init maxcpus before use
[urcu.git] / 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
c1d2c60b 23#define _GNU_SOURCE
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24#include <stdio.h>
25#include <pthread.h>
26#include <signal.h>
27#include <assert.h>
28#include <stdlib.h>
6d841bc2 29#include <stdint.h>
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30#include <string.h>
31#include <errno.h>
32#include <poll.h>
33#include <sys/time.h>
b57aee66 34#include <unistd.h>
c1d2c60b 35#include <sched.h>
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36
37#include "config.h"
38#include "urcu/wfqueue.h"
39#include "urcu-call-rcu.h"
40#include "urcu-pointer.h"
3c24913f 41#include "urcu/list.h"
41849996 42#include "urcu/futex.h"
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43
44/* Data structure that identifies a call_rcu thread. */
45
46struct call_rcu_data {
47 struct cds_wfq_queue cbs;
48 unsigned long flags;
6d841bc2 49 int32_t futex;
73987721 50 unsigned long qlen; /* maintained for debugging. */
b57aee66 51 pthread_t tid;
c1d2c60b 52 int cpu_affinity;
3c24913f 53 struct cds_list_head list;
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54} __attribute__((aligned(CAA_CACHE_LINE_SIZE)));
55
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56/*
57 * List of all call_rcu_data structures to keep valgrind happy.
58 * Protected by call_rcu_mutex.
59 */
60
61CDS_LIST_HEAD(call_rcu_data_list);
62
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63/* Link a thread using call_rcu() to its call_rcu thread. */
64
65static __thread struct call_rcu_data *thread_call_rcu_data;
66
67/* Guard call_rcu thread creation. */
68
69static pthread_mutex_t call_rcu_mutex = PTHREAD_MUTEX_INITIALIZER;
70
71/* If a given thread does not have its own call_rcu thread, this is default. */
72
73static struct call_rcu_data *default_call_rcu_data;
74
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75/*
76 * If the sched_getcpu() and sysconf(_SC_NPROCESSORS_CONF) calls are
77 * available, then we can have call_rcu threads assigned to individual
78 * CPUs rather than only to specific threads.
79 */
80
81#if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF)
82
83/*
84 * Pointer to array of pointers to per-CPU call_rcu_data structures
85 * and # CPUs.
86 */
87
88static struct call_rcu_data **per_cpu_call_rcu_data;
89static long maxcpus;
90
91/* Allocate the array if it has not already been allocated. */
92
93static void alloc_cpu_call_rcu_data(void)
94{
95 struct call_rcu_data **p;
96 static int warned = 0;
97
98 if (maxcpus != 0)
99 return;
100 maxcpus = sysconf(_SC_NPROCESSORS_CONF);
101 if (maxcpus <= 0) {
102 return;
103 }
104 p = malloc(maxcpus * sizeof(*per_cpu_call_rcu_data));
105 if (p != NULL) {
106 memset(p, '\0', maxcpus * sizeof(*per_cpu_call_rcu_data));
107 per_cpu_call_rcu_data = p;
108 } else {
109 if (!warned) {
110 fprintf(stderr, "[error] liburcu: unable to allocate per-CPU pointer array\n");
111 }
112 warned = 1;
113 }
114}
115
116#else /* #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
117
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118/*
119 * per_cpu_call_rcu_data should be constant, but some functions below, used both
120 * for cases where cpu number is available and not available, assume it it not
121 * constant.
