1 // SPDX-FileCopyrightText: 2010 Paul E. McKenney <paulmck@linux.vnet.ibm.com>
2 // SPDX-FileCopyrightText: 2017 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
4 // SPDX-License-Identifier: LGPL-2.1-or-later
7 * Userspace RCU library - Userspace workqeues
23 #include "compat-getcpu.h"
24 #include <urcu/assert.h>
25 #include <urcu/wfcqueue.h>
26 #include <urcu/pointer.h>
27 #include <urcu/list.h>
28 #include <urcu/futex.h>
29 #include <urcu/tls-compat.h>
33 #include "workqueue.h"
35 #define SET_AFFINITY_CHECK_PERIOD (1U << 8) /* 256 */
36 #define SET_AFFINITY_CHECK_PERIOD_MASK (SET_AFFINITY_CHECK_PERIOD - 1)
38 /* Data structure that identifies a workqueue. */
40 struct urcu_workqueue
{
42 * We do not align head on a different cache-line than tail
43 * mainly because workqueue threads use batching ("splice") to
44 * get an entire list of callbacks, which effectively empties
45 * the queue, and requires to touch the tail anyway.
47 struct cds_wfcq_tail cbs_tail
;
48 struct cds_wfcq_head cbs_head
;
51 unsigned long qlen
; /* maintained for debugging. */
54 unsigned long loop_count
;
56 void (*grace_period_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
57 void (*initialize_worker_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
58 void (*finalize_worker_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
59 void (*worker_before_pause_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
60 void (*worker_after_resume_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
61 void (*worker_before_wait_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
62 void (*worker_after_wake_up_fct
)(struct urcu_workqueue
*workqueue
, void *priv
);
63 } __attribute__((aligned(CAA_CACHE_LINE_SIZE
)));
65 struct urcu_workqueue_completion
{
71 struct urcu_workqueue_completion_work
{
72 struct urcu_work work
;
73 struct urcu_workqueue_completion
*completion
;
77 * Periodically retry setting CPU affinity if we migrate.
78 * Losing affinity can be caused by CPU hotunplug/hotplug, or by
81 #ifdef HAVE_SCHED_SETAFFINITY
82 static int set_thread_cpu_affinity(struct urcu_workqueue
*workqueue
)
87 if (workqueue
->cpu_affinity
< 0)
89 if (++workqueue
->loop_count
& SET_AFFINITY_CHECK_PERIOD_MASK
)
91 if (urcu_sched_getcpu() == workqueue
->cpu_affinity
)
95 CPU_SET(workqueue
->cpu_affinity
, &mask
);
96 ret
= sched_setaffinity(0, sizeof(mask
), &mask
);
99 * EINVAL is fine: can be caused by hotunplugged CPUs, or by
100 * cpuset(7). This is why we should always retry if we detect
103 if (ret
&& errno
== EINVAL
) {
110 static int set_thread_cpu_affinity(struct urcu_workqueue
*workqueue
__attribute__((unused
)))
116 static void futex_wait(int32_t *futex
)
118 /* Read condition before read futex */
120 while (uatomic_read(futex
) == -1) {
121 if (!futex_async(futex
, FUTEX_WAIT
, -1, NULL
, NULL
, 0)) {
123 * Prior queued wakeups queued by unrelated code
124 * using the same address can cause futex wait to
125 * return 0 even through the futex value is still
126 * -1 (spurious wakeups). Check the value again
127 * in user-space to validate whether it really
134 /* Value already changed. */
137 /* Retry if interrupted by signal. */
138 break; /* Get out of switch. Check again. */
140 /* Unexpected error. */
146 static void futex_wake_up(int32_t *futex
)
148 /* Write to condition before reading/writing futex */
150 if (caa_unlikely(uatomic_read(futex
) == -1)) {
151 uatomic_set(futex
, 0);
152 if (futex_async(futex
, FUTEX_WAKE
, 1,
158 /* This is the code run by each worker thread. */
160 static void *workqueue_thread(void *arg
)
162 unsigned long cbcount
;
163 struct urcu_workqueue
*workqueue
= (struct urcu_workqueue
*) arg
;
164 int rt
= !!(uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_RT
);
166 if (set_thread_cpu_affinity(workqueue
))
169 if (workqueue
->initialize_worker_fct
)
170 workqueue
->initialize_worker_fct(workqueue
, workqueue
->priv
);
173 uatomic_dec(&workqueue
->futex
);
174 /* Decrement futex before reading workqueue */
178 struct cds_wfcq_head cbs_tmp_head
;
179 struct cds_wfcq_tail cbs_tmp_tail
;
180 struct cds_wfcq_node
*cbs
, *cbs_tmp_n
;
181 enum cds_wfcq_ret splice_ret
;
183 if (set_thread_cpu_affinity(workqueue
))
186 if (uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_PAUSE
) {
188 * Pause requested. Become quiescent: remove
189 * ourself from all global lists, and don't
190 * process any callback. The callback lists may
191 * still be non-empty though.
