It's a lot easier just to reboot and let fsck patch up your filesystem... flushing buffers isn't going to help you get back the last paragraph of your PhD thesis if Libre Office hasn't called write().
In any case, in ~8 years of using Linux, I don't think I've had a freeze that was the kernel and not just X.
In any case, in ~8 years of using Linux, I don't think I've had a freeze that was the kernel and not just X.