Comment # 44 on bug 1017783 from Borislav Petkov

(In reply to Dainius Masiliunas from comment #43)
> I'm not sure if it's the same problem,

Well, "freezes at boot" is not the same as "RCU stalls".

> but with kernel 4.9.0-2 I can boot fine, but after a few minutes I
> start getting RCU stalls. That makes processes hang and rebooting
> impossible (systemd shows that it's waiting for services to turn off,
> but never kills them, and pressing ctrl+alt+del makes it hang too).
> This is a desktop system with i5-3470.
>
> Workaround is to install kernel 4.9.3 from the Kernel:stable repo.

Sounds like the fix for your issue went into 4.9.3 and you're good to
go. Or what is the problem?