Fix undefined NULL pointer arithmetic
[urcu.git] / urcu-bp.c
CommitLineData
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1/*
2 * urcu-bp.c
3 *
4 * Userspace RCU library, "bulletproof" version.
5 *
6982d6d7 6 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
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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
71c811bf 27#define _LGPL_SOURCE
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28#include <stdio.h>
29#include <pthread.h>
30#include <signal.h>
31#include <assert.h>
32#include <stdlib.h>
33#include <string.h>
34#include <errno.h>
35#include <poll.h>
36#include <unistd.h>
37#include <sys/mman.h>
38
d73fb81f 39#include "urcu/wfcqueue.h"
57760d44 40#include "urcu/map/urcu-bp.h"
af7c2dbe 41#include "urcu/static/urcu-bp.h"
618b2595 42#include "urcu-pointer.h"
bd252a04 43#include "urcu/tls-compat.h"
71c811bf 44
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45#include "urcu-die.h"
46
fdee2e6d 47/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
71c811bf 48#undef _LGPL_SOURCE
fdee2e6d 49#include "urcu-bp.h"
71c811bf 50#define _LGPL_SOURCE
fdee2e6d 51
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52#ifndef MAP_ANONYMOUS
53#define MAP_ANONYMOUS MAP_ANON
54#endif
55
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56#ifdef __linux__
57static
58void *mremap_wrapper(void *old_address, size_t old_size,
59 size_t new_size, int flags)
60{
61 return mremap(old_address, old_size, new_size, flags);
62}
63#else
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64
65#define MREMAP_MAYMOVE 1
66#define MREMAP_FIXED 2
67
68/*
95b94246 69 * mremap wrapper for non-Linux systems not allowing MAYMOVE.
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70 * This is not generic.
71*/
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72static
73void *mremap_wrapper(void *old_address, size_t old_size,
74 size_t new_size, int flags)
45a4872f 75{
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76 assert(!(flags & MREMAP_MAYMOVE));
77
78 return MAP_FAILED;
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79}
80#endif
81
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82/* Sleep delay in us */
83#define RCU_SLEEP_DELAY 1000
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84#define INIT_NR_THREADS 8
85#define ARENA_INIT_ALLOC \
86 sizeof(struct registry_chunk) \
87 + INIT_NR_THREADS * sizeof(struct rcu_reader)
fdee2e6d 88
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89/*
90 * Active attempts to check for reader Q.S. before calling sleep().
91 */
92#define RCU_QS_ACTIVE_ATTEMPTS 100
93
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94static
95void __attribute__((constructor)) rcu_bp_init(void);
96static
02be5561 97void __attribute__((destructor)) rcu_bp_exit(void);
fdee2e6d 98
6abb4bd5 99static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
fdee2e6d 100
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101static pthread_mutex_t init_lock = PTHREAD_MUTEX_INITIALIZER;
102static int initialized;
103
104static pthread_key_t urcu_bp_key;
105
fdee2e6d 106#ifdef DEBUG_YIELD
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107unsigned int rcu_yield_active;
108DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
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109#endif
110
c13c2e55 111struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
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112
113/*
114 * Pointer to registry elements. Written to only by each individual reader. Read
115 * by both the reader and the writers.
