Repeated NFS failures

[Vincent <10.50%free.fr@localhost>]

Hi folks,

since quite a bit of time, I experience sporadic but frequent NFS 
failures between my 4.0 i386 server and my amd64-current client.

Sometimes, in the midst of a file transfert (I guess only while writing 
to the server), the transfer would hang. The client is not hung, though, 
so I can access a utility like "nfsstat" which shows an increasing 
number of retries. Yet, "reboot" is stuck and I have to reboot the 
machine the dirty way.

At first, I thought this might been caused by an IPv6 nfs mount. But I 
have the same problem when I export the mount points through IPv4 only.

Sometimes, I got a crash. The kernel obviously go stray, nothing 
responds anymore, not even the ACPI power button, so I have to reboot also.

I've seen there are some issues with NFS/AMD64/Xen. Could it be somewhat 
related?

Vincent