linux-kernel - Re: NULL pointer dereference in pick_next_task

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Date:   Fri, 8 Nov 2019 11:58:10 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        linux-kernel@...r.kernel.org, aaron.lwe@...il.com,
        mingo@...nel.org, pauld@...hat.com, jdesfossez@...italocean.com,
        naravamudan@...italocean.com, vincent.guittot@...aro.org,
        dietmar.eggemann@....com, juri.lelli@...hat.com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        kernel-team@...roid.com, john.stultz@...aro.org
Subject: Re: NULL pointer dereference in pick_next_task_fair

On Friday 08 Nov 2019 at 11:47:44 (+0000), Valentin Schneider wrote:
> I think we can ignore RETRY_TASK because this happens before the picking loop,
> so we'll observe any new DL/RT task that got enqueued while newidle released
> the lock. This also means we can safely break the balance loop in
> pick_next_task() when we get RETRY_TASK, because we've got something to pick
> (some new RT/DL task).

Ah right, the second loop always iterates from DL, so that works.

> This wants a comment though, methinks.

+1 :)

Thanks,
Quentin