Fix: call_rcu: teardown default call_rcu worker on application exit
[urcu.git] / src / urcu-call-rcu-impl.h
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1/*
2 * urcu-call-rcu.c
3 *
4 * Userspace RCU library - batch memory reclamation with kernel API
5 *
6 * Copyright (c) 2010 Paul E. McKenney <paulmck@linux.vnet.ibm.com>
7 *
8 * This library is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Lesser General Public
10 * License as published by the Free Software Foundation; either
11 * version 2.1 of the License, or (at your option) any later version.
12 *
13 * This library is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Lesser General Public License for more details.
17 *
18 * You should have received a copy of the GNU Lesser General Public
19 * License along with this library; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
21 */
22
5161f31e 23#define _LGPL_SOURCE
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24#include <stdio.h>
25#include <pthread.h>
26#include <signal.h>
b57aee66 27#include <stdlib.h>
6d841bc2 28#include <stdint.h>
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29#include <string.h>
30#include <errno.h>
31#include <poll.h>
32#include <sys/time.h>
b57aee66 33#include <unistd.h>
c1d2c60b 34#include <sched.h>
b57aee66 35
a47dd11c 36#include "compat-getcpu.h"
01477510 37#include <urcu/assert.h>
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38#include <urcu/wfcqueue.h>
39#include <urcu/call-rcu.h>
40#include <urcu/pointer.h>
41#include <urcu/list.h>
42#include <urcu/futex.h>
43#include <urcu/tls-compat.h>
44#include <urcu/ref.h>
4a6d7378 45#include "urcu-die.h"
4477a870 46#include "urcu-utils.h"
5cfe81b7 47#include "compat-smp.h"
b57aee66 48
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49#define SET_AFFINITY_CHECK_PERIOD (1U << 8) /* 256 */
50#define SET_AFFINITY_CHECK_PERIOD_MASK (SET_AFFINITY_CHECK_PERIOD - 1)
51
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52/* Data structure that identifies a call_rcu thread. */
53
54struct call_rcu_data {
5161f31e 55 /*
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56 * We do not align head on a different cache-line than tail
57 * mainly because call_rcu callback-invocation threads use
58 * batching ("splice") to get an entire list of callbacks, which
59 * effectively empties the queue, and requires to touch the tail
60 * anyway.
5161f31e 61 */
b9f893b6 62 struct cds_wfcq_tail cbs_tail;
0b8ab7df 63 struct cds_wfcq_head cbs_head;
b57aee66 64 unsigned long flags;
6d841bc2 65 int32_t futex;
73987721 66 unsigned long qlen; /* maintained for debugging. */
b57aee66 67 pthread_t tid;
c1d2c60b 68 int cpu_affinity;
8e3690db 69 unsigned long gp_count;
3c24913f 70 struct cds_list_head list;
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71} __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
72
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73struct call_rcu_completion {
74 int barrier_count;
75 int32_t futex;
81dd9134 76 struct urcu_ref ref;
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77};
78
79struct call_rcu_completion_work {
80 struct rcu_head head;
81 struct call_rcu_completion *completion;
82};
83
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84enum crdf_flags {
85 CRDF_FLAG_JOIN_THREAD = (1 << 0),
86};
87
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88/*
89 * List of all call_rcu_data structures to keep valgrind happy.
90 * Protected by call_rcu_mutex.
91 */
92
bab44e28 93static CDS_LIST_HEAD(call_rcu_data_list);
3c24913f 94
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95/* Link a thread using call_rcu() to its call_rcu thread. */
96
2f661865 97static DEFINE_URCU_TLS(struct call_rcu_data *, thread_call_rcu_data);
b57aee66 98
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99/*
100 * Guard call_rcu thread creation and atfork handlers.
101 */
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102static pthread_mutex_t call_rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
103
104/* If a given thread does not have its own call_rcu thread, this is default. */
105
106static struct call_rcu_data *default_call_rcu_data;
107
d0ec0ed2 108static struct urcu_atfork *registered_rculfhash_atfork;
d0ec0ed2 109
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110/*
111 * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
112 * available, then we can have call_rcu threads assigned to individual
113 * CPUs rather than only to specific threads.
114 */
115
a47dd11c 116#if defined(HAVE_SYSCONF) && (defined(HAVE_SCHED_GETCPU) || defined(HAVE_GETCPUID))
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117
118/*
119 * Pointer to array of pointers to per-CPU call_rcu_data structures
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120 * and # CPUs. per_cpu_call_rcu_data is a RCU-protected pointer to an
121 * array of RCU-protected pointers to call_rcu_data. call_rcu acts as a
122 * RCU read-side and reads per_cpu_call_rcu_data and the per-cpu pointer
123 * without mutex. The call_rcu_mutex protects updates.
