Fix: handle sys_futex() FUTEX_WAIT interrupted by signal
[urcu.git] / urcu-defer-impl.h
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1#ifndef _URCU_DEFER_IMPL_H
2#define _URCU_DEFER_IMPL_H
3
786ee85b 4/*
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5 * urcu-defer-impl.h
6 *
7 * Userspace RCU header - memory reclamation.
786ee85b 8 *
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9 * TO BE INCLUDED ONLY FROM URCU LIBRARY CODE. See urcu-defer.h for linking
10 * dynamically with the userspace rcu reclamation library.
786ee85b 11 *
6982d6d7 12 * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
0376e7b2 13 * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
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14 *
15 * This library is free software; you can redistribute it and/or
16 * modify it under the terms of the GNU Lesser General Public
17 * License as published by the Free Software Foundation; either
18 * version 2.1 of the License, or (at your option) any later version.
19 *
20 * This library is distributed in the hope that it will be useful,
21 * but WITHOUT ANY WARRANTY; without even the implied warranty of
22 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
23 * Lesser General Public License for more details.
24 *
25 * You should have received a copy of the GNU Lesser General Public
26 * License along with this library; if not, write to the Free Software
27 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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28 *
29 * IBM's contributions to this file may be relicensed under LGPLv2 or later.
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30 */
31
0376e7b2 32#include <stdlib.h>
786ee85b 33#include <pthread.h>
0376e7b2 34#include <stdio.h>
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35#include <signal.h>
36#include <assert.h>
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37#include <string.h>
38#include <errno.h>
39#include <poll.h>
4ce9e4f2 40#include <sys/time.h>
4ce9e4f2 41#include <unistd.h>
6d841bc2 42#include <stdint.h>
786ee85b 43
41849996 44#include "urcu/futex.h"
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45
46#include <urcu/compiler.h>
47#include <urcu/arch.h>
a2e7bf9c 48#include <urcu/uatomic.h>
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49#include <urcu/list.h>
50#include <urcu/system.h>
bd252a04 51#include <urcu/tls-compat.h>
4a6d7378 52#include "urcu-die.h"
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53
54/*
55 * Number of entries in the per-thread defer queue. Must be power of 2.
56 */
57#define DEFER_QUEUE_SIZE (1 << 12)
58#define DEFER_QUEUE_MASK (DEFER_QUEUE_SIZE - 1)
59
60/*
61 * Typically, data is aligned at least on the architecture size.
62 * Use lowest bit to indicate that the current callback is changing.
63 * Assumes that (void *)-2L is not used often. Used to encode non-aligned
64 * functions and non-aligned data using extra space.
65 * We encode the (void *)-2L fct as: -2L, fct, data.
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66 * We encode the (void *)-2L data as either:
67 * fct | DQ_FCT_BIT, data (if fct is aligned), or
68 * -2L, fct, data (if fct is not aligned).
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69 * Here, DQ_FCT_MARK == ~DQ_FCT_BIT. Required for the test order.
70 */
71#define DQ_FCT_BIT (1 << 0)
72#define DQ_IS_FCT_BIT(x) ((unsigned long)(x) & DQ_FCT_BIT)
73#define DQ_SET_FCT_BIT(x) \
74 (x = (void *)((unsigned long)(x) | DQ_FCT_BIT))
75#define DQ_CLEAR_FCT_BIT(x) \
76 (x = (void *)((unsigned long)(x) & ~DQ_FCT_BIT))
77#define DQ_FCT_MARK ((void *)(~DQ_FCT_BIT))
78
79/*
80 * This code section can only be included in LGPL 2.1 compatible source code.
81 * See below for the function call wrappers which can be used in code meant to
82 * be only linked with the Userspace RCU library. This comes with a small
83 * performance degradation on the read-side due to the added function calls.
84 * This is required to permit relinking with newer versions of the library.
85 */
86
87#ifdef DEBUG_RCU
88#define rcu_assert(args...) assert(args)
89#else
90#define rcu_assert(args...)
