You'll see the following and the boot process will freeze:
io scheduler noop registered
io scheduler anticipatory registeredio scheduler deadline registeredio scheduler cfq registered (default)
I have struggled with this issue on various systems using all sorts of kernels, kernels where the issue should be "fixed". As far as I can recall through debugging, this is a hang during pci_init.
It's beyond me why such a critical thing could happen and has not been fixed.