tracing/user_events: Hold event_mutex during dyn_event_add

Make sure the event_mutex is properly held during dyn_event_add call.
This is required when adding dynamic events.

Link: https://lkml.kernel.org/r/[e-mail]

Reported-by: Mathieu Desnoyers <[e-mail]>
Signed-off-by: Beau Belgrave <[e-mail]>
Acked-by: Masami Hiramatsu <[e-mail]>
Signed-off-by: Steven Rostedt (Google) <[e-mail]>

kernel/trace/trace_events_user.c

···
 #endif
 
 	mutex_lock(&event_mutex);
+
 	ret = user_event_trace_register(user);
-	mutex_unlock(&event_mutex);
 
 	if (ret)
-		goto put_user;
+		goto put_user_lock;
 
 	user->index = index;
 
···
 	set_bit(user->index, page_bitmap);
 	hash_add(register_table, &user->node, key);
 
+	mutex_unlock(&event_mutex);
+
 	*newuser = user;
 	return 0;
+put_user_lock:
+	mutex_unlock(&event_mutex);
 put_user:
 	user_event_destroy_fields(user);
 	user_event_destroy_validators(user);