diff --git a/drivers/char/diag/diagchar_core.c b/drivers/char/diag/diagchar_core.c
index 128d6ce..3086cce 100644
--- a/drivers/char/diag/diagchar_core.c
+++ b/drivers/char/diag/diagchar_core.c
@@ -1713,14 +1713,18 @@
 {
 	int i;
 
+	mutex_lock(&driver->diagchar_mutex);
 	for (i = 0; i < driver->num_clients; i++)
 		if (driver->client_map[i].pid == current->tgid)
 			break;
 
-	if (i == driver->num_clients)
+	if (i == driver->num_clients) {
+		mutex_unlock(&driver->diagchar_mutex);
 		return -EINVAL;
+	}
 
 	driver->data_ready[i] |= DEINIT_TYPE;
+	mutex_unlock(&driver->diagchar_mutex);
 	wake_up_interruptible(&driver->wait_q);
 
 	return 1;