Btrfs: Add the ability to find and remove dead roots after a crash.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 6d031da..9d2a0a3 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2028,6 +2028,8 @@
 
 	btrfs_set_root_blocknr(&root_item, bh_blocknr(subvol));
 	btrfs_set_root_refs(&root_item, 1);
+	memset(&root_item.drop_progress, 0, sizeof(root_item.drop_progress));
+	root_item.drop_level = 0;
 	brelse(subvol);
 	subvol = NULL;