122 */
123static struct call_rcu_data **per_cpu_call_rcu_data = NULL;
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124static const long maxcpus = -1;
125
126static void alloc_cpu_call_rcu_data(void)
127{
128}
129
130static int sched_getcpu(void)
131{
132 return -1;
133}
134
135#endif /* #else #if defined(HAVE_SCHED_GETCPU) && defined(HAVE_SYSCONF) */
136
137/* Acquire the specified pthread mutex. */
138
139static void call_rcu_lock(pthread_mutex_t *pmp)
140{
141 if (pthread_mutex_lock(pmp) != 0) {
142 perror("pthread_mutex_lock");
143 exit(-1);
144 }
145}
146
147/* Release the specified pthread mutex. */
148
149static void call_rcu_unlock(pthread_mutex_t *pmp)
150{
151 if (pthread_mutex_unlock(pmp) != 0) {
152 perror("pthread_mutex_unlock");
153 exit(-1);
154 }
155}
156
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157#if HAVE_SCHED_SETAFFINITY
158static
159int set_thread_cpu_affinity(struct call_rcu_data *crdp)
160{
161 cpu_set_t mask;
162
163 if (crdp->cpu_affinity < 0)
164 return 0;
165
166 CPU_ZERO(&mask);
167 CPU_SET(crdp->cpu_affinity, &mask);
168#if SCHED_SETAFFINITY_ARGS == 2
169 return sched_setaffinity(0, &mask);
170#else
171 return sched_setaffinity(0, sizeof(mask), &mask);
172#endif
173}
174#else
175static
176int set_thread_cpu_affinity(struct call_rcu_data *crdp)
177{
178 return 0;
179}
180#endif
181
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182static void call_rcu_wait(struct call_rcu_data *crdp)
183{
184 /* Read call_rcu list before read futex */
185 cmm_smp_mb();
186 if (uatomic_read(&crdp->futex) == -1)
187 futex_async(&crdp->futex, FUTEX_WAIT, -1,
188 NULL, NULL, 0);
189}
190
191static void call_rcu_wake_up(struct call_rcu_data *crdp)
192{
193 /* Write to call_rcu list before reading/writing futex */
194 cmm_smp_mb();
195 if (unlikely(uatomic_read(&crdp->futex) == -1)) {
196 uatomic_set(&crdp->futex, 0);
197 futex_async(&crdp->futex, FUTEX_WAKE, 1,
198 NULL, NULL, 0);
199 }
200}
201
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202/* This is the code run by each call_rcu thread. */
203
204static void *call_rcu_thread(void *arg)
205{
206 unsigned long cbcount;
207 struct cds_wfq_node *cbs;
208 struct cds_wfq_node **cbs_tail;
209 struct call_rcu_data *crdp = (struct call_rcu_data *)arg;
210 struct rcu_head *rhp;
2870aa1e 211 int rt = !!(uatomic_read(&crdp->flags) & URCU_CALL_RCU_RT);
b57aee66 212
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213 if (set_thread_cpu_affinity(crdp) != 0) {
214 perror("pthread_setaffinity_np");
215 exit(-1);
216 }
217
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218 /*
219 * If callbacks take a read-side lock, we need to be registered.
220 */
221 rcu_register_thread();
222
b57aee66 223 thread_call_rcu_data = crdp;
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224 if (!rt) {
225 uatomic_dec(&crdp->futex);
226 /* Decrement futex before reading call_rcu list */
227 cmm_smp_mb();
228 }
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229 for (;;) {
230 if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
231 while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
232 poll(NULL, 0, 1);
233 _CMM_STORE_SHARED(crdp->cbs.head, NULL);
234 cbs_tail = (struct cds_wfq_node **)
235 uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
236 synchronize_rcu();
237 cbcount = 0;
238 do {
239 while (cbs->next == NULL &&
240 &cbs->next != cbs_tail)
241 poll(NULL, 0, 1);
242 if (cbs == &crdp->cbs.dummy) {
243 cbs = cbs->next;
244 continue;
245 }
246 rhp = (struct rcu_head *)cbs;
247 cbs = cbs->next;
248 rhp->func(rhp);
249 cbcount++;
250 } while (cbs != NULL);
251 uatomic_sub(&crdp->qlen, cbcount);
252 }
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253 if (uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOP)
254 break;
765f3ead 255 rcu_thread_offline();
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256 if (!rt) {
257 if (&crdp->cbs.head
258 == _CMM_LOAD_SHARED(crdp->cbs.tail)) {
259 call_rcu_wait(crdp);
260 poll(NULL, 0, 10);
261 uatomic_dec(&crdp->futex);
c768e45e 262 /*
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263 * Decrement futex before reading
264 * call_rcu list.
