linux-kernel - Re: INFO: task hung in fsnotify_connector_destroy

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Message-ID: <19a86705-308f-17af-f5d2-9abb150d2bdb@i-love.sakura.ne.jp>
Date:   Tue, 25 Sep 2018 21:30:26 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
To:     Petr Mladek <pmladek@...e.com>, Jiri Kosina <jikos@...nel.org>
Cc:     Amir Goldstein <amir73il@...il.com>,
        syzbot+6fb572170402d311dd39@...kaller.appspotmail.com,
        Jan Kara <jack@...e.cz>, syzkaller-bugs@...glegroups.com,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: Re: INFO: task hung in fsnotify_connector_destroy_workfn (2)

On 2018/09/25 17:55, Petr Mladek wrote:
>> I guess the patch below fixes it, however the kworker should not really be 
>> blocked by this I think ... adding a few more printk folks to double-check 
>> why the kworker would get stuck due to massive printk() flood.
> 
> It seems that the many printk() calls just delay the entire
> process and rcu gets blocked for too long. The messages are
> the same all the time. So some rate limiting looks like
> a reasonable solution.
> 

Yes. Commit 128f380410350012 ("android: binder: Rate-limit debug and userspace triggered err msgs")
chose ratelimiting as a fix for https://syzkaller.appspot.com/bug?id=0e75779a6f0faac461510c6330514e8f0e893038 .

Since syzbot did not reproduce the problem with Jiri's patch applied,
I think we can apply Jiri's patch as a fix for this problem.