Messages in this thread | | | From | John Stultz <> | Date | Wed, 4 Dec 2019 10:16:36 -0800 | Subject | Re: Null pointer crash at find_idlest_group on db845c w/ linus/master |
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On Wed, Dec 4, 2019 at 2:09 AM Vincent Guittot <vincent.guittot@linaro.org> wrote: > > Le Wednesday 04 Dec 2019 à 09:42:17 (+0000), Qais Yousef a écrit : > > On 12/04/19 09:06, Vincent Guittot wrote: > > > Hi John, > > > > > > On Tue, 3 Dec 2019 at 20:15, John Stultz <john.stultz@linaro.org> wrote: > > > > > > > > With today's linus/master on db845c running android, I'm able to > > > > fairly easily reproduce the following crash. I've not had a chance to > > > > bisect it yet, but I'm suspecting its connected to Vincent's recent > > > > rework. > > > > > > Does the crash happen randomly or after a specific action ? > > > I have a db845 so I can try to reproduce it locally. > > > > Isn't there a chance we use local_sgs without initializing it in that function? > > Normally not because the cpu belongs to its sched_domain > > Now, we test that a group has at least one allowed CPU for the task so we > could skip the local group with the correct/wrong p->cpus_ptr > > The path is used for fork/exec ibut also for wakeup path for b.L when the task doesn't fit in the CPUs > > So we can probably imagine a scenario where we change task affinity while > sleeping. If the wakeup happens on a CPU that belongs to the group that is not > allowed, we can imagine that we skip the local_group > > John, > > Could you try the fix below ? > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 08a233e..bcd216d 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -8417,6 +8417,10 @@ find_idlest_group(struct sched_domain *sd, struct task_struct *p, > if (!idlest) > return NULL; > > + /* The local group has been skipped because of cpu affinity */ > + if (!local) > + return idlest; > + > /* > * If the local group is idler than the selected idlest group > * don't try and push the task.
This patch does seem to solve the issue for me! Thanks so much!
Tested-by: John Stultz <john.stultz@linaro.org> -john
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