116 */
bd252a04 117DEFINE_URCU_TLS(struct rcu_reader *, rcu_reader);
fdee2e6d 118
16aa9ee8 119static CDS_LIST_HEAD(registry);
fdee2e6d 120
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121struct registry_chunk {
122 size_t data_len; /* data length */
c1be8fb9 123 size_t used; /* amount of data used */
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124 struct cds_list_head node; /* chunk_list node */
125 char data[];
126};
127
fdee2e6d 128struct registry_arena {
95b94246 129 struct cds_list_head chunk_list;
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130};
131
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132static struct registry_arena registry_arena = {
133 .chunk_list = CDS_LIST_HEAD_INIT(registry_arena.chunk_list),
134};
fdee2e6d 135
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136/* Saved fork signal mask, protected by rcu_gp_lock */
137static sigset_t saved_fork_signal_mask;
138
6abb4bd5 139static void mutex_lock(pthread_mutex_t *mutex)
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140{
141 int ret;
142
143#ifndef DISTRUST_SIGNALS_EXTREME
6abb4bd5 144 ret = pthread_mutex_lock(mutex);
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145 if (ret)
146 urcu_die(ret);
fdee2e6d 147#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
6abb4bd5 148 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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149 if (ret != EBUSY && ret != EINTR)
150 urcu_die(ret);
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151 poll(NULL,0,10);
152 }
153#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
154}
155
6abb4bd5 156static void mutex_unlock(pthread_mutex_t *mutex)
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157{
158 int ret;
159
6abb4bd5 160 ret = pthread_mutex_unlock(mutex);
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161 if (ret)
162 urcu_die(ret);
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163}
164
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165static void wait_for_readers(struct cds_list_head *input_readers,
166 struct cds_list_head *cur_snap_readers,
167 struct cds_list_head *qsreaders)
fdee2e6d 168{
fdee2e6d 169 int wait_loops = 0;
02be5561 170 struct rcu_reader *index, *tmp;
fdee2e6d 171
fdee2e6d 172 /*
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173 * Wait for each thread URCU_TLS(rcu_reader).ctr to either
174 * indicate quiescence (not nested), or observe the current
c13c2e55 175 * rcu_gp.ctr value.
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176 */
177 for (;;) {
178 wait_loops++;
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179 cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
180 switch (rcu_reader_state(&index->ctr)) {
181 case RCU_READER_ACTIVE_CURRENT:
182 if (cur_snap_readers) {
183 cds_list_move(&index->node,
184 cur_snap_readers);
185 break;
186 }
187 /* Fall-through */
188 case RCU_READER_INACTIVE:
189 cds_list_move(&index->node, qsreaders);
190 break;
191 case RCU_READER_ACTIVE_OLD:
192 /*
193 * Old snapshot. Leaving node in
194 * input_readers will make us busy-loop
195 * until the snapshot becomes current or
196 * the reader becomes inactive.
197 */
198 break;
199 }
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200 }
201
52c75091 202 if (cds_list_empty(input_readers)) {
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203 break;
204 } else {
205 if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
206 usleep(RCU_SLEEP_DELAY);
207 else
06f22bdb 208 caa_cpu_relax();
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209 }
210 }
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211}
212
213void synchronize_rcu(void)
214{
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215 CDS_LIST_HEAD(cur_snap_readers);
216 CDS_LIST_HEAD(qsreaders);
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217 sigset_t newmask, oldmask;
218 int ret;
219
6ed4b2e6 220 ret = sigfillset(&newmask);
fdee2e6d 221 assert(!ret);
6ed4b2e6 222 ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
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223 assert(!ret);
224
6abb4bd5 225 mutex_lock(&rcu_gp_lock);
fdee2e6d 226
16aa9ee8 227 if (cds_list_empty(&registry))
2dfb8b5e 228 goto out;
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229
230 /* All threads should read qparity before accessing data structure
2dfb8b5e 231 * where new ptr points to. */
fdee2e6d 232 /* Write new ptr before changing the qparity */
5481ddb3 233 cmm_smp_mb();
fdee2e6d 234
fdee2e6d 235 /*
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236 * Wait for readers to observe original parity or be quiescent.
237 */
52c75091 238 wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
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239
240 /*
241 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
242 * model easier to understand. It does not have a big performance impact
243 * anyway, given this is the write-side.
244 */
245 cmm_smp_mb();
246
247 /* Switch parity: 0 -> 1, 1 -> 0 */
c13c2e55 248 CMM_STORE_SHARED(rcu_gp.ctr, rcu_gp.ctr ^ RCU_GP_CTR_PHASE);
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249
250 /*
251 * Must commit qparity update to memory before waiting for other parity
252 * quiescent state. Failure to do so could result in the writer waiting
253 * forever while new readers are always accessing data (no progress).
254 * Ensured by CMM_STORE_SHARED and CMM_LOAD_SHARED.
fdee2e6d 255 */
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256
257 /*
5481ddb3 258 * Adding a cmm_smp_mb() which is _not_ formally required, but makes the
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259 * model easier to understand. It does not have a big performance impact
260 * anyway, given this is the write-side.
261 */
5481ddb3 262 cmm_smp_mb();
fdee2e6d 263
fdee2e6d 264 /*
dd61d077 265 * Wait for readers to observe new parity or be quiescent.
fdee2e6d 266 */
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267 wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
268
269 /*
270 * Put quiescent reader list back into registry.
