linux-kernel - Re: sched: fair: NULL ptr deref in check_preempt

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Date:	Mon, 17 Feb 2014 16:07:30 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Michael wang <wangyun@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
CC:	Dave Jones <davej@...hat.com>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: sched: fair: NULL ptr deref in check_preempt_wakeup

On 02/17/2014 03:11 AM, Michael wang wrote:
> Hi, Sasha
>
> On 02/16/2014 07:27 AM, Sasha Levin wrote:
>> Hi folks,
>>
>> While fuzzing with trinity inside a KVM tools guest running latest -next
>> kernel, I've
>> stumbled on the following:
>
> I've reproduced the same issue with tip/master, and below patch fixed the
> problem on my box along with some rcu stall info disappeared, would you
> like to have a try?
>
> BTW, I reproduced it by steps:
> 1. change current to RT
> 2. move to a different depth cpu-cgroup
> 3. change it back to FAIR
>
> Seems like it was caused by that RT has no task_move_group() implemented
> which could maintain depth, and that lead to a wrong depth after switched
> back to FAIR...

I *think* it works. There seems to be another sched issue that causes lockups,
so I can't say for certain that this one doesn't occur anymore.

I'm still working on collecting data for the other issue, I'll mail about it soon.


Thanks,
Sasha

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