diff -urBN /usr/src.orig/sys/fs/unionfs/union_subr.c /usr/src/sys/fs/unionfs/union_subr.c
--- /usr/src.orig/sys/fs/unionfs/union_subr.c	2012-04-08 12:31:30.000000000 +0900
+++ /usr/src/sys/fs/unionfs/union_subr.c	2012-04-08 12:43:04.000000000 +0900
@@ -350,19 +350,22 @@
 	uvp = unp->un_uppervp;
 	dvp = unp->un_dvp;
 	unp->un_lowervp = unp->un_uppervp = NULLVP;
-
 	vp->v_vnlock = &(vp->v_lock);
 	vp->v_data = NULL;
-	lockmgr(vp->v_vnlock, LK_EXCLUSIVE | LK_INTERLOCK, VI_MTX(vp));
+	vp->v_object = NULL;
+	VI_UNLOCK(vp);
+
 	if (lvp != NULLVP)
-		VOP_UNLOCK(lvp, 0);
+		VOP_UNLOCK(lvp, LK_RELEASE);
 	if (uvp != NULLVP)
-		VOP_UNLOCK(uvp, 0);
-	vp->v_object = NULL;
+		VOP_UNLOCK(uvp, LK_RELEASE);
 
 	if (dvp != NULLVP && unp->un_hash.le_prev != NULL)
 		unionfs_rem_cached_vnode(unp, dvp);
 
+	if (lockmgr(vp->v_vnlock, LK_EXCLUSIVE, VI_MTX(vp)) != 0)
+		panic("the lock for deletion is unacquirable.");
+
 	if (lvp != NULLVP) {
 		vfslocked = VFS_LOCK_GIANT(lvp->v_mount);
 		vrele(lvp);
@@ -550,7 +553,7 @@
 		cn->cn_flags |= (cnp->cn_flags & SAVESTART);
 
 	vref(dvp);
-	VOP_UNLOCK(dvp, 0);
+	VOP_UNLOCK(dvp, LK_RELEASE);
 
 	if ((error = relookup(dvp, vpp, cn))) {
 		uma_zfree(namei_zone, cn->cn_pnbuf);
@@ -957,7 +957,7 @@
 	*vpp = vp;
 
 unionfs_vn_create_on_upper_free_out1:
-	VOP_UNLOCK(udvp, 0);
+	VOP_UNLOCK(udvp, LK_RELEASE);
 
 unionfs_vn_create_on_upper_free_out2:
 	if (cn.cn_flags & HASBUF) {
diff -urBN /usr/src.orig/sys/fs/unionfs/union_vfsops.c /usr/src/sys/fs/unionfs/union_vfsops.c
--- /usr/src.orig/sys/fs/unionfs/union_vfsops.c	2012-04-08 12:31:30.000000000 +0900
+++ /usr/src/sys/fs/unionfs/union_vfsops.c	2012-04-08 12:43:04.000000000 +0900
@@ -165,7 +165,7 @@
 		uid = va.va_uid;
 		gid = va.va_gid;
 	}
-	VOP_UNLOCK(mp->mnt_vnodecovered, 0);
+	VOP_UNLOCK(mp->mnt_vnodecovered, LK_RELEASE);
 	if (error)
 		return (error);
 
@@ -250,7 +250,7 @@
 	 * Save reference
 	 */
 	if (below) {
-		VOP_UNLOCK(upperrootvp, 0);
+		VOP_UNLOCK(upperrootvp, LK_RELEASE);
 		vn_lock(lowerrootvp, LK_EXCLUSIVE | LK_RETRY);
 		ump->um_lowervp = upperrootvp;
 		ump->um_uppervp = lowerrootvp;
@@ -281,7 +281,7 @@
 	/*
 	 * Unlock the node
 	 */
-	VOP_UNLOCK(ump->um_uppervp, 0);
+	VOP_UNLOCK(ump->um_uppervp, LK_RELEASE);
 
