--- zzzz-none-000/linux-4.4.60/sound/usb/mixer.c	2017-04-08 07:53:53.000000000 +0000
+++ scorpion-7490-727/linux-4.4.60/sound/usb/mixer.c	2021-02-04 17:41:59.000000000 +0000
@@ -2159,6 +2159,9 @@
 
 static void snd_usb_mixer_free(struct usb_mixer_interface *mixer)
 {
+	/* kill pending URBs */
+	snd_usb_mixer_disconnect(mixer);
+
 	kfree(mixer->id_elems);
 	if (mixer->urb) {
 		kfree(mixer->urb->transfer_buffer);
@@ -2502,8 +2505,13 @@
 
 void snd_usb_mixer_disconnect(struct usb_mixer_interface *mixer)
 {
-	usb_kill_urb(mixer->urb);
-	usb_kill_urb(mixer->rc_urb);
+	if (mixer->disconnected)
+		return;
+	if (mixer->urb)
+		usb_kill_urb(mixer->urb);
+	if (mixer->rc_urb)
+		usb_kill_urb(mixer->rc_urb);
+	mixer->disconnected = true;
 }
 
 #ifdef CONFIG_PM