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

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Date:   Wed,  2 Aug 2023 17:41:28 +0200
From:   Christoph Hellwig <hch@....de>
To:     Al Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>
Cc:     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: [PATCH 09/12] ext4: drop s_umount over opening the log device

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>
---
 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