Bug#816621: ioremap error on /sys/firmware/dmi/entries/*/raw is triggered by mcelog

[Sergio Gelato <Sergio.Gelato@astro.su.se>]

A closer look at the events around t=9s (when the page cache mode is switched
to WB) pointed to mcelog as a suspect. Indeed the problem went away after
purging the mcelog package. With mcelog (104-1) installed I was getting the
following message in the logs:

mcelog: failed to prefill DIMM database from DMI data

I still think there is a kernel issue here: mcelog shouldn't be able to
request the wrong page cache mode and spoil things for everyone else.

(Or is it dmi_remap() that's asking for the wrong mode? I'm not quite sure:
if DMI data are non-volatile and read-only (are they always?) why shouldn't
they be cached?)