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Subject: Re: [sched] 10e7071b2f: BUG:kernel_NULL_pointer_dereference,address
To:     Quentin Perret <qperret@google.com>
Cc:     kernel test robot <lkp@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Aaron Lu <aaron.lwe@gmail.com>, Phil Auld <pauld@redhat.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
        Nishanth Aravamudan <naravamudan@digitalocean.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>, lkp@01.org
References: <20191107090808.GW29418@shao2-debian>
 <fc023bbd-e282-c986-b43b-18ac31b2e362@arm.com>
 <20191107120922.GA82729@google.com> <20191107121551.GB82729@google.com>
From:   Valentin Schneider <valentin.schneider@arm.com>
Message-ID: <6a23a062-9b82-668d-7945-8da34f4dc5f0@arm.com>
Date:   Thu, 7 Nov 2019 12:37:09 +0000
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On 07/11/2019 12:15, Quentin Perret wrote:
> On Thursday 07 Nov 2019 at 12:09:22 (+0000), Quentin Perret wrote:
>> sched_move_task() follows what Peter called the 'change' pattern, so I'm
>> thinking this is most likely the same issue. Dropping the lock causes an
>> unmitigated race between sched_move_task() and pick_next_task_dl(), so
>> hilarity ensues (set_next_task() being called twice for instance).
> 
> Bah, scratch that. 10e7071b2 is clearly before the pick_next_task()
> rework, so that's not it :(
> 

And besides we don't drop the lock until reaching pick_next_task_fair(),
and the splat says it died on pick_next_task_dl() which happens earlier.

> Quentin
>