[userspace-rcu.git] / urcu / workqueue-fifo.h

#ifndef _URCU_WORKQUEUE_FIFO_H
#define _URCU_WORKQUEUE_FIFO_H

/*
 * urcu/workqueue-fifo.h
 *
 * Userspace RCU library - work queue scheme with FIFO semantic
 *
 * Copyright (c) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <urcu/uatomic.h>
#include <urcu/lfstack.h>
#include <urcu/waitqueue-lifo.h>
#include <urcu/wfcqueue.h>
#include <urcu/rculist.h>
#include <pthread.h>
#include <assert.h>

/*
 * We use RCU to steal work from siblings. Therefore, one of RCU flavors
 * need to be included before this header. All worker that participate
 * in stealing (initialized with the URCU_WORKER_STEAL flag) need to be
 * registered RCU readers threads.
 */

struct urcu_work {
	struct cds_wfcq_node node;
};

struct urcu_workqueue {
	/* FIFO work queue */
	struct __cds_wfcq_head head;
	struct cds_wfcq_tail tail;

	/* Associated wait queue for LIFO wait/wakeup */
	struct urcu_wait_queue waitqueue;

	/* RCU linked list head of siblings for work stealing. */
	struct cds_list_head sibling_head;
	pthread_mutex_t sibling_lock;	/* Protect sibling list updates */
};

struct urcu_worker {
	struct cds_wfcq_head head;
	struct cds_wfcq_tail tail;

	struct urcu_wait_node wait_node;
	/* RCU linked list node of siblings for work stealing. */
	struct cds_list_head sibling_node;
	int flags;	/* enum urcu_worker_flags */
};

enum urcu_worker_flags {
	URCU_WORKER_STEAL	= (1 << 0),
};

static inline
void urcu_workqueue_init(struct urcu_workqueue *queue)
{
	__cds_wfcq_init(&queue->head, &queue->tail);
	urcu_wait_queue_init(&queue->waitqueue);
	CDS_INIT_LIST_HEAD(&queue->sibling_head);
}

static inline
void urcu_queue_work(struct urcu_workqueue *queue, struct urcu_work *work)
{
	bool was_empty;

	cds_wfcq_node_init(&work->node);

	/* Enqueue work. */
	was_empty = !cds_wfcq_enqueue(&queue->head, &queue->tail,
			&work->node);
	/*
	 * If workqueue was previously empty, wakeup one worker thread.
	 * It will eventually grab the entire content of the work-queue
	 * (therefore grabbing a "work batch"). After having grabbed the
	 * work batch, while that thread is running and taking care of
	 * that work batch, when we enqueue more work, we will wake
	 * another thread (if there is one waiting), which will
	 * eventually grab the new batch, and so on. This scheme ensures
	 * that contiguous batch of work are handled by the same thread
	 * (for locality), and also ensures that we scale work to many
	 * worker threads when threads are busy enough to still be
	 * running when work is enqueued.
	 */
	if (was_empty) {
		rcu_read_lock();	/* Protect stack dequeue */
		(void) urcu_dequeue_wake_single(&queue->waitqueue);
		rcu_read_unlock();	/* Protect stack dequeue */
	}
}

static inline
void urcu_workqueue_wakeup_all(struct urcu_workqueue *queue)
{
	struct urcu_waiters waiters;

	rcu_read_lock();	/* Protect stack dequeue */
	urcu_move_waiters(&waiters, &queue->waitqueue);
	rcu_read_unlock();	/* Protect stack dequeue */

	(void) urcu_wake_all_waiters(&waiters);
}

static inline
void urcu_worker_init(struct urcu_worker *worker, int flags)
{
	cds_wfcq_init(&worker->head, &worker->tail);
	worker->flags = flags;
	urcu_wait_node_init(&worker->wait_node, URCU_WAIT_RUNNING);
}

static inline
void urcu_worker_register(struct urcu_workqueue *queue,
		struct urcu_worker *worker)
{
	if (worker->flags & URCU_WORKER_STEAL) {
		pthread_mutex_lock(&queue->sibling_lock);
		cds_list_add_rcu(&worker->sibling_node, &queue->sibling_head);
		pthread_mutex_unlock(&queue->sibling_lock);
	}
}

static inline
void urcu_worker_unregister(struct urcu_workqueue *queue,
		struct urcu_worker *worker)
{
	enum cds_wfcq_ret wfcq_ret;

	if (worker->flags & URCU_WORKER_STEAL) {
		pthread_mutex_lock(&queue->sibling_lock);
		cds_list_del_rcu(&worker->sibling_node);
		pthread_mutex_unlock(&queue->sibling_lock);
	}