 	/*
 	 * Get the unionfs root vnode.
diff -urBN /usr/src.orig/sys/fs/unionfs/union_vnops.c /usr/src/sys/fs/unionfs/union_vnops.c
--- /usr/src.orig/sys/fs/unionfs/union_vnops.c	2012-04-08 12:31:30.000000000 +0900
+++ /usr/src/sys/fs/unionfs/union_vnops.c	2012-04-08 12:43:04.000000000 +0900
@@ -75,21 +75,6 @@
 	KASSERT(((vp)->v_op == &unionfs_vnodeops), \
 	    ("unionfs: it is not unionfs-vnode"))
 
-/* lockmgr lock <-> reverse table */
-struct lk_lr_table {
-	int	lock;
-	int	revlock;
-};
-
-static struct lk_lr_table un_llt[] = {
-	{LK_SHARED, LK_RELEASE},
-	{LK_EXCLUSIVE, LK_RELEASE},
-	{LK_UPGRADE, LK_DOWNGRADE},
-	{LK_DOWNGRADE, LK_UPGRADE},
-	{0, 0}
-};
-
-
 static int
 unionfs_lookup(struct vop_cachedlookup_args *ap)
 {
@@ -141,7 +126,7 @@
 		if (udvp != NULLVP) {
 			dtmpvp = udvp;
 			if (ldvp != NULLVP)
-				VOP_UNLOCK(ldvp, 0);
+				VOP_UNLOCK(ldvp, LK_RELEASE);
 		}
 		else
 			dtmpvp = ldvp;
@@ -149,7 +134,7 @@
 		error = VOP_LOOKUP(dtmpvp, &vp, cnp);
 
 		if (dtmpvp == udvp && ldvp != NULLVP) {
-			VOP_UNLOCK(udvp, 0);
+			VOP_UNLOCK(udvp, LK_RELEASE);
 			vn_lock(dvp, LK_EXCLUSIVE | LK_RETRY);
 		}
 
@@ -161,10 +146,10 @@
 			 */
 			if (nameiop == DELETE  || nameiop == RENAME ||
 			    (cnp->cn_lkflags & LK_TYPE_MASK))
-				VOP_UNLOCK(vp, 0);
+				VOP_UNLOCK(vp, LK_RELEASE);
 			vrele(vp);
 
-			VOP_UNLOCK(dvp, 0);
+			VOP_UNLOCK(dvp, LK_RELEASE);
 			*(ap->a_vpp) = dunp->un_dvp;
 			vref(dunp->un_dvp);
 
@@ -202,7 +187,7 @@
 			}
 			if (nameiop == DELETE || nameiop == RENAME ||
 			    (cnp->cn_lkflags & LK_TYPE_MASK))
-				VOP_UNLOCK(uvp, 0);
+				VOP_UNLOCK(uvp, LK_RELEASE);
 		}
 
 		/* check whiteout */
@@ -246,7 +231,7 @@
 				return (lerror);
 			}
 			if (cnp->cn_lkflags & LK_TYPE_MASK)
-				VOP_UNLOCK(lvp, 0);
+				VOP_UNLOCK(lvp, LK_RELEASE);
 		}
 	}
 
@@ -281,7 +266,7 @@
 			goto unionfs_lookup_out;
 
 		if (LK_SHARED == (cnp->cn_lkflags & LK_TYPE_MASK))
-			VOP_UNLOCK(vp, 0);
+			VOP_UNLOCK(vp, LK_RELEASE);
 		if (LK_EXCLUSIVE != VOP_ISLOCKED(vp)) {
 			vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 			lockflag = 1;
@@ -289,7 +274,7 @@
 		error = unionfs_mkshadowdir(MOUNTTOUNIONFSMOUNT(dvp->v_mount),
 		    udvp, VTOUNIONFS(vp), cnp, td);
 		if (lockflag != 0)
-			VOP_UNLOCK(vp, 0);
+			VOP_UNLOCK(vp, LK_RELEASE);
 		if (error != 0) {
 			UNIONFSDEBUG("unionfs_lookup: Unable to create shadow dir.");
 			if ((cnp->cn_lkflags & LK_TYPE_MASK) == LK_EXCLUSIVE)
@@ -386,7 +371,7 @@
 		if (vp->v_type == VSOCK)
 			*(ap->a_vpp) = vp;
 		else {
-			VOP_UNLOCK(vp, 0);
+			VOP_UNLOCK(vp, LK_RELEASE);
 			error = unionfs_nodeget(ap->a_dvp->v_mount, vp, NULLVP,
 			    ap->a_dvp, ap->a_vpp, cnp, curthread);
 			vrele(vp);
@@ -460,7 +445,7 @@
 		if (vp->v_type == VSOCK)
 			*(ap->a_vpp) = vp;
 		else {
-			VOP_UNLOCK(vp, 0);
+			VOP_UNLOCK(vp, LK_RELEASE);
 			error = unionfs_nodeget(ap->a_dvp->v_mount, vp, NULLVP,
 			    ap->a_dvp, ap->a_vpp, cnp, curthread);
 			vrele(vp);
@@ -619,7 +604,7 @@
 	unionfs_tryrem_node_status(unp, unsp);
 
