STABLE10-linux-dentry-revalidation-always-revalidate-20010420

STABLE10-linux-dentry-revalidation-always-revalidate-20010420

Based on collaboration with Chas Williams and Chaskiel Grundman

Always force revalidation so if call which caused caching was in another
authentication "context" we don't inadvertantly leak information.

Cases where things matter involve bad caching for negative dentries
(something fails because you don't have permission, then you authenticate
and the negative dentry is not flushed) or when you have l only and
someone with rl caused the dentry to get cached, in which case stat()
information and nothing else is leaked

(cherry picked from commit 8d91087287cb0e4e15ca1b2eb64bca8dbc9077c0)