[PATCH 3/3] tracing: do not update tracing_max_latency when tracer is stopped

[Steven Rostedt]

From: Carsten Emde <Carsten.Emde@xxxxxxxxx>

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@xxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 kernel/trace/trace.c              |    5 +++++
 kernel/trace/trace.h              |    1 +
 kernel/trace/trace_irqsoff.c      |    6 ++++--
 kernel/trace/trace_sched_wakeup.c |    6 ++++--
 4 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 45c3f03..ef82a7f 100644
--- a/kernel/trace/trace.c
+++ b/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
  *
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 28247ce..4ad4e1d 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -461,6 +461,7 @@ void tracing_stop_sched_switch_record(void);
 void tracing_start_sched_switch_record(void);
 int register_tracer(struct tracer *type);
 void unregister_tracer(struct tracer *type);
+int is_tracing_stopped(void);
 
 extern unsigned long nsecs_to_usecs(unsigned long nsecs);
 
diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 06f8ea9..3aa7eaa 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -157,8 +157,10 @@ check_critical_timing(struct trace_array *tr,
 
 	data->critical_end = parent_ip;
 
-	tracing_max_latency = delta;
-	update_max_tr_single(tr, current, cpu);
+	if (likely(!is_tracing_stopped())) {
+		tracing_max_latency = delta;
+		update_max_tr_single(tr, current, cpu);
+	}
 
 	max_sequence++;
 
diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index 6e1529b..26185d7 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -162,8 +162,10 @@ probe_wakeup_sched_switch(struct rq *rq, struct task_struct *prev,
 	if (!report_latency(delta))
 		goto out_unlock;
 
-	tracing_max_latency = delta;
-	update_max_tr(wakeup_trace, wakeup_task, wakeup_cpu);
+	if (likely(!is_tracing_stopped())) {
+		tracing_max_latency = delta;
+		update_max_tr(wakeup_trace, wakeup_task, wakeup_cpu);
+	}
 
 out_unlock:
 	__wakeup_reset(wakeup_trace);
-- 
1.6.3.3

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