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265 */
266 cmm_smp_mb();
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267 } else {
268 poll(NULL, 0, 10);
c768e45e 269 }
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270 } else {
271 poll(NULL, 0, 10);
b57aee66 272 }
765f3ead 273 rcu_thread_online();
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274 }
275 if (!rt) {
276 /*
277 * Read call_rcu list before write futex.
278 */
279 cmm_smp_mb();
280 uatomic_set(&crdp->futex, 0);
b57aee66 281 }
2870aa1e 282 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOPPED);
765f3ead 283 rcu_unregister_thread();
7106ddf8 284 return NULL;
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285}
286
287/*
288 * Create both a call_rcu thread and the corresponding call_rcu_data
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289 * structure, linking the structure in as specified. Caller must hold
290 * call_rcu_mutex.
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291 */
292
3c24913f 293static void call_rcu_data_init(struct call_rcu_data **crdpp,
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294 unsigned long flags,
295 int cpu_affinity)
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296{
297 struct call_rcu_data *crdp;
298
299 crdp = malloc(sizeof(*crdp));
300 if (crdp == NULL) {
301 fprintf(stderr, "Out of memory.\n");
302 exit(-1);
303 }
304 memset(crdp, '\0', sizeof(*crdp));
305 cds_wfq_init(&crdp->cbs);
306 crdp->qlen = 0;
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307 crdp->futex = 0;
308 crdp->flags = flags;
3c24913f 309 cds_list_add(&crdp->list, &call_rcu_data_list);
c1d2c60b 310 crdp->cpu_affinity = cpu_affinity;
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311 cmm_smp_mb(); /* Structure initialized before pointer is planted. */
312 *crdpp = crdp;
313 if (pthread_create(&crdp->tid, NULL, call_rcu_thread, crdp) != 0) {
314 perror("pthread_create");
315 exit(-1);
316 }
317}
318
319/*
320 * Return a pointer to the call_rcu_data structure for the specified
321 * CPU, returning NULL if there is none. We cannot automatically
322 * created it because the platform we are running on might not define
323 * sched_getcpu().
324 */
325
326struct call_rcu_data *get_cpu_call_rcu_data(int cpu)
327{
328 static int warned = 0;
329
330 if (per_cpu_call_rcu_data == NULL)
331 return NULL;
332 if (!warned && maxcpus > 0 && (cpu < 0 || maxcpus <= cpu)) {
333 fprintf(stderr, "[error] liburcu: get CPU # out of range\n");
334 warned = 1;
335 }
336 if (cpu < 0 || maxcpus <= cpu)
337 return NULL;
338 return per_cpu_call_rcu_data[cpu];
339}
340
341/*
342 * Return the tid corresponding to the call_rcu thread whose
343 * call_rcu_data structure is specified.
344 */
345
346pthread_t get_call_rcu_thread(struct call_rcu_data *crdp)
347{
348 return crdp->tid;
349}
350
351/*
352 * Create a call_rcu_data structure (with thread) and return a pointer.
353 */
354
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355static struct call_rcu_data *__create_call_rcu_data(unsigned long flags,
356 int cpu_affinity)
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357{
358 struct call_rcu_data *crdp;
359
c1d2c60b 360 call_rcu_data_init(&crdp, flags, cpu_affinity);
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361 return crdp;
362}
363
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364struct call_rcu_data *create_call_rcu_data(unsigned long flags,
365 int cpu_affinity)
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366{
367 struct call_rcu_data *crdp;
368
369 call_rcu_lock(&call_rcu_mutex);
c1d2c60b 370 crdp = __create_call_rcu_data(flags, cpu_affinity);
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371 call_rcu_unlock(&call_rcu_mutex);
372 return crdp;
373}
374
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375/*
376 * Set the specified CPU to use the specified call_rcu_data structure.
