Configure error 2.2.0 - no locking

[Darrin Yeager]

I've got Redhat 6.2 kernel 2.2.18 and have been running samba 2.07.
When I try to configure samba 2.2.0, the configure bombs out with
an error

ERROR: No locking available. Running Samba would be unsafe

with what I think relevant lines from the configure output are:

checking for Linux kernel oplocks... no
checking for fcntl locking... no

Is there something I have to enable in the Kernel for samba 2.2?