Messages in this thread | | | Subject | Re: WARN ON at kernel/sched/deadline.c task_non_contending | From | "chengjian (D)" <> | Date | Fri, 15 Mar 2019 08:43:00 +0800 |
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On 2019/3/13 22:49, luca abeni wrote: > Hi, > > After looking at the patch a little bit more and running some tests, > I suspect this solution might be racy: > when the timer is already active, (and hrtimer_start() fails), it > relies on its handler to decrease the running bw (by setting > dl_non_contending to 1)... But inactive_task_timer() might have > already checked dl_non_contending, finding it equal to 0 (so, it > ends up doing nothing and the running bw is not decreased). > > > So, I would prefer a different solution. I think this patch should work: > > 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. > > > Thanks, > Luca > > .
Yeah, it looks good.
I can do some experiments with it ,
Do you have some testcases to help me with the test ?
Thanks,
Cheng Jian.
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