91#endif
92
93/*
94 * defer queue.
95 * Contains pointers. Encoded to save space when same callback is often used.
96 * When looking up the next item:
97 * - if DQ_FCT_BIT is set, set the current callback to DQ_CLEAR_FCT_BIT(ptr)
98 * - next element contains pointer to data.
99 * - else if item == DQ_FCT_MARK
100 * - set the current callback to next element ptr
101 * - following next element contains pointer to data.
102 * - else current element contains data
103 */
104struct defer_queue {
105 unsigned long head; /* add element at head */
106 void *last_fct_in; /* last fct pointer encoded */
107 unsigned long tail; /* next element to remove at tail */
108 void *last_fct_out; /* last fct pointer encoded */
109 void **q;
110 /* registry information */
111 unsigned long last_head;
112 struct cds_list_head list; /* list of thread queues */
113};
114
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115/* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
116#include "urcu-defer.h"
117
02be5561 118void __attribute__((destructor)) rcu_defer_exit(void);
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119
120extern void synchronize_rcu(void);
121
122/*
02be5561 123 * rcu_defer_mutex nests inside defer_thread_mutex.
786ee85b 124 */
02be5561 125static pthread_mutex_t rcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
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126static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
127
6d841bc2 128static int32_t defer_thread_futex;
d7ff6cee 129static int32_t defer_thread_stop;
4ce9e4f2 130
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131/*
132 * Written to only by each individual deferer. Read by both the deferer and
133 * the reclamation tread.
134 */
bd252a04 135static DEFINE_URCU_TLS(struct defer_queue, defer_queue);
0376e7b2 136static CDS_LIST_HEAD(registry_defer);
786ee85b 137static pthread_t tid_defer;
4ce9e4f2 138
0376e7b2 139static void mutex_lock_defer(pthread_mutex_t *mutex)
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140{
141 int ret;
142
143#ifndef DISTRUST_SIGNALS_EXTREME
144 ret = pthread_mutex_lock(mutex);
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145 if (ret)
146 urcu_die(ret);
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147#else /* #ifndef DISTRUST_SIGNALS_EXTREME */
148 while ((ret = pthread_mutex_trylock(mutex)) != 0) {
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149 if (ret != EBUSY && ret != EINTR)
150 urcu_die(ret);
c060776f 151 (void) poll(NULL,0,10);
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152 }
153#endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
154}
155
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156/*
157 * Wake-up any waiting defer thread. Called from many concurrent threads.
158 */
159static void wake_up_defer(void)
160{
a0b7f7ea 161 if (caa_unlikely(uatomic_read(&defer_thread_futex) == -1)) {
ec4e58a3 162 uatomic_set(&defer_thread_futex, 0);
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163 if (futex_noasync(&defer_thread_futex, FUTEX_WAKE, 1,
164 NULL, NULL, 0) < 0)
165 urcu_die(errno);
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166 }
167}
168
169static unsigned long rcu_defer_num_callbacks(void)
170{
171 unsigned long num_items = 0, head;
dbc6128f 172 struct defer_queue *index;
04eb9c4f 173
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174 mutex_lock_defer(&rcu_defer_mutex);
175 cds_list_for_each_entry(index, &registry_defer, list) {
6cf3827c 176 head = CMM_LOAD_SHARED(index->head);
dbc6128f 177 num_items += head - index->tail;
04eb9c4f 178 }
6abb4bd5 179 mutex_unlock(&rcu_defer_mutex);
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180 return num_items;
181}
182
183/*
184 * Defer thread waiting. Single thread.
