linux-ext4 - Re: [PATCH 11/12] xfs: drop s_umount over opening the log and RT devices

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Message-ID: <20230805161904.GM11377@frogsfrogsfrogs>
Date:   Sat, 5 Aug 2023 09:19:04 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Jan Kara <jack@...e.cz>, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, Theodore Ts'o <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <chao@...nel.org>,
        Ryusuke Konishi <konishi.ryusuke@...il.com>,
        Jens Axboe <axboe@...nel.dk>, linux-btrfs@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
        linux-nilfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-block@...r.kernel.org
Subject: Re: [PATCH 11/12] xfs: drop s_umount over opening the log and RT
 devices

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@...nel.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?
>