From: Valentin Schneider <valentin.schneider@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Qais Yousef <qais.yousef@arm.com>,
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 14:06:59 +0000 [thread overview]
Message-ID: <db68d480-dc1e-04d5-1a20-966b5eddb26a@arm.com> (raw)
In-Reply-To: <CAKfTPtDZLFn7msw88pTE_wr-BJo2ErqxpOW+ah0Jjcg6vE3SLw@mail.gmail.com>
On 04/12/2019 12:08, Vincent Guittot wrote:
>> 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).
>
> In fact, this will depend of the uninitialized values of local_sgs. I
> have been able to reproduce the situation where we skip local group
> but not to trigger the crash because the values already in the stack
> don't trigger the misfit comparison.
>
One more thing, DB845 has a single DynamIQ cluster that is represented as a
flat hierarchy (unlike regular big.LITTLE, see
arch/arm64/boot/dts/qcom/sdm845.dtsi) so we'll just have a single MC level
with groups being individual CPUs, making the bug easier to reproduce
(than on regular big.LITTLE, that is).
> I wait for John feedback to confirm that this fix his problem and
> will send a clean version of the patch
>>
>>
next prev parent reply other threads:[~2019-12-04 14:07 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
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 [this message]
2019-12-04 18:16 ` John Stultz
2019-12-04 18:19 ` Vincent Guittot
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