1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * Light-weight single-linked queue.
4 *
5 * Entries are enqueued to the head of an llist, with no blocking.
6 * This can happen in any context.
7 *
8 * Entries are dequeued using a spinlock to protect against multiple
9 * access.  The llist is staged in reverse order, and refreshed
10 * from the llist when it exhausts.
11 *
12 * This is particularly suitable when work items are queued in BH or
13 * IRQ context, and where work items are handled one at a time by
14 * dedicated threads.
15 */
16#include <linux/rcupdate.h>
17#include <linux/lwq.h>
18
19struct llist_node *__lwq_dequeue(struct lwq *q)
20{
21	struct llist_node *this;
22
23	if (lwq_empty(q))
24		return NULL;
25	spin_lock(&q->lock);
26	this = q->ready;
27	if (!this && !llist_empty(&q->new)) {
28		/* ensure queue doesn't appear transiently lwq_empty */
29		smp_store_release(&q->ready, (void *)1);
30		this = llist_reverse_order(llist_del_all(&q->new));
31		if (!this)
32			q->ready = NULL;
33	}
34	if (this)
35		q->ready = llist_next(this);
36	spin_unlock(&q->lock);
37	return this;
38}
39EXPORT_SYMBOL_GPL(__lwq_dequeue);
40
41/**
42 * lwq_dequeue_all - dequeue all currently enqueued objects
43 * @q:	the queue to dequeue from
44 *
45 * Remove and return a linked list of llist_nodes of all the objects that were
46 * in the queue. The first on the list will be the object that was least
47 * recently enqueued.
48 */
49struct llist_node *lwq_dequeue_all(struct lwq *q)
50{
51	struct llist_node *r, *t, **ep;
52
53	if (lwq_empty(q))
54		return NULL;
55
56	spin_lock(&q->lock);
57	r = q->ready;
58	q->ready = NULL;
59	t = llist_del_all(&q->new);
60	spin_unlock(&q->lock);
61	ep = &r;
62	while (*ep)
63		ep = &(*ep)->next;
64	*ep = llist_reverse_order(t);
65	return r;
66}
67EXPORT_SYMBOL_GPL(lwq_dequeue_all);
68
69#if IS_ENABLED(CONFIG_LWQ_TEST)
70
71#include <linux/module.h>
72#include <linux/slab.h>
73#include <linux/wait_bit.h>
74#include <linux/kthread.h>
75#include <linux/delay.h>
76struct tnode {
77	struct lwq_node n;
78	int i;
79	int c;
80};
81
82static int lwq_exercise(void *qv)
83{
84	struct lwq *q = qv;
85	int cnt;
86	struct tnode *t;
87
88	for (cnt = 0; cnt < 10000; cnt++) {
89		wait_var_event(q, (t = lwq_dequeue(q, struct tnode, n)) != NULL);
90		t->c++;
91		if (lwq_enqueue(&t->n, q))
92			wake_up_var(q);
93	}
94	while (!kthread_should_stop())
95		schedule_timeout_idle(1);
96	return 0;
97}
98
99static int lwq_test(void)
100{
101	int i;
102	struct lwq q;
103	struct llist_node *l, **t1, *t2;
104	struct tnode *t;
105	struct task_struct *threads[8];
106
107	printk(KERN_INFO "testing lwq....\n");
108	lwq_init(&q);
109	printk(KERN_INFO " lwq: run some threads\n");
110	for (i = 0; i < ARRAY_SIZE(threads); i++)
111		threads[i] = kthread_run(lwq_exercise, &q, "lwq-test-%d", i);
112	for (i = 0; i < 100; i++) {
113		t = kmalloc(sizeof(*t), GFP_KERNEL);
114		if (!t)
115			break;
116		t->i = i;
117		t->c = 0;
118		if (lwq_enqueue(&t->n, &q))
119			wake_up_var(&q);
120	}
121	/* wait for threads to exit */
122	for (i = 0; i < ARRAY_SIZE(threads); i++)
123		if (!IS_ERR_OR_NULL(threads[i]))
124			kthread_stop(threads[i]);
125	printk(KERN_INFO " lwq: dequeue first 50:");
126	for (i = 0; i < 50 ; i++) {
127		if (i && (i % 10) == 0) {
128			printk(KERN_CONT "\n");
129			printk(KERN_INFO " lwq: ... ");
130		}
131		t = lwq_dequeue(&q, struct tnode, n);
132		if (t)
133			printk(KERN_CONT " %d(%d)", t->i, t->c);
134		kfree(t);
135	}
136	printk(KERN_CONT "\n");
137	l = lwq_dequeue_all(&q);
138	printk(KERN_INFO " lwq: delete the multiples of 3 (test lwq_for_each_safe())\n");
139	lwq_for_each_safe(t, t1, t2, &l, n) {
140		if ((t->i % 3) == 0) {
141			t->i = -1;
142			kfree(t);
143			t = NULL;
144		}
145	}
146	if (l)
147		lwq_enqueue_batch(l, &q);
148	printk(KERN_INFO " lwq: dequeue remaining:");
149	while ((t = lwq_dequeue(&q, struct tnode, n)) != NULL) {
150		printk(KERN_CONT " %d", t->i);
151		kfree(t);
152	}
153	printk(KERN_CONT "\n");
154	return 0;
155}
156
157module_init(lwq_test);
158#endif /* CONFIG_LWQ_TEST*/
159