On Tue 2015-07-28 13:18:22, Tejun Heo wrote:

Hello,

On Tue, Jul 28, 2015 at 04:39:20PM +0200, Petr Mladek wrote:

quoted

+/*
+ * Test whether @work is being queued from another work
+ * executing on the same kthread.
+ */
+static bool is_chained_work(struct kthread_worker *worker)
+{
+	struct kthread_worker *current_worker;
+
+	current_worker = current_kthread_worker();
+	/*
+	 * Return %true if I'm a kthread worker executing a work item on
+	 * the given @worker.
+	 */
+	return current_worker && current_worker == worker;
+}

I'm not sure full-on chained work detection is necessary here.
kthread worker's usages tend to be significantly simpler and draining
is only gonna be used for destruction.

I think that it might be useful to detect bugs when someone
depends on the worker when it is being destroyed. For example,
I tried to convert "khubd" kthread and there was not easy to
double check that this worked as expected.

I actually think about replacing

    WARN_ON_ONCE(!is_chained_work(worker)))

with

    WARN_ON(!is_chained_work(worker)))

in queue_kthread_work, so that we get the warning for all misused
workers.

quoted

+void drain_kthread_worker(struct kthread_worker *worker)
+{
+	int flush_cnt = 0;
+
+	spin_lock_irq(&worker->lock);
+	worker->nr_drainers++;
+
+	while (!list_empty(&worker->work_list)) {
+		/*
+		 * Unlock, so we could move forward. Note that queuing
+		 * is limited by @nr_drainers > 0.
+		 */
+		spin_unlock_irq(&worker->lock);
+
+		flush_kthread_worker(worker);
+
+		if (++flush_cnt == 10 ||
+		    (flush_cnt % 100 == 0 && flush_cnt <= 1000))
+			pr_warn("kthread worker %s: drain_kthread_worker() isn't complete after %u tries\n",
+				worker->task->comm, flush_cnt);
+
+		spin_lock_irq(&worker->lock);
+	}

I'd just do something like WARN_ONCE(flush_cnt++ > 10, "kthread worker: ...").

This would print the warning only for one broken worker. But I do not
have strong opinion about it.

Best Regards,
Petr