r=adilger

r=adilger
Patch from SuSE:
revalidate_special() is called from link_path_walk as the last path component is
(".."). In revalidate_special() we called

real_lookup(dentry->d_parent,&dentry->d_name, nd), which called cifs_lookup().
which doesnot initialises dentry->d_op pointer if there is no corresponding
inode to the dentry. cifs_lookup() returned NULL dentry with d_op() as NULL.

so, in the second iteration of the loop in revalidate_special() we have d_op
as NULL and hence the crash in

  if (!dentry->d_op->d_revalidate(dentry, nd)) {