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Date: Thu, 16 Jun 2016 10:06:00 -0700 From: bsegall@...gle.com To: Konstantin Khlebnikov <khlebnikov@...dex-team.ru> Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org, stable@...r.kernel.org Subject: Re: [PATCH] sched/fair: do not announce throttled next buddy in dequeue_task_fair Konstantin Khlebnikov <khlebnikov@...dex-team.ru> writes: > Hierarchy could be already throttled at this point. Throttled next > buddy could trigger null pointer dereference in pick_next_task_fair(). > > Signed-off-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru> Reviewed-by: Ben Segall <bsegall@...gle.com> > Cc: Stable <stable@...r.kernel.org> # v3.2+ > --- > kernel/sched/fair.c | 9 ++++----- > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index fe809fe169d2..3c6b038cb734 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -4519,15 +4519,14 @@ static void dequeue_task_fair(struct rq *rq, struct task_struct *p, int flags) > > /* Don't dequeue parent if it has other entities besides us */ > if (cfs_rq->load.weight) { > + /* avoid re-evaluating load for this entity */ > + se = parent_entity(se); > /* > * Bias pick_next to pick a task from this cfs_rq, as > * p is sleeping when it is within its sched_slice. > */ > - if (task_sleep && parent_entity(se)) > - set_next_buddy(parent_entity(se)); > - > - /* avoid re-evaluating load for this entity */ > - se = parent_entity(se); > + if (task_sleep && se && !throttled_hierarchy(cfs_rq)) > + set_next_buddy(se); > break; > } > flags |= DEQUEUE_SLEEP;
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