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Date: Thu, 11 Oct 2018 10:17:30 +0900
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: INFO: rcu detected stall in shmem_fault
Message-ID: <20181011011730.GA728@jagdpanzerIV>
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To: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Dmitry Vyukov <dvyukov@google.com>, Michal Hocko <mhocko@kernel.org>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, syzbot <syzbot+77e6b28a7a7106ad0def@syzkaller.appspotmail.com>, Johannes Weiner <hannes@cmpxchg.org>, Andrew Morton <akpm@linux-foundation.org>, guro@fb.com, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, LKML <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org>, David Rientjes <rientjes@google.com>, syzkaller-bugs <syzkaller-bugs@googlegroups.com>, Yang Shi <yang.s@alibaba-inc.com>, Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>, Petr Mladek <pmladek@suse.com>

On (10/10/18 22:10), Tetsuo Handa wrote:
> >> I've found at least 1 place that uses DEFAULT_RATELIMIT_INTERVAL*10:
> >> https://elixir.bootlin.com/linux/latest/source/fs/btrfs/extent-tree.c#L8365
> >> Probably we need something similar here.
> 
> Since printk() is a significantly CPU consuming operation, I think that what
> we need to guarantee is interval between the end of an OOM killer messages
> and the beginning of next OOM killer messages is large enough. For example,
> setup a timer with 5 seconds timeout upon the end of an OOM killer messages
> and check whether the timer already fired upon the beginning of next OOM killer
> messages.

Hmm, there is no way to make sure that previous OOM report made it to
consoles. So maybe timer approach will be as good as rate-limiting.

	-ss