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124 */
125
126static struct call_rcu_data **per_cpu_call_rcu_data;
5cfe81b7 127static long cpus_array_len;
b57aee66 128
5cfe81b7 129static void cpus_array_len_reset(void)
60af049d 130{
5cfe81b7 131 cpus_array_len = 0;
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132}
133
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134/* Allocate the array if it has not already been allocated. */
135
136static void alloc_cpu_call_rcu_data(void)
137{
138 struct call_rcu_data **p;
139 static int warned = 0;
140
5cfe81b7 141 if (cpus_array_len != 0)
b57aee66 142 return;
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143 cpus_array_len = get_possible_cpus_array_len();
144 if (cpus_array_len <= 0) {
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145 return;
146 }
5cfe81b7 147 p = malloc(cpus_array_len * sizeof(*per_cpu_call_rcu_data));
b57aee66 148 if (p != NULL) {
5cfe81b7 149 memset(p, '\0', cpus_array_len * sizeof(*per_cpu_call_rcu_data));
618b2595 150 rcu_set_pointer(&per_cpu_call_rcu_data, p);
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151 } else {
152 if (!warned) {
153 fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
154 }
155 warned = 1;
156 }
157}
158
63b495d8 159#else /* #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
b57aee66 160
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161/*
162 * per_cpu_call_rcu_data should be constant, but some functions below, used both
163 * for cases where cpu number is available and not available, assume it it not
164 * constant.
165 */
166static struct call_rcu_data **per_cpu_call_rcu_data = NULL;
5cfe81b7 167static const long cpus_array_len = -1;
b57aee66 168
5cfe81b7 169static void cpus_array_len_reset(void)
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170{
171}
172
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173static void alloc_cpu_call_rcu_data(void)
174{
175}
176
63b495d8 177#endif /* #else #if defined(HAVE_SYSCONF) && defined(HAVE_SCHED_GETCPU) */
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178
179/* Acquire the specified pthread mutex. */
180
181static void call_rcu_lock(pthread_mutex_t *pmp)
182{
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183 int ret;
184
185 ret = pthread_mutex_lock(pmp);
186 if (ret)
187 urcu_die(ret);
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188}
189
190/* Release the specified pthread mutex. */
191
192static void call_rcu_unlock(pthread_mutex_t *pmp)
193{
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194 int ret;
195
196 ret = pthread_mutex_unlock(pmp);
197 if (ret)
198 urcu_die(ret);
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199}
200
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201/*
202 * Periodically retry setting CPU affinity if we migrate.
203 * Losing affinity can be caused by CPU hotunplug/hotplug, or by
204 * cpuset(7).
205 */
2388c075 206#ifdef HAVE_SCHED_SETAFFINITY
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207static
208int set_thread_cpu_affinity(struct call_rcu_data *crdp)
209{
210 cpu_set_t mask;
8e3690db 211 int ret;
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212
213 if (crdp->cpu_affinity < 0)
214 return 0;
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215 if (++crdp->gp_count & SET_AFFINITY_CHECK_PERIOD_MASK)
216 return 0;
217 if (urcu_sched_getcpu() == crdp->cpu_affinity)
218 return 0;
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219
220 CPU_ZERO(&mask);
221 CPU_SET(crdp->cpu_affinity, &mask);
8e3690db 222 ret = sched_setaffinity(0, sizeof(mask), &mask);
0614a2e6 223
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224 /*
225 * EINVAL is fine: can be caused by hotunplugged CPUs, or by
226 * cpuset(7). This is why we should always retry if we detect
227 * migration.
228 */
229 if (ret && errno == EINVAL) {
230 ret = 0;
231 errno = 0;
232 }
233 return ret;
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234}
235#else
236static
a142df4e 237int set_thread_cpu_affinity(struct call_rcu_data *crdp __attribute__((unused)))
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238{
239 return 0;
240}
241#endif
242
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243static void call_rcu_wait(struct call_rcu_data *crdp)
244{
245 /* Read call_rcu list before read futex */
246 cmm_smp_mb();
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247 while (uatomic_read(&crdp->futex) == -1) {
248 if (!futex_async(&crdp->futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
249 /*
250 * Prior queued wakeups queued by unrelated code
251 * using the same address can cause futex wait to
252 * return 0 even through the futex value is still
253 * -1 (spurious wakeups). Check the value again
254 * in user-space to validate whether it really
255 * differs from -1.
256 */
257 continue;
258 }
b0a841b4 259 switch (errno) {
98d705dd 260 case EAGAIN:
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261 /* Value already changed. */
262 return;
263 case EINTR:
264 /* Retry if interrupted by signal. */
98d705dd 265 break; /* Get out of switch. Check again. */
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266 default:
267 /* Unexpected error. */
268 urcu_die(errno);
269 }
270 }
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271}
272
273static void call_rcu_wake_up(struct call_rcu_data *crdp)
274{
275 /* Write to call_rcu list before reading/writing futex */
276 cmm_smp_mb();
a0b7f7ea 277 if (caa_unlikely(uatomic_read(&crdp->futex) == -1)) {
03fe58b3 278 uatomic_set(&crdp->futex, 0);
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279 if (futex_async(&crdp->futex, FUTEX_WAKE, 1,
280 NULL, NULL, 0) < 0)
281 urcu_die(errno);
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282 }
283}
284
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285static void call_rcu_completion_wait(struct call_rcu_completion *completion)
286{
287 /* Read completion barrier count before read futex */
288 cmm_smp_mb();
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289 while (uatomic_read(&completion->futex) == -1) {
290 if (!futex_async(&completion->futex, FUTEX_WAIT, -1, NULL, NULL, 0)) {
291 /*
292 * Prior queued wakeups queued by unrelated code
293 * using the same address can cause futex wait to
294 * return 0 even through the futex value is still
295 * -1 (spurious wakeups). Check the value again
296 * in user-space to validate whether it really
297 * differs from -1.
