NFS client kernel issue?

[Andy Whitcroft]

On Mon, Jun 29, 2009 at 04:29:25PM -0700, Keith Jackson wrote:
> Hi,
> I've run into a strange problem, and I'm not sure where to ask about  
> it. It appears to be kernel related, so hopefully someone here can  
> shed some light on it for me. I have a over a dozen ubuntu 9 server  
> machines that share an NFS filesystem served up on a FreeBSD machine.  
> We recently upgraded the FreeBSD box to FreeBSD 7.2. The ubuntu  
> machines are running the standard 2.6.28-11-server kernel.
> 
> At this point, we started having problems with NFS on all of the  
> ubuntu machines. They would come up, mount the NFS shares and then  
> 5-10 minutes later NFS would be hung. I ran wireshark on one of them,  
> while doing "ls -l ~username". When NFS was working everything looked  
> fine. Once it hung, I would see the normal YP MATCH RPC call looking  
> for the entry for "username". The NIS server would return the password  
> entry for "username" as I'd expect. When things were working, I'd then  
> see the standard NFS traffic. When NFS was hosed, the YP MATCH reply  
> would be the last net traffic I would see to the NFS server. Nothing  
> NFS related would ever happen. An strace would show that the ls was  
> hung in a stat64 call.
> 
> A reboot of the system would cause things to start working for a  
> while, but 5-10 minutes later NFS would hang. I eventually updated to   
> a 2.6.30 kernel from: http://kernel.ubuntu.com/~kernel-ppa/mainline/v2.6.30/ 
>   This has fixed the problem.
> 
> Any thoughts on what the problem might be, or how I might go about  
> debugging it better?

I am unsure whether the YP stuff is done in the kernel, but there do
seem to be a number of reverted patches in the v2.6.28 to v2.6.30
period.  As an example:

    nfsd: Revert "svcrpc: take advantage of tcp autotuning"

It would be worth testing v2.6.29 as the midpoint to try and split the
difference and help reduce the gap.  Also get a bug filed in launchpad
and let us know its number.

-apw