Why is my file different on two NFS v3 clients?

Resolving The Problem

A nfs bug in Platform Rocks 4.0 can make a file permanently different on two nfs v3 clients that
mount (rw) a common directory. Permanent here means that no (known) amount of time fixes it
only cache invalidation (updating the file) or reboot helps.

SYMPTONS

This nfs bug is reported as that the nfs client updates it's meta-data correctly but
fails to invalidate it's data cache.
The bug has been reproduced on both 32- and 64-bit and with both 2.6.9-5.0.5smp
and 2.6.9-11smp. Since 2.6.9-11 is the kernel version for Platform Rocks 4.0, PR
4.0 hits this bug.

Steps to Reproduce:

requirements: two clients (n1, n2) that rw-mount a common nfs v3 directory
n1 $ echo foo > file
n2 $ cat file
foo
n1 $ touch .
n1 $ echo fxx > file
n2 $ touch file
n2 $ cat file
foo

Note that some discussions mentioned that how idle the hosts are may make a
difference to this bug: if two machines are idle, the bug will be triggled more often.Platform Rocks * is constrained to use the Redhat kernels and components. In terms of kernel update, this bug has been fixed in kernel 2.6.9-34, which is the kernel for Platform Rocks 4.1. So the affected PR 4.0 could resolve this bug by upgrading to Platform Rocks 4.1.

* This product includes software developed by the Rocks Cluster Group at the San Diego Supercomputer Center at the University of California, San Diego and its contributors.