The problem seems to be that 30-rcX thinks that there are dependencies
to update (such as include/config/kernel.release and version.h.tmp)
during a make-install operation. Since I am on a root-squashed NFS
mount, these files cannot be updated and thus the install fails. Previous trees prior to linux-current (at least up to 2.6.29) did not
try to update these files so the install would succeed.
It is because arch/x86/Makefile has
a dependency on vmlinux for the install target.
I know hpa has had a fix for it but it is not applied.
I recall there was a trivial bug in the first version.