Index: head/sys/dev/hyperv/vmbus/vmbus.c
===================================================================
--- head/sys/dev/hyperv/vmbus/vmbus.c
+++ head/sys/dev/hyperv/vmbus/vmbus.c
@@ -307,6 +307,13 @@
 	return error;
 }
 
+void
+vmbus_msghc_exec_cancel(struct vmbus_softc *sc __unused, struct vmbus_msghc *mh)
+{
+
+	vmbus_xact_deactivate(mh->mh_xact);
+}
+
 const struct vmbus_message *
 vmbus_msghc_wait_result(struct vmbus_softc *sc __unused, struct vmbus_msghc *mh)
 {
Index: head/sys/dev/hyperv/vmbus/vmbus_var.h
===================================================================
--- head/sys/dev/hyperv/vmbus/vmbus_var.h
+++ head/sys/dev/hyperv/vmbus/vmbus_var.h
@@ -157,6 +157,8 @@
 void		*vmbus_msghc_dataptr(struct vmbus_msghc *);
 int		vmbus_msghc_exec_noresult(struct vmbus_msghc *);
 int		vmbus_msghc_exec(struct vmbus_softc *, struct vmbus_msghc *);
+void		vmbus_msghc_exec_cancel(struct vmbus_softc *,
+		    struct vmbus_msghc *);
 const struct vmbus_message *
 		vmbus_msghc_wait_result(struct vmbus_softc *,
 		    struct vmbus_msghc *);