2017-03-08 19:40:44

by Luis Henriques

Subject: NULL pointer dereference in cgroup

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,
--
Lu?s

2017-03-08 23:36:02

by Eric W. Biederman

Subject: Re: NULL pointer dereference in cgroup

Luis Henriques <[email protected]> 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

2017-03-09 09:08:35

by Luis Henriques

Subject: Re: NULL pointer dereference in cgroup

On Wed, Mar 08, 2017 at 05:30:29PM -0600, Eric W. Biederman wrote:
> Luis Henriques <[email protected]> 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,
--
Lu?s

2017-03-13 17:05:09

by Tejun Heo

Subject: Re: NULL pointer dereference in cgroup

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