Index: subr_autoconf.c
===================================================================
RCS file: /cvs/src/sys/kern/subr_autoconf.c,v
retrieving revision 1.80
diff -u -p -r1.80 subr_autoconf.c
--- subr_autoconf.c	18 Sep 2014 18:54:29 -0000	1.80
+++ subr_autoconf.c	5 Jan 2015 04:05:14 -0000
@@ -935,8 +935,10 @@ device_ref(struct device *dv)
 void
 device_unref(struct device *dv)
 {
+	struct cfattach *ca = dv->dv_cfdata->cf_attach;
+
 	dv->dv_ref--;
 	if (dv->dv_ref == 0) {
-		free(dv, M_DEVBUF, 0);
+		free(dv, M_DEVBUF, ca->ca_devsize);
 	}
 }