Index: sys/xen/xen_intr.c
===================================================================
--- sys/xen/xen_intr.c
+++ sys/xen/xen_intr.c
@@ -268,7 +268,7 @@
  *          object or NULL.
  */
 static struct xenisrc *
-xen_intr_alloc_isrc(enum evtchn_type type)
+xen_intr_alloc_isrc(enum evtchn_type type, evtchn_port_t port)
 {
 	static int warned;
 	struct xenisrc *isrc;
@@ -279,7 +279,7 @@
 
 	if (isrc != NULL) {
 		mtx_unlock(&xen_intr_x86_lock);
-		return (isrc);
+		goto out;
 	}
 
 	if (xen_intr_auto_vector_count >= NR_EVENT_CHANNELS) {
@@ -304,8 +304,23 @@
 	isrc->xi_type = type;
 	if (intr_register_source(&isrc->xi_arch.xai_intsrc) != 0) {
 		free(isrc, M_XENINTR);
-		isrc = NULL;
+		return (NULL);
+	}
+
+out:
+	/* xen_intr_assign_cpu() requires this to be set */
+	isrc->xi_port = port;
+
+#ifdef SMP
+	if (type == EVTCHN_TYPE_PORT) {
+		/*
+		 * By default all interrupts are assigned to vCPU#0
+		 * unless specified otherwise, so shuffle them to balance
+		 * the interrupt load.
+		 */
+		xen_intr_assign_cpu(isrc, intr_next_cpu(0));
 	}
+#endif
 
 	return (isrc);
 }
@@ -394,11 +409,10 @@
 		return (EINVAL);
 	}
 
-	isrc = xen_intr_alloc_isrc(type);
+	isrc = xen_intr_alloc_isrc(type, local_port);
 	if (isrc == NULL)
 		return (ENOSPC);
 	mtx_lock(&xen_intr_isrc_lock);
-	isrc->xi_port = local_port;
 	xen_intr_port_to_isrc[isrc->xi_port] = isrc;
 	refcount_init(&isrc->xi_refcount, 1);
 	mtx_unlock(&xen_intr_isrc_lock);
@@ -406,17 +420,6 @@
 	/* Assign the opaque handler */
 	*port_handlep = xen_intr_handle_from_isrc(isrc);
 
-#ifdef SMP
-	if (type == EVTCHN_TYPE_PORT) {
-		/*
-		 * By default all interrupts are assigned to vCPU#0
-		 * unless specified otherwise, so shuffle them to balance
-		 * the interrupt load.
-		 */
-		xen_intr_assign_cpu(isrc, intr_next_cpu(0));
-	}
-#endif
-
 	if (filter == NULL && handler == NULL) {
 		/*
 		 * No filter/handler provided, leave the event channel