drm/mm: Fix caching of leftmost node in the interval tree

When we descend the tree to find our slot, if we step to the right, we
are no longer the leftmost node.

Fixes: f808c13f ("lib/interval_tree: fast overlap detection")
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: Davidlohr Bueso <dbueso@suse.de>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Christian König <christian.koenig@amd.com>
Reviewed-by: NJoonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Christian König <christian.koenig@amd.com> for now.
Link: https://patchwork.freedesktop.org/patch/msgid/20180220093738.1461-1-chris@chris-wilson.co.uk

drivers/gpu/drm/drm_mm.c

@@ -180,7 +180,7 @@ static void drm_mm_interval_tree_add_node(struct drm_mm_node *hole_node,
 	struct drm_mm *mm = hole_node->mm;
 	struct rb_node **link, *rb;
 	struct drm_mm_node *parent;
-	bool leftmost = true;
+	bool leftmost;
 
 	node->__subtree_last = LAST(node);
 
@@ -201,6 +201,7 @@ static void drm_mm_interval_tree_add_node(struct drm_mm_node *hole_node,
 	} else {
 		rb = NULL;
 		link = &mm->interval_tree.rb_root.rb_node;
+		leftmost = true;
 	}
 
 	while (*link) {
@@ -208,11 +209,11 @@ static void drm_mm_interval_tree_add_node(struct drm_mm_node *hole_node,
 		parent = rb_entry(rb, struct drm_mm_node, rb);
 		if (parent->__subtree_last < node->__subtree_last)
 			parent->__subtree_last = node->__subtree_last;
-		if (node->start < parent->start)
+		if (node->start < parent->start) {
 			link = &parent->rb.rb_left;
-		else {
+		} else {
 			link = &parent->rb.rb_right;
-			leftmost = true;
+			leftmost = false;
 		}
 	}