271 */
272 cds_list_splice(&qsreaders, &registry);
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273
274 /*
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275 * Finish waiting for reader threads before letting the old ptr being
276 * freed.
fdee2e6d 277 */
5481ddb3 278 cmm_smp_mb();
2dfb8b5e 279out:
6abb4bd5 280 mutex_unlock(&rcu_gp_lock);
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281 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
282 assert(!ret);
283}
284
285/*
286 * library wrappers to be used by non-LGPL compatible source code.
287 */
288
289void rcu_read_lock(void)
290{
291 _rcu_read_lock();
292}
293
294void rcu_read_unlock(void)
295{
296 _rcu_read_unlock();
297}
298
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299int rcu_read_ongoing(void)
300{
301 return _rcu_read_ongoing();
302}
303
fdee2e6d 304/*
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305 * Only grow for now. If empty, allocate a ARENA_INIT_ALLOC sized chunk.
306 * Else, try expanding the last chunk. If this fails, allocate a new
307 * chunk twice as big as the last chunk.
308 * Memory used by chunks _never_ moves. A chunk could theoretically be
309 * freed when all "used" slots are released, but we don't do it at this
310 * point.
fdee2e6d 311 */
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312static
313void expand_arena(struct registry_arena *arena)
fdee2e6d 314{
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315 struct registry_chunk *new_chunk, *last_chunk;
316 size_t old_chunk_len, new_chunk_len;
317
318 /* No chunk. */
319 if (cds_list_empty(&arena->chunk_list)) {
320 assert(ARENA_INIT_ALLOC >=
321 sizeof(struct registry_chunk)
322 + sizeof(struct rcu_reader));
323 new_chunk_len = ARENA_INIT_ALLOC;
324 new_chunk = mmap(NULL, new_chunk_len,
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325 PROT_READ | PROT_WRITE,
326 MAP_ANONYMOUS | MAP_PRIVATE,
327 -1, 0);
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328 if (new_chunk == MAP_FAILED)
329 abort();
330 bzero(new_chunk, new_chunk_len);
331 new_chunk->data_len =
332 new_chunk_len - sizeof(struct registry_chunk);
333 cds_list_add_tail(&new_chunk->node, &arena->chunk_list);
334 return; /* We're done. */
335 }
9d8612b7 336
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337 /* Try expanding last chunk. */
338 last_chunk = cds_list_entry(arena->chunk_list.prev,
339 struct registry_chunk, node);
340 old_chunk_len =
341 last_chunk->data_len + sizeof(struct registry_chunk);
342 new_chunk_len = old_chunk_len << 1;
343
344 /* Don't allow memory mapping to move, just expand. */
345 new_chunk = mremap_wrapper(last_chunk, old_chunk_len,
346 new_chunk_len, 0);
347 if (new_chunk != MAP_FAILED) {
348 /* Should not have moved. */
349 assert(new_chunk == last_chunk);
350 bzero((char *) last_chunk + old_chunk_len,
351 new_chunk_len - old_chunk_len);
352 last_chunk->data_len =
353 new_chunk_len - sizeof(struct registry_chunk);
354 return; /* We're done. */
355 }
0617bf4c 356
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357 /* Remap did not succeed, we need to add a new chunk. */
358 new_chunk = mmap(NULL, new_chunk_len,
359 PROT_READ | PROT_WRITE,
360 MAP_ANONYMOUS | MAP_PRIVATE,
361 -1, 0);
362 if (new_chunk == MAP_FAILED)
363 abort();
364 bzero(new_chunk, new_chunk_len);
365 new_chunk->data_len =
366 new_chunk_len - sizeof(struct registry_chunk);
367 cds_list_add_tail(&new_chunk->node, &arena->chunk_list);
368}
fdee2e6d 369
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370static
371struct rcu_reader *arena_alloc(struct registry_arena *arena)
372{
373 struct registry_chunk *chunk;
374 struct rcu_reader *rcu_reader_reg;
375 int expand_done = 0; /* Only allow to expand once per alloc */
376 size_t len = sizeof(struct rcu_reader);
377
378retry:
379 cds_list_for_each_entry(chunk, &arena->chunk_list, node) {
380 if (chunk->data_len - chunk->used < len)
381 continue;
382 /* Find spot */
383 for (rcu_reader_reg = (struct rcu_reader *) &chunk->data[0];
384 rcu_reader_reg < (struct rcu_reader *) &chunk->data[chunk->data_len];
385 rcu_reader_reg++) {
386 if (!rcu_reader_reg->alloc) {
387 rcu_reader_reg->alloc = 1;
388 chunk->used += len;
389 return rcu_reader_reg;
390 }
391 }
392 }
393
394 if (!expand_done) {
395 expand_arena(arena);
396 expand_done = 1;
397 goto retry;
398 }
