linux-ext4 - Re: [PATCH] ext4: Fix lockdep warning when enabling MMP

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Message-ID: <ZE6YeCaQa01nAWYT@mit.edu>
Date:   Sun, 30 Apr 2023 12:34:00 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org, Christian Brauner <brauner@...nel.org>,
        syzbot+aacb82fca60873422114@...kaller.appspotmail.com,
        syzbot+6b7df7d5506b32467149@...kaller.appspotmail.com
Subject: Re: [PATCH] ext4: Fix lockdep warning when enabling MMP

On Tue, Apr 11, 2023 at 02:10:19PM +0200, Jan Kara wrote:
> When we enable MMP in ext4_multi_mount_protect() during mount or
> remount, we end up calling sb_start_write() from write_mmp_block(). This
> triggers lockdep warning because freeze protection ranks above s_umount
> semaphore we are holding during mount / remount. The problem is harmless
> because we are guaranteed the filesystem is not frozen during mount /
> remount but still let's fix the warning by not grabbing freeze
> protection from ext4_multi_mount_protect().
> 
> Reported-by: syzbot+aacb82fca60873422114@...kaller.appspotmail.com

I believe this is the wrong Reported-by.  The correct one looks like
it should be:

Reported-by: syzbot+6b7df7d5506b32467149@...kaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?id=ab7e5b6f400b7778d46f01841422e5718fb81843

It's also helpful to add a Link line to the Syzkaller dashboard to
make it easier to find the relevant Syzbot report.

I'll put this on my todo list to grab for the next batch of ext4
fixups.

						- Ted