--- x/sound/usb/midi.c
+++ y/sound/usb/midi.c
@@ -307,6 +307,8 @@ static void snd_usbmidi_do_output(struct
 	for (;;) {
 		if (!(ep->active_urbs & (1 << urb_index))) {
 			urb = ep->urbs[urb_index].urb;
+			if (!urb)
+				goto next;
 			urb->transfer_buffer_length = 0;
 			ep->umidi->usb_protocol_ops->output(ep, urb);
 			if (urb->transfer_buffer_length == 0)
@@ -319,6 +321,7 @@ static void snd_usbmidi_do_output(struct
 				break;
 			ep->active_urbs |= 1 << urb_index;
 		}
+	next:
 		if (++urb_index >= OUTPUT_URBS)
 			urb_index = 0;
 		if (urb_index == ep->next_urb)
@@ -1396,13 +1399,19 @@ static int snd_usbmidi_in_endpoint_creat
 static void snd_usbmidi_out_endpoint_clear(struct snd_usb_midi_out_endpoint *ep)
 {
 	unsigned int i;
+	unsigned long flags;
 
+	spin_lock_irqsave(&ep->buffer_lock, flags);
 	for (i = 0; i < OUTPUT_URBS; ++i)
 		if (ep->urbs[i].urb) {
-			free_urb_and_buffer(ep->umidi, ep->urbs[i].urb,
-					    ep->max_transfer);
+			struct urb *urb = ep->urbs[i].urb;
+
 			ep->urbs[i].urb = NULL;
+			spin_unlock_irqrestore(&ep->buffer_lock, flags);
+			free_urb_and_buffer(ep->umidi, urb, ep->max_transfer);
+			spin_lock_irqsave(&ep->buffer_lock, flags);
 		}
+	spin_unlock_irqrestore(&ep->buffer_lock, flags);
 }
 
 static void snd_usbmidi_out_endpoint_delete(struct snd_usb_midi_out_endpoint *ep)