On Mon, Feb 22, 2016 at 03:56:54PM +0100, Petr Mladek wrote:

+/**
+ * drain_kthread_worker - drain a kthread worker
+ * @worker: worker to be drained
+ *
+ * Wait until there is no work queued for the given kthread worker.
+ * @worker is flushed repeatedly until it becomes empty.  The number
+ * of flushing is determined by the depth of chaining and should
+ * be relatively short.  Whine if it takes too long.
+ *
+ * The caller is responsible for blocking all users of this kthread
+ * worker from queuing new works. Also it is responsible for blocking
+ * the already queued works from an infinite re-queuing!
+ */
+void drain_kthread_worker(struct kthread_worker *worker)
+{
+	int flush_cnt = 0;
+
+	spin_lock_irq(&worker->lock);

Would it not make sense to set a flag here that inhibits (or warns)
queueing new work?

Otherwise this can, as you point out, last forever.

And I think its a logic fail if you both want to drain it and keeping
adding new work.

+	while (!list_empty(&worker->work_list)) {
+		spin_unlock_irq(&worker->lock);
+
+		flush_kthread_worker(worker);
+		WARN_ONCE(flush_cnt++ > 10,
+			  "kthread worker %s: drain_kthread_worker() isn't complete after %u tries\n",
+			  worker->task->comm, flush_cnt);
+
+		spin_lock_irq(&worker->lock);
+	}
+
+	spin_unlock_irq(&worker->lock);
+}
+EXPORT_SYMBOL(drain_kthread_worker);
-- 
1.8.5.6

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