Index: sys/xen/xen_intr.c
===================================================================
--- sys/xen/xen_intr.c
+++ sys/xen/xen_intr.c
@@ -769,6 +769,9 @@
 	for (i = 0; i < nitems(s->evtchn_mask); i++)
 		atomic_store_rel_long(&s->evtchn_mask[i], ~0);
 
+	/* Protect xen_intr_port_to_isrc[] / ->xi_port */
+	mtx_lock(&xen_intr_isrc_lock);
+
 	/* Clear existing port mappings */
 	for (isrc_idx = 0; isrc_idx < NR_EVENT_CHANNELS; ++isrc_idx)
 		if (xen_intr_port_to_isrc[isrc_idx] != NULL)
@@ -805,6 +808,9 @@
 			cur = next;
 		} while (cur != NULL);
 	}
+
+	/* Done with xen_intr_port_to_isrc[] / ->xi_port */
+	mtx_unlock(&xen_intr_isrc_lock);
 }
 #endif