Fix powerpc uatomic 4-byte cmpxchg (cmpd -> cmpw)
[urcu.git] / urcu-bp.c
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1/*
2 * urcu-bp.c
3 *
4 * Userspace RCU library, "bulletproof" version.
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
0617bf4c 26#define _GNU_SOURCE
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27#include <stdio.h>
28#include <pthread.h>
29#include <signal.h>
30#include <assert.h>
31#include <stdlib.h>
32#include <string.h>
33#include <errno.h>
34#include <poll.h>
35#include <unistd.h>
36#include <sys/mman.h>
37
38#include "urcu-bp-static.h"
39/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
40#include "urcu-bp.h"
41
42/* Sleep delay in us */
43#define RCU_SLEEP_DELAY 1000
44#define ARENA_INIT_ALLOC 16
45
02be5561 46void __attribute__((destructor)) rcu_bp_exit(void);
fdee2e6d 47
6abb4bd5 48static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
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49
50#ifdef DEBUG_YIELD
51unsigned int yield_active;
52unsigned int __thread rand_yield;
53#endif
54
55/*
56 * Global grace period counter.
02be5561 57 * Contains the current RCU_GP_CTR_PHASE.
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58 * Also has a RCU_GP_COUNT of 1, to accelerate the reader fast path.
59 * Written to only by writer with mutex taken. Read by both writer and readers.
60 */
02be5561 61long rcu_gp_ctr = RCU_GP_COUNT;
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62
63/*
64 * Pointer to registry elements. Written to only by each individual reader. Read
65 * by both the reader and the writers.
66 */
02be5561 67struct rcu_reader __thread *rcu_reader;
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68
69static LIST_HEAD(registry);
70
71struct registry_arena {
72 void *p;
73 size_t len;
74 size_t used;
75};
76
77static struct registry_arena registry_arena;
78
79static void rcu_gc_registry(void);
80
6abb4bd5 81static void mutex_lock(pthread_mutex_t *mutex)
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82{
83 int ret;
84
85#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5 86 ret = pthread_mutex_lock(mutex);
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87 if (ret) {
88 perror("Error in pthread mutex lock");
89 exit(-1);
90 }
91#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5 92 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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93 if (ret != EBUSY && ret != EINTR) {
94 printf("ret = %d, errno = %d\n", ret, errno);
95 perror("Error in pthread mutex lock");
96 exit(-1);
97 }
02be5561 98 if (rcu_reader.need_mb) {
fdee2e6d 99 smp_mb();
02be5561 100 rcu_reader.need_mb = 0;
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101 smp_mb();
102 }
103 poll(NULL,0,10);
104 }
105#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
106}
107
6abb4bd5 108static void mutex_unlock(pthread_mutex_t *mutex)
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109{
110 int ret;
111
6abb4bd5 112 ret = pthread_mutex_unlock(mutex);
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113 if (ret) {
114 perror("Error in pthread mutex unlock");
115 exit(-1);
116 }
117}
118
2dfb8b5e 119void update_counter_and_wait(void)
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120{
121 LIST_HEAD(qsreaders);
122 int wait_loops = 0;
02be5561 123 struct rcu_reader *index, *tmp;
fdee2e6d 124
32c15e4e 125 /* Switch parity: 0 -> 1, 1 -> 0 */
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126 STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
127
128 /*
129 * Must commit qparity update to memory before waiting for other parity
130 * quiescent state. Failure to do so could result in the writer waiting
131 * forever while new readers are always accessing data (no progress).
132 * Ensured by STORE_SHARED and LOAD_SHARED.
133 */
134
135 /*
136 * Adding a smp_mb() which is _not_ formally required, but makes the
137 * model easier to understand. It does not have a big performance impact
138 * anyway, given this is the write-side.
139 */
140 smp_mb();
141
fdee2e6d 142 /*
02be5561 143 * Wait for each thread rcu_reader.ctr count to become 0.
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144 */
145 for (;;) {
146 wait_loops++;
18c3778a 147 list_for_each_entry_safe(index, tmp, &registry, node) {
fdee2e6d 148 if (!rcu_old_gp_ongoing(&index->ctr))
18c3778a 149 list_move(&index->node, &qsreaders);
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150 }
151
152 if (list_empty(&registry)) {
153 break;
154 } else {
155 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
156 usleep(RCU_SLEEP_DELAY);
157 else
158 cpu_relax();
159 }
160 }
161 /* put back the reader list in the registry */
162 list_splice(&qsreaders, &registry);
163}
164
165void synchronize_rcu(void)
166{
167 sigset_t newmask, oldmask;
168 int ret;
169
170 ret = sigemptyset(&newmask);
171 assert(!ret);
172 ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
173 assert(!ret);
174
6abb4bd5 175 mutex_lock(&rcu_gp_lock);
fdee2e6d 176
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177 if (list_empty(&registry))
178 goto out;
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179
180 /* All threads should read qparity before accessing data structure
2dfb8b5e 181 * where new ptr points to. */
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182 /* Write new ptr before changing the qparity */
183 smp_mb();
184
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185 /* Remove old registry elements */
186 rcu_gc_registry();
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187
188 /*
189 * Wait for previous parity to be empty of readers.
