Hi Juri,
On Fri, 22 Mar 2019 15:32:32 +0100 Juri Lelli <juri.le...@redhat.com> wrote:
[...]
> > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> > index 6a73e41a2016..43901fa3f269 100644
> > --- a/kernel/sched/deadline.c
> > +++ b/kernel/sched/deadline.c
> > @@ -252,7 +252,6 @@ static void task_non_contending(struct
> > task_struct *p) if (dl_entity_is_special(dl_se))
> > return;
> >
> > - WARN_ON(hrtimer_active(&dl_se->inactive_timer));
> > WARN_ON(dl_se->dl_non_contending);
> >
> > zerolag_time = dl_se->deadline -
> > @@ -269,7 +268,7 @@ static void task_non_contending(struct
> > task_struct *p)
> > * If the "0-lag time" already passed, decrease the active
> > * utilization now, instead of starting a timer
> > */
> > - if (zerolag_time < 0) {
> > + if ((zerolag_time < 0) ||
> > hrtimer_active(&dl_se->inactive_timer)) { if (dl_task(p))
> > sub_running_bw(dl_se, dl_rq);
> > if (!dl_task(p) || p->state == TASK_DEAD) {
> >
> >
> > The idea is that if the timer is active, we leave dl_non_contending
> > set to 0 (so that the timer handler does nothing), and we
> > immediately decrease the running bw.
> > I think this is OK, because this situation can happen only if the
> > task blocks, wakes up while the timer handler is running, and then
> > immediately blocks again - while the timer handler is still
> > running. So, the "zero lag time" cannot be too much in the future.
>
> And if we get here and the handler is running it means that the
> handler is spinning on rq->lock waiting the dequeue to release it.
> So, this looks safe to me as well.
>
> BTW, I could reproduce with Steve's deadline_test [1], and this seems
> to fix it.
>
> Would you mind sending out a proper patch Luca?
Thanks for looking at this. I'll try to prepare and send a patch in
next week.
Thanks,
Luca
