--- src.orig/sys/kern/vfs_vnops.c	Sat Jan 14 13:15:09 2006
+++ src/sys/kern/vfs_vnops.c	Tue Jan 17 22:32:19 2006
@@ -885,6 +885,11 @@
 	if ((mp = *mpp) == NULL)
 		return (0);
 	MNT_ILOCK(mp);
+	/* Stop if the mount point is being unmounted. */
+	if (mp->mnt_kern_flag & MNTK_UNMOUNT) {
+		error = EBUSY;
+		goto unlock;
+	}
 	/*
 	 * Check on status of suspension.
 	 */