Re: [PATCH 2/6] mm,oom: don't abort on exiting processes when selecting a victim.

[Tetsuo Handa]

Michal Hocko wrote:
> On Wed 17-02-16 19:30:41, Tetsuo Handa wrote:
> > >From 22bd036766e70f0df38c38f3ecc226e857d20faf Mon Sep 17 00:00:00 2001
> > From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
> > Date: Wed, 17 Feb 2016 16:30:59 +0900
> > Subject: [PATCH 2/6] mm,oom: don't abort on exiting processes when selecting a victim.
> > 
> > Currently, oom_scan_process_thread() returns OOM_SCAN_ABORT when there
> > is a thread which is exiting. But it is possible that that thread is
> > blocked at down_read(&mm->mmap_sem) in exit_mm() called from do_exit()
> > whereas one of threads sharing that memory is doing a GFP_KERNEL
> > allocation between down_write(&mm->mmap_sem) and up_write(&mm->mmap_sem)
> > (e.g. mmap()). Under such situation, the OOM killer does not choose a
> > victim, which results in silent OOM livelock problem.
> 
> Again, such a thread/task will have fatal_signal_pending and so have
> access to memory reserves. So the text is slightly misleading imho.
> Sure if the memory reserves are depleted then we will not move on but
> then it is not clear whether the current patch helps either.

I don't think so.
Please see http://lkml.kernel.org/r/201602151958.HCJ48972.FFOFOLMHSQVJtO@xxxxxxxxxxxxxxxxxxx .
There is a race window before such a thread/task receives SIGKILL.