tracing: Use pause-on-trace with the latency tracers

commit da7f84c upstream.

Eaerlier, tracing was disabled when reading the trace file. This behavior
was changed with:

commit 06e0a54 ("tracing: Do not disable tracing when reading the
trace file").

This doesn't seem to work with the latency tracers.

The above mentioned commit dit not only change the behavior but also added
an option to emulate the old behavior. The idea with this patch is to
enable this pause-on-trace option when the latency tracers are used.

Link: https://lkml.kernel.org/r/20210119164344.37500-2-Viktor.Rosendahl@bmw.de

Cc: stable@vger.kernel.org
Fixes: 06e0a54 ("tracing: Do not disable tracing when reading the trace file")
Signed-off-by: Viktor Rosendahl <Viktor.Rosendahl@bmw.de>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

kernel/trace/trace_irqsoff.c

@@ -562,6 +562,8 @@ static int __irqsoff_tracer_init(struct trace_array *tr)
 	/* non overwrite screws up the latency tracers */
 	set_tracer_flag(tr, TRACE_ITER_OVERWRITE, 1);
 	set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, 1);
+	/* without pause, we will produce garbage if another latency occurs */
+	set_tracer_flag(tr, TRACE_ITER_PAUSE_ON_TRACE, 1);
 
 	tr->max_latency = 0;
 	irqsoff_trace = tr;
@@ -583,11 +585,13 @@ static void __irqsoff_tracer_reset(struct trace_array *tr)
 {
 	int lat_flag = save_flags & TRACE_ITER_LATENCY_FMT;
 	int overwrite_flag = save_flags & TRACE_ITER_OVERWRITE;
+	int pause_flag = save_flags & TRACE_ITER_PAUSE_ON_TRACE;
 
 	stop_irqsoff_tracer(tr, is_graph(tr));
 
 	set_tracer_flag(tr, TRACE_ITER_LATENCY_FMT, lat_flag);
 	set_tracer_flag(tr, TRACE_ITER_OVERWRITE, overwrite_flag);
+	set_tracer_flag(tr, TRACE_ITER_PAUSE_ON_TRACE, pause_flag);
 	ftrace_reset_array_ops(tr);
 
 	irqsoff_busy = false;