298 */
299 continue;
300 }
b0a841b4 301 switch (errno) {
98d705dd 302 case EAGAIN:
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303 /* Value already changed. */
304 return;
305 case EINTR:
306 /* Retry if interrupted by signal. */
98d705dd 307 break; /* Get out of switch. Check again. */
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308 default:
309 /* Unexpected error. */
310 urcu_die(errno);
311 }
312 }
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313}
314
315static void call_rcu_completion_wake_up(struct call_rcu_completion *completion)
316{
317 /* Write to completion barrier count before reading/writing futex */
318 cmm_smp_mb();
319 if (caa_unlikely(uatomic_read(&completion->futex) == -1)) {
320 uatomic_set(&completion->futex, 0);
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321 if (futex_async(&completion->futex, FUTEX_WAKE, 1,
322 NULL, NULL, 0) < 0)
323 urcu_die(errno);
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324 }
325}
326
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327/* This is the code run by each call_rcu thread. */
328
329static void *call_rcu_thread(void *arg)
330{
331 unsigned long cbcount;
5161f31e 332 struct call_rcu_data *crdp = (struct call_rcu_data *) arg;
2870aa1e 333 int rt = !!(uatomic_read(&crdp->flags) & URCU_CALL_RCU_RT);
b57aee66 334
8e3690db 335 if (set_thread_cpu_affinity(crdp))
4a6d7378 336 urcu_die(errno);
c1d2c60b 337
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338 /*
339 * If callbacks take a read-side lock, we need to be registered.
340 */
341 rcu_register_thread();
342
bd252a04 343 URCU_TLS(thread_call_rcu_data) = crdp;
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344 if (!rt) {
345 uatomic_dec(&crdp->futex);
346 /* Decrement futex before reading call_rcu list */
347 cmm_smp_mb();
348 }
b57aee66 349 for (;;) {
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350 struct cds_wfcq_head cbs_tmp_head;
351 struct cds_wfcq_tail cbs_tmp_tail;
352 struct cds_wfcq_node *cbs, *cbs_tmp_n;
ae25b7e2 353 enum cds_wfcq_ret splice_ret;
5161f31e 354
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355 if (set_thread_cpu_affinity(crdp))
356 urcu_die(errno);
357
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358 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) {
359 /*
360 * Pause requested. Become quiescent: remove
361 * ourself from all global lists, and don't
362 * process any callback. The callback lists may
363 * still be non-empty though.
364 */
365 rcu_unregister_thread();
366 cmm_smp_mb__before_uatomic_or();
367 uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSED);
368 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSE) != 0)
109105b7 369 (void) poll(NULL, 0, 1);
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370 uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSED);
371 cmm_smp_mb__after_uatomic_and();
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372 rcu_register_thread();
373 }
374
5161f31e 375 cds_wfcq_init(&cbs_tmp_head, &cbs_tmp_tail);
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376 splice_ret = __cds_wfcq_splice_blocking(&cbs_tmp_head,
377 &cbs_tmp_tail, &crdp->cbs_head, &crdp->cbs_tail);
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378 urcu_posix_assert(splice_ret != CDS_WFCQ_RET_WOULDBLOCK);
379 urcu_posix_assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
ae25b7e2 380 if (splice_ret != CDS_WFCQ_RET_SRC_EMPTY) {
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381 synchronize_rcu();
382 cbcount = 0;
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383 __cds_wfcq_for_each_blocking_safe(&cbs_tmp_head,
384 &cbs_tmp_tail, cbs, cbs_tmp_n) {
385 struct rcu_head *rhp;
386
387 rhp = caa_container_of(cbs,
388 struct rcu_head, next);
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389 rhp->func(rhp);
390 cbcount++;
5161f31e 391 }
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392 uatomic_sub(&crdp->qlen, cbcount);
393 }
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394 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOP)
395 break;
765f3ead 396 rcu_thread_offline();
bc94ca9b 397 if (!rt) {
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398 if (cds_wfcq_empty(&crdp->cbs_head,
399 &crdp->cbs_tail)) {
bc94ca9b 400 call_rcu_wait(crdp);
109105b7 401 (void) poll(NULL, 0, 10);
bc94ca9b 402 uatomic_dec(&crdp->futex);
c768e45e 403 /*
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404 * Decrement futex before reading
405 * call_rcu list.
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406 */
407 cmm_smp_mb();
ccbac24d 408 } else {
109105b7 409 (void) poll(NULL, 0, 10);
c768e45e 410 }
bc94ca9b 411 } else {
109105b7 412 (void) poll(NULL, 0, 10);
b57aee66 413 }
765f3ead 414 rcu_thread_online();
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415 }
416 if (!rt) {
417 /*
418 * Read call_rcu list before write futex.
419 */
420 cmm_smp_mb();
421 uatomic_set(&crdp->futex, 0);
b57aee66 422 }
2870aa1e 423 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOPPED);
765f3ead 424 rcu_unregister_thread();
7106ddf8 425 return NULL;
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426}
427
428/*
429 * Create both a call_rcu thread and the corresponding call_rcu_data
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430 * structure, linking the structure in as specified. Caller must hold
431 * call_rcu_mutex.
