tracing: do not update tracing_max_latency when tracer is stopped

The state of the function pair tracing_stop()/tracing_start() is
correctly considered when tracer data are updated. However, the global
and externally accessible variable tracing_max_latency is always updated
- even when tracing is stopped.

The update should only occur, if tracing was not stopped.

Signed-off-by: Carsten Emde <C.Emde@osadl.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -825,6 +825,11 @@ static void trace_init_cmdlines(void)
 	cmdline_idx = 0;
 }
 
+int is_tracing_stopped(void)
+{
+	return trace_stop_count;
+}
+
 /**
  * ftrace_off_permanent - disable all ftrace code permanently
  *