Index: kern_synch.c
===================================================================
RCS file: /cvs/src/sys/kern/kern_synch.c,v
retrieving revision 1.127
diff -u -p -r1.127 kern_synch.c
--- kern_synch.c	15 Jan 2016 11:42:47 -0000	1.127
+++ kern_synch.c	1 Feb 2016 12:45:30 -0000
@@ -607,7 +607,14 @@ refcnt_init(struct refcnt *r)
 void
 refcnt_take(struct refcnt *r)
 {
+#ifdef DIAGNOSTIC
+	u_int refcnt;
+
+	refcnt = atomic_inc_int_nv(&r->refs);
+	KASSERT(refcnt != 0);
+#else
 	atomic_inc_int(&r->refs);
+#endif
 }
 
 int