Index: sys/fs/nullfs/null_subr.c
===================================================================
--- sys/fs/nullfs/null_subr.c	(revision 243249)
+++ sys/fs/nullfs/null_subr.c	(working copy)
@@ -186,6 +186,8 @@
 null_insmntque_dtr(struct vnode *vp, void *xp)
 {
 
+	ASSERT_VOP_ELOCKED(vp, "null_insmntque_dtr: non-locked vp");
+
 	vput(((struct null_node *)xp)->null_lowervp);
 	null_destroy_proto(vp, xp);
 }
Index: sys/fs/devfs/devfs_vnops.c
===================================================================
--- sys/fs/devfs/devfs_vnops.c	(revision 243249)
+++ sys/fs/devfs/devfs_vnops.c	(working copy)
@@ -371,6 +371,8 @@
 {
 	struct devfs_dirent *de;
 
+	ASSERT_VOP_ELOCKED(vp, "devfs_insmntque_dtr: non-locked vp");
+
 	de = (struct devfs_dirent *)arg;
 	mtx_lock(&devfs_de_interlock);
 	vp->v_data = NULL;
Index: sys/fs/fdescfs/fdesc_vnops.c
===================================================================
--- sys/fs/fdescfs/fdesc_vnops.c	(revision 243249)
+++ sys/fs/fdescfs/fdesc_vnops.c	(working copy)
@@ -121,6 +121,8 @@
 fdesc_insmntque_dtr(struct vnode *vp, void *arg)
 {
 
+	ASSERT_VOP_ELOCKED(vp, "fdesc_insmntque_dtr: non-locked vp");
+
 	vgone(vp);
 	vput(vp);
 }
Index: sys/kern/vfs_subr.c
===================================================================
--- sys/kern/vfs_subr.c	(revision 243249)
+++ sys/kern/vfs_subr.c	(working copy)
@@ -1109,12 +1109,10 @@
 insmntque_stddtr(struct vnode *vp, void *dtr_arg)
 {
 
+	ASSERT_VOP_ELOCKED(vp, "insmntque_stddtr: non-locked vp");
+
 	vp->v_data = NULL;
 	vp->v_op = &dead_vnodeops;
-	/* XXX non mp-safe fs may still call insmntque with vnode
-	   unlocked */
-	if (!VOP_ISLOCKED(vp))
-		vn_lock(vp, LK_EXCLUSIVE | LK_RETRY);
 	vgone(vp);
 	vput(vp);
 }
@@ -1126,7 +1124,6 @@
 insmntque1(struct vnode *vp, struct mount *mp,
 	void (*dtr)(struct vnode *, void *), void *dtr_arg)
 {
-	int locked;
 
 	KASSERT(vp->v_mount == NULL,
 		("insmntque: vnode already on per mount vnode list"));
@@ -1144,18 +1141,15 @@
 	 */
 	MNT_ILOCK(mp);
 	VI_LOCK(vp);
-	if ((mp->mnt_kern_flag & MNTK_NOINSMNTQ) != 0 &&
+	if (((mp->mnt_kern_flag & MNTK_NOINSMNTQ) != 0 &&
 	    ((mp->mnt_kern_flag & MNTK_UNMOUNTF) != 0 ||
-	     mp->mnt_nvnodelistsize == 0)) {
-		locked = VOP_ISLOCKED(vp);
-		if (!locked || (locked == LK_EXCLUSIVE &&
-		     (vp->v_vflag & VV_FORCEINSMQ) == 0)) {
-			VI_UNLOCK(vp);
-			MNT_IUNLOCK(mp);
-			if (dtr != NULL)
-				dtr(vp, dtr_arg);
-			return (EBUSY);
-		}
+	     mp->mnt_nvnodelistsize == 0)) &&
+	    (vp->v_vflag & VV_FORCEINSMQ) == 0) {
+		VI_UNLOCK(vp);
+		MNT_IUNLOCK(mp);
+		if (dtr != NULL)
+			dtr(vp, dtr_arg);
+		return (EBUSY);
 	}
 	vp->v_mount = mp;
 	MNT_REF(mp);