linux-kernel - Re: yama: lockdep warning on yama_ptracer

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Message-ID: <50AA818F.4020900@oracle.com>
Date:	Mon, 19 Nov 2012 13:59:27 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Kees Cook <keescook@...omium.org>
CC:	Sasha Levin <levinsasha928@...il.com>, james.l.morris@...cle.com,
	John Johansen <john.johansen@...onical.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-security-module@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dave Jones <davej@...hat.com>
Subject: Re: yama: lockdep warning on yama_ptracer_del

On 11/19/2012 11:23 AM, Kees Cook wrote:
> On Sun, Nov 18, 2012 at 8:05 PM, Sasha Levin <levinsasha928@...il.com> wrote:
>> Hi Kees,
>>
>> On Thu, Oct 18, 2012 at 6:39 PM, Kees Cook <keescook@...omium.org> wrote:
>>> On Wed, Oct 17, 2012 at 8:10 PM, Sasha Levin <sasha.levin@...cle.com> wrote:
>>>> Hi all,
>>>>
>>>> I was fuzzing with trinity within a KVM tools guest (lkvm) on a linux-next kernel, and got the
>>>> following dump which I believe to be noise due to how the timers work - but I'm not 100% sure.
>>>> ...
>>>> [  954.674123]  Possible interrupt unsafe locking scenario:
>>>> [  954.674123]
>>>> [  954.674123]        CPU0                    CPU1
>>>> [  954.674123]        ----                    ----
>>>> [  954.674123]   lock(ptracer_relations_lock);
>>>> [  954.674123]                                local_irq_disable();
>>>> [  954.674123]                                lock(&(&new_timer->it_lock)->rlock);
>>>> [  954.674123]                                lock(ptracer_relations_lock);
>>>> [  954.674123]   <Interrupt>
>>>> [  954.674123]     lock(&(&new_timer->it_lock)->rlock);
>>>> [  954.674123]
>>>> [  954.674123]  *** DEADLOCK ***
>>>
>>> I've been wanting to get rid of the Yama ptracer_relations_lock
>>> anyway, so maybe I should do that now just to avoid this case at all?
>>
>> I still see this one in -rc6, is there anything to get rid of it
>> before the release?
> 
> I'm not sure about changes to the timer locks, but I haven't been able
> to get rid of the locking on Yama's task_free path. I did send a patch
> to get rid of locking during a read, though:
> 
> https://lkml.org/lkml/2012/11/13/808

Aw, alrighty. It didn't make it to -next yet though.

I'll add the patch to my tree and test with it.


Thanks,
Sasha

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