &registry);
6abb4bd5 359 mutex_unlock(&rcu_gp_lock);
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360}
361
121a5d44 362void rcu_unregister_thread(void)
27b012e2 363{
6abb4bd5 364 mutex_lock(&rcu_gp_lock);
16aa9ee8 365 cds_list_del(&rcu_reader.node);
6abb4bd5 366 mutex_unlock(&rcu_gp_lock);
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367}
368
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369#ifdef RCU_MEMBARRIER
370void rcu_init(void)
371{
372 if (init_done)
373 return;
374 init_done = 1;
cf5271ee 375 if (!membarrier(MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY))
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376 has_sys_membarrier = 1;
377}
378#endif
379
380#ifdef RCU_SIGNAL
02be5561 381static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 382{
40e140c9 383 /*
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384 * Executing this cmm_smp_mb() is the only purpose of this signal handler.
385 * It punctually promotes cmm_barrier() into cmm_smp_mb() on every thread it is
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386 * executed on.
387 */
5481ddb3 388 cmm_smp_mb();
6cf3827c 389 _CMM_STORE_SHARED(rcu_reader.need_mb, 0);
5481ddb3 390 cmm_smp_mb();
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391}
392
8a5fb4c9 393/*
02be5561 394 * rcu_init constructor. Called when the library is linked, but also when
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395 * reader threads are calling rcu_register_thread().
396 * Should only be called by a single thread at a given time. This is ensured by
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397 * holing the rcu_gp_lock from rcu_register_thread() or by running at library
398 * load time, which should not be executed by multiple threads nor concurrently
399 * with rcu_register_thread() anyway.
8a5fb4c9 400 */
02be5561 401void rcu_init(void)
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402{
403 struct sigaction act;
404 int ret;
405
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406 if (init_done)
407 return;
408 init_done = 1;
409
02be5561 410 act.sa_sigaction = sigrcu_handler;
dd052bd3 411 act.sa_flags = SA_SIGINFO | SA_RESTART;
c297c21c 412 sigemptyset(&act.sa_mask);
02be5561 413 ret = sigaction(SIGRCU, &act, NULL);
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414 if (ret) {
415 perror("Error in sigaction");
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416 exit(-1);
417 }
418}
419
02be5561 420void rcu_exit(void)
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421{
422 struct sigaction act;
423 int ret;
424
02be5561 425 ret = sigaction(SIGRCU, NULL, &act);
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426 if (ret) {
427 perror("Error in sigaction");
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428 exit(-1);
429 }
02be5561 430 assert(act.sa_sigaction == sigrcu_handler);
16aa9ee8 431 assert(cds_list_empty(&registry));
27b012e2 432}
5e77fc1f 433
fdf01eed 434#endif /* #ifdef RCU_SIGNAL */
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435
436#include "urcu-call-rcu-impl.h"
0376e7b2 437#include "urcu-defer-impl.h"
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