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432 */
433
3c24913f 434static void call_rcu_data_init(struct call_rcu_data **crdpp,
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435 unsigned long flags,
436 int cpu_affinity)
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437{
438 struct call_rcu_data *crdp;
4a6d7378 439 int ret;
ea3a28a3 440 sigset_t newmask, oldmask;
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441
442 crdp = malloc(sizeof(*crdp));
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443 if (crdp == NULL)
444 urcu_die(errno);
b57aee66 445 memset(crdp, '\0', sizeof(*crdp));
5161f31e 446 cds_wfcq_init(&crdp->cbs_head, &crdp->cbs_tail);
b57aee66 447 crdp->qlen = 0;
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448 crdp->futex = 0;
449 crdp->flags = flags;
3c24913f 450 cds_list_add(&crdp->list, &call_rcu_data_list);
c1d2c60b 451 crdp->cpu_affinity = cpu_affinity;
8e3690db 452 crdp->gp_count = 0;
90f72b8c 453 rcu_set_pointer(crdpp, crdp);
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454
455 ret = sigfillset(&newmask);
456 urcu_posix_assert(!ret);
457 ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
458 urcu_posix_assert(!ret);
459
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460 ret = pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp);
461 if (ret)
462 urcu_die(ret);
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463
464 ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
465 urcu_posix_assert(!ret);
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466}
467
468/*
469 * Return a pointer to the call_rcu_data structure for the specified
470 * CPU, returning NULL if there is none. We cannot automatically
471 * created it because the platform we are running on might not define
63b495d8 472 * urcu_sched_getcpu().
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473 *
474 * The call to this function and use of the returned call_rcu_data
475 * should be protected by RCU read-side lock.
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476 */
477
478struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
479{
480 static int warned = 0;
618b2595 481 struct call_rcu_data **pcpu_crdp;
b57aee66 482
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483 pcpu_crdp = rcu_dereference(per_cpu_call_rcu_data);
484 if (pcpu_crdp == NULL)
b57aee66 485 return NULL;
5cfe81b7 486 if (!warned && cpus_array_len > 0 && (cpu < 0 || cpus_array_len <= cpu)) {
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487 fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
488 warned = 1;
489 }
5cfe81b7 490 if (cpu < 0 || cpus_array_len <= cpu)
b57aee66 491 return NULL;
618b2595 492 return rcu_dereference(pcpu_crdp[cpu]);
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493}
494
495/*
496 * Return the tid corresponding to the call_rcu thread whose
497 * call_rcu_data structure is specified.
498 */
499
500pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
501{
502 return crdp->tid;
503}
504
505/*
506 * Create a call_rcu_data structure (with thread) and return a pointer.
507 */
508
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509static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
510 int cpu_affinity)
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511{
512 struct call_rcu_data *crdp;
513
c1d2c60b 514 call_rcu_data_init(&crdp, flags, cpu_affinity);
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515 return crdp;
516}
517
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518struct call_rcu_data *create_call_rcu_data(unsigned long flags,
519 int cpu_affinity)
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520{
521 struct call_rcu_data *crdp;
522
523 call_rcu_lock(&call_rcu_mutex);
c1d2c60b 524 crdp = __create_call_rcu_data(flags, cpu_affinity);
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525 call_rcu_unlock(&call_rcu_mutex);
526 return crdp;
527}
528
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529/*
530 * Set the specified CPU to use the specified call_rcu_data structure.
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531 *
532 * Use NULL to remove a CPU's call_rcu_data structure, but it is
533 * the caller's responsibility to dispose of the removed structure.
534 * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
535 * (prior to NULLing it out, of course).
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536 *
537 * The caller must wait for a grace-period to pass between return from
538 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
539 * previous call rcu data as argument.
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540 */
541
542int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
543{
dcfc8165 544 static int warned = 0;
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545
546 call_rcu_lock(&call_rcu_mutex);
f3776786 547 alloc_cpu_call_rcu_data();
5cfe81b7 548 if (cpu < 0 || cpus_array_len <= cpu) {
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549 if (!warned) {
550 fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
551 warned = 1;
552 }
553 call_rcu_unlock(&call_rcu_mutex);
554 errno = EINVAL;
555 return -EINVAL;
556 }
53a55535 557
b57aee66 558 if (per_cpu_call_rcu_data == NULL) {
3670fef2 559 call_rcu_unlock(&call_rcu_mutex);
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560 errno = ENOMEM;
561 return -ENOMEM;
562 }
53a55535
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563
564 if (per_cpu_call_rcu_data[cpu] != NULL && crdp != NULL) {
565 call_rcu_unlock(&call_rcu_mutex);
566 errno = EEXIST;
567 return -EEXIST;
568 }
569
618b2595 570 rcu_set_pointer(&per_cpu_call_rcu_data[cpu], crdp);
3670fef2 571 call_rcu_unlock(&call_rcu_mutex);
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572 return 0;
573}
574
575/*
576 * Return a pointer to the default call_rcu_data structure, creating
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577 * one if need be.
578 *
579 * The call to this function with intent to use the returned
580 * call_rcu_data should be protected by RCU read-side lock.