185 */
186static void wait_defer(void)
187{
ec4e58a3 188 uatomic_dec(&defer_thread_futex);
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189 /* Write futex before read queue */
190 /* Write futex before read defer_thread_stop */
191 cmm_smp_mb();
192 if (_CMM_LOAD_SHARED(defer_thread_stop)) {
193 uatomic_set(&defer_thread_futex, 0);
194 pthread_exit(0);
195 }
04eb9c4f 196 if (rcu_defer_num_callbacks()) {
5481ddb3 197 cmm_smp_mb(); /* Read queue before write futex */
04eb9c4f 198 /* Callbacks are queued, don't wait. */
ec4e58a3 199 uatomic_set(&defer_thread_futex, 0);
04eb9c4f 200 } else {
5481ddb3 201 cmm_smp_rmb(); /* Read queue before read futex */
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202 if (uatomic_read(&defer_thread_futex) != -1)
203 return;
204 while (futex_noasync(&defer_thread_futex, FUTEX_WAIT, -1,
205 NULL, NULL, 0)) {
206 switch (errno) {
207 case EWOULDBLOCK:
208 /* Value already changed. */
209 return;
210 case EINTR:
211 /* Retry if interrupted by signal. */
212 break; /* Get out of switch. */
213 default:
214 /* Unexpected error. */
215 urcu_die(errno);
216 }
217 }
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218 }
219}
220
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221/*
222 * Must be called after Q.S. is reached.
223 */
224static void rcu_defer_barrier_queue(struct defer_queue *queue,
804b4375 225 unsigned long head)
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226{
227 unsigned long i;
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228 void (*fct)(void *p);
229 void *p;
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230
231 /*
232 * Tail is only modified when lock is held.
233 * Head is only modified by owner thread.
234 */
235
804b4375 236 for (i = queue->tail; i != head;) {
5481ddb3 237 cmm_smp_rmb(); /* read head before q[]. */
6cf3827c 238 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
a0b7f7ea 239 if (caa_unlikely(DQ_IS_FCT_BIT(p))) {
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240 DQ_CLEAR_FCT_BIT(p);
241 queue->last_fct_out = p;
6cf3827c 242 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
a0b7f7ea 243 } else if (caa_unlikely(p == DQ_FCT_MARK)) {
6cf3827c 244 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
804b4375 245 queue->last_fct_out = p;
6cf3827c 246 p = CMM_LOAD_SHARED(queue->q[i++ & DEFER_QUEUE_MASK]);
29cdb8d8 247 }
804b4375 248 fct = queue->last_fct_out;
804b4375 249 fct(p);
786ee85b 250 }
5481ddb3 251 cmm_smp_mb(); /* push tail after having used q[] */
6cf3827c 252 CMM_STORE_SHARED(queue->tail, i);
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253}
254
255static void _rcu_defer_barrier_thread(void)
256{
0d0e6c21 257 unsigned long head, num_items;
786ee85b 258
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259 head = URCU_TLS(defer_queue).head;
260 num_items = head - URCU_TLS(defer_queue).tail;
a0b7f7ea 261 if (caa_unlikely(!num_items))
0d0e6c21 262 return;
786ee85b 263 synchronize_rcu();
bd252a04 264 rcu_defer_barrier_queue(&URCU_TLS(defer_queue), head);
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265}
266
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267void rcu_defer_barrier_thread(void)
268{
0376e7b2 269 mutex_lock_defer(&rcu_defer_mutex);
786ee85b 270 _rcu_defer_barrier_thread();
6abb4bd5 271 mutex_unlock(&rcu_defer_mutex);
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272}
273
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274/*
275 * rcu_defer_barrier - Execute all queued rcu callbacks.
276 *
277 * Execute all RCU callbacks queued before rcu_defer_barrier() execution.
278 * All callbacks queued on the local thread prior to a rcu_defer_barrier() call
279 * are guaranteed to be executed.
280 * Callbacks queued by other threads concurrently with rcu_defer_barrier()
281 * execution are not guaranteed to be executed in the current batch (could
282 * be left for the next batch). These callbacks queued by other threads are only
283 * guaranteed to be executed if there is explicit synchronization between
284 * the thread adding to the queue and the thread issuing the defer_barrier call.
