urcu (mb/signal): fix list move implementation
[urcu.git] / urcu-qsbr.c
CommitLineData
9f1621ca 1/*
7ac06cef 2 * urcu-qsbr.c
9f1621ca 3 *
7ac06cef 4 * Userspace RCU QSBR library
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5 *
6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
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
26#include <stdio.h>
27#include <pthread.h>
28#include <signal.h>
29#include <assert.h>
30#include <stdlib.h>
31#include <string.h>
32#include <errno.h>
33#include <poll.h>
34
727f819d 35#define BUILD_QSBR_LIB
7ac06cef 36#include "urcu-qsbr-static.h"
9f1621ca 37/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
7ac06cef 38#include "urcu-qsbr.h"
9f1621ca 39
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40void __attribute__((destructor)) rcu_exit(void);
41
81d1f1f5 42static pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
9f1621ca 43
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44int gp_futex;
45
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46/*
47 * Global grace period counter.
48 */
ac258107 49unsigned long urcu_gp_ctr = RCU_GP_ONLINE;
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50
51/*
52 * Written to only by each individual reader. Read by both the reader and the
53 * writers.
54 */
4f8e3380 55struct urcu_reader __thread urcu_reader;
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56
57#ifdef DEBUG_YIELD
58unsigned int yield_active;
59unsigned int __thread rand_yield;
60#endif
61
4f8e3380 62static LIST_HEAD(registry);
9f1621ca 63
90c1618a 64static void internal_urcu_lock(void)
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65{
66 int ret;
67
68#ifndef DISTRUST_SIGNALS_EXTREME
69 ret = pthread_mutex_lock(&urcu_mutex);
70 if (ret) {
71 perror("Error in pthread mutex lock");
72 exit(-1);
73 }
74#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
75 while ((ret = pthread_mutex_trylock(&urcu_mutex)) != 0) {
76 if (ret != EBUSY && ret != EINTR) {
77 printf("ret = %d, errno = %d\n", ret, errno);
78 perror("Error in pthread mutex lock");
79 exit(-1);
80 }
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81 poll(NULL,0,10);
82 }
83#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
84}
85
90c1618a 86static void internal_urcu_unlock(void)
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87{
88 int ret;
89
90 ret = pthread_mutex_unlock(&urcu_mutex);
91 if (ret) {
92 perror("Error in pthread mutex unlock");
93 exit(-1);
94 }
95}
96
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97/*
98 * synchronize_rcu() waiting. Single thread.
99 */
4f8e3380 100static void wait_gp(struct urcu_reader *index)
bc6c15bb 101{
ec4e58a3 102 uatomic_dec(&gp_futex);
bc6c15bb 103 smp_mb(); /* Write futex before read reader_gp */
4f8e3380 104 if (!rcu_gp_ongoing(&index->ctr)) {
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105 /* Read reader_gp before write futex */
106 smp_mb();
107 /* Callbacks are queued, don't wait. */
ec4e58a3 108 uatomic_set(&gp_futex, 0);
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109 } else {
110 /* Read reader_gp before read futex */
111 smp_rmb();
ec4e58a3 112 if (uatomic_read(&gp_futex) == -1)
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113 futex(&gp_futex, FUTEX_WAIT, -1,
114 NULL, NULL, 0);
115 }
116}
117
90c1618a 118static void wait_for_quiescent_state(void)
9f1621ca 119{
4f8e3380 120 struct urcu_reader *index;
9f1621ca 121
4f8e3380 122 if (list_empty(&registry))
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123 return;
124 /*
3395d46c 125 * Wait for each thread rcu_reader_qs_gp count to become 0.
9f1621ca 126 */
4f8e3380 127 list_for_each_entry(index, &registry, head) {
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128 int wait_loops = 0;
129
4f8e3380 130 while (rcu_gp_ongoing(&index->ctr)) {
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131 if (wait_loops++ == RCU_QS_ACTIVE_ATTEMPTS) {
132 wait_gp(index);
133 } else {
9f1621ca 134#ifndef HAS_INCOHERENT_CACHES
bc6c15bb 135 cpu_relax();
9f1621ca 136#else /* #ifndef HAS_INCOHERENT_CACHES */
bc6c15bb 137 smp_mb();
9f1621ca 138#endif /* #else #ifndef HAS_INCOHERENT_CACHES */
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139 }
140 }
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141 }
142}
143
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144/*
145 * Using a two-subphases algorithm for architectures with smaller than 64-bit
146 * long-size to ensure we do not encounter an overflow bug.
147 */
148
149#if (BITS_PER_LONG < 64)
150/*
151 * called with urcu_mutex held.
152 */
153static void switch_next_urcu_qparity(void)
154{
155 STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR);
156}
157
158void synchronize_rcu(void)
159{
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160 unsigned long was_online;
161
4f8e3380 162 was_online = urcu_reader.ctr;
bc49c323 163
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164 /* All threads should read qparity before accessing data structure
165 * where new ptr points to.
166 */
167 /* Write new ptr before changing the qparity */
168 smp_mb();
169
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170 /*
171 * Mark the writer thread offline to make sure we don't wait for
172 * our own quiescent state. This allows using synchronize_rcu() in
173 * threads registered as readers.
