can't access wp-admin after 3.9 upgrade

I can’t log into my site after upgrading wordpress. When I try to access the log in page I get redirected to my front page.
I’ve tried disabling plugins and the htaccess file without success. I can log in to my sub domains but when I then try to access the main site from there I again get redirected to my front page.
Any suggestions as to how I get out of that loop? It sounds like the permalinks need to be updated but as I can’t get in I can’t do it via the normal user interface.