[PATCH] tracing: Avoid adding duplicated tracer options when update_tracer_options is running in parallel

[Mark-PK Tsai]

When update_tracer_options is running in parallel,
tr->tops might be updated before the trace_types list traversal.
Let update_tracer_options traverse the trace_types list safely in
kernel init time and avoid the tr->tops update before it finish.

Link: https://lore.kernel.org/lkml/20220322133339.GA32582@xsang-OptiPlex-9020/
Reported-by: kernel test robot <oliver.sang at intel.com>
Signed-off-by: Mark-PK Tsai <mark-pk.tsai at mediatek.com>
---
 kernel/trace/trace.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index adb37e437a05..2974ae056068 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6317,12 +6317,18 @@ static void tracing_set_nop(struct trace_array *tr)
 	tr->current_trace = &nop_trace;
 }
 
+static bool tracer_options_updated;
+
 static void add_tracer_options(struct trace_array *tr, struct tracer *t)
 {
 	/* Only enable if the directory has been created already. */
 	if (!tr->dir)
 		return;
 
+	/* Only create trace option files after update_tracer_options finish */
+	if (!tracer_options_updated)
+		return;
+
 	create_trace_option_files(tr, t);
 }
 
@@ -9133,6 +9139,7 @@ static void update_tracer_options(struct trace_array *tr)
 {
 	mutex_lock(&trace_types_lock);
 	__update_tracer_options(tr);
+	tracer_options_updated = true;
 	mutex_unlock(&trace_types_lock);
 }
 
-- 
2.18.0