From: Valentin Schneider <valentin.schneider@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>,
Qais Yousef <qais.yousef@arm.com>
Cc: John Stultz <john.stultz@linaro.org>,
Quentin Perret <qperret@google.com>,
Peter Zijlstra <peterz@infradead.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Juri Lelli <juri.lelli@redhat.com>,
Patrick Bellasi <Patrick.Bellasi@arm.com>,
Ingo Molnar <mingo@kernel.org>,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: Null pointer crash at find_idlest_group on db845c w/ linus/master
Date: Wed, 4 Dec 2019 10:41:12 +0000 [thread overview]
Message-ID: <629cca09-dde7-5d77-42e1-c68f2c1820d2@arm.com> (raw)
In-Reply-To: <20191204100925.GA15727@linaro.org>
On 04/12/2019 10:09, Vincent Guittot wrote:
> 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
>
Shoot, I think you're right. If it is the local group that is NULL, then
we most likely splat on:
if (local->sgc->max_capacity >= idlest->sgc->max_capacity)
return NULL;
We don't splat before because we just use local_sgs, which is uninitialized
but on the stack.
Also; does it really have to involve an affinity "race"? AFAIU affinity
could have been changed a while back, but the waking CPU isn't allowed
so we skip the local_group (in simpler cases where each CPU is a group).
next prev parent reply other threads:[~2019-12-04 10:41 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-03 19:15 John Stultz
2019-12-03 23:20 ` Valentin Schneider
2019-12-03 23:49 ` Valentin Schneider
2019-12-04 0:13 ` Valentin Schneider
2019-12-04 3:46 ` John Stultz
2019-12-04 10:05 ` Valentin Schneider
2019-12-04 8:06 ` Vincent Guittot
2019-12-04 8:22 ` Vincent Guittot
2019-12-04 9:59 ` Valentin Schneider
2019-12-04 9:42 ` Qais Yousef
2019-12-04 10:09 ` Valentin Schneider
2019-12-04 10:09 ` Vincent Guittot
2019-12-04 10:41 ` Valentin Schneider [this message]
2019-12-04 12:08 ` Vincent Guittot
2019-12-04 13:32 ` Qais Yousef
2019-12-04 13:48 ` Vincent Guittot
2019-12-04 13:55 ` Qais Yousef
2019-12-04 14:06 ` Valentin Schneider
2019-12-04 18:16 ` John Stultz
2019-12-04 18:19 ` Vincent Guittot
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