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Date: Fri, 22 Mar 2019 15:38:01 +0100 From: luca abeni <luca.abeni@...tannapisa.it> To: Juri Lelli <juri.lelli@...hat.com> Cc: "chengjian (D)" <cj.chengjian@...wei.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Li Bin <huawei.libin@...wei.com>, "Xiexiuqi (Xie XiuQi)" <xiexiuqi@...wei.com>, mingo@...hat.com, Peter Zijlstra <peterz@...radead.org> Subject: Re: WARN ON at kernel/sched/deadline.c task_non_contending Hi Juri, On Fri, 22 Mar 2019 15:32:32 +0100 Juri Lelli <juri.lelli@...hat.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
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