From: David Howells <dhowe...@redhat.com>

[ Upstream commit dd7bc8158b413e0b580c491e8bd18cb91057c7c2 ]

Commit 6fcf0c72e4b9, a fix to get_tree_bdev() put a missing blkdev_put() in
the wrong place, before a warnf() that displays the bdev under
consideration rather after it.

This results in a silent lockup in printk("%pg") called via warnf() from
get_tree_bdev() under some circumstances when there's a race with the
blockdev being frozen.  This can be caused by xfstests/tests/generic/085 in
combination with Lukas Czerner's ext4 mount API conversion patchset.  It
looks like it ought to occur with other users of get_tree_bdev() such as
XFS, but apparently doesn't.

Fix this by switching the order of the lines.

Fixes: 6fcf0c72e4b9 ("vfs: add missing blkdev_put() in get_tree_bdev()")
Reported-by: Lukas Czerner <lczer...@redhat.com>
Signed-off-by: David Howells <dhowe...@redhat.com>
cc: Ian Kent <ra...@themaw.net>
cc: Al Viro <v...@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Sasha Levin <sas...@kernel.org>
---
 fs/super.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/super.c b/fs/super.c
index cd352530eca90..a288cd60d2aed 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1302,8 +1302,8 @@ int get_tree_bdev(struct fs_context *fc,
        mutex_lock(&bdev->bd_fsfreeze_mutex);
        if (bdev->bd_fsfreeze_count > 0) {
                mutex_unlock(&bdev->bd_fsfreeze_mutex);
-               blkdev_put(bdev, mode);
                warnf(fc, "%pg: Can't mount, blockdev is frozen", bdev);
+               blkdev_put(bdev, mode);
                return -EBUSY;
        }
 
-- 
2.20.1

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