Somewhere in the neighborhood of the 4.8.12 patchet, I stopped being able to boot my arch linux grsecurity hardened kernel. It would get about half-way through, then just have an inconsistently flashing cursor. I've tried soft-moding PAX, tons of different compilation flags, nothing seemed to fix it. I also was unable to ever get good logs. I've finally gotten some command line dumping to get some info during boot. It appears that systemd-logind creates a tmpfs for the root user (120), mounts it, then chdirs into it. Immediately after, it unmounts the tmpfs, and chdirs back to the previous location. Systemd-logind then repeats this. It repeats thousands of times. It seems similar, but slightly different from an older bug with SELINUX: https://bugzilla.redhat.com/show_bug.cgi?id=1075835
I only have this particular issue when using gdm, when using lightdm, the system gets to the display manager, then hangs after logging in, I guess it calls logind after authenticating on the dm?
My build is a fork of the one built for Arch Linux, you can find the pkgbuild and config here: https://github.com/osteichthyes/linux-grsec
I'm in the process of testing and will post more when I have some more information.