Thomas Gleixner wrote:
>
> +static int internal_restart_ktimer(struct ktimer *timer, nsec_t *tim,
> + int mode)
> +{
> + struct ktimer_base *base, *new_base;
> + unsigned long flags;
> + int ret;
> +
> + BUG_ON(!timer->function);
> +
> + retry:
> + base = lock_ktimer_base(timer, &flags);
> +
> + /* Remove an active timer from the queue */
> + ret = remove_ktimer(timer, base);
> +
> + /* Switch the timer base, if necessary */
> + new_base = switch_ktimer_base(timer, base);
> +
> + /* SMP */
> + if (ktimer_base_can_change && unlikely(!new_base)){
> + spin_unlock_irqrestore(&base->lock, flags);
> + wait_for_ktimer(timer);
> + goto retry;
> + }
This is deadlockable.
The caller of modify_ktimer()->internal_restart_ktimer() can hold locks
which would prevent the completion of the ktimer->function().
Also, I don't understand why the timer is deleted _before_ checking that
new_base != NULL. This way you can delete the timer (ret == 1), then goto
retry, then get ret == 0.
Oleg.
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