I have a system which was upgraded from SL301 to SL302 by following
the procedure at
https://www.scientificlinux.org/documentation/howto/upgrade

Prior to the upgrade, the system had the kernel development RPMs
installed.

I now find that I can't do kernel development nor build kernel modules
on this.  The symptoms are lots of errors about symbols being
redefined or undefined.

I haven't looked too closely into this yet.  Just thought I'd try a
quick query as to whether this really is a consequence of having
followed the upgrade procedure, or whether I should be looking for
some other cause?