NULL pointer dereference in cgroup

NULL pointer dereference in cgroup

[Luis Henriques]

Hi,

I've seen this only once, and can't reproduce it.  But here it is anyway:

https://postimg.org/image/pn94k1yov

(Not sure png files are accepted on LKML.)

This occurred in a VM while booting 4.11.0-rc1

Cheers,
--
Luís

Re: NULL pointer dereference in cgroup

[Eric W. Biederman]

Luis Henriques <henrix@camandro.org> writes:

> Hi,
>
> I've seen this only once, and can't reproduce it.  But here it is anyway:
>
> https://postimg.org/image/pn94k1yov
>
> (Not sure png files are accepted on LKML.)
>
> This occurred in a VM while booting 4.11.0-rc1

Any idea what was happening when you triggered this?  A little context
usually helps quite a bit when tracking things like this down.

Eric

Re: NULL pointer dereference in cgroup

[Luis Henriques]

On Wed, Mar 08, 2017 at 05:30:29PM -0600, Eric W. Biederman wrote:
> Luis Henriques <henrix@camandro.org> writes:
> 
> > Hi,
> >
> > I've seen this only once, and can't reproduce it.  But here it is anyway:
> >
> > https://postimg.org/image/pn94k1yov
> >
> > (Not sure png files are accepted on LKML.)
> >
> > This occurred in a VM while booting 4.11.0-rc1
> 
> Any idea what was happening when you triggered this?  A little context
> usually helps quite a bit when tracking things like this down.

Sorry, but I don't have more details.  As I said, I just booted a VM with
this kernel and when I looked again I saw this.  I assumed this happen
during boot.  I had used this kernel in this VM before without problems,
and I still use it -- only saw this once.

I'll keep an eye on it and see if I can gather more info if it happens
again.

Cheers,
--
Luís

Re: NULL pointer dereference in cgroup

[Tejun Heo]

Hello,

On Wed, Mar 08, 2017 at 06:46:16PM +0000, Luis Henriques wrote:
> Hi,
> 
> I've seen this only once, and can't reproduce it.  But here it is anyway:
> 
> https://postimg.org/image/pn94k1yov
> 
> (Not sure png files are accepted on LKML.)
> 
> This occurred in a VM while booting 4.11.0-rc1

It was trying to migrate a process and encountered a NULL deref while
trying to find the destination css_set.  Unfortunately, it's difficult
to tell what went wrong with just the posted backtrace.  If you built
the kernel with debuginfo, the output of addr2line could help quite a
bit.

Thanks.

-- 
tejun