urcu signal-based renames
[urcu.git] / urcu.c
CommitLineData
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1/*
2 * urcu.c
3 *
4 * Userspace RCU library
5 *
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6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
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
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26#include <stdio.h>
27#include <pthread.h>
28#include <signal.h>
29#include <assert.h>
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30#include <stdlib.h>
31#include <string.h>
09a9f986 32#include <errno.h>
e8043c1b 33#include <poll.h>
27b012e2 34
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35#include "urcu-static.h"
36/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
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37#include "urcu.h"
38
02be5561 39#ifndef RCU_MB
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40static int init_done;
41
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42void __attribute__((constructor)) rcu_init(void);
43void __attribute__((destructor)) rcu_exit(void);
e90a6e9c 44#else
02be5561 45void rcu_init(void)
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46{
47}
48#endif
8a5fb4c9 49
02be5561 50static pthread_mutex_t rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
27b012e2 51
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52int gp_futex;
53
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54/*
55 * Global grace period counter.
02be5561 56 * Contains the current RCU_GP_CTR_PHASE.
afb8f2c9 57 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
b0d5e790 58 * Written to only by writer with mutex taken. Read by both writer and readers.
128166c9 59 */
02be5561 60long rcu_gp_ctr = RCU_GP_COUNT;
27b012e2 61
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62/*
63 * Written to only by each individual reader. Read by both the reader and the
64 * writers.
65 */
02be5561 66struct rcu_reader __thread rcu_reader;
27b012e2 67
cf380c2f 68#ifdef DEBUG_YIELD
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69unsigned int yield_active;
70unsigned int __thread rand_yield;
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71#endif
72
e3b0cef0 73static LIST_HEAD(registry);
27b012e2 74
02be5561 75static void internal_rcu_lock(void)
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76{
77 int ret;
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78
79#ifndef DISTRUST_SIGNALS_EXTREME
02be5561 80 ret = pthread_mutex_lock(&rcu_mutex);
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81 if (ret) {
82 perror("Error in pthread mutex lock");
83 exit(-1);
84 }
09a9f986 85#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
02be5561 86 while ((ret = pthread_mutex_trylock(&rcu_mutex)) != 0) {
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87 if (ret != EBUSY && ret != EINTR) {
88 printf("ret = %d, errno = %d\n", ret, errno);
89 perror("Error in pthread mutex lock");
90 exit(-1);
91 }
02be5561 92 if (rcu_reader.need_mb) {
09a9f986 93 smp_mb();
02be5561 94 rcu_reader.need_mb = 0;
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95 smp_mb();
96 }
97 poll(NULL,0,10);
98 }
99#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
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100}
101
02be5561 102static void internal_rcu_unlock(void)
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103{
104 int ret;
105
02be5561 106 ret = pthread_mutex_unlock(&rcu_mutex);
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107 if (ret) {
108 perror("Error in pthread mutex unlock");
109 exit(-1);
110 }
111}
112
27b012e2 113/*
02be5561 114 * called with rcu_mutex held.
27b012e2 115 */
02be5561 116static void switch_next_rcu_qparity(void)
27b012e2 117{
02be5561 118 STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
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119}
120
02be5561 121#ifdef RCU_MB
9d7e3f89 122static void smp_mb_heavy()
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123{
124 smp_mb();
125}
9d7e3f89 126#else
78ff9419 127static void force_mb_all_readers(void)
27b012e2 128{
02be5561 129 struct rcu_reader *index;
e3b0cef0 130
27b012e2 131 /*
b715b99e 132 * Ask for each threads to execute a smp_mb() so we can consider the
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133 * compiler barriers around rcu read lock as real memory barriers.
134 */
e3b0cef0 135 if (list_empty(&registry))
27b012e2 136 return;
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137 /*
138 * pthread_kill has a smp_mb(). But beware, we assume it performs
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139 * a cache flush on architectures with non-coherent cache. Let's play
140 * safe and don't assume anything : we use smp_mc() to make sure the
141 * cache flush is enforced.
3a86deba 142 */
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143 list_for_each_entry(index, &registry, head) {
144 index->need_mb = 1;
09a9f986 145 smp_mc(); /* write need_mb before sending the signal */
02be5561 146 pthread_kill(index->tid, SIGRCU);
09a9f986 147 }
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148 /*
149 * Wait for sighandler (and thus mb()) to execute on every thread.
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150 *
151 * Note that the pthread_kill() will never be executed on systems
152 * that correctly deliver signals in a timely manner. However, it
153 * is not uncommon for kernels to have bugs that can result in
154 * lost or unduly delayed signals.
155 *
156 * If you are seeing the below pthread_kill() executing much at
157 * all, we suggest testing the underlying kernel and filing the
158 * relevant bug report. For Linux kernels, we recommend getting
159 * the Linux Test Project (LTP).