	/*
	 * Wait for grace period before freeing or reusing
	 * "worker" because used by RCU linked list.
	 * Also prevents ABA for waitqueue stack dequeue: matches RCU
	 * read-side critical sections around dequeue and move all
	 * operations on waitqueue).
	 */
	synchronize_rcu();

	/*
	 * Put any local work we still have back into the workqueue.
	 */
	wfcq_ret = __cds_wfcq_splice_blocking(&queue->head,
			&queue->tail,
			&worker->head,
			&worker->tail);
	if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY
			&& wfcq_ret == CDS_WFCQ_RET_DEST_EMPTY) {
		/*
		 * Wakeup worker thread if we have put work back into
		 * workqueue that was previously empty.
		 */
		rcu_read_lock();	/* Protect stack dequeue */
		(void) urcu_dequeue_wake_single(&queue->waitqueue);
		rcu_read_unlock();	/* Protect stack dequeue */
	}
}

/*
 * Try stealing work from siblings when we have nothing to do.
 */
static inline
bool ___urcu_steal_work(struct urcu_worker *worker,
		struct urcu_worker *sibling)
{
	enum cds_wfcq_ret splice_ret;

	/*
	 * Don't bother grabbing the sibling queue lock if it is empty.
	 */
	if (cds_wfcq_empty(&sibling->head, &sibling->tail))
		return false;
	splice_ret = cds_wfcq_splice_blocking(&worker->head,
			&worker->tail,
			&sibling->head,
			&sibling->tail);
	/* Ensure that we preserve FIFO work order. */
	assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
	return splice_ret != CDS_WFCQ_RET_SRC_EMPTY;
}

static inline
bool __urcu_steal_work(struct urcu_workqueue *queue,
		struct urcu_worker *worker)
{
	struct urcu_worker *sibling_prev, *sibling_next;
	struct cds_list_head *sibling_node;
	bool steal_performed = 0;

	if (!(worker->flags & URCU_WORKER_STEAL))
		return false;

	rcu_read_lock();

	sibling_node = rcu_dereference(worker->sibling_node.next);
	if (sibling_node == &queue->sibling_head)
		sibling_node = rcu_dereference(sibling_node->next);
	sibling_next = caa_container_of(sibling_node, struct urcu_worker,
			sibling_node);
	if (sibling_next != worker)
		steal_performed = ___urcu_steal_work(worker, sibling_next);
	if (steal_performed)
		goto end;

	sibling_node = rcu_dereference(worker->sibling_node.prev);
	if (sibling_node == &queue->sibling_head)
		sibling_node = rcu_dereference(sibling_node->prev);
	sibling_prev = caa_container_of(sibling_node, struct urcu_worker,
			sibling_node);
	if (sibling_prev != worker && sibling_prev != sibling_next)
		steal_performed =  ___urcu_steal_work(worker, sibling_prev);
end:
	rcu_read_unlock();

	return steal_performed;
}

static inline
bool ___urcu_wakeup_sibling(struct urcu_worker *sibling)
{
	return urcu_adaptative_wake_up(&sibling->wait_node);
}

static inline
bool __urcu_wakeup_siblings(struct urcu_workqueue *queue,
		struct urcu_worker *worker)
{
	struct urcu_worker *sibling_prev, *sibling_next;
	struct cds_list_head *sibling_node;
	bool wakeup_performed = 0;

	if (!(worker->flags & URCU_WORKER_STEAL))
		return;

