radix-tree: fix extending the tree for multi-order entries at offset 0

The current code will insert entries at each level, as if we're going to
add a new entry at the bottom level, so we then get an -EEXIST when we
try to insert the entry into the tree.  The best way to fix this is to
not check 'order' when inserting into an empty tree.

We still need to 'extend' the tree to the height necessary for the maximum
index corresponding to this entry, so pass that value to
radix_tree_extend() rather than the index we're asked to create, or we
won't create a tree that's deep enough.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
Cc: Jan Kara <jack@suse.com>
Cc: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/radix-tree.c

@@ -432,7 +432,7 @@ static unsigned radix_tree_load_root(struct radix_tree_root *root,
  *	Extend a radix tree so it can store key @index.
  */
 static int radix_tree_extend(struct radix_tree_root *root,
-				unsigned long index, unsigned order)
+				unsigned long index)
 {
 	struct radix_tree_node *node;
 	struct radix_tree_node *slot;
@@ -444,7 +444,7 @@ static int radix_tree_extend(struct radix_tree_root *root,
 	while (index > radix_tree_maxindex(height))
 		height++;
 
-	if ((root->rnode == NULL) && (order == 0)) {
+	if (root->rnode == NULL) {
 		root->height = height;
 		goto out;
 	}
@@ -467,7 +467,7 @@ static int radix_tree_extend(struct radix_tree_root *root,
 		node->count = 1;
 		node->parent = NULL;
 		slot = root->rnode;
-		if (radix_tree_is_indirect_ptr(slot) && newheight > 1) {
+		if (radix_tree_is_indirect_ptr(slot)) {
 			slot = indirect_to_ptr(slot);
 			slot->parent = node;
 			slot = ptr_to_indirect(slot);
@@ -478,7 +478,7 @@ static int radix_tree_extend(struct radix_tree_root *root,
 		root->height = newheight;
 	} while (height > root->height);
 out:
-	return 0;
+	return height * RADIX_TREE_MAP_SHIFT;
 }
 
 /**
@@ -503,20 +503,26 @@ int __radix_tree_create(struct radix_tree_root *root, unsigned long index,
 			void ***slotp)
 {
 	struct radix_tree_node *node = NULL, *slot;
+	unsigned long maxindex;
 	unsigned int height, shift, offset;
-	int error;
+	unsigned long max = index | ((1UL << order) - 1);
+
+	shift = radix_tree_load_root(root, &slot, &maxindex);
 
 	/* Make sure the tree is high enough.  */
-	if (index > radix_tree_maxindex(root->height)) {
-		error = radix_tree_extend(root, index, order);
-		if (error)
+	if (max > maxindex) {
+		int error = radix_tree_extend(root, max);
+		if (error < 0)
 			return error;
+		shift = error;
+		slot = root->rnode;
+		if (order == shift) {
+			shift += RADIX_TREE_MAP_SHIFT;
+			root->height++;
+		}
 	}
 
-	slot = root->rnode;
-
 	height = root->height;
-	shift = height * RADIX_TREE_MAP_SHIFT;
 
 	offset = 0;			/* uninitialised var warning */
 	while (shift > order) {