diff --git a/sys/fs/nullfs/null_vfsops.c b/sys/fs/nullfs/null_vfsops.c
--- a/sys/fs/nullfs/null_vfsops.c
+++ b/sys/fs/nullfs/null_vfsops.c
@@ -201,6 +201,12 @@
 		    &xmp->notify_node);
 	}
 
+	if (lowerrootvp == mp->mnt_vnodecovered) {
+		vn_lock(lowerrootvp, LK_EXCLUSIVE | LK_RETRY | LK_CANRECURSE);
+		lowerrootvp->v_vflag |= VV_CROSSLOCK;
+		VOP_UNLOCK(lowerrootvp);
+	}
+
 	MNT_ILOCK(mp);
 	if ((xmp->nullm_flags & NULLM_CACHE) != 0) {
 		mp->mnt_kern_flag |= lowerrootvp->v_mount->mnt_kern_flag &
@@ -261,6 +267,11 @@
 		vfs_unregister_for_notification(mntdata->nullm_vfs,
 		    &mntdata->notify_node);
 	}
+	if (mntdata->nullm_lowerrootvp == mp->mnt_vnodecovered) {
+		vn_lock(mp->mnt_vnodecovered, LK_EXCLUSIVE | LK_RETRY | LK_CANRECURSE);
+		mp->mnt_vnodecovered->v_vflag &= ~VV_CROSSLOCK;
+		VOP_UNLOCK(mp->mnt_vnodecovered);
+	}
 	vfs_unregister_upper(mntdata->nullm_vfs, &mntdata->upper_node);
 	vrele(mntdata->nullm_lowerrootvp);
 	mp->mnt_data = NULL;
diff --git a/sys/fs/unionfs/union_vfsops.c b/sys/fs/unionfs/union_vfsops.c
--- a/sys/fs/unionfs/union_vfsops.c
+++ b/sys/fs/unionfs/union_vfsops.c
@@ -329,7 +329,7 @@
 	 * order unionfs currently requires.
 	 */
 	if (!below) {
-		vn_lock(mp->mnt_vnodecovered, LK_EXCLUSIVE | LK_RETRY);
+		vn_lock(mp->mnt_vnodecovered, LK_EXCLUSIVE | LK_RETRY | LK_CANRECURSE);
 		mp->mnt_vnodecovered->v_vflag |= VV_CROSSLOCK;
 		VOP_UNLOCK(mp->mnt_vnodecovered);
 	}
@@ -386,7 +386,7 @@
 	if (error)
 		return (error);
 
-	vn_lock(mp->mnt_vnodecovered, LK_EXCLUSIVE | LK_RETRY);
+	vn_lock(mp->mnt_vnodecovered, LK_EXCLUSIVE | LK_RETRY | LK_CANRECURSE);
 	mp->mnt_vnodecovered->v_vflag &= ~VV_CROSSLOCK;
 	VOP_UNLOCK(mp->mnt_vnodecovered);
 	vfs_unregister_upper(ump->um_lowervp->v_mount, &ump->um_lower_link);
diff --git a/sys/kern/vfs_lookup.c b/sys/kern/vfs_lookup.c
--- a/sys/kern/vfs_lookup.c
+++ b/sys/kern/vfs_lookup.c
@@ -1265,14 +1265,28 @@
 		crosslock = (dp->v_vflag & VV_CROSSLOCK) != 0;
 		crosslkflags = compute_cn_lkflags(mp, cnp->cn_lkflags,
 		    cnp->cn_flags);
-		if (__predict_false(crosslock) &&
-		    (crosslkflags & LK_EXCLUSIVE) != 0 &&
-		    VOP_ISLOCKED(dp) != LK_EXCLUSIVE) {
-			vn_lock(dp, LK_UPGRADE | LK_RETRY);
-			if (VN_IS_DOOMED(dp)) {
-				error = ENOENT;
-				goto bad2;
-			}
+		if (__predict_false(crosslock)) {
+			/*
+			 * We are going to be holding the vnode lock, which
+			 * in this case is shared by the root vnode of the
+			 * filesystem mounted at mp, across the call to
+			 * VFS_ROOT().  Make the situation clear to the
+			 * filesystem by passing LK_CANRECURSE if the
+			 * lock is held exclusive, or by clearinng
+			 * LK_NODDLKTREAT to allow recursion on the shared
+			 * lock in the presence of an exclusive waiter.
+			 */
+			if (VOP_ISLOCKED(dp) == LK_EXCLUSIVE) {
+				crosslkflags &= ~LK_SHARED;
+				crosslkflags |= (LK_EXCLUSIVE | LK_CANRECURSE);
+			} else if ((crosslkflags & LK_EXCLUSIVE) != 0) {
+				vn_lock(dp, LK_UPGRADE | LK_RETRY);
+				if (VN_IS_DOOMED(dp)) {
+					error = ENOENT;
+					goto bad2;
+				}
+			} else
+				crosslkflags &= ~LK_NODDLKTREAT;
 		}
 		if (vfs_busy(mp, 0) != 0)
 			continue;