	/* Only wakeup siblings if we have work in our own queue. */
	if (cds_wfcq_empty(&worker->head, &worker->tail))
		return;

	rcu_read_lock();

	sibling_node = rcu_dereference(worker->sibling_node.next);
	if (sibling_node == &queue->sibling_head)
		sibling_node = rcu_dereference(sibling_node->next);
	sibling_next = caa_container_of(sibling_node, struct urcu_worker,
			sibling_node);
	if (sibling_next != worker)
		wakeup_performed = ___urcu_wakeup_sibling(sibling_next);
	if (wakeup_performed)
		goto end;

	sibling_node = rcu_dereference(worker->sibling_node.prev);
	if (sibling_node == &queue->sibling_head)
		sibling_node = rcu_dereference(sibling_node->prev);
	sibling_prev = caa_container_of(sibling_node, struct urcu_worker,
			sibling_node);
	if (sibling_prev != worker && sibling_prev != sibling_next)
		wakeup_performed = ___urcu_wakeup_sibling(sibling_prev);
end:
	rcu_read_unlock();

	return wakeup_performed;
}

static inline
void urcu_accept_work(struct urcu_workqueue *queue,
		struct urcu_worker *worker,
		int blocking)
{
	enum cds_wfcq_ret wfcq_ret;

	wfcq_ret = __cds_wfcq_splice_blocking(&worker->head,
			&worker->tail,
			&queue->head,
			&queue->tail);
	/* Don't wait if we have work to do. */
	if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY
			|| !cds_wfcq_empty(&worker->head,
				&worker->tail))
		goto do_work;
	/* Try to steal work from sibling instead of blocking */
	if (__urcu_steal_work(queue, worker))
		goto do_work;
	if (!blocking)
		return;
	urcu_wait_set_state(&worker->wait_node,
			URCU_WAIT_WAITING);
	if (!CMM_LOAD_SHARED(worker->wait_node.node.next)) {
		int was_empty;

		/*
		 * NULL next pointer. We are therefore not in
		 * the queue.
		 */
		cds_lfs_node_init(&worker->wait_node.node);
		/* Protect stack dequeue against ABA */
		synchronize_rcu();
		was_empty = !urcu_wait_add(&queue->waitqueue,
				&worker->wait_node);
		/*
		 * If the wait queue was empty, it means we are the
		 * first thread to be put back into an otherwise empty
		 * wait queue. Re-check if work queue is empty after
		 * adding ourself to wait queue, so we can wakeup the
		 * top of wait queue since new work have appeared, and
		 * work enqueuer may not have seen that it needed to do
		 * a wake up.
		 */
		if (was_empty && !cds_wfcq_empty(&queue->head,
						&queue->tail)) {
			rcu_read_lock();	/* Protect stack dequeue */
			(void) urcu_dequeue_wake_single(&queue->waitqueue);
			rcu_read_unlock();	/* Protect stack dequeue */
		}
	} else {
		/*
		 * Non-NULL next pointer. We are therefore in
		 * the queue, or the dispatcher just removed us
		 * from it (after we read the next pointer), and
		 * is therefore awakening us. The state will
		 * therefore have been changed from WAITING to
		 * some other state, which will let the busy
		 * wait pass through.
		 */
	}
	urcu_adaptative_busy_wait(&worker->wait_node);
	return;

do_work:
	/*
	 * We will be busy handling the work batch, awaken siblings so
	 * they can steal from us.
	 */
	(void) __urcu_wakeup_siblings(queue, worker);
}

static inline
struct urcu_work *urcu_dequeue_work(struct urcu_worker *worker)
{
	struct cds_wfcq_node *node;

	/*
	 * If we are registered for work stealing, we need to dequeue
	 * safely against siblings.
	 */
	if (worker->flags & URCU_WORKER_STEAL) {
		/*
		 * Don't bother grabbing the worker queue lock if it is
		 * empty.
		 */
		if (cds_wfcq_empty(&worker->head, &worker->tail))
			return NULL;
		node = cds_wfcq_dequeue_blocking(&worker->head,
				&worker->tail);
	} else {
		node = ___cds_wfcq_dequeue_with_state(&worker->head,
				&worker->tail, NULL, 1, 0);
	}
	if (!node)
		return NULL;
	return caa_container_of(node, struct urcu_work, node);
}

