From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Darrick J. Wong" <djwong@kernel.org>
Subject: Re: [PATCH 11/12] xfs: drop s_umount over opening the log and RT
 devices
Date: Sat, 5 Aug 2023 09:19:04 -0700
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To: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>, Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>, Chris Mason <clm@fb.com>, Josef Bacik <josef@toxicpanda.com>, David Sterba <dsterba@suse.com>, Theodore Ts'o <tytso@mit.edu>, Andreas Dilger <adilger.kernel@dilger.ca>, Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <chao@kernel.org>, Ryusuke Konishi <konishi.ryusuke@gmail.com>, Jens Axboe <axboe@kernel.dk>, linux-btrfs@vger.kernel.org, linux-ext4@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, linux-nilfs@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org, linux-block@vger.kernel.org

On Sat, Aug 05, 2023 at 10:32:39AM +0200, Christoph Hellwig wrote:
> On Wed, Aug 02, 2023 at 09:32:19AM -0700, Darrick J. Wong wrote:
> > > +	/* see get_tree_bdev why this is needed and safe */
> > 
> > Which part of get_tree_bdev?  Is it this?
> > 
> > 		/*
> > 		 * s_umount nests inside open_mutex during
> > 		 * __invalidate_device().  blkdev_put() acquires
> > 		 * open_mutex and can't be called under s_umount.  Drop
> > 		 * s_umount temporarily.  This is safe as we're
> > 		 * holding an active reference.
> > 		 */
> > 		up_write(&s->s_umount);
> > 		blkdev_put(bdev, fc->fs_type);
> > 		down_write(&s->s_umount);
> 
> Yes.  With the refactoring earlier in the series get_tree_bdev should
> be trivial enough to not need a more specific reference.  If you
> think there's a better way to refer to it I can update the comment,
> though.

How about:

	/*
	 * blkdev_put can't be called under s_umount, see the comment in
	 * get_tree_bdev for more details
	 */

with that and the label name change,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D


> > >  		mp->m_logdev_targp = mp->m_ddev_targp;
> > >  	}
> > >  
> > > -	return 0;
> > > +	error = 0;
> > > +out_unlock:
> > > +	down_write(&sb->s_umount);
> > 
> > Isn't down_write taking s_umount?  I think the label should be
> > out_relock or something less misleading.
> 
> Agreed.  Christian, can you just change this in your branch, or should
> I send an incremental patch?
>