While rebooting a machine for example to apply a kernel update, it hangs. You try older kernels, and it hangs too. Not necessarily at the same spot. Here are some examples:

...io scheduler cfq registered (default)
...Real Time Clock Driver v1.12ac

These kernel hangs during boot are interestingly traceable to the USB keyboard. If you use a PS2 keyboard instead, the kernel may just continue booting. No comment.