From: David Rientjes <rientjes@google.com>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Michal Hocko <mhocko@kernel.org>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Andrew Morton <akpm@linux-foundation.org>,
Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
Oleg Nesterov <oleg@redhat.com>, Hugh Dickins <hughd@google.com>,
linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm, oom: allow oom reaper to race with exit_mmap
Date: Mon, 14 Aug 2017 17:20:58 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.10.1708141719090.50317@chino.kir.corp.google.com> (raw)
In-Reply-To: <20170726162912.GA29716@redhat.com>
On Wed, 26 Jul 2017, Andrea Arcangeli wrote:
> From 3d9001490ee1a71f39c7bfaf19e96821f9d3ff16 Mon Sep 17 00:00:00 2001
> From: Andrea Arcangeli <aarcange@redhat.com>
> Date: Tue, 25 Jul 2017 20:02:27 +0200
> Subject: [PATCH 1/1] mm: oom: let oom_reap_task and exit_mmap to run
> concurrently
>
> This is purely required because exit_aio() may block and exit_mmap() may
> never start, if the oom_reap_task cannot start running on a mm with
> mm_users == 0.
>
> At the same time if the OOM reaper doesn't wait at all for the memory
> of the current OOM candidate to be freed by exit_mmap->unmap_vmas, it
> would generate a spurious OOM kill.
>
> If it wasn't because of the exit_aio or similar blocking functions in
> the last mmput, it would be enough to change the oom_reap_task() in
> the case it finds mm_users == 0, to wait for a timeout or to wait for
> __mmput to set MMF_OOM_SKIP itself, but it's not just exit_mmap the
> problem here so the concurrency of exit_mmap and oom_reap_task is
> apparently warranted.
>
> It's a non standard runtime, exit_mmap() runs without mmap_sem, and
> oom_reap_task runs with the mmap_sem for reading as usual (kind of
> MADV_DONTNEED).
>
> The race between the two is solved with a combination of
> tsk_is_oom_victim() (serialized by task_lock) and MMF_OOM_SKIP
> (serialized by a dummy down_write/up_write cycle on the same lines of
> the ksm_exit method).
>
> If the oom_reap_task() may be running concurrently during exit_mmap,
> exit_mmap will wait it to finish in down_write (before taking down mm
> structures that would make the oom_reap_task fail with use after
> free).
>
> If exit_mmap comes first, oom_reap_task() will skip the mm if
> MMF_OOM_SKIP is already set and in turn all memory is already freed
> and furthermore the mm data structures may already have been taken
> down by free_pgtables.
>
> Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
With your follow-up one liner to include linux/oom.h folded in:
Tested-by: David Rientjes <rientjes@google.com>
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next prev parent reply other threads:[~2017-08-15 0:21 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-24 7:23 [PATCH] mm, oom: allow oom reaper to race with exit_mmap Michal Hocko
2017-07-24 14:00 ` Kirill A. Shutemov
2017-07-24 14:15 ` Michal Hocko
2017-07-24 14:51 ` Kirill A. Shutemov
2017-07-24 16:11 ` Michal Hocko
2017-07-25 14:17 ` Kirill A. Shutemov
2017-07-25 14:26 ` Michal Hocko
2017-07-25 15:07 ` Kirill A. Shutemov
2017-07-25 15:15 ` Michal Hocko
2017-07-25 14:26 ` Michal Hocko
2017-07-25 15:17 ` Kirill A. Shutemov
2017-07-25 15:23 ` Michal Hocko
2017-07-25 15:31 ` Kirill A. Shutemov
2017-07-25 16:04 ` Michal Hocko
2017-07-25 19:19 ` Andrea Arcangeli
2017-07-26 5:45 ` Michal Hocko
2017-07-26 16:29 ` Andrea Arcangeli
2017-07-26 16:43 ` Andrea Arcangeli
2017-07-27 6:50 ` Michal Hocko
2017-07-27 14:55 ` Andrea Arcangeli
2017-07-28 6:23 ` Michal Hocko
2017-07-28 1:58 ` [PATCH 1/1] mm: oom: let oom_reap_task and exit_mmap to run kbuild test robot
2017-08-15 0:20 ` David Rientjes [this message]
2017-07-24 15:27 ` [PATCH] mm, oom: allow oom reaper to race with exit_mmap Michal Hocko
2017-07-24 16:42 ` kbuild test robot
2017-07-24 18:12 ` Michal Hocko
2017-07-25 15:26 ` Andrea Arcangeli
2017-07-25 15:45 ` Michal Hocko
2017-07-25 18:26 ` Andrea Arcangeli
2017-07-26 5:45 ` Michal Hocko
2017-07-26 16:39 ` Andrea Arcangeli
2017-07-27 6:32 ` Michal Hocko
2017-08-10 8:16 Michal Hocko
2017-08-10 18:05 ` Andrea Arcangeli
2017-08-10 18:51 ` Michal Hocko
2017-08-10 20:36 ` Michal Hocko
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