285 */
286
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287void rcu_defer_barrier(void)
288{
dbc6128f 289 struct defer_queue *index;
0d0e6c21 290 unsigned long num_items = 0;
786ee85b 291
0376e7b2 292 if (cds_list_empty(&registry_defer))
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293 return;
294
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295 mutex_lock_defer(&rcu_defer_mutex);
296 cds_list_for_each_entry(index, &registry_defer, list) {
6cf3827c 297 index->last_head = CMM_LOAD_SHARED(index->head);
dbc6128f 298 num_items += index->last_head - index->tail;
0d0e6c21 299 }
a0b7f7ea 300 if (caa_likely(!num_items)) {
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301 /*
302 * We skip the grace period because there are no queued
303 * callbacks to execute.
304 */
305 goto end;
306 }
786ee85b 307 synchronize_rcu();
0376e7b2 308 cds_list_for_each_entry(index, &registry_defer, list)
dbc6128f 309 rcu_defer_barrier_queue(index, index->last_head);
0d0e6c21 310end:
6abb4bd5 311 mutex_unlock(&rcu_defer_mutex);
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312}
313
2c22932b 314/*
b4f313b7 315 * _defer_rcu - Queue a RCU callback.
2c22932b 316 */
f50c11aa 317static void _defer_rcu(void (*fct)(void *p), void *p)
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318{
319 unsigned long head, tail;
320
321 /*
322 * Head is only modified by ourself. Tail can be modified by reclamation
323 * thread.
324 */
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325 head = URCU_TLS(defer_queue).head;
326 tail = CMM_LOAD_SHARED(URCU_TLS(defer_queue).tail);
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327
328 /*
ec8e44cf 329 * If queue is full, or reached threshold. Empty queue ourself.
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330 * Worse-case: must allow 2 supplementary entries for fct pointer.
331 */
a0b7f7ea 332 if (caa_unlikely(head - tail >= DEFER_QUEUE_SIZE - 2)) {
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333 assert(head - tail <= DEFER_QUEUE_SIZE);
334 rcu_defer_barrier_thread();
bd252a04 335 assert(head - CMM_LOAD_SHARED(URCU_TLS(defer_queue).tail) == 0);
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336 }
337
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338 /*
339 * Encode:
340 * if the function is not changed and the data is aligned and it is
341 * not the marker:
342 * store the data
343 * otherwise if the function is aligned and its not the marker:
344 * store the function with DQ_FCT_BIT
345 * store the data
346 * otherwise:
347 * store the marker (DQ_FCT_MARK)
348 * store the function
349 * store the data
350 *
351 * Decode: see the comments before 'struct defer_queue'
352 * or the code in rcu_defer_barrier_queue().
353 */
bd252a04 354 if (caa_unlikely(URCU_TLS(defer_queue).last_fct_in != fct
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355 || DQ_IS_FCT_BIT(p)
356 || p == DQ_FCT_MARK)) {
bd252a04 357 URCU_TLS(defer_queue).last_fct_in = fct;
a0b7f7ea 358 if (caa_unlikely(DQ_IS_FCT_BIT(fct) || fct == DQ_FCT_MARK)) {
bd252a04 359 _CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK],
2c22932b 360 DQ_FCT_MARK);
bd252a04 361 _CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK],
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362 fct);
363 } else {
364 DQ_SET_FCT_BIT(fct);
bd252a04 365 _CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK],
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366 fct);
367 }
2c22932b 368 }
bd252a04 369 _CMM_STORE_SHARED(URCU_TLS(defer_queue).q[head++ & DEFER_QUEUE_MASK], p);
5481ddb3 370 cmm_smp_wmb(); /* Publish new pointer before head */
2c22932b 371 /* Write q[] before head. */
bd252a04 372 CMM_STORE_SHARED(URCU_TLS(defer_queue).head, head);
5481ddb3 373 cmm_smp_mb(); /* Write queue head before read futex */
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374 /*
375 * Wake-up any waiting defer thread.
