[RFC PATCH] mm/init: fix zone boundary creation

[oliver]

On Fri, May 27, 2016 at 7:21 AM, Andrew Morton
<akpm at linux-foundation.org> wrote:
> hm, this is all ten year old Mel code.
>
> What's the priority on this?  What are the user-visible runtime
> effects, how many people are affected, etc?

Low priority. To get bitten by this you need to enable a zone that appears
after ZONE_MOVABLE in the zone_type enum. As far as I can tell this means
running a kernel with ZONE_DEVICE or ZONE_CMA enabled, so I can't see this
affecting too many people.

I only noticed this because I've been fiddling with ZONE_DEVICE on powerpc and
4.6 broke my test kernel. This bug, in conjunction with the changes in Taku
Izumi's kernelcore=mirror patch (d91749c1dda71) and powerpc being the odd
architecture which initialises max_zone_pfn[] to ~0ul instead of 0 caused all
of system memory to be placed into ZONE_DEVICE at boot, followed a
panic since device memory cannot be used for kernel allocations. I've already
submitted a patch to fix the powerpc specific bits, but I figured this should
be fixed too.

oliver