193 if (workqueue
->worker_before_pause_fct
)
194 workqueue
->worker_before_pause_fct(workqueue
, workqueue
->priv
);
195 cmm_smp_mb__before_uatomic_or();
196 uatomic_or(&workqueue
->flags
, URCU_WORKQUEUE_PAUSED
);
197 while ((uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_PAUSE
) != 0)
198 (void) poll(NULL
, 0, 1);
199 uatomic_and(&workqueue
->flags
, ~URCU_WORKQUEUE_PAUSED
);
200 cmm_smp_mb__after_uatomic_and();
201 if (workqueue
->worker_after_resume_fct
)
202 workqueue
->worker_after_resume_fct(workqueue
, workqueue
->priv
);
205 cds_wfcq_init(&cbs_tmp_head
, &cbs_tmp_tail
);
206 splice_ret
= __cds_wfcq_splice_blocking(&cbs_tmp_head
,
207 &cbs_tmp_tail
, &workqueue
->cbs_head
, &workqueue
->cbs_tail
);
208 urcu_posix_assert(splice_ret
!= CDS_WFCQ_RET_WOULDBLOCK
);
209 urcu_posix_assert(splice_ret
!= CDS_WFCQ_RET_DEST_NON_EMPTY
);
210 if (splice_ret
!= CDS_WFCQ_RET_SRC_EMPTY
) {
211 if (workqueue
->grace_period_fct
)
212 workqueue
->grace_period_fct(workqueue
, workqueue
->priv
);
214 __cds_wfcq_for_each_blocking_safe(&cbs_tmp_head
,
215 &cbs_tmp_tail
, cbs
, cbs_tmp_n
) {
216 struct urcu_work
*uwp
;
218 uwp
= caa_container_of(cbs
,
219 struct urcu_work
, next
);
223 uatomic_sub(&workqueue
->qlen
, cbcount
);
225 if (uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_STOP
)
227 if (workqueue
->worker_before_wait_fct
)
228 workqueue
->worker_before_wait_fct(workqueue
, workqueue
->priv
);
230 if (cds_wfcq_empty(&workqueue
->cbs_head
,
231 &workqueue
->cbs_tail
)) {
232 futex_wait(&workqueue
->futex
);
233 uatomic_dec(&workqueue
->futex
);
235 * Decrement futex before reading
241 if (cds_wfcq_empty(&workqueue
->cbs_head
,
242 &workqueue
->cbs_tail
)) {
243 (void) poll(NULL
, 0, 10);
246 if (workqueue
->worker_after_wake_up_fct
)
247 workqueue
->worker_after_wake_up_fct(workqueue
, workqueue
->priv
);
251 * Read urcu_work list before write futex.