#endif /* _URCU_WORKQUEUE_FIFO_H */
Commit	Line	Data
13652c4b MD	1	#ifndef _URCU_WORKQUEUE_FIFO_H
	2	#define _URCU_WORKQUEUE_FIFO_H
	3
	4	/*
	5	* urcu/workqueue-fifo.h
	6	*
	7	* Userspace RCU library - work queue scheme with FIFO semantic
	8	*
	9	* Copyright (c) 2014 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
	10	*
	11	* This library is free software; you can redistribute it and/or
	12	* modify it under the terms of the GNU Lesser General Public
	13	* License as published by the Free Software Foundation; either
	14	* version 2.1 of the License, or (at your option) any later version.
	15	*
	16	* This library is distributed in the hope that it will be useful,
	17	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	18	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	19	* Lesser General Public License for more details.
	20	*
	21	* You should have received a copy of the GNU Lesser General Public
	22	* License along with this library; if not, write to the Free Software
	23	* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
	24	*/
	25
	26	#include <urcu/uatomic.h>
7a618cf7	27	#include <urcu/lfstack.h>
13652c4b MD	28	#include <urcu/waitqueue-lifo.h>
	29	#include <urcu/wfcqueue.h>
	30	#include <urcu/rculist.h>
	31	#include <pthread.h>
e10c65b3	32	#include <assert.h>
13652c4b MD	33
	34	/*
	35	* We use RCU to steal work from siblings. Therefore, one of RCU flavors
	36	* need to be included before this header. All worker that participate
	37	* in stealing (initialized with the URCU_WORKER_STEAL flag) need to be
	38	* registered RCU readers threads.
	39	*/
	40
	41	struct urcu_work {
	42	struct cds_wfcq_node node;
	43	};
	44
	45	struct urcu_workqueue {
	46	/* FIFO work queue */
	47	struct __cds_wfcq_head head;
	48	struct cds_wfcq_tail tail;
	49
	50	/* Associated wait queue for LIFO wait/wakeup */
	51	struct urcu_wait_queue waitqueue;
	52
	53	/* RCU linked list head of siblings for work stealing. */
	54	struct cds_list_head sibling_head;
	55	pthread_mutex_t sibling_lock; /* Protect sibling list updates */
	56	};
	57
	58	struct urcu_worker {
	59	struct cds_wfcq_head head;
	60	struct cds_wfcq_tail tail;
	61
	62	struct urcu_wait_node wait_node;
	63	/* RCU linked list node of siblings for work stealing. */
	64	struct cds_list_head sibling_node;
	65	int flags; /* enum urcu_worker_flags */
	66	};
	67
	68	enum urcu_worker_flags {
	69	URCU_WORKER_STEAL = (1 << 0),
	70	};
	71
	72	static inline
	73	void urcu_workqueue_init(struct urcu_workqueue *queue)
	74	{
	75	__cds_wfcq_init(&queue->head, &queue->tail);
	76	urcu_wait_queue_init(&queue->waitqueue);
	77	CDS_INIT_LIST_HEAD(&queue->sibling_head);
	78	}
	79
	80	static inline
	81	void urcu_queue_work(struct urcu_workqueue queue, struct urcu_work work)
	82	{
	83	bool was_empty;
	84
	85	cds_wfcq_node_init(&work->node);
	86
	87	/* Enqueue work. */
	88	was_empty = !cds_wfcq_enqueue(&queue->head, &queue->tail,
	89	&work->node);
	90	/*
	91	* If workqueue was previously empty, wakeup one worker thread.
	92	* It will eventually grab the entire content of the work-queue
	93	* (therefore grabbing a "work batch"). After having grabbed the
	94	* work batch, while that thread is running and taking care of
	95	* that work batch, when we enqueue more work, we will wake
	96	* another thread (if there is one waiting), which will
