Re: [PATCH] mm,oom: Set ->signal->oom_mm to all thread groups sharing the victim's mm.

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

Michal Hocko wrote:
> On Tue 28-11-17 21:41:28, Tetsuo Handa wrote:
> > Due to commit 696453e66630ad45 ("mm, oom: task_will_free_mem should skip
> > oom_reaped tasks") and patch "mm,oom: Use ALLOC_OOM for OOM victim's last
> > second allocation.", thread groups sharing the OOM victim's mm without
> > setting ->signal->oom_mm before task_will_free_mem(current) is called
> > might fail to try ALLOC_OOM allocation attempt.
> 
> Look, this is getting insane. The code complexity grows without any
> real users asking for this.

This is the result of applying "mm,oom: Use ALLOC_OOM for OOM victim's
last second allocation." instead of "mm, oom: task_will_free_mem(current)
should ignore MMF_OOM_SKIP for once." More you go per-mm oriented rather
than per-signal oriented or per-thread oriented, more atomicity will be
needed.

>                             While this might look like an interesting
> excercise to you I really hate the direction you are heading. This code
> will always be just a heuristic and the more complicated it will be the
> bigger chances of other side effects there will be as well.
> 
> So NACK to this unless I you can show a _real_ usecase that would
> _suffer_ by this corner case.

But we send SIGKILL to all thread groups sharing the OOM victim's memory.
This means that (though it might be artificial/malicious) there can be
programs which hit this corner case.

This resembles setting TIF_MEMDIE to all threads at mark_oom_victim(),
and (if I understand correctly) cgroup-aware OOM killer discussion is
after all trying to split oom_kill_process() into "printk()" part and
"non-printk()" part.

Also, please don't preserve outdated comments.

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