NFS clients freeze and can not disconnect

[Francisco Reyes]

I have a series of machines 6.0 stable (various dates), 6.1 stable (various 
dates) that freeze if the NFS sever they are connected to becomes 
unresponsive or crashes. Was able to confirm this behavior for both i386 and 
AMD64.

A 5.3 machine connected to the same nfs server was able to "umount -f" the 
volume.

I was able to reproduce the problem in a test environment.
Tried TCP, UDP connections, soft mount and a retry count of 1.

It doesn't seem to matter whether the server is 6.X or 5.X (tested in both), 
it is the 6.X client that has the problem.

Searching the archives seem to be a known issue.
Is there a patch? Or has it recently being fixed? 
The dates of my 6.X client machines varies, but are 6.0 stable up to 
6.1Stable may 29.