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-rw-r--r--lib/lwq.c158
1 files changed, 158 insertions, 0 deletions
diff --git a/lib/lwq.c b/lib/lwq.c
new file mode 100644
index 0000000000..57d080a4d5
--- /dev/null
+++ b/lib/lwq.c
@@ -0,0 +1,158 @@
+// 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*/