Btrfs: Avoid calling into the FS for the final iput on fake root inodes

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 7654368..56c54a4 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1739,6 +1739,7 @@
 		free_extent_buffer(root->fs_info->dev_root->node);
 
 	btrfs_free_block_groups(root->fs_info);
+	fs_info->closing = 2;
 	del_fs_roots(fs_info);
 
 	filemap_write_and_wait(fs_info->btree_inode->i_mapping);