Index: xbd_xenbus.c
===================================================================
RCS file: /cvsroot/src/sys/arch/xen/xen/xbd_xenbus.c,v
retrieving revision 1.82
diff -u -p -r1.82 xbd_xenbus.c
--- xbd_xenbus.c	15 Aug 2018 15:49:15 -0000	1.82
+++ xbd_xenbus.c	20 Aug 2018 19:43:17 -0000
@@ -932,6 +932,7 @@ xbd_diskstart(device_t self, struct buf 
 	vaddr_t va;
 	int nsects, nbytes, seg;
 	int notify, error = 0;
+	int s;
 
 	DPRINTF(("xbd_diskstart(%p): b_bcount = %ld\n",
 	    bp, (long)bp->b_bcount));
@@ -947,6 +948,8 @@ xbd_diskstart(device_t self, struct buf 
 		goto err;
 	}
 
+	s = splbio();	/* XXX SMP */
+
 	if (__predict_false(
 	    sc->sc_backend_status == BLKIF_STATE_SUSPENDED)) {
 		/* device is suspended, do not consume buffer */
@@ -1024,6 +1027,7 @@ out:
 	RING_PUSH_REQUESTS_AND_CHECK_NOTIFY(&sc->sc_ring, notify);
 	if (notify)
 		hypervisor_notify_via_evtchn(sc->sc_evtchn);
+	splx(s);	/* XXXSMP */
 err:
 	return error;
 }