97	* eventually grab the new batch, and so on. This scheme ensures
98	* that contiguous batch of work are handled by the same thread
99	* (for locality), and also ensures that we scale work to many
100	* worker threads when threads are busy enough to still be
101	* running when work is enqueued.
102	*/
d3afe039 MD	103	if (was_empty) {
d3afe039 MD	104	rcu_read_lock(); /* Protect stack dequeue */
13652c4b	105	(void) urcu_dequeue_wake_single(&queue->waitqueue);
d3afe039 MD	106	rcu_read_unlock(); /* Protect stack dequeue */
d3afe039 MD	107	}
13652c4b MD	108	}
	109
	110	static inline
	111	void urcu_workqueue_wakeup_all(struct urcu_workqueue *queue)
	112	{
	113	struct urcu_waiters waiters;
	114
d3afe039	115	rcu_read_lock(); /* Protect stack dequeue */
13652c4b	116	urcu_move_waiters(&waiters, &queue->waitqueue);
d3afe039 MD	117	rcu_read_unlock(); /* Protect stack dequeue */
d3afe039 MD	118
13652c4b MD	119	(void) urcu_wake_all_waiters(&waiters);
	120	}
	121
	122	static inline
	123	void urcu_worker_init(struct urcu_worker *worker, int flags)
	124	{
	125	cds_wfcq_init(&worker->head, &worker->tail);
	126	worker->flags = flags;
	127	urcu_wait_node_init(&worker->wait_node, URCU_WAIT_RUNNING);
	128	}
	129
	130	static inline
	131	void urcu_worker_register(struct urcu_workqueue *queue,
	132	struct urcu_worker *worker)
	133	{
	134	if (worker->flags & URCU_WORKER_STEAL) {
	135	pthread_mutex_lock(&queue->sibling_lock);
	136	cds_list_add_rcu(&worker->sibling_node, &queue->sibling_head);
	137	pthread_mutex_unlock(&queue->sibling_lock);
	138	}
	139	}
	140
	141	static inline
	142	void urcu_worker_unregister(struct urcu_workqueue *queue,
	143	struct urcu_worker *worker)
	144	{
	145	enum cds_wfcq_ret wfcq_ret;
	146
	147	if (worker->flags & URCU_WORKER_STEAL) {
	148	pthread_mutex_lock(&queue->sibling_lock);
	149	cds_list_del_rcu(&worker->sibling_node);
	150	pthread_mutex_unlock(&queue->sibling_lock);
13652c4b MD	151	}
13652c4b MD	152
d3afe039 MD	153	/*
	154	* Wait for grace period before freeing or reusing
	155	* "worker" because used by RCU linked list.
	156	* Also prevents ABA for waitqueue stack dequeue: matches RCU
	157	* read-side critical sections around dequeue and move all
	158	* operations on waitqueue).
	159	*/
	160	synchronize_rcu();
	161
13652c4b MD	162	/*
	163	* Put any local work we still have back into the workqueue.
	164	*/
	165	wfcq_ret = __cds_wfcq_splice_blocking(&queue->head,
	166	&queue->tail,
	167	&worker->head,
	168	&worker->tail);
	169	if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY
	170	&& wfcq_ret == CDS_WFCQ_RET_DEST_EMPTY) {
	171	/*
	172	* Wakeup worker thread if we have put work back into
	173	* workqueue that was previously empty.
	174	*/
d3afe039	175	rcu_read_lock(); /* Protect stack dequeue */
13652c4b	176	(void) urcu_dequeue_wake_single(&queue->waitqueue);
d3afe039	177	rcu_read_unlock(); /* Protect stack dequeue */
13652c4b MD	178	}
	179	}
	180
	181	/*
	182	* Try stealing work from siblings when we have nothing to do.
	183	*/
	184	static inline
e10c65b3	185	bool ___urcu_steal_work(struct urcu_worker *worker,
13652c4b MD	186	struct urcu_worker *sibling)
13652c4b MD	187	{
e10c65b3 MD	188	enum cds_wfcq_ret splice_ret;
e10c65b3 MD	189
30926570 MD	190	/*
	191	* Don't bother grabbing the sibling queue lock if it is empty.
	192	*/
	193	if (cds_wfcq_empty(&sibling->head, &sibling->tail))
