tracing/ftrace: fix a bug when switch current tracer to sched tracer

Impact: fix boot tracer + sched tracer coupling bug

Fix a bug that made the sched_switch tracer unable to run
if set as the current_tracer after the boot tracer.
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace_boot.c

@@ -37,9 +37,9 @@ void disable_boot_trace(void)
 		tracing_stop_cmdline_record();
 }
 
-void reset_boot_trace(struct trace_array *tr)
+static void reset_boot_trace(struct trace_array *tr)
 {
-	disable_boot_trace();
+	sched_switch_trace.reset(tr);
 }
 
 static void boot_trace_init(struct trace_array *tr)

kernel/trace/trace_sched_switch.c

@@ -173,7 +173,7 @@ static void sched_switch_trace_init(struct trace_array *tr)
 
 static void sched_switch_trace_reset(struct trace_array *tr)
 {
-	if (tr->ctrl)
+	if (tr->ctrl && sched_ref)
 		stop_sched_trace(tr);
 }