Yesterday I was bitten by kernel update (to 4.10.5) on my main computer (I use Fedora 25). The boot process would at some point just stop, with nothing suspicious in the last visible boot messages; the machine was responsive, though, and Ctrl-Alt-Del reboot was possible. Booting using the previous kernel was fine. After reviewing the boot log (where -1 means second-to-last boot, -0 would be the last (successful) boot etc.):

journalctl -k -b -1

it turned out there was a problem uploading firmware blob to my Radeon R7 370 (I use the standard open-source driver):

kernel: [drm] radeon: 2048M of VRAM memory ready
kernel: [drm] radeon: 2048M of GTT memory ready.
kernel: [drm] Loading pitcairn Microcode
kernel: radeon 0000:01:00.0: Direct firmware load for radeon/si58_mc.bin failed with error -2
kernel: [drm] radeon/PITCAIRN_mc2.bin: 31100 bytes
kernel: si_fw: mixing new and old firmware!
kernel: [drm:si_init [radeon]] *ERROR* Failed to load firmware!
kernel: radeon 0000:01:00.0: Fatal error during GPU init

Indeed, for my particular Radeon model the newer kernel tries to upload si58_mc.bin, but the file was missing.

The solution was to get the file from https://people.freedesktop.org/~agd5f/radeon_ucode/, put it in /usr/lib/firmware/radeon and regenerate initramfs images:

dracut --regenerate-all --force