Re: general protection fault in oom_unkillable_task

[Shakeel Butt]

On Sat, Jun 15, 2019 at 9:49 AM Tetsuo Handa
<penguin-kernel@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On 2019/06/16 1:11, Shakeel Butt wrote:
> > On Sat, Jun 15, 2019 at 6:50 AM Michal Hocko <mhocko@xxxxxxxxxx> 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))
>