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

Signed-off-by: NChris Mason <chris.mason@oracle.com>

fs/btrfs/disk-io.c

@@ -1739,6 +1739,7 @@ int close_ctree(struct btrfs_root *root)
 		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);

fs/btrfs/inode.c

@@ -2092,6 +2092,9 @@ int btrfs_write_inode(struct inode *inode, int wait)
 	struct btrfs_trans_handle *trans;
 	int ret = 0;
 
+	if (root->fs_info->closing > 1)
+		return 0;
+
 	if (wait) {
 		trans = btrfs_join_transaction(root, 1);
 		btrfs_set_trans_block_group(trans, inode);