linux-kernel - Re: [PATCH v2] sched: Fix out-of-bound access in uclamp

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Message-ID: <98a96d35-a6ae-f913-13f9-b5c17689039c@arm.com>
Date:   Fri, 30 Apr 2021 17:04:31 +0200
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        Quentin Perret <qperret@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Qais Yousef <qais.yousef@....com>,
        Android Kernel Team <kernel-team@...roid.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Patrick Bellasi <patrick.bellasi@...bug.net>
Subject: Re: [PATCH v2] sched: Fix out-of-bound access in uclamp

On 30/04/2021 16:16, Vincent Guittot wrote:
> On Fri, 30 Apr 2021 at 15:14, Quentin Perret <qperret@...gle.com> wrote:
>>
>> On Friday 30 Apr 2021 at 15:00:00 (+0200), Dietmar Eggemann wrote:
>>> On 30/04/2021 14:03, Vincent Guittot wrote:

[...]

>>> Looks like this will fix a lot of possible configs:
>>>
>>> nbr buckets 1-4, 7-8, 10-12, 14-17, *20*, 26, 29-32 ...
>>>
>>> We would still introduce larger last buckets, right?
>>
>> Indeed. The only better alternative I could see was to 'spread' the
>> error accross multiple buckets (e.g. make the last few buckets a bit
>> bigger instead of having all of it accumulated on the last one), but not
>> sure it is worth the overhead.
> 
> I don't think it's worth the overhead.

Me neither.

[...]