254 uatomic_set(&workqueue
->futex
, 0);
256 if (workqueue
->finalize_worker_fct
)
257 workqueue
->finalize_worker_fct(workqueue
, workqueue
->priv
);
261 struct urcu_workqueue
*urcu_workqueue_create(unsigned long flags
,
262 int cpu_affinity
, void *priv
,
263 void (*grace_period_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
264 void (*initialize_worker_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
265 void (*finalize_worker_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
266 void (*worker_before_wait_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
267 void (*worker_after_wake_up_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
268 void (*worker_before_pause_fct
)(struct urcu_workqueue
*workqueue
, void *priv
),
269 void (*worker_after_resume_fct
)(struct urcu_workqueue
*workqueue
, void *priv
))
271 struct urcu_workqueue
*workqueue
;
273 sigset_t newmask
, oldmask
;
275 workqueue
= malloc(sizeof(*workqueue
));
276 if (workqueue
== NULL
)
278 memset(workqueue
, '\0', sizeof(*workqueue
));
279 cds_wfcq_init(&workqueue
->cbs_head
, &workqueue
->cbs_tail
);
281 workqueue
->futex
= 0;
282 workqueue
->flags
= flags
;
283 workqueue
->priv
= priv
;
284 workqueue
->grace_period_fct
= grace_period_fct
;
285 workqueue
->initialize_worker_fct
= initialize_worker_fct
;
286 workqueue
->finalize_worker_fct
= finalize_worker_fct
;
287 workqueue
->worker_before_wait_fct
= worker_before_wait_fct
;
288 workqueue
->worker_after_wake_up_fct
= worker_after_wake_up_fct
;
289 workqueue
->worker_before_pause_fct
= worker_before_pause_fct
;
290 workqueue
->worker_after_resume_fct
= worker_after_resume_fct
;
291 workqueue
->cpu_affinity
= cpu_affinity
;
292 workqueue
->loop_count
= 0;
293 cmm_smp_mb(); /* Structure initialized before pointer is planted. */
295 ret
= sigfillset(&newmask
);
296 urcu_posix_assert(!ret
);
297 ret
= pthread_sigmask(SIG_BLOCK
, &newmask
, &oldmask
);
298 urcu_posix_assert(!ret
);
300 ret
= pthread_create(&workqueue
->tid
, NULL
, workqueue_thread
, workqueue
);
305 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
306 urcu_posix_assert(!ret
);
311 static void wake_worker_thread(struct urcu_workqueue
*workqueue
)
313 if (!(_CMM_LOAD_SHARED(workqueue
->flags
) & URCU_WORKQUEUE_RT
))
314 futex_wake_up(&workqueue
->futex
);
317 static int urcu_workqueue_destroy_worker(struct urcu_workqueue
*workqueue
)
322 uatomic_or(&workqueue
->flags
, URCU_WORKQUEUE_STOP
);
323 wake_worker_thread(workqueue
);
325 ret
= pthread_join(workqueue
->tid
, &retval
);
329 if (retval
!= NULL
) {
332 workqueue
->flags
&= ~URCU_WORKQUEUE_STOP
;
337 void urcu_workqueue_destroy(struct urcu_workqueue
*workqueue
)
339 if (workqueue
== NULL
) {
342 if (urcu_workqueue_destroy_worker(workqueue
)) {
345 urcu_posix_assert(cds_wfcq_empty(&workqueue
->cbs_head
, &workqueue
->cbs_tail
));
349 void urcu_workqueue_queue_work(struct urcu_workqueue
*workqueue
,
350 struct urcu_work
*work
,
351 void (*func
)(struct urcu_work
*work
))
353 cds_wfcq_node_init(&work
->next
);
355 cds_wfcq_enqueue(&workqueue
->cbs_head
, &workqueue
->cbs_tail
, &work
->next
);
356 uatomic_inc(&workqueue
->qlen
);
357 wake_worker_thread(workqueue
);
361 void free_completion(struct urcu_ref
*ref
)
363 struct urcu_workqueue_completion
*completion
;
365 completion