376 */
377 wake_up_defer();
378}
379
c961f4f3 380static void *thr_defer(void *args)
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381{
382 for (;;) {
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383 /*
384 * "Be green". Don't wake up the CPU if there is no RCU work
385 * to perform whatsoever. Aims at saving laptop battery life by
386 * leaving the processor in sleep state when idle.
387 */
4ce9e4f2 388 wait_defer();
4ce9e4f2 389 /* Sleeping after wait_defer to let many callbacks enqueue */
c060776f 390 (void) poll(NULL,0,100); /* wait for 100ms */
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391 rcu_defer_barrier();
392 }
393
394 return NULL;
395}
396
397/*
398 * library wrappers to be used by non-LGPL compatible source code.
399 */
400
3614f13c 401void defer_rcu(void (*fct)(void *p), void *p)
786ee85b 402{
3614f13c 403 _defer_rcu(fct, p);
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404}
405
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406static void start_defer_thread(void)
407{
408 int ret;
409
dbc6128f 410 ret = pthread_create(&tid_defer, NULL, thr_defer, NULL);
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411 assert(!ret);
412}
413
414static void stop_defer_thread(void)
415{
416 int ret;
417 void *tret;
418
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419 _CMM_STORE_SHARED(defer_thread_stop, 1);
420 /* Store defer_thread_stop before testing futex */
421 cmm_smp_mb();
4ce9e4f2 422 wake_up_defer();
d7ff6cee 423
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424 ret = pthread_join(tid_defer, &tret);
425 assert(!ret);
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426
427 CMM_STORE_SHARED(defer_thread_stop, 0);
428 /* defer thread should always exit when futex value is 0 */
429 assert(uatomic_read(&defer_thread_futex) == 0);
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430}
431
7fdbbd61 432int rcu_defer_register_thread(void)
786ee85b 433{
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434 int was_empty;
435
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436 assert(URCU_TLS(defer_queue).last_head == 0);
437 assert(URCU_TLS(defer_queue).q == NULL);
438 URCU_TLS(defer_queue).q = malloc(sizeof(void *) * DEFER_QUEUE_SIZE);
439 if (!URCU_TLS(defer_queue).q)
7fdbbd61 440 return -ENOMEM;
786ee85b 441
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442 mutex_lock_defer(&defer_thread_mutex);
443 mutex_lock_defer(&rcu_defer_mutex);
444 was_empty = cds_list_empty(&registry_defer);
bd252a04 445 cds_list_add(&URCU_TLS(defer_queue).list, &registry_defer);
6abb4bd5 446 mutex_unlock(&rcu_defer_mutex);
786ee85b 447
dbc6128f 448 if (was_empty)
786ee85b 449 start_defer_thread();
6abb4bd5 450 mutex_unlock(&defer_thread_mutex);
7fdbbd61 451 return 0;
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452}
453
454void rcu_defer_unregister_thread(void)
455{
dbc6128f 456 int is_empty;
786ee85b 457
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458 mutex_lock_defer(&defer_thread_mutex);
459 mutex_lock_defer(&rcu_defer_mutex);
bd252a04 460 cds_list_del(&URCU_TLS(defer_queue).list);
786ee85b 461 _rcu_defer_barrier_thread();
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462 free(URCU_TLS(defer_queue).q);
463 URCU_TLS(defer_queue).q = NULL;
0376e7b2 464 is_empty = cds_list_empty(&registry_defer);
6abb4bd5 465 mutex_unlock(&rcu_defer_mutex);
786ee85b 466
dbc6128f 467 if (is_empty)
786ee85b 468 stop_defer_thread();
6abb4bd5 469 mutex_unlock(&defer_thread_mutex);
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470}
471
02be5561 472void rcu_defer_exit(void)
786ee85b 473{
0376e7b2 474 assert(cds_list_empty(&registry_defer));
786ee85b 475}
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476
477#endif /* _URCU_DEFER_IMPL_H */
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