perf callchain: Check return value of add_child()

The create_child() in add_child() can return NULL in case of memory
allocation failure.  So check the return value and bail out.  The proper
error handling will be added later.
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1455631723-17345-3-git-send-email-namhyung@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/callchain.c

@@ -453,6 +453,9 @@ add_child(struct callchain_node *parent,
 	struct callchain_node *new;
 
 	new = create_child(parent, false);
+	if (new == NULL)
+		return NULL;
+
 	fill_node(new, cursor);
 
 	new->children_hit = 0;
@@ -524,6 +527,8 @@ split_add_child(struct callchain_node *parent,
 
 		node = callchain_cursor_current(cursor);
 		new = add_child(parent, cursor, period);
+		if (new == NULL)
+			return;
 
 		/*
 		 * This is second child since we moved parent's children
@@ -585,6 +590,9 @@ append_chain_children(struct callchain_node *root,
 	}
 	/* nothing in children, add to the current node */
 	rnode = add_child(root, cursor, period);
+	if (rnode == NULL)
+		return;
+
 	rb_link_node(&rnode->rb_node_in, parent, p);
 	rb_insert_color(&rnode->rb_node_in, &root->rb_root_in);