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Date:   Mon, 3 May 2021 16:45:16 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc:     Vincent Guittot <vincent.guittot@linaro.org>,
        Quentin Perret <qperret@google.com>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>,
        Qais Yousef <qais.yousef@arm.com>,
        Android Kernel Team <kernel-team@android.com>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        Patrick Bellasi <patrick.bellasi@matbug.net>
Subject: Re: [PATCH v3] sched: Fix out-of-bound access in uclamp
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 <562004ff-9f60-bf37-df4c-547415ae2cd5@arm.com>
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On Mon, May 03, 2021 at 12:55:34PM +0200, Dietmar Eggemann wrote:
> On 30/04/2021 17:27, Vincent Guittot wrote:
> > On Fri, 30 Apr 2021 at 17:14, Quentin Perret <qperret@google.com> wrote:
> >>
> >> Util-clamp places tasks in different buckets based on their clamp values
> >> for performance reasons. However, the size of buckets is currently
> >> computed using a rounding division, which can lead to an off-by-one
> >> error in some configurations.
> >>
> >> For instance, with 20 buckets, the bucket size will be 1024/20=51. A
> >> task with a clamp of 1024 will be mapped to bucket id 1024/51=20. Sadly,
> >> correct indexes are in range [0,19], hence leading to an out of bound
> >> memory access.
> >>
> >> Clamp the bucket id to fix the issue.
> >>
> >> Fixes: 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
> >> Suggested-by: Qais Yousef <qais.yousef@arm.com>
> >> Signed-off-by: Quentin Perret <qperret@google.com>
> > 
> > Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>

> Reviewed-by: Dietmar Eggemann <dietmar.eggemann@arm.com>

Thanks!