[PATCH v2] tracing: make tracer_init_tracefs initcall asynchronous

[Mark-PK Tsai]

Move trace_eval_init() to subsys_initcall to make it start
earlier.
And to avoid tracer_init_tracefs being blocked by
trace_event_sem which trace_eval_init() hold [1],
queue tracer_init_tracefs() to eval_map_wq to let
the two works being executed sequentially.

It can speed up the initialization of kernel as result
of making tracer_init_tracefs asynchronous.

On my arm64 platform, it reduce ~20ms of 125ms which total
time do_initcalls spend.

[1]: https://lore.kernel.org/r/68d7b3327052757d0cd6359a6c9015a85b437232.camel@xxxxxxxxxxxxxx
Signed-off-by: Mark-PK Tsai <mark-pk.tsai@xxxxxxxxxxxx>
---
 kernel/trace/trace.c | 31 +++++++++++++++++++++----------
 1 file changed, 21 insertions(+), 10 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index eb44418574f9..adb37e437a05 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9564,6 +9564,7 @@ extern struct trace_eval_map *__stop_ftrace_eval_maps[];
 
 static struct workqueue_struct *eval_map_wq __initdata;
 static struct work_struct eval_map_work __initdata;
+static struct work_struct tracerfs_init_work __initdata;
 
 static void __init eval_map_work_func(struct work_struct *work)
 {
@@ -9589,6 +9590,8 @@ static int __init trace_eval_init(void)
 	return 0;
 }
 
+subsys_initcall(trace_eval_init);
+
 static int __init trace_eval_sync(void)
 {
 	/* Make sure the eval map updates are finished */
@@ -9671,15 +9674,8 @@ static struct notifier_block trace_module_nb = {
 };
 #endif /* CONFIG_MODULES */
 
-static __init int tracer_init_tracefs(void)
+static __init void tracer_init_tracefs_work_func(struct work_struct *work)
 {
-	int ret;
-
-	trace_access_lock_init();
-
-	ret = tracing_init_dentry();
-	if (ret)
-		return 0;
 
 	event_trace_init();
 
@@ -9701,8 +9697,6 @@ static __init int tracer_init_tracefs(void)
 	trace_create_file("saved_tgids", TRACE_MODE_READ, NULL,
 			NULL, &tracing_saved_tgids_fops);
 
-	trace_eval_init();
-
 	trace_create_eval_file(NULL);
 
 #ifdef CONFIG_MODULES
@@ -9717,6 +9711,23 @@ static __init int tracer_init_tracefs(void)
 	create_trace_instances(NULL);
 
 	update_tracer_options(&global_trace);
+}
+
+static __init int tracer_init_tracefs(void)
+{
+	int ret;
+
+	trace_access_lock_init();
+
+	ret = tracing_init_dentry();
+	if (ret)
+		return 0;
+
+	INIT_WORK(&tracerfs_init_work, tracer_init_tracefs_work_func);
+	if (!eval_map_wq)
+		tracer_init_tracefs_work_func(&tracerfs_init_work);
+	else
+		queue_work(eval_map_wq, &tracerfs_init_work);
 
 	return 0;
 }
-- 
2.18.0