nfs4 hangs, unkillable, using lots of CPU time

[gpk]

This is a continuation of a bug report that originally seemed to be a bzr bug.
For more details, see https://bugs.launchpad.net/bugs/665082 .
I do not know if this is a nfs-client bug or nfs-server.

Bzr hangs in a ftruncate() call (as shown by strace) and cannot be killed
by kill -9. The client and server are both rather busy (50% CPU) and there
are tens of thousands of requests per second going back and forth between
them (as shown by nfsstat).

Despite that all, both systems remain operational, and NFS4 continues to work
for other processes. When the client == the server (and possibly in other cases)
the machine hangs when I attempt a shutdown. I need to do a hard restart.

I attach a tar file for the .bzr directory that causes the problem:

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: nfs-common 1:1.2.2-1ubuntu1
ProcVersionSignature: Ubuntu 2.6.35-22.35-generic 2.6.35.4
Uname: Linux 2.6.35-22-generic x86_64
NonfreeKernelModules: fglrx
Architecture: amd64
Date: Sat Oct 23 17:53:22 2010
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Beta amd64 (20100901.1)
ProcEnviron:
 PATH=(custom, user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: nfs-utils