On Mon, Aug 20, 2018 at 08:02:30PM +0900, Tetsuo Handa wrote:

On 2018/08/20 19:53, Michal Hocko wrote:

quoted

On Mon 20-08-18 19:37:45, Tetsuo Handa wrote:

quoted

Commit 696453e66630ad45 ("mm, oom: task_will_free_mem should skip
oom_reaped tasks") changed to select next OOM victim as soon as
MMF_OOM_SKIP is set. But since OOM victims can try ALLOC_OOM allocation
and then give up (if !memcg OOM) or can use forced charge and then retry
(if memcg OOM), OOM victims do not need to select next OOM victim unless
they are doing __GFP_NOFAIL allocations.

I do not like this at all. It seems hackish to say the least. And more
importantly...

quoted

This is a quick mitigation because syzbot is hitting WARN(1) caused by
this race window [1]. More robust fix (e.g. make it possible to reclaim
more memory before MMF_OOM_SKIP is set, wait for some more after
MMF_OOM_SKIP is set) is a future work.

.. there is already a patch (by Johannes) for that warning IIRC.

You mean http://lkml.kernel.org/r/20180808144515.GA9276@cmpxchg.org ?
But I can't find that patch in linux-next.git . And as far as I know,
no patch was sent to linux.git for handling this problem. Therefore,
I wrote this patch so that we can apply for 4.19-rc1.

I assume it'll go in soon, it's the first patch in the -mm tree:

$ cat http://ozlabs.org/~akpm/mmots/series
origin.patch
#NEXT_PATCHES_START linus
#NEXT_PATCHES_END
#NEXT_PATCHES_START mainline-urgent (this week, approximately)
#NEXT_PATCHES_END
#NEXT_PATCHES_START mainline-later (next week, approximately)
mm-memcontrol-print-proper-oom-header-when-no-eligible-victim-left.patch