27b012e2 160 */
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161 list_for_each_entry(index, &registry, head) {
162 while (index->need_mb) {
02be5561 163 pthread_kill(index->tid, SIGRCU);
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164 poll(NULL, 0, 1);
165 }
166 }
167 smp_mb(); /* read ->need_mb before ending the barrier */
27b012e2 168}
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169
170static void smp_mb_heavy()
171{
172 force_mb_all_readers();
173}
02be5561 174#endif /* #else #ifdef RCU_MB */
27b012e2 175
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176/*
177 * synchronize_rcu() waiting. Single thread.
178 */
cfe78e25 179static void wait_gp(void)
bc6c15bb 180{
cfe78e25 181 /* Read reader_gp before read futex */
9d7e3f89 182 smp_mb_heavy();
cfe78e25 183 if (uatomic_read(&gp_futex) == -1)
0854ccff 184 futex_async(&gp_futex, FUTEX_WAIT, -1,
cfe78e25 185 NULL, NULL, 0);
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186}
187
1430ee0b 188void wait_for_quiescent_state(void)
27b012e2 189{
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190 LIST_HEAD(qsreaders);
191 int wait_loops = 0;
02be5561 192 struct rcu_reader *index, *tmp;
27b012e2 193
e3b0cef0 194 if (list_empty(&registry))
27b012e2 195 return;
40e140c9 196 /*
02be5561 197 * Wait for each thread rcu_reader.ctr count to become 0.
27b012e2 198 */
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199 for (;;) {
200 wait_loops++;
201 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
202 uatomic_dec(&gp_futex);
203 /* Write futex before read reader_gp */
9d7e3f89 204 smp_mb_heavy();
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205 }
206
23758cc9 207 list_for_each_entry_safe(index, tmp, &registry, head) {
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208 if (!rcu_old_gp_ongoing(&index->ctr))
209 list_move(&index->head, &qsreaders);
210 }
211
e8043c1b 212#ifndef HAS_INCOHERENT_CACHES
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213 if (list_empty(&registry)) {
214 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
215 /* Read reader_gp before write futex */
9d7e3f89 216 smp_mb_heavy();
cfe78e25 217 uatomic_set(&gp_futex, 0);
bc6c15bb 218 }
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219 break;
220 } else {
221 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
222 wait_gp();
223 else
224 cpu_relax();
bc6c15bb 225 }
e8043c1b 226#else /* #ifndef HAS_INCOHERENT_CACHES */
27b012e2 227 /*
40e140c9 228 * BUSY-LOOP. Force the reader thread to commit its
02be5561 229 * rcu_reader.ctr update to memory if we wait for too long.
27b012e2 230 */
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231 if (list_empty(&registry)) {
232 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS) {
233 /* Read reader_gp before write futex */
9d7e3f89 234 smp_mb_heavy();
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235 uatomic_set(&gp_futex, 0);
236 }
237 break;
238 } else {
239 switch (wait_loops) {
bc6c15bb 240 case RCU_QS_ACTIVE_ATTEMPTS:
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241 wait_gp();
242 break; /* only escape switch */
bc6c15bb 243 case KICK_READER_LOOPS:
9d7e3f89 244 smp_mb_heavy();
40e140c9 245 wait_loops = 0;
cfe78e25 246 break; /* only escape switch */
bc6c15bb 247 default:
3b55dbf4 248 cpu_relax();
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249 }
250 }
e8043c1b 251#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
27b012e2 252 }
cfe78e25 253 /* put back the reader list in the registry */
23758cc9 254 list_splice(&qsreaders, &registry);
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255}
256
9598a481 257void synchronize_rcu(void)
2bc59bd7 258{
02be5561 259 internal_rcu_lock();
135530fd 260
9598a481 261 /* All threads should read qparity before accessing data structure
02be5561 262 * where new ptr points to. Must be done within internal_rcu_lock
135530fd 263 * because it iterates on reader threads.*/
9598a481 264 /* Write new ptr before changing the qparity */
9d7e3f89 265 smp_mb_heavy();
9598a481 266
02be5561 267 switch_next_rcu_qparity(); /* 0 -> 1 */
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268
269 /*
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270 * Must commit qparity update to memory before waiting for parity
271 * 0 quiescent state. Failure to do so could result in the writer
272 * waiting forever while new readers are always accessing data (no
273 * progress).
b0d5e790 274 * Ensured by STORE_SHARED and LOAD_SHARED.
2bc59bd7 275 */
2bc59bd7 276
67c2d80b 277 /*
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278 * Adding a smp_mb() which is _not_ formally required, but makes the
279 * model easier to understand. It does not have a big performance impact
280 * anyway, given this is the write-side.