 	if (locked != 0)
-		VOP_UNLOCK(ap->a_vp, 0);
+		VOP_UNLOCK(ap->a_vp, LK_RELEASE);
 
 	UNIONFS_INTERNAL_DEBUG("unionfs_close: leave (%d)\n", error);
 
@@ -914,7 +899,7 @@
 	unionfs_get_node_status(unp, ap->a_td, &unsp);
 	ovp = (unsp->uns_upper_opencnt ? unp->un_uppervp : unp->un_lowervp);
 	unionfs_tryrem_node_status(unp, unsp);
-	VOP_UNLOCK(ap->a_vp, 0);
+	VOP_UNLOCK(ap->a_vp, LK_RELEASE);
 
 	if (ovp == NULLVP)
 		return (EBADF);
@@ -941,7 +926,7 @@
 	unionfs_get_node_status(unp, ap->a_td, &unsp);
 	ovp = (unsp->uns_upper_opencnt ? unp->un_uppervp : unp->un_lowervp);
 	unionfs_tryrem_node_status(unp, unsp);
-	VOP_UNLOCK(ap->a_vp, 0);
+	VOP_UNLOCK(ap->a_vp, LK_RELEASE);
 
 	if (ovp == NULLVP)
 		return (EBADF);
@@ -1001,7 +986,7 @@
 		ump = NULL;
 		vp = uvp = lvp = NULLVP;
 		/* search vnode */
-		VOP_UNLOCK(ap->a_vp, 0);
+		VOP_UNLOCK(ap->a_vp, LK_RELEASE);
 		error = unionfs_relookup(udvp, &vp, cnp, &cn, td,
 		    cnp->cn_nameptr, strlen(cnp->cn_nameptr), DELETE);
 		if (error != 0 && error != ENOENT) {
@@ -1204,7 +1189,7 @@
 			if ((error = vn_lock(fvp, LK_EXCLUSIVE)) != 0)
 				goto unionfs_rename_abort;
 			error = unionfs_copyfile(unp, 1, fcnp->cn_cred, td);
-			VOP_UNLOCK(fvp, 0);
+			VOP_UNLOCK(fvp, LK_RELEASE);
 			if (error != 0)
 				goto unionfs_rename_abort;
 			break;
@@ -1212,7 +1197,7 @@
 			if ((error = vn_lock(fvp, LK_EXCLUSIVE)) != 0)
 				goto unionfs_rename_abort;
 			error = unionfs_mkshadowdir(ump, rfdvp, unp, fcnp, td);
-			VOP_UNLOCK(fvp, 0);
+			VOP_UNLOCK(fvp, LK_RELEASE);
 			if (error != 0)
 				goto unionfs_rename_abort;
 			break;
@@ -1269,13 +1254,13 @@
 		if ((error = vn_lock(fdvp, LK_EXCLUSIVE)) != 0)
 			goto unionfs_rename_abort;
 		error = unionfs_relookup_for_delete(fdvp, fcnp, td);
-		VOP_UNLOCK(fdvp, 0);
+		VOP_UNLOCK(fdvp, LK_RELEASE);
 		if (error != 0)
 			goto unionfs_rename_abort;
 
