I believe the pointer lh can never be null.

Index: isofs/udf/udf_vnops.c
================================================== =================
RCS file: /cvs/src/sys/isofs/udf/udf_vnops.c,v
retrieving revision 1.30
diff -u -r1.30 udf_vnops.c
--- isofs/udf/udf_vnops.c 9 Dec 2007 20:54:01 -0000 1.30
+++ isofs/udf/udf_vnops.c 28 Dec 2007 18:23:19 -0000
@@ -133,8 +133,6 @@
vn_lock(up->u_vnode, LK_EXCLUSIVE | LK_RETRY, p);
mtx_enter(&ump->um_hashmtx);
lh = &ump->um_hashtbl[up->u_ino & ump->um_hashsz];
- if (lh == NULL)
- LIST_INIT(lh);
LIST_INSERT_HEAD(lh, up, u_le);
mtx_leave(&ump->um_hashmtx);