Re: crash during oom reaper

[Vegard Nossum]

On 12/16/2016 02:14 PM, Vegard Nossum wrote:
> On 12/16/2016 11:11 AM, Michal Hocko wrote:
> > On Fri 16-12-16 10:43:52, Vegard Nossum wrote:
> > [...]
> > > I don't think it's a bug in the OOM reaper itself, but either of the
> > > following two patches will fix the problem (without my understand how or
> > > why):
> > What is the atual crash?
>
> Annoyingly it doesn't seem to reproduce with the very latest
> linus/master, so maybe it's been fixed recently after all and I missed it.
>
> I've started a bisect to see what fixed it. Just in case, I added 4
> different crashes I saw with various kernels. I think there may have
> been a few others too (I remember seeing one in a page fault path), but
> these were the most frequent ones.

The bisect points to:

commit 6b94780e45c17b83e3e75f8aaca5a328db583c74
Author: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Date:   Thu Dec 8 17:56:54 2016 +0100

    sched/core: Use load_avg for selecting idlest group

as fixing the crash, which seems odd to me. The only bit that sticks out
from the changelog to me:

"""
For use case like hackbench, this enable the scheduler to select
different CPUs during the fork sequence and to spread tasks across the
system.
"""

Reverting it from linus/master doesn't reintroduce the crash, but the
commit just before (6b94780e4^) does crash, so I'm not sure what's going
on. Maybe the crash is just really sensitive to scheduling decisions or
something.


Vegard