radix-tree: rewrite __radix_tree_lookup

			  struct radix_tree_node **nodep, void ***slotp)

{

	struct radix_tree_node *node, *parent;

	unsigned int height, shift;

	unsigned long maxindex;

	unsigned int shift;

	void **slot;

	node = rcu_dereference_raw(root->rnode);

	if (node == NULL)

		return NULL;

	if (!radix_tree_is_indirect_ptr(node)) {

		if (index > 0)

			return NULL;

		if (nodep)

			*nodep = NULL;

		if (slotp)

			*slotp = (void **)&root->rnode;

		return node;

	}

	node = indirect_to_ptr(node);

	height = node->path & RADIX_TREE_HEIGHT_MASK;

	if (index > radix_tree_maxindex(height))

 restart:

	parent = NULL;

	slot = (void **)&root->rnode;

	shift = radix_tree_load_root(root, &node, &maxindex);

	if (index > maxindex)

		return NULL;

	shift = (height-1) * RADIX_TREE_MAP_SHIFT;

	do {

		parent = node;

		slot = node->slots + ((index >> shift) & RADIX_TREE_MAP_MASK);

		node = rcu_dereference_raw(*slot);

		if (node == NULL)

			return NULL;

		if (!radix_tree_is_indirect_ptr(node))

			break;

		node = indirect_to_ptr(node);

	while (radix_tree_is_indirect_ptr(node)) {

		unsigned offset;

		if (node == RADIX_TREE_RETRY)

			goto restart;

		parent = indirect_to_ptr(node);

		shift -= RADIX_TREE_MAP_SHIFT;

		height--;

	} while (height > 0);

		offset = (index >> shift) & RADIX_TREE_MAP_MASK;

		offset = radix_tree_descend(parent, &node, offset);

		slot = parent->slots + offset;

	}

	if (nodep)

		*nodep = parent;