linux-ext4 - Re: [PATCH] ext4: avoid huge mmp update interval value

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Message-ID: <YQw/2PuZ8z22Qice@mit.edu>
Date:   Thu, 5 Aug 2021 15:45:28 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Pavel Skripkin <paskripkin@...il.com>
Cc:     adilger.kernel@...ger.ca, johann@...mcloud.com,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        syzbot+c9ff4822a62eee994ea3@...kaller.appspotmail.com
Subject: Re: [PATCH] ext4: avoid huge mmp update interval value

On Thu, Aug 05, 2021 at 06:14:18PM +0300, Pavel Skripkin wrote:
> Syzbot reported task hung bug in ext4_fill_super(). The problem was in
> too huge mmp update interval.
> 
> Syzkaller reproducer setted s_mmp_update_interval to 39785 seconds. This
> update interaval is unreasonable huge and it can cause tasks to hung on
> kthread_stop() call, since it will wait until timeout timer expires.

I must be missing something.  kthread_stop() should wake up the
kmmpd() thread, which should see kthread_should_stop(), and then it
should exit.  What is causing it to wait until the timeout timer
expires?

					- Ted