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581 */
582
583struct call_rcu_data *get_default_call_rcu_data(void)
584{
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585 struct call_rcu_data *crdp;
586
587 crdp = rcu_dereference(default_call_rcu_data);
588 if (crdp != NULL)
589 return crdp;
590
b57aee66 591 call_rcu_lock(&call_rcu_mutex);
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592 if (default_call_rcu_data == NULL)
593 call_rcu_data_init(&default_call_rcu_data, 0, -1);
594 crdp = default_call_rcu_data;
b57aee66 595 call_rcu_unlock(&call_rcu_mutex);
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596
597 return crdp;
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598}
599
600/*
601 * Return the call_rcu_data structure that applies to the currently
602 * running thread. Any call_rcu_data structure assigned specifically
603 * to this thread has first priority, followed by any call_rcu_data
604 * structure assigned to the CPU on which the thread is running,
605 * followed by the default call_rcu_data structure. If there is not
606 * yet a default call_rcu_data structure, one will be created.
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607 *
608 * Calls to this function and use of the returned call_rcu_data should
609 * be protected by RCU read-side lock.
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610 */
611struct call_rcu_data *get_call_rcu_data(void)
612{
9744f3bb 613 struct call_rcu_data *crd;
b57aee66 614
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615 if (URCU_TLS(thread_call_rcu_data) != NULL)
616 return URCU_TLS(thread_call_rcu_data);
9744f3bb 617
5cfe81b7 618 if (cpus_array_len > 0) {
63b495d8 619 crd = get_cpu_call_rcu_data(urcu_sched_getcpu());
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620 if (crd)
621 return crd;
b57aee66 622 }
9744f3bb 623
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624 return get_default_call_rcu_data();
625}
626
627/*
628 * Return a pointer to this task's call_rcu_data if there is one.
629 */
630
631struct call_rcu_data *get_thread_call_rcu_data(void)
632{
bd252a04 633 return URCU_TLS(thread_call_rcu_data);
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634}
635
636/*
637 * Set this task's call_rcu_data structure as specified, regardless
638 * of whether or not this task already had one. (This allows switching
639 * to and from real-time call_rcu threads, for example.)
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640 *
641 * Use NULL to remove a thread's call_rcu_data structure, but it is
642 * the caller's responsibility to dispose of the removed structure.
643 * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
644 * (prior to NULLing it out, of course).
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645 */
646
647void set_thread_call_rcu_data(struct call_rcu_data *crdp)
648{
bd252a04 649 URCU_TLS(thread_call_rcu_data) = crdp;
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650}
651
652/*
653 * Create a separate call_rcu thread for each CPU. This does not
654 * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
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655 * function if you want that behavior. Should be paired with
656 * free_all_cpu_call_rcu_data() to teardown these call_rcu worker
657 * threads.
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658 */
659
660int create_all_cpu_call_rcu_data(unsigned long flags)
661{
662 int i;
663 struct call_rcu_data *crdp;
664 int ret;
665
666 call_rcu_lock(&call_rcu_mutex);
667 alloc_cpu_call_rcu_data();
668 call_rcu_unlock(&call_rcu_mutex);
5cfe81b7 669 if (cpus_array_len <= 0) {
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670 errno = EINVAL;
671 return -EINVAL;
672 }
673 if (per_cpu_call_rcu_data == NULL) {
674 errno = ENOMEM;
675 return -ENOMEM;
676 }
5cfe81b7 677 for (i = 0; i < cpus_array_len; i++) {
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678 call_rcu_lock(&call_rcu_mutex);
679 if (get_cpu_call_rcu_data(i)) {
680 call_rcu_unlock(&call_rcu_mutex);
681 continue;
682 }
c1d2c60b 683 crdp = __create_call_rcu_data(flags, i);
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684 if (crdp == NULL) {
685 call_rcu_unlock(&call_rcu_mutex);
686 errno = ENOMEM;
687 return -ENOMEM;
688 }
689 call_rcu_unlock(&call_rcu_mutex);
690 if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
356c8794
LJ
691 call_rcu_data_free(crdp);
692
693 /* it has been created by other thread */
694 if (ret == -EEXIST)
695 continue;
696
697 return ret;
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698 }
699 }
700 return 0;
701}
702
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703/*
704 * Wake up the call_rcu thread corresponding to the specified
705 * call_rcu_data structure.
706 */
707static void wake_call_rcu_thread(struct call_rcu_data *crdp)
708{
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709 if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT))
710 call_rcu_wake_up(crdp);
7106ddf8
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711}
712
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713static void _call_rcu(struct rcu_head *head,
714 void (*func)(struct rcu_head *head),
715 struct call_rcu_data *crdp)
716{
717 cds_wfcq_node_init(&head->next);
718 head->func = func;
719 cds_wfcq_enqueue(&crdp->cbs_head, &crdp->cbs_tail, &head->next);
720 uatomic_inc(&crdp->qlen);
721 wake_call_rcu_thread(crdp);
722}
723
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724/*
725 * Schedule a function to be invoked after a following grace period.
726 * This is the only function that must be called -- the others are
727 * only present to allow applications to tune their use of RCU for
728 * maximum performance.
