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Subject: Re: WARNING in try_charge
To:     mhocko@kernel.org, David Rientjes <rientjes@google.com>
Cc:     syzbot <syzbot+bab151e82a4e973fa325@syzkaller.appspotmail.com>,
        cgroups@vger.kernel.org, hannes@cmpxchg.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org,
        syzkaller-bugs@googlegroups.com, vdavydov.dev@gmail.com
References: <0000000000005e979605729c1564@google.com>
 <4660f164-b3e3-28a0-9898-718c5fa6b84d@I-love.SAKURA.ne.jp>
From:   Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Message-ID: <3d4ca33d-54cb-ca5d-95cc-034fe62e5a35@I-love.SAKURA.ne.jp>
Date:   Sun, 5 Aug 2018 20:33:11 +0900
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On 2018/08/04 22:45, Tetsuo Handa wrote:
> syzbot is hitting WARN(1) because of mem_cgroup_out_of_memory() == false.

Since syzbot found a syz reproducer, I asked syzbot to try two patches.

Setting MMF_OOM_SKIP under oom_lock to prevent from races
( https://syzkaller.appspot.com/x/patch.diff?x=10fb3fd0400000 ) was not sufficient.

Waiting until __mmput() completes (with timeout using OOM score feedback)
( https://syzkaller.appspot.com/x/patch.diff?x=101e449c400000 ) solved this race.