= caa_container_of(ref
, struct urcu_workqueue_completion
, ref
);
370 void _urcu_workqueue_wait_complete(struct urcu_work
*work
)
372 struct urcu_workqueue_completion_work
*completion_work
;
373 struct urcu_workqueue_completion
*completion
;
375 completion_work
= caa_container_of(work
, struct urcu_workqueue_completion_work
, work
);
376 completion
= completion_work
->completion
;
377 if (!uatomic_sub_return(&completion
->barrier_count
, 1))
378 futex_wake_up(&completion
->futex
);
379 urcu_ref_put(&completion
->ref
, free_completion
);
380 free(completion_work
);
383 struct urcu_workqueue_completion
*urcu_workqueue_create_completion(void)
385 struct urcu_workqueue_completion
*completion
;
387 completion
= calloc(1, sizeof(*completion
));
390 urcu_ref_set(&completion
->ref
, 1);
391 completion
->barrier_count
= 0;
395 void urcu_workqueue_destroy_completion(struct urcu_workqueue_completion
*completion
)
397 urcu_ref_put(&completion
->ref
, free_completion
);
400 void urcu_workqueue_wait_completion(struct urcu_workqueue_completion
*completion
)
404 uatomic_dec(&completion
->futex
);
405 /* Decrement futex before reading barrier_count */
407 if (!uatomic_read(&completion
->barrier_count
))
409 futex_wait(&completion
->futex
);
413 void urcu_workqueue_queue_completion(struct urcu_workqueue
*workqueue
,
414 struct urcu_workqueue_completion
*completion
)
416 struct urcu_workqueue_completion_work
*work
;
418 work
= calloc(1, sizeof(*work
));
421 work
->completion
= completion
;
422 urcu_ref_get(&completion
->ref
);
423 uatomic_inc(&completion
->barrier_count
);
424 urcu_workqueue_queue_work(workqueue
, &work
->work
, _urcu_workqueue_wait_complete
);
428 * Wait for all in-flight work to complete execution.
430 void urcu_workqueue_flush_queued_work(struct urcu_workqueue
*workqueue
)
432 struct urcu_workqueue_completion
*completion
;
434 completion
= urcu_workqueue_create_completion();
437 urcu_workqueue_queue_completion(workqueue
, completion
);
438 urcu_workqueue_wait_completion(completion
);
439 urcu_workqueue_destroy_completion(completion
);
442 /* To be used in before fork handler. */
443 void urcu_workqueue_pause_worker(struct urcu_workqueue
*workqueue
)
445 uatomic_or(&workqueue
->flags
, URCU_WORKQUEUE_PAUSE
);
446 cmm_smp_mb__after_uatomic_or();
447 wake_worker_thread(workqueue
);
449 while ((uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_PAUSED
) == 0)
450 (void) poll(NULL
, 0, 1);
453 /* To be used in after fork parent handler. */
454 void urcu_workqueue_resume_worker(struct urcu_workqueue
*workqueue
)
456 uatomic_and(&workqueue
->flags
, ~URCU_WORKQUEUE_PAUSE
);
457 while ((uatomic_read(&workqueue
->flags
) & URCU_WORKQUEUE_PAUSED
) != 0)
458 (void) poll(NULL
, 0, 1);
461 void urcu_workqueue_create_worker(struct urcu_workqueue
*workqueue
)
464 sigset_t newmask
, oldmask
;
466 /* Clear workqueue state from parent. */
467 workqueue
->flags
&= ~URCU_WORKQUEUE_PAUSED
;
468 workqueue
->flags
&= ~URCU_WORKQUEUE_PAUSE
;
471 ret
= sigfillset(&newmask
);
472 urcu_posix_assert(!ret
);
473 ret
= pthread_sigmask(SIG_BLOCK
, &newmask
, &oldmask
);
474 urcu_posix_assert(!ret
);
476 ret
= pthread_create(&workqueue
->tid
, NULL
, workqueue_thread
, workqueue
);
481 ret
= pthread_sigmask(SIG_SETMASK
, &oldmask
, NULL
);
482 urcu_posix_assert(!ret
);