729 *
730 * Note that unless a call_rcu thread has not already been created,
731 * the first invocation of call_rcu() will create one. So, if you
732 * need the first invocation of call_rcu() to be fast, make sure
733 * to create a call_rcu thread first. One way to accomplish this is
734 * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
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735 *
736 * call_rcu must be called by registered RCU read-side threads.
b57aee66 737 */
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738void call_rcu(struct rcu_head *head,
739 void (*func)(struct rcu_head *head))
740{
741 struct call_rcu_data *crdp;
742
618b2595 743 /* Holding rcu read-side lock across use of per-cpu crdp */
ffb4aaa7 744 _rcu_read_lock();
b57aee66 745 crdp = get_call_rcu_data();
b7f721d9 746 _call_rcu(head, func, crdp);
ffb4aaa7 747 _rcu_read_unlock();
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748}
749
750/*
751 * Free up the specified call_rcu_data structure, terminating the
752 * associated call_rcu thread. The caller must have previously
753 * removed the call_rcu_data structure from per-thread or per-CPU
754 * usage. For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
755 * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
756 * per-thread call_rcu_data structures.
757 *
758 * We silently refuse to free up the default call_rcu_data structure
759 * because that is where we put any leftover callbacks. Note that
760 * the possibility of self-spawning callbacks makes it impossible
761 * to execute all the callbacks in finite time without putting any
762 * newly spawned callbacks somewhere else. The "somewhere else" of
763 * last resort is the default call_rcu_data structure.
764 *
765 * We also silently refuse to free NULL pointers. This simplifies
766 * the calling code.
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767 *
768 * The caller must wait for a grace-period to pass between return from
769 * set_cpu_call_rcu_data() and call to call_rcu_data_free() passing the
770 * previous call rcu data as argument.
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771 *
772 * Note: introducing __cds_wfcq_splice_blocking() in this function fixed
773 * a list corruption bug in the 0.7.x series. The equivalent fix
774 * appeared in 0.6.8 for the stable-0.6 branch.
7106ddf8 775 */
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776static
777void _call_rcu_data_free(struct call_rcu_data *crdp, unsigned int flags)
7106ddf8 778{
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779 if (crdp == NULL || crdp == default_call_rcu_data) {
780 return;
781 }
2870aa1e
PB
782 if ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0) {
783 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOP);
7106ddf8 784 wake_call_rcu_thread(crdp);
2870aa1e 785 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
109105b7 786 (void) poll(NULL, 0, 1);
7106ddf8 787 }
51b98c3c 788 call_rcu_lock(&call_rcu_mutex);
5161f31e 789 if (!cds_wfcq_empty(&crdp->cbs_head, &crdp->cbs_tail)) {
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790 call_rcu_unlock(&call_rcu_mutex);
791 /* Create default call rcu data if need be. */
792 /* CBs queued here will be handed to the default list. */
698d0778 793 (void) get_default_call_rcu_data();
51b98c3c 794 call_rcu_lock(&call_rcu_mutex);
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795 __cds_wfcq_splice_blocking(&default_call_rcu_data->cbs_head,
796 &default_call_rcu_data->cbs_tail,
797 &crdp->cbs_head, &crdp->cbs_tail);
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798 uatomic_add(&default_call_rcu_data->qlen,
799 uatomic_read(&crdp->qlen));
1e92aa15 800 wake_call_rcu_thread(default_call_rcu_data);
7106ddf8 801 }
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802
803 cds_list_del(&crdp->list);
b75dffe6
LJ
804 call_rcu_unlock(&call_rcu_mutex);
805
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806 if (flags & CRDF_FLAG_JOIN_THREAD) {
807 int ret;
808
809 ret = pthread_join(get_call_rcu_thread(crdp), NULL);
810 if (ret)
811 urcu_die(ret);
812 }
59dc9e9d 813 free(crdp);
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814}
815
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816void call_rcu_data_free(struct call_rcu_data *crdp)
817{
818 _call_rcu_data_free(crdp, CRDF_FLAG_JOIN_THREAD);
819}
820
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821/*
822 * Clean up all the per-CPU call_rcu threads.
823 */
824void free_all_cpu_call_rcu_data(void)
825{
826 int cpu;
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827 struct call_rcu_data **crdp;
828 static int warned = 0;
7106ddf8 829
5cfe81b7 830 if (cpus_array_len <= 0)
7106ddf8 831 return;
618b2595 832
5cfe81b7 833 crdp = malloc(sizeof(*crdp) * cpus_array_len);
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MD
834 if (!crdp) {
835 if (!warned) {
836 fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
837 }
838 warned = 1;
d31150b4 839 return;
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MD
840 }
841
5cfe81b7 842 for (cpu = 0; cpu < cpus_array_len; cpu++) {
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843 crdp[cpu] = get_cpu_call_rcu_data(cpu);
844 if (crdp[cpu] == NULL)
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845 continue;
846 set_cpu_call_rcu_data(cpu, NULL);
7106ddf8 847 }
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848 /*
849 * Wait for call_rcu sites acting as RCU readers of the
850 * call_rcu_data to become quiescent.