67c2d80b 281 */
5dba80f9 282 smp_mb();
67c2d80b 283
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284 /*
285 * Wait for previous parity to be empty of readers.
286 */
287 wait_for_quiescent_state(); /* Wait readers in parity 0 */
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288
289 /*
290 * Must finish waiting for quiescent state for parity 0 before
291 * committing qparity update to memory. Failure to do so could result in
292 * the writer waiting forever while new readers are always accessing
293 * data (no progress).
b0d5e790 294 * Ensured by STORE_SHARED and LOAD_SHARED.
9598a481 295 */
9598a481 296
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297 /*
298 * Adding a smp_mb() which is _not_ formally required, but makes the
299 * model easier to understand. It does not have a big performance impact
300 * anyway, given this is the write-side.
301 */
302 smp_mb();
67c2d80b 303
02be5561 304 switch_next_rcu_qparity(); /* 1 -> 0 */
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305
306 /*
307 * Must commit qparity update to memory before waiting for parity
308 * 1 quiescent state. Failure to do so could result in the writer
309 * waiting forever while new readers are always accessing data (no
310 * progress).
b0d5e790 311 * Ensured by STORE_SHARED and LOAD_SHARED.
9598a481 312 */
9598a481 313
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314 /*
315 * Adding a smp_mb() which is _not_ formally required, but makes the
316 * model easier to understand. It does not have a big performance impact
317 * anyway, given this is the write-side.
318 */
319 smp_mb();
67c2d80b 320
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321 /*
322 * Wait for previous parity to be empty of readers.
323 */
324 wait_for_quiescent_state(); /* Wait readers in parity 1 */
9598a481 325
9598a481 326 /* Finish waiting for reader threads before letting the old ptr being
02be5561 327 * freed. Must be done within internal_rcu_lock because it iterates on
135530fd 328 * reader threads. */
9d7e3f89 329 smp_mb_heavy();
135530fd 330
02be5561 331 internal_rcu_unlock();
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332}
333
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334/*
335 * library wrappers to be used by non-LGPL compatible source code.
336 */
337
338void rcu_read_lock(void)
339{
340 _rcu_read_lock();
341}
342
343void rcu_read_unlock(void)
344{
345 _rcu_read_unlock();
346}
347
121a5d44 348void rcu_register_thread(void)
27b012e2 349{
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350 rcu_reader.tid = pthread_self();
351 assert(rcu_reader.need_mb == 0);
352 assert(rcu_reader.ctr == 0);
353
354 internal_rcu_lock();
355 rcu_init(); /* In case gcc does not support constructor attribute */
356 list_add(&rcu_reader.head, &registry);
357 internal_rcu_unlock();
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358}
359
121a5d44 360void rcu_unregister_thread(void)
27b012e2 361{
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362 internal_rcu_lock();
363 list_del(&rcu_reader.head);
364 internal_rcu_unlock();
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365}
366
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367#ifndef RCU_MB
368static void sigrcu_handler(int signo, siginfo_t *siginfo, void *context)
27b012e2 369{
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370 /*
371 * Executing this smp_mb() is the only purpose of this signal handler.
372 * It punctually promotes barrier() into smp_mb() on every thread it is
373 * executed on.
374 */
b715b99e 375 smp_mb();
02be5561 376 rcu_reader.need_mb = 0;
09a9f986 377 smp_mb();
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378}
379
8a5fb4c9 380/*
02be5561 381 * rcu_init constructor. Called when the library is linked, but also when
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382 * reader threads are calling rcu_register_thread().
383 * Should only be called by a single thread at a given time. This is ensured by
02be5561 384 * holing the internal_rcu_lock() from rcu_register_thread() or by running at
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385 * library load time, which should not be executed by multiple threads nor
386 * concurrently with rcu_register_thread() anyway.
387 */
02be5561 388void rcu_init(void)
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389{
390 struct sigaction act;
391 int ret;
392
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393 if (init_done)
394 return;
395 init_done = 1;
396
02be5561 397 act.sa_sigaction = sigrcu_handler;
dd052bd3 398 act.sa_flags = SA_SIGINFO | SA_RESTART;
c297c21c 399 sigemptyset(&act.sa_mask);
02be5561 400 ret = sigaction(SIGRCU, &act, NULL);
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401 if (ret) {
402 perror("Error in sigaction");
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403 exit(-1);
404 }
405}
406
02be5561 407void rcu_exit(void)
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408{
409 struct sigaction act;
410 int ret;
411
02be5561 412 ret = sigaction(SIGRCU, NULL, &act);
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413 if (ret) {
414 perror("Error in sigaction");
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415 exit(-1);
416 }
02be5561 417 assert(act.sa_sigaction == sigrcu_handler);
e3b0cef0 418 assert(list_empty(&registry));
27b012e2 419}
02be5561 420#endif /* #ifndef RCU_MB */
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