+/**
+ * drain_workqueue - drain a workqueue
+ * @wq: workqueue to drain
+ *
+ * Wait until the workqueue becomes empty. While draining is in progress,
+ * only chain queueing is allowed. IOW, only currently pending or running
+ * work items on @wq can queue further work items on it. @wq is flushed
+ * repeatedly until it becomes empty. The number of flushing is detemined
+ * by the depth of chaining and should be relatively short. Whine if it
+ * takes too long.
+ */
+void drain_workqueue(struct workqueue_struct *wq)
+{
+ unsigned int flush_cnt = 0;
+ unsigned int cpu;
+
+ /*
+ * __queue_work() needs to test whether there are drainers, is much
+ * hotter than drain_workqueue() and already looks at @wq->flags.
+ * Use WQ_DRAINING so that queue doesn't have to check nr_drainers.
+ */
+ spin_lock(&workqueue_lock);
+ if (!wq->nr_drainers++)
+ wq->flags |= WQ_DRAINING;
+ spin_unlock(&workqueue_lock);
+reflush:
+ flush_workqueue(wq);
+
+ for_each_cwq_cpu(cpu, wq) {
+ struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
+
+ if (!cwq->nr_active && list_empty(&cwq->delayed_works))
+ continue;
+
+ if (++flush_cnt == 10 ||
+ (flush_cnt % 100 == 0 && flush_cnt <= 1000))
+ pr_warning("workqueue %s: flush on destruction isn't complete after %u tries\n",
+ wq->name, flush_cnt);
+ goto reflush;
+ }
+
+ spin_lock(&workqueue_lock);
+ if (!--wq->nr_drainers)
+ wq->flags &= ~WQ_DRAINING;
+ spin_unlock(&workqueue_lock);
+}
+EXPORT_SYMBOL_GPL(drain_workqueue);
+