ftrace: Add check of sched_stopped for probe_sched_wakeup

The wakeup tracing in sched_switch does not stop when a user
disables tracing. This is because the probe_sched_wakeup() is missing
the check to prevent the wakeup from being traced.

Signed-off-by: Zhao Lei <[e-mail]>
LKML-Reference: <[e-mail]>
Signed-off-by: Steven Rostedt <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

kernel/trace/trace_sched_switch.c

···
 	pc = preempt_count();
 	tracing_record_cmdline(current);
 
+	if (sched_stopped)
+		return;
+
 	local_irq_save(flags);
 	cpu = raw_smp_processor_id();
 	data = ctx_trace->data[cpu];