nfs4 hangs, unkillable, using lots of CPU time

bzr diff
on a repository that is mounted via NFSv4 triggers a bug.
The result is that bzr hangs and is unkillable by any means, including kill -9. Another result is a NFS4 packet storm involving repeated failures of a WRITE request.

This seems to be a very specific corner case, as NFS4 works perfectly for everything else. Reading other bug reports and the bzr code, it seems to involve some kind of interaction between file locking and the ftruncate() system call.

Complete information can be found in bug https://bugs.launchpad.net/bugs/651806 .

To reproduce, unpack the attached tar file to make a directory called "bar" containing a .bzr repository.
Unpack this somewhere that is mounted over nfs4.
cd bar
bzr diff

enjoy!

ProblemType: Bug
DistroRelease: Ubuntu 10.10
Package: linux-image-2.6.35-23-generic 2.6.35-23.36
Regression: Yes
Reproducible: Yes
ProcVersionSignature: Ubuntu 2.6.35-23.36-generic 2.6.35.7
Uname: Linux 2.6.35-23-generic x86_64
NonfreeKernelModules: fglrx
AlsaVersion: Advanced Linux Sound Architecture Driver Version 1.0.23.
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: gpk 5100 F.... pulseaudio
 /dev/snd/pcmC0D0p: gpk 5100 F...m pulseaudio
CRDA: Error: [Errno 2] No such file or directory
Card0.Amixer.info:
 Card hw:0 'SB'/'HDA ATI SB at 0xfe024000 irq 16'
   Mixer name : 'Realtek ALC887'
   Components : 'HDA:10ec0887,1458a002,00100202'
   Controls : 38
   Simple ctrls : 21
Date: Sat Oct 30 18:05:38 2010
HibernationDevice: RESUME=UUID=6f657719-3b2e-4471-b419-bd2d396aeac2
InstallationMedia: Ubuntu 10.10 "Maverick Meerkat" - Beta amd64 (20100901.1)
IwConfig:
 lo no wireless extensions.

 eth0 no wireless extensions.

 vboxnet0 no wireless extensions.
MachineType: Gigabyte Technology Co., Ltd. GA-MA78LMT-S2
ProcCmdLine: BOOT_IMAGE=/boot/vmlinuz-2.6.35-23-generic root=UUID=f52187b6-c1df-4ee2-9996-bfac2bc98c2d ro quiet splash
ProcEnviron:
 PATH=(custom, user)
 LANG=en_GB.utf8
 SHELL=/bin/bash
RelatedPackageVersions: linux-firmware 1.38
RfKill:

SourcePackage: linux
dmi.bios.date: 03/18/2010
dmi.bios.vendor: Award Software International, Inc.
dmi.bios.version: F6
dmi.board.name: GA-MA78LMT-S2
dmi.board.vendor: Gigabyte Technology Co., Ltd.
dmi.board.version: x.x
dmi.chassis.type: 3
dmi.chassis.vendor: Gigabyte Technology Co., Ltd.
dmi.modalias: dmi:bvnAwardSoftwareInternational,Inc.:bvrF6:bd03/18/2010:svnGigabyteTechnologyCo.,Ltd.:pnGA-MA78LMT-S2:pvr:rvnGigabyteTechnologyCo.,Ltd.:rnGA-MA78LMT-S2:rvrx.x:cvnGigabyteTechnologyCo.,Ltd.:ct3:cvr:
dmi.product.name: GA-MA78LMT-S2
dmi.sys.vendor: Gigabyte Technology Co., Ltd.