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From:   Christoph Hellwig <hch@lst.de>
To:     Al Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>
Cc:     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>,
        "Darrick J. Wong" <djwong@kernel.org>,
        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
Subject: [PATCH 11/12] xfs: drop s_umount over opening the log and RT devices
Date:   Wed,  2 Aug 2023 17:41:30 +0200
Message-Id: <20230802154131.2221419-12-hch@lst.de>
In-Reply-To: <20230802154131.2221419-1-hch@lst.de>
References: <20230802154131.2221419-1-hch@lst.de>
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Just like get_tree_bdev needs to drop s_umount when opening the main
device, we need to do the same for the xfs log and RT devices 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@lst.de>
---
 fs/xfs/xfs_super.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 8185102431301d..d5042419ed9997 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -448,17 +448,21 @@ STATIC int
 xfs_open_devices(
 	struct xfs_mount	*mp)
 {
-	struct block_device	*ddev = mp->m_super->s_bdev;
+	struct super_block	*sb = mp->m_super;
+	struct block_device	*ddev = sb->s_bdev;
 	struct block_device	*logdev = NULL, *rtdev = NULL;
 	int			error;
 
+	/* see get_tree_bdev why this is needed and safe */
+	up_write(&sb->s_umount);
+
 	/*
 	 * Open real time and log devices - order is important.
 	 */
 	if (mp->m_logname) {
 		error = xfs_blkdev_get(mp, mp->m_logname, &logdev);
 		if (error)
-			return error;
+			goto out_unlock;
 	}
 
 	if (mp->m_rtname) {
@@ -496,7 +500,10 @@ xfs_open_devices(
 		mp->m_logdev_targp = mp->m_ddev_targp;
 	}
 
-	return 0;
+	error = 0;
+out_unlock:
+	down_write(&sb->s_umount);
+	return error;
 
  out_free_rtdev_targ:
 	if (mp->m_rtdev_targp)
@@ -508,7 +515,7 @@ xfs_open_devices(
  out_close_logdev:
 	if (logdev && logdev != ddev)
 		xfs_blkdev_put(mp, logdev);
-	return error;
+	goto out_unlock;
 }
 
 /*
-- 
2.39.2