Re: [PATCH v3 09/22] kthread: Allow to cancel kthread work

[Tejun Heo]

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);

Thanks.

-- 
tejun
--
To unsubscribe from this list: send the line "unsubscribe linux-api" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html