Index: head/sys/vm/uma_core.c
===================================================================
--- head/sys/vm/uma_core.c
+++ head/sys/vm/uma_core.c
@@ -1940,6 +1940,20 @@
 	args.dtor = dtor;
 	args.uminit = uminit;
 	args.fini = fini;
+#ifdef  INVARIANTS
+	/*
+	 * If a zone is being created with an empty constructor and
+	 * destructor, pass UMA constructor/destructor which checks for
+	 * memory use after free.
+	 */
+	if ((!(flags & UMA_ZONE_ZINIT)) && ctor == NULL && dtor == NULL &&
+	    uminit == NULL && fini == NULL) {
+		args.ctor = trash_ctor;
+		args.dtor = trash_dtor;
+		args.uminit = trash_init;
+		args.fini = trash_fini;
+	}
+#endif
 	args.align = align;
 	args.flags = flags;
 	args.keg = NULL;
Index: head/sys/vm/uma_dbg.c
===================================================================
--- head/sys/vm/uma_dbg.c
+++ head/sys/vm/uma_dbg.c
@@ -69,8 +69,13 @@
 
 	for (p = mem; cnt > 0; cnt--, p++)
 		if (*p != uma_junk) {
+#ifdef INVARIANTS
+			panic("Memory modified after free %p(%d) val=%x @ %p\n",
+			    mem, size, *p, p);
+#else
 			printf("Memory modified after free %p(%d) val=%x @ %p\n",
 			    mem, size, *p, p);
+#endif
 			return (0);
 		}
 	return (0);