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

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Date:   Sun, 30 Apr 2023 12:44:15 -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,
        syzkaller-bugs@...glegroups.com
Subject: Re: [PATCH] ext4: Fix lockdep warning when enabling MMP

On Sun, Apr 30, 2023 at 12:34:00PM -0400, Theodore Ts'o wrote:
> 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: ...

By the way, I noticed because I was browsing the syzbot dashboard for
the ext4 subsystem, and the Syzbot page for "possible deadlock in
sys_quotactl_fd"[1], I saw a discussion link to lore for the patch
"[PATCH] ext4: Fix lockdep warning when enabling MMP", and said,
"Hmm.... that looks wrong."  :-)

[1] https://syzkaller.appspot.com/bug?id=1680b22e0e5eb9245a6faff10221ed76b8c5eb81

Anyway, thanks to the Syzbot team for adding Disscusion links to the
Syzbot pages.  It makes it a lot easier to find discussions related to
a particular issue.

Note: you can also manually add a thread to the discussions section by
simply adding a CC to the Reported-by link for the particular issue (for
example, "Cc: syzbot+aacb82fca60873422114@...kaller.appspotmail.com").

Cheers,

						- Ted