Hi.

I've been looking at a bugzilla which describes a problem where
a customer was advised to use either the "noac" or "actimeo=0"
mount options to solve a consistency problem that they were
seeing in the file attributes.  It turned out that this solution
did not work reliably for them because sometimes, the local
attribute cache was believed to be valid and not timed out.
(With an attribute cache timeout of 0, the cache should always
appear to be timed out.)

In looking at this situation, it appears to me that the problem
is that the attribute cache timeout code has an off-by-one
error in it.  It is assuming that the cache is valid in the
region, [read_cache_jiffies, read_cache_jiffies + attrtimeo].  The
cache should be considered valid only in the region,
[read_cache_jiffies, read_cache_jiffies + attrtimeo).  With this
change, the options, "noac" and "actimeo=0", work as originally
expected.

While I was there, I addressed a problem with the jiffies
overflowing on 32 bit systems.  When overflow occurs, the
value of read_cache_jiffies + attrtimeo can be less then the
value of read_cache_jiffies.  This would cause an unnecessary
GETATTR over the wire.

Thoughts and/or comments?  This is an updated patch which includes
the previous support which was added to correct the noac/actimeo=0
handling.

  Thanx...

     ps

Signed-off-by: Peter Staubach <staubach@redhat.com>