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377 *
378 * Use NULL to remove a CPU's call_rcu_data structure, but it is
379 * the caller's responsibility to dispose of the removed structure.
380 * Use get_cpu_call_rcu_data() to obtain a pointer to the old structure
381 * (prior to NULLing it out, of course).
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382 */
383
384int set_cpu_call_rcu_data(int cpu, struct call_rcu_data *crdp)
385{
dcfc8165 386 static int warned = 0;
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387
388 call_rcu_lock(&call_rcu_mutex);
f3776786 389 alloc_cpu_call_rcu_data();
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390 if (cpu < 0 || maxcpus <= cpu) {
391 if (!warned) {
392 fprintf(stderr, "[error] liburcu: set CPU # out of range\n");
393 warned = 1;
394 }
395 call_rcu_unlock(&call_rcu_mutex);
396 errno = EINVAL;
397 return -EINVAL;
398 }
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399 call_rcu_unlock(&call_rcu_mutex);
400 if (per_cpu_call_rcu_data == NULL) {
401 errno = ENOMEM;
402 return -ENOMEM;
403 }
404 per_cpu_call_rcu_data[cpu] = crdp;
405 return 0;
406}
407
408/*
409 * Return a pointer to the default call_rcu_data structure, creating
410 * one if need be. Because we never free call_rcu_data structures,
411 * we don't need to be in an RCU read-side critical section.
412 */
413
414struct call_rcu_data *get_default_call_rcu_data(void)
415{
416 if (default_call_rcu_data != NULL)
417 return rcu_dereference(default_call_rcu_data);
418 call_rcu_lock(&call_rcu_mutex);
419 if (default_call_rcu_data != NULL) {
420 call_rcu_unlock(&call_rcu_mutex);
421 return default_call_rcu_data;
422 }
c1d2c60b 423 call_rcu_data_init(&default_call_rcu_data, 0, -1);
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424 call_rcu_unlock(&call_rcu_mutex);
425 return default_call_rcu_data;
426}
427
428/*
429 * Return the call_rcu_data structure that applies to the currently
430 * running thread. Any call_rcu_data structure assigned specifically
431 * to this thread has first priority, followed by any call_rcu_data
432 * structure assigned to the CPU on which the thread is running,
433 * followed by the default call_rcu_data structure. If there is not
434 * yet a default call_rcu_data structure, one will be created.
435 */
436struct call_rcu_data *get_call_rcu_data(void)
437{
438 int curcpu;
439 static int warned = 0;
440
441 if (thread_call_rcu_data != NULL)
442 return thread_call_rcu_data;
443 if (maxcpus <= 0)
444 return get_default_call_rcu_data();
445 curcpu = sched_getcpu();
446 if (!warned && (curcpu < 0 || maxcpus <= curcpu)) {
447 fprintf(stderr, "[error] liburcu: gcrd CPU # out of range\n");
448 warned = 1;
449 }
450 if (curcpu >= 0 && maxcpus > curcpu &&
451 per_cpu_call_rcu_data != NULL &&
452 per_cpu_call_rcu_data[curcpu] != NULL)
453 return per_cpu_call_rcu_data[curcpu];
454 return get_default_call_rcu_data();
455}
456
457/*
458 * Return a pointer to this task's call_rcu_data if there is one.
459 */
460
461struct call_rcu_data *get_thread_call_rcu_data(void)
462{
463 return thread_call_rcu_data;
464}
465
466/*
467 * Set this task's call_rcu_data structure as specified, regardless
468 * of whether or not this task already had one. (This allows switching
469 * to and from real-time call_rcu threads, for example.)
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470 *
471 * Use NULL to remove a thread's call_rcu_data structure, but it is
472 * the caller's responsibility to dispose of the removed structure.
473 * Use get_thread_call_rcu_data() to obtain a pointer to the old structure
474 * (prior to NULLing it out, of course).
