linux-ext4 - Re: [PATCH 09/12] ext4: drop s_umount over opening the log device

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Date:   Thu, 3 Aug 2023 15:25:49 +0200
From:   Jan Kara <jack@...e.cz>
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>,
        "Darrick J. Wong" <djwong@...nel.org>,
        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 09/12] ext4: drop s_umount over opening the log device

On Wed 02-08-23 17:41:28, Christoph Hellwig wrote:
> Just like get_tree_bdev needs to drop s_umount when opening the main
> device, we need to do the same for the ext4 log device to avoid a
> potential lock order reversal with s_unmount for the mark_dead path.
> 
> It might be preferable to just drop s_umount over ->fill_super entirely,
> but that will require a fairly massive audit first, so we'll do the easy
> version here first.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
>  fs/ext4/super.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index 193d665813b611..2ccb19d345c6dd 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -5854,7 +5854,10 @@ static journal_t *ext4_get_dev_journal(struct super_block *sb,
>  	if (WARN_ON_ONCE(!ext4_has_feature_journal(sb)))
>  		return NULL;
>  
> +	/* see get_tree_bdev why this is needed and safe */
> +	up_write(&sb->s_umount);
>  	bdev = ext4_blkdev_get(j_dev, sb);
> +	down_write(&sb->s_umount);
>  	if (bdev == NULL)
>  		return NULL;
>  
> -- 
> 2.39.2
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR