linux-kernel - Re: general protection fault in oom_unkillable

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Message-ID: <5bb1fe5d-f0e1-678b-4f64-82c8d5d81f61@i-love.sakura.ne.jp>
Date:   Sun, 16 Jun 2019 01:48:31 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...nel.org>
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 2019/06/16 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. 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))