NeilBrown | de9e82c | 2023-09-11 10:39:43 -0400 | [diff] [blame] | 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(&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 | } |
| 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(&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 | } |
| 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(&t->n, q)) |
| 92 | wake_up_var(q); |
| 93 | } |
| 94 | while (!kthread_should_stop()) |
| 95 | schedule_timeout_idle(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); |
| 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 | |
| 157 | module_init(lwq_test); |
| 158 | #endif /* CONFIG_LWQ_TEST*/ |