There is an '8139cp' driver too, it's supposed to be working better
as well, perhaps that one might not free the pages that are to be
zero_copied across the network before they are sent?! That is the real
problem if I understand Andrew's mail correctly.
You might send a 'linux 8139too sendfile() panic' kind of bugreport
to the 'netdev@xxxxxxxxxxx' mailing list. That is the list where the
networking gurus are supposed to be hanging out. Although IMVHO this bug
is more on the kernel than on the network side. Also filing an entry to
bugzilla.kernel.org might speed up someone fixing the real problem.
Easiest workaround might be to just use a customised distcc for the
machines involved: just download the source from 'distcc.samba.org', do
a regular './configure', and then in the generated 'src/config.h' hand
edit '#undef HAVE_SENDFILE' and '#undef HAVE_SYS_SENDFILE_H'. That
should stop distcc from using sendfile().