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// SPDX-License-Identifier: GPL-2.0-only
/*
* Light-weight single-linked queue.
*
* Entries are enqueued to the head of an llist, with no blocking.
* This can happen in any context.
*
* Entries are dequeued using a spinlock to protect against multiple
* access. The llist is staged in reverse order, and refreshed
* from the llist when it exhausts.
*
* This is particularly suitable when work items are queued in BH or
* IRQ context, and where work items are handled one at a time by
* dedicated threads.
*/
#include <linux/rcupdate.h>
#include <linux/lwq.h>
struct llist_node *__lwq_dequeue(struct lwq *q)
{
struct llist_node *this;
if (lwq_empty(q))
return NULL;
spin_lock(&q->lock);
this = q->ready;
if (!this && !llist_empty(&q->new)) {
/* ensure queue doesn't appear transiently lwq_empty */
smp_store_release(&q->ready, (void *)1);
this = llist_reverse_order(llist_del_all(&q->new));
if (!this)
q->ready = NULL;
}
if (this)
q->ready = llist_next(this);
spin_unlock(&q->lock);
return this;
}
EXPORT_SYMBOL_GPL(__lwq_dequeue);
/**
* lwq_dequeue_all - dequeue all currently enqueued objects
* @q: the queue to dequeue from
*
* Remove and return a linked list of llist_nodes of all the objects that were
* in the queue. The first on the list will be the object that was least
* recently enqueued.
*/
struct llist_node *lwq_dequeue_all(struct lwq *q)
{
struct llist_node *r, *t, **ep;
if (lwq_empty(q))
return NULL;
spin_lock(&q->lock);
r = q->ready;
q->ready = NULL;
t = llist_del_all(&q->new);
spin_unlock(&q->lock);
ep = &r;
while (*ep)
ep = &(*ep)->next;
*ep = llist_reverse_order(t);
return r;
}
EXPORT_SYMBOL_GPL(lwq_dequeue_all);
#if IS_ENABLED(CONFIG_LWQ_TEST)
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/wait_bit.h>
#include <linux/kthread.h>
#include <linux/delay.h>
struct tnode {
struct lwq_node n;
int i;
int c;
};
static int lwq_exercise(void *qv)
{
struct lwq *q = qv;
int cnt;
struct tnode *t;
for (cnt = 0; cnt < 10000; cnt++) {
wait_var_event(q, (t = lwq_dequeue(q, struct tnode, n)) != NULL);
t->c++;
if (lwq_enqueue(&t->n, q))
wake_up_var(q);
}
while (!kthread_should_stop())
schedule_timeout_idle(1);
return 0;
}
static int lwq_test(void)
{
int i;
struct lwq q;
struct llist_node *l, **t1, *t2;
struct tnode *t;
struct task_struct *threads[8];
printk(KERN_INFO "testing lwq....\n");
lwq_init(&q);
printk(KERN_INFO " lwq: run some threads\n");
for (i = 0; i < ARRAY_SIZE(threads); i++)
threads[i] = kthread_run(lwq_exercise, &q, "lwq-test-%d", i);
for (i = 0; i < 100; i++) {
t = kmalloc(sizeof(*t), GFP_KERNEL);
if (!t)
break;
t->i = i;
t->c = 0;
if (lwq_enqueue(&t->n, &q))
wake_up_var(&q);
}
/* wait for threads to exit */
for (i = 0; i < ARRAY_SIZE(threads); i++)
if (!IS_ERR_OR_NULL(threads[i]))
kthread_stop(threads[i]);
printk(KERN_INFO " lwq: dequeue first 50:");
for (i = 0; i < 50 ; i++) {
if (i && (i % 10) == 0) {
printk(KERN_CONT "\n");
printk(KERN_INFO " lwq: ... ");
}
t = lwq_dequeue(&q, struct tnode, n);
if (t)
printk(KERN_CONT " %d(%d)", t->i, t->c);
kfree(t);
}
printk(KERN_CONT "\n");
l = lwq_dequeue_all(&q);
printk(KERN_INFO " lwq: delete the multiples of 3 (test lwq_for_each_safe())\n");
lwq_for_each_safe(t, t1, t2, &l, n) {
if ((t->i % 3) == 0) {
t->i = -1;
kfree(t);
t = NULL;
}
}
if (l)
lwq_enqueue_batch(l, &q);
printk(KERN_INFO " lwq: dequeue remaining:");
while ((t = lwq_dequeue(&q, struct tnode, n)) != NULL) {
printk(KERN_CONT " %d", t->i);
kfree(t);
}
printk(KERN_CONT "\n");
return 0;
}
module_init(lwq_test);
#endif /* CONFIG_LWQ_TEST*/
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