ftrace: Set callback to ftrace_stub when no ops are registered

The clean up that adds the helper function ftrace_ops_get_func()
caused the default function to not change when DYNAMIC_FTRACE was not
set and no ftrace_ops were registered. Although static tracing is
not very useful (not having DYNAMIC_FTRACE set), it is still supported
and we don't want to break it.

Clean up the if statement even more to specifically have the default
function call ftrace_stub when no ftrace_ops are registered. This
fixes the small bug for static tracing as well as makes the code a
bit more understandable.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -253,18 +253,25 @@ static void update_ftrace_function(void)
 {
 	ftrace_func_t func;
 
+	/*
+	 * Prepare the ftrace_ops that the arch callback will use.
+	 * If there's only one ftrace_ops registered, the ftrace_ops_list
+	 * will point to the ops we want.
+	 */
+	set_function_trace_op = ftrace_ops_list;
+
+	/* If there's no ftrace_ops registered, just call the stub function */
+	if (ftrace_ops_list == &ftrace_list_end) {
+		func = ftrace_stub;
+
 	/*
 	 * If we are at the end of the list and this ops is
 	 * recursion safe and not dynamic and the arch supports passing ops,
 	 * then have the mcount trampoline call the function directly.
 	 */
-	if (ftrace_ops_list == &ftrace_list_end ||
+	} else if (ftrace_ops_list->next == &ftrace_list_end) {
-	    (ftrace_ops_list->next == &ftrace_list_end)) {
-
-		/* Set the ftrace_ops that the arch callback uses */
-		set_function_trace_op = ftrace_ops_list;
-
 		func = ftrace_ops_get_func(ftrace_ops_list);
+
 	} else {
 		/* Just use the default ftrace_ops */
 		set_function_trace_op = &ftrace_list_end;