851 */
852 synchronize_rcu();
5cfe81b7 853 for (cpu = 0; cpu < cpus_array_len; cpu++) {
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854 if (crdp[cpu] == NULL)
855 continue;
856 call_rcu_data_free(crdp[cpu]);
857 }
858 free(crdp);
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859}
860
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KF
861static
862void free_completion(struct urcu_ref *ref)
863{
864 struct call_rcu_completion *completion;
865
866 completion = caa_container_of(ref, struct call_rcu_completion, ref);
867 free(completion);
868}
869
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870static
871void _rcu_barrier_complete(struct rcu_head *head)
872{
873 struct call_rcu_completion_work *work;
874 struct call_rcu_completion *completion;
875
876 work = caa_container_of(head, struct call_rcu_completion_work, head);
877 completion = work->completion;
81dd9134
KF
878 if (!uatomic_sub_return(&completion->barrier_count, 1))
879 call_rcu_completion_wake_up(completion);
880 urcu_ref_put(&completion->ref, free_completion);
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881 free(work);
882}
883
884/*
885 * Wait for all in-flight call_rcu callbacks to complete execution.
886 */
887void rcu_barrier(void)
888{
889 struct call_rcu_data *crdp;
81dd9134 890 struct call_rcu_completion *completion;
63f0fc6d 891 int count = 0;
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892 int was_online;
893
894 /* Put in offline state in QSBR. */
ffb4aaa7 895 was_online = _rcu_read_ongoing();
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MD
896 if (was_online)
897 rcu_thread_offline();
898 /*
899 * Calling a rcu_barrier() within a RCU read-side critical
900 * section is an error.
901 */
ffb4aaa7 902 if (_rcu_read_ongoing()) {
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MD
903 static int warned = 0;
904
905 if (!warned) {
906 fprintf(stderr, "[error] liburcu: rcu_barrier() called from within RCU read-side critical section.\n");
907 }
908 warned = 1;
909 goto online;
910 }
911
81dd9134
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912 completion = calloc(sizeof(*completion), 1);
913 if (!completion)
914 urcu_die(errno);
915
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MD
916 call_rcu_lock(&call_rcu_mutex);
917 cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
918 count++;
919
81dd9134
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920 /* Referenced by rcu_barrier() and each call_rcu thread. */
921 urcu_ref_set(&completion->ref, count + 1);
922 completion->barrier_count = count;
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923
924 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
925 struct call_rcu_completion_work *work;
926
927 work = calloc(sizeof(*work), 1);
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MD
928 if (!work)
929 urcu_die(errno);
81dd9134 930 work->completion = completion;
b7f721d9 931 _call_rcu(&work->head, _rcu_barrier_complete, crdp);
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MD
932 }
933 call_rcu_unlock(&call_rcu_mutex);
934
b7f721d9
MD
935 /* Wait for them */
936 for (;;) {
81dd9134 937 uatomic_dec(&completion->futex);
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MD
938 /* Decrement futex before reading barrier_count */
939 cmm_smp_mb();
81dd9134 940 if (!uatomic_read(&completion->barrier_count))
b7f721d9 941 break;
81dd9134 942 call_rcu_completion_wait(completion);
b7f721d9 943 }
81dd9134
KF
944
945 urcu_ref_put(&completion->ref, free_completion);
946
b7f721d9
MD
947online:
948 if (was_online)
949 rcu_thread_online();
950}
951
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952/*
953 * Acquire the call_rcu_mutex in order to ensure that the child sees
e85451a1
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954 * all of the call_rcu() data structures in a consistent state. Ensure
955 * that all call_rcu threads are in a quiescent state across fork.
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956 * Suitable for pthread_atfork() and friends.
957 */
958void call_rcu_before_fork(void)
959{
e85451a1 960 struct call_rcu_data *crdp;
d0ec0ed2 961 struct urcu_atfork *atfork;
e85451a1 962
81ad2e19 963 call_rcu_lock(&call_rcu_mutex);
e85451a1 964
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MD
965 atfork = registered_rculfhash_atfork;
966 if (atfork)
967 atfork->before_fork(atfork->priv);
968
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MD
969 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
970 uatomic_or(&crdp->flags, URCU_CALL_RCU_PAUSE);
971 cmm_smp_mb__after_uatomic_or();
972 wake_call_rcu_thread(crdp);
973 }
974 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
975 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) == 0)
109105b7 976 (void) poll(NULL, 0, 1);
e85451a1 977 }
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978}
979
980/*
981 * Clean up call_rcu data structures in the parent of a successful fork()
982 * that is not followed by exec() in the child. Suitable for
983 * pthread_atfork() and friends.
984 */
985void call_rcu_after_fork_parent(void)
986{
e85451a1 987 struct call_rcu_data *crdp;
d0ec0ed2 988 struct urcu_atfork *atfork;
e85451a1
MD
989
990 cds_list_for_each_entry(crdp, &call_rcu_data_list, list)
991 uatomic_and(&crdp->flags, ~URCU_CALL_RCU_PAUSE);
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992 cds_list_for_each_entry(crdp, &call_rcu_data_list, list) {
993 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_PAUSED) != 0)
109105b7 994 (void) poll(NULL, 0, 1);
fc236e5e 995 }
d0ec0ed2
MD
996 atfork = registered_rculfhash_atfork;
997 if (atfork)
998 atfork->after_fork_parent(atfork->priv);
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999 call_rcu_unlock(&call_rcu_mutex);
1000}
1001
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1002/*
1003 * Clean up call_rcu data structures in the child of a successful fork()
81ad2e19
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1004 * that is not followed by exec(). Suitable for pthread_atfork() and
1005 * friends.