399
400 return NULL;
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401}
402
403/* Called with signals off and mutex locked */
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404static
405void add_thread(void)
fdee2e6d 406{
02be5561 407 struct rcu_reader *rcu_reader_reg;
c1be8fb9 408 int ret;
fdee2e6d 409
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410 rcu_reader_reg = arena_alloc(&registry_arena);
411 if (!rcu_reader_reg)
412 abort();
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413 ret = pthread_setspecific(urcu_bp_key, rcu_reader_reg);
414 if (ret)
415 abort();
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416
417 /* Add to registry */
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418 rcu_reader_reg->tid = pthread_self();
419 assert(rcu_reader_reg->ctr == 0);
16aa9ee8 420 cds_list_add(&rcu_reader_reg->node, &registry);
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421 /*
422 * Reader threads are pointing to the reader registry. This is
423 * why its memory should never be relocated.
424 */
bd252a04 425 URCU_TLS(rcu_reader) = rcu_reader_reg;
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426}
427
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428/* Called with mutex locked */
429static
430void cleanup_thread(struct registry_chunk *chunk,
431 struct rcu_reader *rcu_reader_reg)
432{
433 rcu_reader_reg->ctr = 0;
434 cds_list_del(&rcu_reader_reg->node);
435 rcu_reader_reg->tid = 0;
436 rcu_reader_reg->alloc = 0;
437 chunk->used -= sizeof(struct rcu_reader);
438}
439
440static
441struct registry_chunk *find_chunk(struct rcu_reader *rcu_reader_reg)
fdee2e6d 442{
95b94246 443 struct registry_chunk *chunk;
fdee2e6d 444
95b94246 445 cds_list_for_each_entry(chunk, &registry_arena.chunk_list, node) {
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446 if (rcu_reader_reg < (struct rcu_reader *) &chunk->data[0])
447 continue;
448 if (rcu_reader_reg >= (struct rcu_reader *) &chunk->data[chunk->data_len])
449 continue;
450 return chunk;
451 }
452 return NULL;
453}
95b94246 454
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455/* Called with signals off and mutex locked */
456static
457void remove_thread(void)
458{
459 struct rcu_reader *rcu_reader_reg;
95b94246 460
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461 rcu_reader_reg = URCU_TLS(rcu_reader);
462 cleanup_thread(find_chunk(rcu_reader_reg), rcu_reader_reg);
463 URCU_TLS(rcu_reader) = NULL;
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464}
465
466/* Disable signals, take mutex, add to registry */
467void rcu_bp_register(void)
468{
469 sigset_t newmask, oldmask;
470 int ret;
471
6ed4b2e6 472 ret = sigfillset(&newmask);
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473 if (ret)
474 abort();
6ed4b2e6 475 ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
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476 if (ret)
477 abort();
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478
479 /*
480 * Check if a signal concurrently registered our thread since
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481 * the check in rcu_read_lock().
482 */
bd252a04 483 if (URCU_TLS(rcu_reader))
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484 goto end;
485
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486 /*
487 * Take care of early registration before urcu_bp constructor.
488 */
489 rcu_bp_init();
490
6abb4bd5 491 mutex_lock(&rcu_gp_lock);
fdee2e6d 492 add_thread();
6abb4bd5 493 mutex_unlock(&rcu_gp_lock);
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494end:
495 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
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496 if (ret)
497 abort();
498}
499
500/* Disable signals, take mutex, remove from registry */
501static
502void rcu_bp_unregister(void)
503{
504 sigset_t newmask, oldmask;
505 int ret;
506
507 ret = sigfillset(&newmask);
508 if (ret)
509 abort();
510 ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
511 if (ret)
512 abort();
513
514 mutex_lock(&rcu_gp_lock);
515 remove_thread();
516 mutex_unlock(&rcu_gp_lock);
517 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
518 if (ret)
519 abort();
520}
521
522/*
523 * Remove thread from the registry when it exits, and flag it as
524 * destroyed so garbage collection can take care of it.