e10c65b3	194	return false;
0695bd20	195	splice_ret = cds_wfcq_splice_blocking(&worker->head,
13652c4b MD	196	&worker->tail,
	197	&sibling->head,
	198	&sibling->tail);
e10c65b3 MD	199	/* Ensure that we preserve FIFO work order. */
	200	assert(splice_ret != CDS_WFCQ_RET_DEST_NON_EMPTY);
	201	return splice_ret != CDS_WFCQ_RET_SRC_EMPTY;
13652c4b MD	202	}
	203
	204	static inline
e10c65b3	205	bool __urcu_steal_work(struct urcu_workqueue *queue,
13652c4b MD	206	struct urcu_worker *worker)
	207	{
	208	struct urcu_worker sibling_prev, sibling_next;
	209	struct cds_list_head *sibling_node;
e10c65b3	210	bool steal_performed = 0;
13652c4b MD	211
13652c4b MD	212	if (!(worker->flags & URCU_WORKER_STEAL))
e10c65b3	213	return false;
13652c4b MD	214
	215	rcu_read_lock();
	216
	217	sibling_node = rcu_dereference(worker->sibling_node.next);
	218	if (sibling_node == &queue->sibling_head)
	219	sibling_node = rcu_dereference(sibling_node->next);
	220	sibling_next = caa_container_of(sibling_node, struct urcu_worker,
	221	sibling_node);
	222	if (sibling_next != worker)
e10c65b3 MD	223	steal_performed = ___urcu_steal_work(worker, sibling_next);
	224	if (steal_performed)
	225	goto end;
13652c4b MD	226
	227	sibling_node = rcu_dereference(worker->sibling_node.prev);
	228	if (sibling_node == &queue->sibling_head)
	229	sibling_node = rcu_dereference(sibling_node->prev);
	230	sibling_prev = caa_container_of(sibling_node, struct urcu_worker,
	231	sibling_node);
	232	if (sibling_prev != worker && sibling_prev != sibling_next)
e10c65b3 MD	233	steal_performed = ___urcu_steal_work(worker, sibling_prev);
e10c65b3 MD	234	end:
13652c4b MD	235	rcu_read_unlock();
13652c4b MD	236
e10c65b3	237	return steal_performed;
13652c4b MD	238	}
	239
	240	static inline
5d30bf32	241	bool ___urcu_wakeup_sibling(struct urcu_worker *sibling)
13652c4b	242	{
5d30bf32	243	return urcu_adaptative_wake_up(&sibling->wait_node);
13652c4b MD	244	}
	245
	246	static inline
5d30bf32	247	bool __urcu_wakeup_siblings(struct urcu_workqueue *queue,
13652c4b MD	248	struct urcu_worker *worker)
	249	{
	250	struct urcu_worker sibling_prev, sibling_next;
	251	struct cds_list_head *sibling_node;
5d30bf32	252	bool wakeup_performed = 0;
13652c4b MD	253
	254	if (!(worker->flags & URCU_WORKER_STEAL))
	255	return;
	256
	257	/* Only wakeup siblings if we have work in our own queue. */
	258	if (cds_wfcq_empty(&worker->head, &worker->tail))
	259	return;
	260
	261	rcu_read_lock();
	262
	263	sibling_node = rcu_dereference(worker->sibling_node.next);
	264	if (sibling_node == &queue->sibling_head)
	265	sibling_node = rcu_dereference(sibling_node->next);
	266	sibling_next = caa_container_of(sibling_node, struct urcu_worker,
	267	sibling_node);
	268	if (sibling_next != worker)
5d30bf32 MD	269	wakeup_performed = ___urcu_wakeup_sibling(sibling_next);
	270	if (wakeup_performed)
	271	goto end;
13652c4b MD	272
	273	sibling_node = rcu_dereference(worker->sibling_node.prev);
	274	if (sibling_node == &queue->sibling_head)
	275	sibling_node = rcu_dereference(sibling_node->prev);
	276	sibling_prev = caa_container_of(sibling_node, struct urcu_worker,
	277	sibling_node);
	278	if (sibling_prev != worker && sibling_prev != sibling_next)
5d30bf32 MD	279	wakeup_performed = ___urcu_wakeup_sibling(sibling_prev);
5d30bf32 MD	280	end:
13652c4b	281	rcu_read_unlock();
5d30bf32 MD	282