174 */
175 if (was_online)
4f8e3380 176 STORE_SHARED(urcu_reader.ctr, 0);
bc49c323 177
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178 internal_urcu_lock();
179
180 switch_next_urcu_qparity(); /* 0 -> 1 */
181
182 /*
183 * Must commit qparity update to memory before waiting for parity
184 * 0 quiescent state. Failure to do so could result in the writer
185 * waiting forever while new readers are always accessing data (no
186 * progress).
187 * Ensured by STORE_SHARED and LOAD_SHARED.
188 */
189
190 /*
191 * Wait for previous parity to be empty of readers.
192 */
193 wait_for_quiescent_state(); /* Wait readers in parity 0 */
194
195 /*
196 * Must finish waiting for quiescent state for parity 0 before
197 * committing qparity update to memory. Failure to do so could result in
198 * the writer waiting forever while new readers are always accessing
199 * data (no progress).
200 * Ensured by STORE_SHARED and LOAD_SHARED.
201 */
202
203 switch_next_urcu_qparity(); /* 1 -> 0 */
204
205 /*
206 * Must commit qparity update to memory before waiting for parity
207 * 1 quiescent state. Failure to do so could result in the writer
208 * waiting forever while new readers are always accessing data (no
209 * progress).
210 * Ensured by STORE_SHARED and LOAD_SHARED.
211 */
212
213 /*
214 * Wait for previous parity to be empty of readers.
215 */
216 wait_for_quiescent_state(); /* Wait readers in parity 1 */
217
218 internal_urcu_unlock();
219
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220 /*
221 * Finish waiting for reader threads before letting the old ptr being
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222 * freed.
223 */
bc49c323 224 if (was_online)
4f8e3380 225 _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr));
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226 smp_mb();
227}
228#else /* !(BITS_PER_LONG < 64) */
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229void synchronize_rcu(void)
230{
f0f7dbdd 231 unsigned long was_online;
ff2f67a0 232
4f8e3380 233 was_online = urcu_reader.ctr;
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234
235 /*
236 * Mark the writer thread offline to make sure we don't wait for
237 * our own quiescent state. This allows using synchronize_rcu() in
238 * threads registered as readers.
239 */
8f50d1ce 240 smp_mb();
ff2f67a0 241 if (was_online)
4f8e3380 242 STORE_SHARED(urcu_reader.ctr, 0);
ff2f67a0 243
4e27f058 244 internal_urcu_lock();
55570466 245 STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr + RCU_GP_CTR);
9f1621ca 246 wait_for_quiescent_state();
9f1621ca 247 internal_urcu_unlock();
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248
249 if (was_online)
4f8e3380 250 _STORE_SHARED(urcu_reader.ctr, LOAD_SHARED(urcu_gp_ctr));
8f50d1ce 251 smp_mb();
9f1621ca 252}
47d2f29e 253#endif /* !(BITS_PER_LONG < 64) */
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254
255/*
256 * library wrappers to be used by non-LGPL compatible source code.
257 */
258
259void rcu_read_lock(void)
260{
261 _rcu_read_lock();
262}
263
264void rcu_read_unlock(void)
265{
266 _rcu_read_unlock();
267}
268
269void *rcu_dereference(void *p)
270{
271 return _rcu_dereference(p);
272}
273
274void *rcu_assign_pointer_sym(void **p, void *v)
275{
276 wmb();
277 return STORE_SHARED(p, v);
278}
279
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280void *rcu_cmpxchg_pointer_sym(void **p, void *old, void *_new)
281{
282 wmb();
ec4e58a3 283 return uatomic_cmpxchg(p, old, _new);
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284}
285
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286void *rcu_xchg_pointer_sym(void **p, void *v)
287{
288 wmb();
ec4e58a3 289 return uatomic_xchg(p, v);
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290}
291
292void *rcu_publish_content_sym(void **p, void *v)
293{
294 void *oldptr;
295
296 oldptr = _rcu_xchg_pointer(p, v);
297 synchronize_rcu();
298 return oldptr;
299}
300
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301void rcu_quiescent_state(void)
302{
303 _rcu_quiescent_state();
304}
305
306void rcu_thread_offline(void)
307{
308 _rcu_thread_offline();
309}
310
311void rcu_thread_online(void)
312{
313 _rcu_thread_online();
314}
315
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316void rcu_register_thread(void)
317{
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318 urcu_reader.tid = pthread_self();
319 assert(urcu_reader.ctr == 0);
320
9f1621ca 321 internal_urcu_lock();
4f8e3380 322 list_add(&urcu_reader.head, &registry);
9f1621ca 323 internal_urcu_unlock();
5f373c84 324 _rcu_thread_online();
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325}
326
327void rcu_unregister_thread(void)
328{
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329 /*
330 * We have to make the thread offline otherwise we end up dealocking
331 * with a waiting writer.
332 */
333 _rcu_thread_offline();
9f1621ca 334 internal_urcu_lock();
4f8e3380 335 list_del(&urcu_reader.head);
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336 internal_urcu_unlock();
337}
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338
339void rcu_exit(void)
340{
341 assert(list_empty(&registry));
342}
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