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:
> > +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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