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475 */
476
477void set_thread_call_rcu_data(struct call_rcu_data *crdp)
478{
479 thread_call_rcu_data = crdp;
480}
481
482/*
483 * Create a separate call_rcu thread for each CPU. This does not
484 * replace a pre-existing call_rcu thread -- use the set_cpu_call_rcu_data()
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485 * function if you want that behavior. Should be paired with
486 * free_all_cpu_call_rcu_data() to teardown these call_rcu worker
487 * threads.
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488 */
489
490int create_all_cpu_call_rcu_data(unsigned long flags)
491{
492 int i;
493 struct call_rcu_data *crdp;
494 int ret;
495
496 call_rcu_lock(&call_rcu_mutex);
497 alloc_cpu_call_rcu_data();
498 call_rcu_unlock(&call_rcu_mutex);
499 if (maxcpus <= 0) {
500 errno = EINVAL;
501 return -EINVAL;
502 }
503 if (per_cpu_call_rcu_data == NULL) {
504 errno = ENOMEM;
505 return -ENOMEM;
506 }
507 for (i = 0; i < maxcpus; i++) {
508 call_rcu_lock(&call_rcu_mutex);
509 if (get_cpu_call_rcu_data(i)) {
510 call_rcu_unlock(&call_rcu_mutex);
511 continue;
512 }
c1d2c60b 513 crdp = __create_call_rcu_data(flags, i);
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514 if (crdp == NULL) {
515 call_rcu_unlock(&call_rcu_mutex);
516 errno = ENOMEM;
517 return -ENOMEM;
518 }
519 call_rcu_unlock(&call_rcu_mutex);
520 if ((ret = set_cpu_call_rcu_data(i, crdp)) != 0) {
521 /* FIXME: Leaks crdp for now. */
522 return ret; /* Can happen on race. */
523 }
524 }
525 return 0;
526}
527
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528/*
529 * Wake up the call_rcu thread corresponding to the specified
530 * call_rcu_data structure.
531 */
532static void wake_call_rcu_thread(struct call_rcu_data *crdp)
533{
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534 if (!(_CMM_LOAD_SHARED(crdp->flags) & URCU_CALL_RCU_RT))
535 call_rcu_wake_up(crdp);
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536}
537
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538/*
539 * Schedule a function to be invoked after a following grace period.
540 * This is the only function that must be called -- the others are
541 * only present to allow applications to tune their use of RCU for
542 * maximum performance.
543 *
544 * Note that unless a call_rcu thread has not already been created,
545 * the first invocation of call_rcu() will create one. So, if you
546 * need the first invocation of call_rcu() to be fast, make sure
547 * to create a call_rcu thread first. One way to accomplish this is
548 * "get_call_rcu_data();", and another is create_all_cpu_call_rcu_data().
549 */
550
551void call_rcu(struct rcu_head *head,
552 void (*func)(struct rcu_head *head))
553{
554 struct call_rcu_data *crdp;
555
556 cds_wfq_node_init(&head->next);
557 head->func = func;
558 crdp = get_call_rcu_data();
559 cds_wfq_enqueue(&crdp->cbs, &head->next);
560 uatomic_inc(&crdp->qlen);
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561 wake_call_rcu_thread(crdp);
562}
563
564/*
565 * Free up the specified call_rcu_data structure, terminating the
566 * associated call_rcu thread. The caller must have previously
567 * removed the call_rcu_data structure from per-thread or per-CPU
568 * usage. For example, set_cpu_call_rcu_data(cpu, NULL) for per-CPU
569 * call_rcu_data structures or set_thread_call_rcu_data(NULL) for
570 * per-thread call_rcu_data structures.
571 *
572 * We silently refuse to free up the default call_rcu_data structure
573 * because that is where we put any leftover callbacks. Note that
574 * the possibility of self-spawning callbacks makes it impossible
575 * to execute all the callbacks in finite time without putting any
576 * newly spawned callbacks somewhere else. The "somewhere else" of
577 * last resort is the default call_rcu_data structure.
578 *
579 * We also silently refuse to free NULL pointers. This simplifies
580 * the calling code.
