linux-kernel - Re: INFO: rcu detected stall in shmem

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Date:   Thu, 11 Oct 2018 10:17:30 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
To:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        syzbot <syzbot+77e6b28a7a7106ad0def@...kaller.appspotmail.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>, guro@...com,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        David Rientjes <rientjes@...gle.com>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Yang Shi <yang.s@...baba-inc.com>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Petr Mladek <pmladek@...e.com>
Subject: Re: INFO: rcu detected stall in shmem_fault

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