 		/* Locke of tvp is canceled in order to avoid recursive lock. */
 		if (tvp != NULLVP && tvp != tdvp)
-			VOP_UNLOCK(tvp, 0);
+			VOP_UNLOCK(tvp, LK_RELEASE);
 		error = unionfs_relookup_for_rename(tdvp, tcnp, td);
 		if (tvp != NULLVP && tvp != tdvp)
 			vn_lock(tvp, LK_EXCLUSIVE | LK_RETRY);
@@ -1293,11 +1278,11 @@
 	}
 
 	if (ltdvp != NULLVP)
-		VOP_UNLOCK(ltdvp, 0);
+		VOP_UNLOCK(ltdvp, LK_RELEASE);
 	if (tdvp != rtdvp)
 		vrele(tdvp);
 	if (ltvp != NULLVP)
-		VOP_UNLOCK(ltvp, 0);
+		VOP_UNLOCK(ltvp, LK_RELEASE);
 	if (tvp != rtvp && tvp != NULLVP) {
 		if (rtvp == NULLVP)
 			vput(tvp);
@@ -1371,7 +1356,7 @@
 		}
 
 		if ((error = VOP_MKDIR(udvp, &uvp, cnp, ap->a_vap)) == 0) {
-			VOP_UNLOCK(uvp, 0);
+			VOP_UNLOCK(uvp, LK_RELEASE);
 			cnp->cn_lkflags = LK_EXCLUSIVE;
 			error = unionfs_nodeget(ap->a_dvp->v_mount, uvp, NULLVP,
 			    ap->a_dvp, ap->a_vpp, cnp, td);
@@ -1467,7 +1452,7 @@
 	if (udvp != NULLVP) {
 		error = VOP_SYMLINK(udvp, &uvp, cnp, ap->a_vap, ap->a_target);
 		if (error == 0) {
-			VOP_UNLOCK(uvp, 0);
+			VOP_UNLOCK(uvp, LK_RELEASE);
 			cnp->cn_lkflags = LK_EXCLUSIVE;
 			error = unionfs_nodeget(ap->a_dvp->v_mount, uvp, NULLVP,
 			    ap->a_dvp, ap->a_vpp, cnp, td);
@@ -1490,6 +1475,7 @@
 	struct unionfs_node *unp;
 	struct unionfs_node_status *unsp;
 	struct uio     *uio;
+	struct vnode   *vp;
 	struct vnode   *uvp;
 	struct vnode   *lvp;
 	struct thread  *td;
@@ -1505,41 +1491,49 @@
 	error = 0;
 	eofflag = 0;
 	locked = 0;
-	unp = VTOUNIONFS(ap->a_vp);
 	uio = ap->a_uio;
-	uvp = unp->un_uppervp;
-	lvp = unp->un_lowervp;
+	uvp = NULLVP;
+	lvp = NULLVP;
 	td = uio->uio_td;
 	ncookies_bk = 0;
 	cookies_bk = NULL;
 
-	if (ap->a_vp->v_type != VDIR)
+	vp = ap->a_vp;
+	if (vp->v_type != VDIR)
 		return (ENOTDIR);
 
-	/* check opaque */
-	if (uvp != NULLVP && lvp != NULLVP) {
-		if ((error = VOP_GETATTR(uvp, &va, ap->a_cred)) != 0)
-			goto unionfs_readdir_exit;
-		if (va.va_flags & OPAQUE)
-			lvp = NULLVP;
-	}
-
 	/* check the open count. unionfs needs to open before readdir. */
-	if (VOP_ISLOCKED(ap->a_vp) != LK_EXCLUSIVE) {
-		vn_lock(ap->a_vp, LK_UPGRADE | LK_RETRY);
+	if (VOP_ISLOCKED(vp) != LK_EXCLUSIVE) {
+		if (vn_lock(vp, LK_UPGRADE) != 0)
+			vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 		locked = 1;
 	}
-	unionfs_get_node_status(unp, td, &unsp);
-	if ((uvp != NULLVP && unsp->uns_upper_opencnt <= 0) ||
-	    (lvp != NULLVP && unsp->uns_lower_opencnt <= 0)) {
-		unionfs_tryrem_node_status(unp, unsp);
+	unp = VTOUNIONFS(vp);
+	if (unp == NULL)
 		error = EBADF;
+	else {
+		uvp = unp->un_uppervp;
+		lvp = unp->un_lowervp;
+		unionfs_get_node_status(unp, td, &unsp);
+		if ((uvp != NULLVP && unsp->uns_upper_opencnt <= 0) ||
+			(lvp != NULLVP && unsp->uns_lower_opencnt <= 0)) {
+			unionfs_tryrem_node_status(unp, unsp);
+			error = EBADF;
+		}
 	}
-	if (locked == 1)
-		vn_lock(ap->a_vp, LK_DOWNGRADE | LK_RETRY);
+	if (locked)
+		vn_lock(vp, LK_DOWNGRADE | LK_RETRY);
 	if (error != 0)
 		goto unionfs_readdir_exit;
 
