lwq.h

  1/* SPDX-License-Identifier: GPL-2.0-only */
  2
  3#ifndef LWQ_H
  4#define LWQ_H
  5/*
  6 * Light-weight single-linked queue built from llist
  7 *
  8 * Entries can be enqueued from any context with no locking.
  9 * Entries can be dequeued from process context with integrated locking.
 10 *
 11 * This is particularly suitable when work items are queued in
 12 * BH or IRQ context, and where work items are handled one at a time
 13 * by dedicated threads.
 14 */
 15#include <linux/container_of.h>
 16#include <linux/spinlock.h>
 17#include <linux/llist.h>
 18
 19struct lwq_node {
 20	struct llist_node node;
 21};
 22
 23struct lwq {
 24	spinlock_t		lock;
 25	struct llist_node	*ready;		/* entries to be dequeued */
 26	struct llist_head	new;		/* entries being enqueued */
 27};
 28
 29/**
 30 * lwq_init - initialise a lwq
 31 * @q:	the lwq object
 32 */
 33static inline void lwq_init(struct lwq *q)
 34{
 35	spin_lock_init(&q->lock);
 36	q->ready = NULL;
 37	init_llist_head(&q->new);
 38}
 39
 40/**
 41 * lwq_empty - test if lwq contains any entry
 42 * @q:	the lwq object
 43 *
 44 * This empty test contains an acquire barrier so that if a wakeup
 45 * is sent when lwq_dequeue returns true, it is safe to go to sleep after
 46 * a test on lwq_empty().
 47 */
 48static inline bool lwq_empty(struct lwq *q)
 49{
 50	/* acquire ensures ordering wrt lwq_enqueue() */
 51	return smp_load_acquire(&q->ready) == NULL && llist_empty(&q->new);
 52}
 53
 54struct llist_node *__lwq_dequeue(struct lwq *q);
 55/**
 56 * lwq_dequeue - dequeue first (oldest) entry from lwq
 57 * @q:		the queue to dequeue from
 58 * @type:	the type of object to return
 59 * @member:	them member in returned object which is an lwq_node.
 60 *
 61 * Remove a single object from the lwq and return it.  This will take
 62 * a spinlock and so must always be called in the same context, typcially
 63 * process contet.
 64 */
 65#define lwq_dequeue(q, type, member)					\
 66	({ struct llist_node *_n = __lwq_dequeue(q);			\
 67	  _n ? container_of(_n, type, member.node) : NULL; })
 68
 69struct llist_node *lwq_dequeue_all(struct lwq *q);
 70
 71/**
 72 * lwq_for_each_safe - iterate over detached queue allowing deletion
 73 * @_n:		iterator variable
 74 * @_t1:	temporary struct llist_node **
 75 * @_t2:	temporary struct llist_node *
 76 * @_l:		address of llist_node pointer from lwq_dequeue_all()
 77 * @_member:	member in _n where lwq_node is found.
 78 *
 79 * Iterate over members in a dequeued list.  If the iterator variable
 80 * is set to NULL, the iterator removes that entry from the queue.
 81 */
 82#define lwq_for_each_safe(_n, _t1, _t2, _l, _member)			\
 83	for (_t1 = (_l);						\
 84	     *(_t1) ? (_n = container_of(*(_t1), typeof(*(_n)), _member.node),\
 85		       _t2 = ((*_t1)->next),				\
 86		       true)						\
 87	     : false;							\
 88	     (_n) ? (_t1 = &(_n)->_member.node.next, 0)			\
 89	     : ((*(_t1) = (_t2)),  0))
 90
 91/**
 92 * lwq_enqueue - add a new item to the end of the queue
 93 * @n	- the lwq_node embedded in the item to be added
 94 * @q	- the lwq to append to.
 95 *
 96 * No locking is needed to append to the queue so this can
 97 * be called from any context.
 98 * Return %true is the list may have previously been empty.
 99 */
100static inline bool lwq_enqueue(struct lwq_node *n, struct lwq *q)
101{
102	/* acquire enqures ordering wrt lwq_dequeue */
103	return llist_add(&n->node, &q->new) &&
104		smp_load_acquire(&q->ready) == NULL;
105}
106
107/**
108 * lwq_enqueue_batch - add a list of new items to the end of the queue
109 * @n	- the lwq_node embedded in the first item to be added
110 * @q	- the lwq to append to.
111 *
112 * No locking is needed to append to the queue so this can
113 * be called from any context.
114 * Return %true is the list may have previously been empty.
115 */
116static inline bool lwq_enqueue_batch(struct llist_node *n, struct lwq *q)
117{
118	struct llist_node *e = n;
119
120	/* acquire enqures ordering wrt lwq_dequeue */
121	return llist_add_batch(llist_reverse_order(n), e, &q->new) &&
122		smp_load_acquire(&q->ready) == NULL;
123}
124#endif /* LWQ_H */