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

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Date:   Wed,  2 Aug 2023 17:41:30 +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 11/12] xfs: drop s_umount over opening the log and RT devices

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@....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