rbtree_test: add test for postorder iteration

Just check that we examine all nodes in the tree for the postorder
iteration.

Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com>
Reviewed-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: David Woodhouse <David.Woodhouse@intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Michel Lespinasse <walken@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/rbtree_test.c

@@ -114,6 +114,16 @@ static int black_path_count(struct rb_node *rb)
 	return count;
 }
 
+static void check_postorder(int nr_nodes)
+{
+	struct rb_node *rb;
+	int count = 0;
+	for (rb = rb_first_postorder(&root); rb; rb = rb_next_postorder(rb))
+		count++;
+
+	WARN_ON_ONCE(count != nr_nodes);
+}
+
 static void check(int nr_nodes)
 {
 	struct rb_node *rb;
@@ -136,6 +146,8 @@ static void check(int nr_nodes)
 
 	WARN_ON_ONCE(count != nr_nodes);
 	WARN_ON_ONCE(count < (1 << black_path_count(rb_last(&root))) - 1);
+
+	check_postorder(nr_nodes);
 }
 
 static void check_augmented(int nr_nodes)