[patch] fs: fix use after free in get_tree_bdev

[Jeff Moyer <jmoyer@xxxxxxxxxx>]

Commit 6fcf0c72e4b9 ("vfs: add missing blkdev_put() in get_tree_bdev()")
introduced a use-after-free of the bdev.  This was caught by fstests
generic/085, which now results in a kernel panic.  Fix it.

Cc: stable@xxxxxxxxxxxxxxx # v5.4+
Fixes: 6fcf0c72e4b9 ("vfs: add missing blkdev_put() in get_tree_bdev()")
Signed-off-by: Jeff Moyer <jmoyer@xxxxxxxxxx>

diff --git a/fs/super.c b/fs/super.c
index cd352530eca9..a288cd60d2ae 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;
 	}