Ok, an update.

I've tried with a 2.0 kernel and with the BBA instead of the LAN
adapter and it still reboots. It happened while I was extracting a
cross-compiled base.tgz (from nfs) over my root partition (also nfs).

I previously tried to extract the base.tgz with a LAN adapter and it
rebooted, too.

The problem seems to be independent of the DC network card.

Matt, you wrote:

> Not seen anything on my Jornada (hpcsh). Been building stuff 
> on it quite
> happily over an NFS root and swap, and it appears to have been up for
> 80-odd days so far (quite by accident :-).

and Nick wrote

> I've been told that the sh4 specific cache handling is suspected.
 

So I think it should also happen on your Jornada. Can you stress test
it a bit? Try to extract base.tgz or another big archive over nfs,
maybe repeatedly, and see whether it reboots or crashes.

regards,
chris