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1006 */
1007void call_rcu_after_fork_child(void)
1008{
077ff173 1009 struct call_rcu_data *crdp, *next;
d0ec0ed2 1010 struct urcu_atfork *atfork;
7106ddf8 1011
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1012 /* Release the mutex. */
1013 call_rcu_unlock(&call_rcu_mutex);
1014
d0ec0ed2
MD
1015 atfork = registered_rculfhash_atfork;
1016 if (atfork)
1017 atfork->after_fork_child(atfork->priv);
1018
ad1b9909
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1019 /* Do nothing when call_rcu() has not been used */
1020 if (cds_list_empty(&call_rcu_data_list))
1021 return;
1022
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1023 /*
1024 * Allocate a new default call_rcu_data structure in order
1025 * to get a working call_rcu thread to go with it.
1026 */
1027 default_call_rcu_data = NULL;
1028 (void)get_default_call_rcu_data();
1029
60af049d 1030 /* Cleanup call_rcu_data pointers before use */
5cfe81b7 1031 cpus_array_len_reset();
60af049d 1032 free(per_cpu_call_rcu_data);
618b2595 1033 rcu_set_pointer(&per_cpu_call_rcu_data, NULL);
bd252a04 1034 URCU_TLS(thread_call_rcu_data) = NULL;
60af049d 1035
e85451a1
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1036 /*
1037 * Dispose of all of the rest of the call_rcu_data structures.
1038 * Leftover call_rcu callbacks will be merged into the new
1039 * default call_rcu thread queue.
1040 */
077ff173 1041 cds_list_for_each_entry_safe(crdp, next, &call_rcu_data_list, list) {
7106ddf8 1042 if (crdp == default_call_rcu_data)
077ff173 1043 continue;
2870aa1e 1044 uatomic_set(&crdp->flags, URCU_CALL_RCU_STOPPED);
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MD
1045 /*
1046 * Do not join the thread because it does not exist in
1047 * the child.
1048 */
1049 _call_rcu_data_free(crdp, 0);
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1050 }
1051}
d0ec0ed2
MD
1052
1053void urcu_register_rculfhash_atfork(struct urcu_atfork *atfork)
1054{
b047e7a7
MD
1055 if (CMM_LOAD_SHARED(registered_rculfhash_atfork))
1056 return;
d0ec0ed2 1057 call_rcu_lock(&call_rcu_mutex);
b047e7a7
MD
1058 if (!registered_rculfhash_atfork)
1059 registered_rculfhash_atfork = atfork;
d0ec0ed2
MD
1060 call_rcu_unlock(&call_rcu_mutex);
1061}
1062
b047e7a7
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1063/*
1064 * This unregistration function is deprecated, meant only for internal
1065 * use by rculfhash.
1066 */
1067__attribute__((noreturn))
70469b43 1068void urcu_unregister_rculfhash_atfork(struct urcu_atfork *atfork __attribute__((unused)))
d0ec0ed2 1069{
b047e7a7 1070 urcu_die(EPERM);
d0ec0ed2 1071}
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MD
1072
1073/*
1074 * Teardown the default call_rcu worker thread if there are no queued
1075 * callbacks on process exit. This prevents leaking memory.
1076 *
1077 * Here is how an application can ensure graceful teardown of this
1078 * worker thread:
1079 *
1080 * - An application queuing call_rcu callbacks should invoke
1081 * rcu_barrier() before it exits.
1082 * - When chaining call_rcu callbacks, the number of calls to
1083 * rcu_barrier() on application exit must match at least the maximum
1084 * number of chained callbacks.
1085 * - If an application chains callbacks endlessly, it would have to be
1086 * modified to stop chaining callbacks when it detects an application
1087 * exit (e.g. with a flag), and wait for quiescence with rcu_barrier()
1088 * after setting that flag.
1089 * - The statements above apply to a library which queues call_rcu
1090 * callbacks, only it needs to invoke rcu_barrier in its library
1091 * destructor.
1092 *
1093 * Note that this function does not presume it is being called when the
1094 * application is single-threaded even though this is invoked from a
1095 * destructor: this function synchronizes against concurrent calls to
1096 * get_default_call_rcu_data().
1097 */
1098static void urcu_call_rcu_exit(void)
1099{
1100 struct call_rcu_data *crdp;
1101 bool teardown = true;
1102
1103 if (default_call_rcu_data == NULL)
1104 return;
1105 call_rcu_lock(&call_rcu_mutex);
1106 /*
1107 * If the application leaves callbacks in the default call_rcu
1108 * worker queue, keep the default worker in place.
1109 */
1110 crdp = default_call_rcu_data;
1111 if (!crdp) {
1112 teardown = false;
1113 goto unlock;
1114 }
1115 if (!cds_wfcq_empty(&crdp->cbs_head, &crdp->cbs_tail)) {
1116 teardown = false;
1117 goto unlock;
1118 }
1119 rcu_set_pointer(&default_call_rcu_data, NULL);
1120unlock:
1121 call_rcu_unlock(&call_rcu_mutex);
1122 if (teardown) {
1123 synchronize_rcu();
1124 call_rcu_data_free(crdp);
1125 }
1126}
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