linux-kernel - Re: general protection fault in oom_unkillable

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Date:   Mon, 17 Jun 2019 08:33:19 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     syzbot <syzbot+d0fc9d3c166bc5e4a94b@...kaller.appspotmail.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Roman Gushchin <guro@...com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jérôme Glisse <jglisse@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        yuzhoujian@...ichuxing.com
Subject: Re: general protection fault in oom_unkillable_task

On Sat 15-06-19 09:11:37, Shakeel Butt wrote:
> On Sat, Jun 15, 2019 at 6:50 AM Michal Hocko <mhocko@...nel.org> wrote:
[...]
> > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
> > index 5a58778c91d4..43eb479a5dc7 100644
> > --- a/mm/oom_kill.c
> > +++ b/mm/oom_kill.c
> > @@ -161,8 +161,8 @@ static bool oom_unkillable_task(struct task_struct *p,
> >                 return true;
> >
> >         /* When mem_cgroup_out_of_memory() and p is not member of the group */
> > -       if (memcg && !task_in_mem_cgroup(p, memcg))
> > -               return true;
> > +       if (memcg)
> > +               return false;
> 
> This will break the dump_tasks() usage of oom_unkillable_task(). We
> can change dump_tasks() to traverse processes like
> mem_cgroup_scan_tasks() for memcg OOMs.

Right you are. Doing a similar trick to the oom victim selection is
indeed better. We should really strive to not doing a global process
iteration when we can do a targeted scan. Care to send a patch?

Thanks!
-- 
Michal Hocko
SUSE Labs