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Date: Fri, 31 Aug 2018 17:10:49 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Vincent Guittot <vincent.guittot@...aro.org> Cc: mingo@...hat.com, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2] sched/pelt: fix update_blocked_averages() for dl and rt On Fri, Aug 31, 2018 at 05:07:21PM +0200, Peter Zijlstra wrote: > On Fri, Aug 31, 2018 at 04:56:19PM +0200, Vincent Guittot wrote: > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 309c93f..bc1de21 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -7262,6 +7262,7 @@ static void update_blocked_averages(int cpu) > > { > > struct rq *rq = cpu_rq(cpu); > > struct cfs_rq *cfs_rq, *pos; > > + const struct sched_class *curr_class = rq->curr->sched_class; > > struct rq_flags rf; > > bool done = true; > > Can you do me a v3 where you move that rq->curr dereference under the > rq->lock? > > I _think_ it is actually OK, but it is really dodgy. Moving it under > rq->lock makes it obvious correct. Ah, it is not correct. I only checked to see if preemption was disabled and if we're calling this on the local CPU (which I think is true), which would guarantee rq->curr's existence. But that is not sufficient to make rq->curr->sched_class stable. > > @@ -7298,8 +7299,8 @@ static void update_blocked_averages(int cpu) > > if (cfs_rq_has_blocked(cfs_rq)) > > done = false; > > } > > - update_rt_rq_load_avg(rq_clock_task(rq), rq, 0); > > - update_dl_rq_load_avg(rq_clock_task(rq), rq, 0); > > + update_rt_rq_load_avg(rq_clock_task(rq), rq, curr_class == &rt_sched_class); > > + update_dl_rq_load_avg(rq_clock_task(rq), rq, curr_class == &dl_sched_class); > > update_irq_load_avg(rq, 0); > > /* Don't need periodic decay once load/util_avg are null */ > > if (others_have_blocked(rq))
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