linux-kernel - Re: general protection fault in oom_unkillable

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Date:   Mon, 17 Jun 2019 18:56:47 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Michal Hocko <mhocko@...nel.org>,
        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>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        yuzhoujian@...ichuxing.com
Subject: Re: general protection fault in oom_unkillable_task

On 2019/06/17 15:33, Michal Hocko wrote:
> 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?

I posted a patch that (as a side effect) avoids oom_unkillable_task() from dump_tasks() at
https://lore.kernel.org/linux-mm/1558519686-16057-2-git-send-email-penguin-kernel@I-love.SAKURA.ne.jp/ .
What do you think?