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

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Message-ID: <20230502095124.gzjjnmfquciimucf@quack3>
Date:   Tue, 2 May 2023 11:51:24 +0200
From:   Jan Kara <jack@...e.cz>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Jan Kara <jack@...e.cz>, 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 Sun 30-04-23 12:34:00, 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:
> 
> Reported-by: syzbot+6b7df7d5506b32467149@...kaller.appspotmail.com
> Link: https://syzkaller.appspot.com/bug?id=ab7e5b6f400b7778d46f01841422e5718fb81843

Well, one of the reports of this problem has also the ID I have referenced
(https://syzkaller.appspot.com/bug?extid=6b7df7d5506b32467149).  There are
apparently multiple ones...

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

Right, I'll do that next time. Thanks for the idea.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR