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 | |
19 | struct 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(lock: &q->lock); |
26 | this = q->ready; |
27 | if (!this && !llist_empty(head: &q->new)) { |
28 | /* ensure queue doesn't appear transiently lwq_empty */ |
29 | smp_store_release(&q->ready, (void *)1); |
30 | this = llist_reverse_order(head: llist_del_all(head: &q->new)); |
31 | if (!this) |
32 | q->ready = NULL; |
33 | } |
34 | if (this) |
35 | q->ready = llist_next(node: this); |
36 | spin_unlock(lock: &q->lock); |
37 | return this; |
38 | } |
39 | EXPORT_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 | */ |
49 | struct 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(lock: &q->lock); |
57 | r = q->ready; |
58 | q->ready = NULL; |
59 | t = llist_del_all(head: &q->new); |
60 | spin_unlock(lock: &q->lock); |
61 | ep = &r; |
62 | while (*ep) |
63 | ep = &(*ep)->next; |
64 | *ep = llist_reverse_order(head: t); |
65 | return r; |
66 | } |
67 | EXPORT_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> |
76 | struct tnode { |
77 | struct lwq_node n; |
78 | int i; |
79 | int c; |
80 | }; |
81 | |
82 | static 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(n: &t->n, q)) |
92 | wake_up_var(var: q); |
93 | } |
94 | while (!kthread_should_stop()) |
95 | schedule_timeout_idle(timeout: 1); |
96 | return 0; |
97 | } |
98 | |
99 | static 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: &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(size: sizeof(*t), GFP_KERNEL); |
114 | if (!t) |
115 | break; |
116 | t->i = i; |
117 | t->c = 0; |
118 | if (lwq_enqueue(n: &t->n, q: &q)) |
119 | wake_up_var(var: &q); |
120 | } |
121 | /* wait for threads to exit */ |
122 | for (i = 0; i < ARRAY_SIZE(threads); i++) |
123 | if (!IS_ERR_OR_NULL(ptr: threads[i])) |
124 | kthread_stop(k: 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(objp: 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(objp: t); |
143 | t = NULL; |
144 | } |
145 | } |
146 | if (l) |
147 | lwq_enqueue_batch(n: l, q: &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(objp: t); |
152 | } |
153 | printk(KERN_CONT "\n" ); |
154 | return 0; |
155 | } |
156 | |
157 | module_init(lwq_test); |
158 | #endif /* CONFIG_LWQ_TEST*/ |
159 | |