190 */
2dfb8b5e 191 update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */
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192
193 /*
194 * Adding a smp_mb() which is _not_ formally required, but makes the
195 * model easier to understand. It does not have a big performance impact
196 * anyway, given this is the write-side.
197 */
198 smp_mb();
199
fdee2e6d 200 /*
2dfb8b5e 201 * Wait for previous parity to be empty of readers.
fdee2e6d 202 */
2dfb8b5e 203 update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */
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204
205 /*
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206 * Finish waiting for reader threads before letting the old ptr being
207 * freed.
fdee2e6d 208 */
fdee2e6d 209 smp_mb();
2dfb8b5e 210out:
6abb4bd5 211 mutex_unlock(&rcu_gp_lock);
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212 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
213 assert(!ret);
214}
215
216/*
217 * library wrappers to be used by non-LGPL compatible source code.
218 */
219
220void rcu_read_lock(void)
221{
222 _rcu_read_lock();
223}
224
225void rcu_read_unlock(void)
226{
227 _rcu_read_unlock();
228}
229
230/*
231 * only grow for now.
232 */
233static void resize_arena(struct registry_arena *arena, size_t len)
234{
235 void *new_arena;
236
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237 if (!arena->p)
238 new_arena = mmap(arena->p, len,
239 PROT_READ | PROT_WRITE,
240 MAP_ANONYMOUS | MAP_PRIVATE,
241 -1, 0);
242 else
243 new_arena = mremap(arena->p, arena->len,
244 len, MREMAP_MAYMOVE);
245 assert(new_arena != MAP_FAILED);
246
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247 /*
248 * re-used the same region ?
249 */
250 if (new_arena == arena->p)
251 return;
252
253 memcpy(new_arena, arena->p, arena->len);
254 bzero(new_arena + arena->len, len - arena->len);
255 arena->p = new_arena;
256}
257
258/* Called with signals off and mutex locked */
259static void add_thread(void)
260{
02be5561 261 struct rcu_reader *rcu_reader_reg;
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262
263 if (registry_arena.len
02be5561 264 < registry_arena.used + sizeof(struct rcu_reader))
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265 resize_arena(&registry_arena,
266 max(registry_arena.len << 1, ARENA_INIT_ALLOC));
267 /*
268 * Find a free spot.
269 */
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270 for (rcu_reader_reg = registry_arena.p;
271 (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
272 rcu_reader_reg++) {
273 if (!rcu_reader_reg->alloc)
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274 break;
275 }
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276 rcu_reader_reg->alloc = 1;
277 registry_arena.used += sizeof(struct rcu_reader);
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278
279 /* Add to registry */
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280 rcu_reader_reg->tid = pthread_self();
281 assert(rcu_reader_reg->ctr == 0);
18c3778a 282 list_add(&rcu_reader_reg->node, &registry);
02be5561 283 rcu_reader = rcu_reader_reg;
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284}
285
286/* Called with signals off and mutex locked */
287static void rcu_gc_registry(void)
288{
02be5561 289 struct rcu_reader *rcu_reader_reg;
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290 pthread_t tid;
291 int ret;
292
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293 for (rcu_reader_reg = registry_arena.p;
294 (void *)rcu_reader_reg < registry_arena.p + registry_arena.len;
295 rcu_reader_reg++) {
296 if (!rcu_reader_reg->alloc)
fdee2e6d 297 continue;
02be5561 298 tid = rcu_reader_reg->tid;
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299 ret = pthread_kill(tid, 0);
300 assert(ret != EINVAL);
301 if (ret == ESRCH) {
18c3778a 302 list_del(&rcu_reader_reg->node);
79266051 303 rcu_reader_reg->ctr = 0;
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304 rcu_reader_reg->alloc = 0;
305 registry_arena.used -= sizeof(struct rcu_reader);
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306 }
307 }
308}
309
310/* Disable signals, take mutex, add to registry */
311void rcu_bp_register(void)
312{
313 sigset_t newmask, oldmask;
314 int ret;
315
316 ret = sigemptyset(&newmask);
317 assert(!ret);
318 ret = pthread_sigmask(SIG_SETMASK, &newmask, &oldmask);
319 assert(!ret);
320
321 /*
322 * Check if a signal concurrently registered our thread since
323 * the check in rcu_read_lock(). */
02be5561 324 if (rcu_reader)
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325 goto end;
326
6abb4bd5 327 mutex_lock(&rcu_gp_lock);
fdee2e6d 328 add_thread();
6abb4bd5 329 mutex_unlock(&rcu_gp_lock);
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330end:
331 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
332 assert(!ret);
333}
334
02be5561 335void rcu_bp_exit()
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336{
337 munmap(registry_arena.p, registry_arena.len);
338}
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