525 */
526static
527void urcu_bp_thread_exit_notifier(void *rcu_key)
528{
529 assert(rcu_key == URCU_TLS(rcu_reader));
530 rcu_bp_unregister();
531}
532
533static
534void rcu_bp_init(void)
535{
536 mutex_lock(&init_lock);
537 if (!initialized) {
538 int ret;
539
540 ret = pthread_key_create(&urcu_bp_key,
541 urcu_bp_thread_exit_notifier);
542 if (ret)
543 abort();
544 initialized = 1;
545 }
546 mutex_unlock(&init_lock);
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547}
548
c1be8fb9 549static
9380711a 550void rcu_bp_exit(void)
fdee2e6d 551{
95b94246 552 struct registry_chunk *chunk, *tmp;
c1be8fb9 553 int ret;
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554
555 cds_list_for_each_entry_safe(chunk, tmp,
556 &registry_arena.chunk_list, node) {
557 munmap(chunk, chunk->data_len + sizeof(struct registry_chunk));
558 }
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559 ret = pthread_key_delete(urcu_bp_key);
560 if (ret)
561 abort();
fdee2e6d 562}
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563
564/*
565 * Holding the rcu_gp_lock across fork will make sure we fork() don't race with
566 * a concurrent thread executing with this same lock held. This ensures that the
567 * registry is in a coherent state in the child.
568 */
569void rcu_bp_before_fork(void)
570{
571 sigset_t newmask, oldmask;
572 int ret;
573
6ed4b2e6 574 ret = sigfillset(&newmask);
4cf1675f 575 assert(!ret);
6ed4b2e6 576 ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
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577 assert(!ret);
578 mutex_lock(&rcu_gp_lock);
579 saved_fork_signal_mask = oldmask;
580}
581
582void rcu_bp_after_fork_parent(void)
583{
584 sigset_t oldmask;
585 int ret;
586
587 oldmask = saved_fork_signal_mask;
588 mutex_unlock(&rcu_gp_lock);
589 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
590 assert(!ret);
591}
592
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593/*
594 * Prune all entries from registry except our own thread. Fits the Linux
595 * fork behavior. Called with rcu_gp_lock held.
596 */
597static
598void urcu_bp_prune_registry(void)
599{
600 struct registry_chunk *chunk;
601 struct rcu_reader *rcu_reader_reg;
602
603 cds_list_for_each_entry(chunk, &registry_arena.chunk_list, node) {
604 for (rcu_reader_reg = (struct rcu_reader *) &chunk->data[0];
605 rcu_reader_reg < (struct rcu_reader *) &chunk->data[chunk->data_len];
606 rcu_reader_reg++) {
607 if (!rcu_reader_reg->alloc)
608 continue;
609 if (rcu_reader_reg->tid == pthread_self())
610 continue;
611 cleanup_thread(chunk, rcu_reader_reg);
612 }
613 }
614}
615
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616void rcu_bp_after_fork_child(void)
617{
618 sigset_t oldmask;
619 int ret;
620
c1be8fb9 621 urcu_bp_prune_registry();
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622 oldmask = saved_fork_signal_mask;
623 mutex_unlock(&rcu_gp_lock);
624 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
625 assert(!ret);
626}
5e77fc1f 627
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628void *rcu_dereference_sym_bp(void *p)
629{
630 return _rcu_dereference(p);
631}
632
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633void *rcu_set_pointer_sym_bp(void **p, void *v)
634{
635 cmm_wmb();
424d4ed5
MD
636 uatomic_set(p, v);
637 return v;
5efd3cd2
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638}
639
640void *rcu_xchg_pointer_sym_bp(void **p, void *v)
641{
642 cmm_wmb();
643 return uatomic_xchg(p, v);
644}
645
646void *rcu_cmpxchg_pointer_sym_bp(void **p, void *old, void *_new)
647{
648 cmm_wmb();
649 return uatomic_cmpxchg(p, old, _new);
650}
651
5e6b23a6 652DEFINE_RCU_FLAVOR(rcu_flavor);
541d828d 653
5e77fc1f 654#include "urcu-call-rcu-impl.h"
0376e7b2 655#include "urcu-defer-impl.h"
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