On Mon 2015-11-23 17:58:23, Tejun Heo wrote:

Hello,

On Wed, Nov 18, 2015 at 02:25:14PM +0100, Petr Mladek wrote:

quoted

+static int
+try_to_cancel_kthread_work(struct kthread_work *work,
+				   spinlock_t *lock,
+				   unsigned long *flags)
+{
+	int ret = 0;
+
+	if (work->timer) {
+		/* Try to cancel the timer if pending. */
+		if (del_timer(work->timer)) {
+			ret = 1;
+			goto out;
+		}
+
+		/* Are we racing with the timer callback? */
+		if (timer_active(work->timer)) {
+			/* Bad luck, need to avoid a deadlock. */
+			spin_unlock_irqrestore(lock, *flags);
+			del_timer_sync(work->timer);
+			ret = -EAGAIN;
+			goto out;
+		}

As the timer side is already kinda trylocking anyway, can't the cancel
path be made simpler?  Sth like

	lock(worker);
	work->canceling = true;
	del_timer_sync(work->timer);
	unlock(worker);

And the timer can do (ignoring the multiple worker support, do we even
need that?)

	while (!trylock(worker)) {
		if (work->canceling)
			return;
		cpu_relax();
	}
	queue;
	unlock(worker);

Why did I not find out this myself ?:-)

Thanks for hint,
Petr

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