Index: usr.sbin/bhyve/pci_xhci.c
===================================================================
--- usr.sbin/bhyve/pci_xhci.c
+++ usr.sbin/bhyve/pci_xhci.c
@@ -1,5 +1,6 @@
 /*-
  * Copyright (c) 2014 Leon Dang <ldang@nahannisys.com>
+ * Copyright 2018 Joyent, Inc.
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -1661,7 +1662,6 @@
 	do_intr = 0;
 
 	xfer = devep->ep_xfer;
-	USB_DATA_XFER_LOCK(xfer);
 
 	/* outstanding requests queued up */
 	if (dev->dev_ue->ue_data != NULL) {
@@ -1684,9 +1684,6 @@
 		}
 	}
 
-	USB_DATA_XFER_UNLOCK(xfer);
-
-
 	return (err);
 }
 
@@ -1917,7 +1914,9 @@
 
 	/* handle pending transfers */
 	if (devep->ep_xfer->ndata > 0) {
+		USB_DATA_XFER_LOCK(devep->ep_xfer);
 		pci_xhci_try_usb_xfer(sc, dev, devep, ep_ctx, slot, epid);
+		USB_DATA_XFER_UNLOCK(devep->ep_xfer);
 		return;
 	}