nfsfh.c:nfsd_findparent lookup("..") failure fix in 2.4.4 - xfs related?

[Peter Wächtler]

The following diff was made in 2.4.4.
 
diff -u --recursive --new-file v2.4.4/linux/fs/nfsd/nfsfh.c linux/fs/nfsd/nfsfh.c
--- v2.4.4/linux/fs/nfsd/nfsfh.c        Fri Feb  9 11:29:44 2001
+++ linux/fs/nfsd/nfsfh.c       Sat May 19 17:47:55 2001
@@ -244,6 +245,11 @@
         */
        pdentry = child->d_inode->i_op->lookup(child->d_inode, tdentry);
        d_drop(tdentry); /* we never want ".." hashed */
+       if (!pdentry && tdentry->d_inode == NULL) {
+               /* File system cannot find ".." ... sad but possible */
+               dput(tdentry);
+               pdentry = ERR_PTR(-EINVAL);
+       }

Umh. How is it possible to have a valid dentry which has no parent?
Even "/.." is linked to "/."

Is this xfs related? At least it was triggered on 2.4.3-xfs with
exported xfs filesystems.