Re: [PATCH v2 1/1] sched: watchdog: Touch kernel watchdog with sched count

[Xi Wang]

On Wed, Oct 21, 2020 at 3:13 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> On Tue, Oct 20, 2020 at 01:57:04PM -0700, Xi Wang wrote:
>
> > +     if (watchdog_touch_with_sched) {
> > +             /* Trigger reschedule for the next round */
> > +             set_tsk_need_resched(current);
> > +             set_preempt_need_resched();
>
> Blergh.. that's gross. This relies on this being in IRQ context and
> either: PREEMPT=y *OR* this always being from userspace. Otherwise
> there's no guarantee the return-from-interrupt will actually schedule.
>

Maybe I missed something but I think immediate rescheduling is not
required? E.g. software watchdog should fire if there is a kernel busy
loop and kernel preemption is not enabled. The current method ends up
with a thread wakeup so there is no guaranteed reschedule either?

-Xi