linux-kernel - Re: general protection fault in oom_unkillable

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CALvZod4etSv9Hv4UD=E6D7U4vyjCqhxQgq61AoTUCd+VubofFg@mail.gmail.com>
Date:   Sat, 15 Jun 2019 11:50:31 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Michal Hocko <mhocko@...nel.org>,
        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>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        yuzhoujian@...ichuxing.com
Subject: Re: general protection fault in oom_unkillable_task

On Sat, Jun 15, 2019 at 9:49 AM Tetsuo Handa
<penguin-kernel@...ove.sakura.ne.jp> wrote:
>
> On 2019/06/16 1:11, 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.
>
> While dump_tasks() traverses only each thread group, mem_cgroup_scan_tasks()
> traverses each thread.

I think mem_cgroup_scan_tasks() traversing threads is not intentional
and css_task_iter_start in it should use CSS_TASK_ITER_PROCS as the
oom killer only cares about the processes or more specifically
mm_struct (though two different thread groups can have same mm_struct
but that is fine).

> To avoid printk()ing all threads in a thread group,
> moving that check to
>
>         if (memcg && !task_in_mem_cgroup(p, memcg))
>                 continue;
>
> in dump_tasks() is better?
>
> >
> >>
> >>         /* p may not have freeable memory in nodemask */
> >>         if (!has_intersects_mems_allowed(p, nodemask))
>