+	/* check opaque */
+	if (uvp != NULLVP && lvp != NULLVP) {
+		if ((error = VOP_GETATTR(uvp, &va, ap->a_cred)) != 0)
+			goto unionfs_readdir_exit;
+		if (va.va_flags & OPAQUE)
+			lvp = NULLVP;
+	}
+
 	/* upper only */
 	if (uvp != NULLVP && lvp == NULLVP) {
 		error = VOP_READDIR(uvp, uio, ap->a_cred, ap->a_eofflag,
@@ -1743,18 +1737,66 @@
 }
 
 static int
-unionfs_get_llt_revlock(int flags)
+unionfs_islocked(struct vop_islocked_args *ap)
 {
-	int count;
+	struct unionfs_node *unp;
 
-	flags &= LK_TYPE_MASK;
-	for (count = 0; un_llt[count].lock != 0; count++) {
-		if (flags == un_llt[count].lock) {
-			return un_llt[count].revlock;
-		}
+	KASSERT_UNIONFS_VNODE(ap->a_vp);
+
+	unp = VTOUNIONFS(ap->a_vp);
+	if (unp == NULL)
+		return (vop_stdislocked(ap));
+
+	if (unp->un_uppervp != NULLVP)
+		return (VOP_ISLOCKED(unp->un_uppervp));
+	if (unp->un_lowervp != NULLVP)
+		return (VOP_ISLOCKED(unp->un_lowervp));
+	return (vop_stdislocked(ap));
+}
+
+static int
+unionfs_get_llt_revlock(struct vnode *vp, int flags)
+{
+	int revlock;
+
+	revlock = 0;
+
+	switch (flags & LK_TYPE_MASK) {
+	case LK_SHARED:
+		if (VOP_ISLOCKED(vp) == LK_EXCLUSIVE)
+			revlock = LK_UPGRADE;
+		else
+			revlock = LK_RELEASE;
+		break;
+	case LK_EXCLUSIVE:
+	case LK_UPGRADE:
+		revlock = LK_RELEASE;
+		break;
+	case LK_DOWNGRADE:
+		revlock = LK_UPGRADE;
+		break;
+	default:
+		break;
 	}
 
-	return 0;
+	return (revlock);
+}
+
+/*
+ * The state of an acquired lock is adjusted similarly to
+ * the time of error generating. 
+ * flags: LK_RELEASE or LK_UPGRADE
+ */
+static void
+unionfs_revlock(struct vnode *vp, int flags)
+{
+	if (flags & LK_RELEASE)
+		VOP_UNLOCK(vp, flags);
+	else {
+		/* UPGRADE */
+		if (vn_lock(vp, flags) != 0)
+			vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
+	}
 }
 
 static int
@@ -1763,6 +1805,7 @@
 	int		error;
 	int		flags;
 	int		revlock;
+	int		interlock;
 	int		uhold;
 	struct mount   *mp;
 	struct unionfs_mount *ump;
@@ -1774,15 +1817,13 @@
 	KASSERT_UNIONFS_VNODE(ap->a_vp);
 
 	error = 0;
+	interlock = 1;
 	uhold = 0;
 	flags = ap->a_flags;
 	vp = ap->a_vp;
 
 	if (LK_RELEASE == (flags & LK_TYPE_MASK) || !(flags & LK_TYPE_MASK))
-		return (VOP_UNLOCK(vp, flags));
-
-	if ((revlock = unionfs_get_llt_revlock(flags)) == 0)
-		panic("unknown lock type: 0x%x", flags & LK_TYPE_MASK);
+		return (VOP_UNLOCK(vp, flags | LK_RELEASE));
 
 	if ((flags & LK_INTERLOCK) == 0)
 		VI_LOCK(vp);
@@ -1798,6 +1839,9 @@
 	lvp = unp->un_lowervp;
 	uvp = unp->un_uppervp;
 
