ftrace: Do no disable function tracing on enabling function tracing

When function tracing is being updated function_trace_stop is set to
keep from tracing the updates. This was fine when function tracing
was done from stop machine. But it is no longer done that way and
this can cause real tracing to be missed.

Remove it.
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ftrace.c

@@ -2261,11 +2261,6 @@ static void ftrace_run_update_code(int command)
 	FTRACE_WARN_ON(ret);
 	if (ret)
 		return;
-	/*
-	 * Do not call function tracer while we update the code.
-	 * We are in stop machine.
-	 */
-	function_trace_stop++;
 
 	/*
 	 * By default we use stop_machine() to modify the code.
@@ -2275,8 +2270,6 @@ static void ftrace_run_update_code(int command)
 	 */
 	arch_ftrace_update_code(command);
 
-	function_trace_stop--;
-
 	ret = ftrace_arch_code_modify_post_process();
 	FTRACE_WARN_ON(ret);