581 */
582void call_rcu_data_free(struct call_rcu_data *crdp)
583{
584 struct cds_wfq_node *cbs;
585 struct cds_wfq_node **cbs_tail;
586 struct cds_wfq_node **cbs_endprev;
587
588 if (crdp == NULL || crdp == default_call_rcu_data) {
589 return;
590 }
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591 if ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0) {
592 uatomic_or(&crdp->flags, URCU_CALL_RCU_STOP);
7106ddf8 593 wake_call_rcu_thread(crdp);
2870aa1e 594 while ((uatomic_read(&crdp->flags) & URCU_CALL_RCU_STOPPED) == 0)
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595 poll(NULL, 0, 1);
596 }
597 if (&crdp->cbs.head != _CMM_LOAD_SHARED(crdp->cbs.tail)) {
598 while ((cbs = _CMM_LOAD_SHARED(crdp->cbs.head)) == NULL)
599 poll(NULL, 0, 1);
600 _CMM_STORE_SHARED(crdp->cbs.head, NULL);
601 cbs_tail = (struct cds_wfq_node **)
602 uatomic_xchg(&crdp->cbs.tail, &crdp->cbs.head);
603 cbs_endprev = (struct cds_wfq_node **)
604 uatomic_xchg(&default_call_rcu_data, cbs_tail);
605 *cbs_endprev = cbs;
606 uatomic_add(&default_call_rcu_data->qlen,
607 uatomic_read(&crdp->qlen));
608 cds_list_del(&crdp->list);
609 free(crdp);
610 }
611}
612
613/*
614 * Clean up all the per-CPU call_rcu threads.
615 */
616void free_all_cpu_call_rcu_data(void)
617{
618 int cpu;
619 struct call_rcu_data *crdp;
620
621 if (maxcpus <= 0)
622 return;
623 for (cpu = 0; cpu < maxcpus; cpu++) {
624 crdp = get_cpu_call_rcu_data(cpu);
625 if (crdp == NULL)
626 continue;
627 set_cpu_call_rcu_data(cpu, NULL);
628 call_rcu_data_free(crdp);
629 }
630}
631
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632/*
633 * Acquire the call_rcu_mutex in order to ensure that the child sees
634 * all of the call_rcu() data structures in a consistent state.
635 * Suitable for pthread_atfork() and friends.
636 */
637void call_rcu_before_fork(void)
638{
639 call_rcu_lock(&call_rcu_mutex);
640}
641
642/*
643 * Clean up call_rcu data structures in the parent of a successful fork()
644 * that is not followed by exec() in the child. Suitable for
645 * pthread_atfork() and friends.
646 */
647void call_rcu_after_fork_parent(void)
648{
649 call_rcu_unlock(&call_rcu_mutex);
650}
651
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652/*
653 * Clean up call_rcu data structures in the child of a successful fork()
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654 * that is not followed by exec(). Suitable for pthread_atfork() and
655 * friends.
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656 */
657void call_rcu_after_fork_child(void)
658{
659 struct call_rcu_data *crdp;
660
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661 /* Release the mutex. */
662 call_rcu_unlock(&call_rcu_mutex);
663
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664 /*
665 * Allocate a new default call_rcu_data structure in order
666 * to get a working call_rcu thread to go with it.
667 */
668 default_call_rcu_data = NULL;
669 (void)get_default_call_rcu_data();
670
671 /* Dispose of all of the rest of the call_rcu_data structures. */
672 while (call_rcu_data_list.next != call_rcu_data_list.prev) {
673 crdp = cds_list_entry(call_rcu_data_list.prev,
674 struct call_rcu_data, list);
675 if (crdp == default_call_rcu_data)
676 crdp = cds_list_entry(crdp->list.prev,
677 struct call_rcu_data, list);
2870aa1e 678 uatomic_set(&crdp->flags, URCU_CALL_RCU_STOPPED);
7106ddf8 679 call_rcu_data_free(crdp);
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680 }
681}
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