5d30bf32 MD	283	return wakeup_performed;
13652c4b MD	284	}
	285
	286	static inline
	287	void urcu_accept_work(struct urcu_workqueue *queue,
	288	struct urcu_worker *worker,
	289	int blocking)
	290	{
	291	enum cds_wfcq_ret wfcq_ret;
	292
	293	wfcq_ret = __cds_wfcq_splice_blocking(&worker->head,
	294	&worker->tail,
	295	&queue->head,
	296	&queue->tail);
	297	/* Don't wait if we have work to do. */
	298	if (wfcq_ret != CDS_WFCQ_RET_SRC_EMPTY
	299	\|\| !cds_wfcq_empty(&worker->head,
	300	&worker->tail))
	301	goto do_work;
	302	/* Try to steal work from sibling instead of blocking */
	303	if (__urcu_steal_work(queue, worker))
	304	goto do_work;
	305	if (!blocking)
	306	return;
	307	urcu_wait_set_state(&worker->wait_node,
	308	URCU_WAIT_WAITING);
	309	if (!CMM_LOAD_SHARED(worker->wait_node.node.next)) {
	310	int was_empty;
	311
	312	/*
	313	* NULL next pointer. We are therefore not in
	314	* the queue.
	315	*/
7a618cf7	316	cds_lfs_node_init(&worker->wait_node.node);
d3afe039 MD	317	/* Protect stack dequeue against ABA */
d3afe039 MD	318	synchronize_rcu();
13652c4b MD	319	was_empty = !urcu_wait_add(&queue->waitqueue,
	320	&worker->wait_node);
	321	/*
	322	* If the wait queue was empty, it means we are the
	323	* first thread to be put back into an otherwise empty
	324	* wait queue. Re-check if work queue is empty after
	325	* adding ourself to wait queue, so we can wakeup the
	326	* top of wait queue since new work have appeared, and
	327	* work enqueuer may not have seen that it needed to do
	328	* a wake up.
	329	*/
	330	if (was_empty && !cds_wfcq_empty(&queue->head,
d3afe039 MD	331	&queue->tail)) {
d3afe039 MD	332	rcu_read_lock(); /* Protect stack dequeue */
13652c4b	333	(void) urcu_dequeue_wake_single(&queue->waitqueue);
d3afe039 MD	334	rcu_read_unlock(); /* Protect stack dequeue */
d3afe039 MD	335	}
13652c4b MD	336	} else {
	337	/*
	338	* Non-NULL next pointer. We are therefore in
	339	* the queue, or the dispatcher just removed us
	340	* from it (after we read the next pointer), and
	341	* is therefore awakening us. The state will
	342	* therefore have been changed from WAITING to
	343	* some other state, which will let the busy
	344	* wait pass through.
	345	*/
	346	}
	347	urcu_adaptative_busy_wait(&worker->wait_node);
	348	return;
	349
	350	do_work:
	351	/*
	352	* We will be busy handling the work batch, awaken siblings so
	353	* they can steal from us.
	354	*/
5d30bf32	355	(void) __urcu_wakeup_siblings(queue, worker);
13652c4b MD	356	}
	357
	358	static inline
	359	struct urcu_work urcu_dequeue_work(struct urcu_worker worker)
	360	{
	361	struct cds_wfcq_node *node;
	362
	363	/*
	364	* If we are registered for work stealing, we need to dequeue
	365	* safely against siblings.
	366	*/
30926570 MD	367	if (worker->flags & URCU_WORKER_STEAL) {
	368	/*
	369	* Don't bother grabbing the worker queue lock if it is
	370	* empty.
	371	*/
	372	if (cds_wfcq_empty(&worker->head, &worker->tail))
	373	return NULL;
13652c4b MD	374	node = cds_wfcq_dequeue_blocking(&worker->head,
13652c4b MD	375	&worker->tail);
30926570	376	} else {
13652c4b MD	377	node = ___cds_wfcq_dequeue_with_state(&worker->head,
13652c4b MD	378	&worker->tail, NULL, 1, 0);
30926570	379	}
13652c4b MD	380	if (!node)
	381	return NULL;
	382	return caa_container_of(node, struct urcu_work, node);
	383	}
	384
	385	#endif /* _URCU_WORKQUEUE_FIFO_H */