+	if ((revlock = unionfs_get_llt_revlock(vp, flags)) == 0)
+		panic("unknown lock type: 0x%x", flags & LK_TYPE_MASK);
+
 	if ((mp->mnt_kern_flag & MNTK_MPSAFE) != 0 &&
 	    (vp->v_iflag & VI_OWEINACT) != 0)
 		flags |= LK_NOWAIT;
@@ -1823,12 +1867,22 @@
 		VI_LOCK(vp);
 		unp = VTOUNIONFS(vp);
 		if (unp == NULL) {
+			/* vnode is released. */
 			VI_UNLOCK(vp);
 			if (error == 0)
-				VOP_UNLOCK(lvp, 0);
+				VOP_UNLOCK(lvp, LK_RELEASE);
 			vdrop(lvp);
 			return (vop_stdlock(ap));
 		}
+		if (error != 0 && flags & LK_UPGRADE && uvp != NULLVP) {
+			/* if upgrade failed, the lock needs release. */
+			VI_LOCK_FLAGS(uvp, MTX_DUPOK);
+			vholdl(uvp);
+			uhold = 1;
+			VI_UNLOCK(vp);
+			VOP_UNLOCK(uvp, LK_RELEASE | LK_INTERLOCK);
+			interlock = 0;
+		}
 	}
 
 	if (error == 0 && uvp != NULLVP) {
@@ -1845,30 +1899,27 @@
 		VI_LOCK(vp);
 		unp = VTOUNIONFS(vp);
 		if (unp == NULL) {
+			/* vnode is released. */
 			VI_UNLOCK(vp);
-			if (error == 0) {
-				VOP_UNLOCK(uvp, 0);
-				if (lvp != NULLVP)
-					VOP_UNLOCK(lvp, 0);
-			}
-			if (lvp != NULLVP)
-				vdrop(lvp);
+			if (error == 0)
+				VOP_UNLOCK(uvp, LK_RELEASE);
 			vdrop(uvp);
+			if (lvp != NULLVP) {
+				VOP_UNLOCK(lvp, LK_RELEASE);
+				vdrop(lvp);
+			}
 			return (vop_stdlock(ap));
 		}
-
 		if (error != 0 && lvp != NULLVP) {
+			/* rollback */
 			VI_UNLOCK(vp);
-			if ((revlock & LK_TYPE_MASK) == LK_RELEASE)
-				VOP_UNLOCK(lvp, revlock);
-			else
-				vn_lock(lvp, revlock | LK_RETRY);
-			goto unionfs_lock_abort;
+			unionfs_revlock(lvp, revlock);
+			interlock = 0;
 		}
 	}
 
-	VI_UNLOCK(vp);
-unionfs_lock_abort:
+	if (interlock)
+		VI_UNLOCK(vp);
 	if (lvp != NULLVP)
 		vdrop(lvp);
 	if (uhold != 0)
@@ -2013,7 +2064,7 @@
 			unionfs_tryrem_node_status(unp, unsp);
 	}
 
-	VOP_UNLOCK(vp, 0);
+	VOP_UNLOCK(vp, LK_RELEASE);
 
 	error = VOP_ADVLOCK(uvp, ap->a_id, ap->a_op, ap->a_fl, ap->a_flags);
 
@@ -2022,7 +2073,7 @@
 	return error;
 
 unionfs_advlock_abort:
-	VOP_UNLOCK(vp, 0);
+	VOP_UNLOCK(vp, LK_RELEASE);
 
 	UNIONFS_INTERNAL_DEBUG("unionfs_advlock: leave (%d)\n", error);
 
@@ -2435,6 +2486,7 @@
 	.vop_getextattr =	unionfs_getextattr,
 	.vop_getwritemount =	unionfs_getwritemount,
 	.vop_inactive =		unionfs_inactive,
+	.vop_islocked =		unionfs_islocked,
 	.vop_ioctl =		unionfs_ioctl,
 	.vop_link =		unionfs_link,
 	.vop_listextattr =	unionfs_listextattr,