NFS lockups in Xen/amd64 -currentish?

[Johan Ihren <johani%johani.org@localhost>]

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Hi,

In a Xen environment where I run an amd64 DOM0 with either amd64 or  
i386pae DOMUs I ran into the problem that amd64 DOMUs could not NFS  
mount anything from the DOM0. As soon as they touched NFS they hang  
hard. Now, I know that NFS problems tend to make things hang, and it  
is sometimes hard to distinguish between "hang" as in "kernel is hung"  
or as in "kernel is waiting for something".

This was -current as of mid-August and as I was short on time I  
switched to using i386pae DOMUs instead, where NFS (against the same  
DOM0) worked just fine. So I never sorted out the NFS hang issue.

Fast forward to tonight.

I now have the need to use ipfilter/ipnat on the DOMUs and now I  
realize that I never upgraded the DOMU userland from 4.0-REL. I.e. my  
currentish i386pae DOMUs have been running on an old 4.0 userland, but  
that fails the kernel version check in the ipfilter tools.

So I upgrade the userland and I'm immediately stuck in the same NFS  
hang for the i386pae DOMUs that I had a few weeks ago for amd64 DOMUs.

As NFS works just fine with the old 4.0 userland I can only assume  
that the DOM0 NFS server (running amd64/current) is fine. And as NFS  
works fine with a current i386pae kernel and an old userland I would  
guess that that kernel is fine.

So as it is only with "current" userlands in the DOMUs (regardless of  
arch) that I have problems I have to suspect the userland.

Does anyone know of any recent NFS issues that cause hangs? The i386  
userland is from August 28 and the amd64 userland is from August 11.  
Or does anyone have some bright idea what I might have done wrong  
(which would be fabolous, especially given the lack of clues)?

Regards,

Johan

PS. I should add that my ability to debug right now is fairly limited  
as I'm departing tomorrow for the other side of the planet (the lower  
half) for two weeks. Therefore I'm very much in the "grateful for any  
sort of ugly workaround heard of" mode of operation...
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