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