Since exp_parent can fail by returning an error (-EAGAIN) in addition to by
returning NULL, we should check for that case in exp_rootfh.

(TODO: we should check that userland handles these errors too.)
Signed-off-by: NJ. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: NNeil Brown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>