Re: [PATCH 2/2] base/memory, hotplug: fix a kernel oops in show_valid_zones()

From: Kani, Toshimitsu
Date: Thu Jan 26 2017 - 17:44:50 EST

On Thu, 2017-01-26 at 13:52 -0800, Andrew Morton wrote:
> On Thu, 26 Jan 2017 14:44:15 -0700 Toshi Kani <toshi.kani@xxxxxxx>
> wrote:
> > Reading a sysfs memoryN/valid_zones file leads to the following
> > oops when the first page of a range is not backed by struct page.
> > show_valid_zones() assumes that 'start_pfn' is always valid for
> > page_zone().
> >
> > ÂBUG: unable to handle kernel paging request at ffffea017a000000
> > ÂIP: show_valid_zones+0x6f/0x160
> >
> > Since test_pages_in_a_zone() already checks holes, extend this
> > function to return 'valid_start' and 'valid_end' for a given range.
> > show_valid_zones() then proceeds with the valid range.
> This doesn't apply to current mainline due to changes in
> zone_can_shift().ÂÂPlease redo and resend.

Sorry, I will rebase to the -mm tree and resend the patches.

> Please also update the changelog to provide sufficient information
> for others to decide which kernel(s) need the fix.ÂÂIn particular:
> under what circumstances will it occur?ÂÂOn real machines which real
> people own?

Yes, this issue happens on real x86 machines with 64GiB or more memory.
On such systems, the memory block size is bumped up to 2GiB. [1]

Here is an example system. 0x3240000000 is only aligned by 1GiB and
its memory block starts from 0x3200000000, which is not backed by
struct page.

ÂBIOS-e820: [memÂ0x0000003240000000-0x000000603fffffff] usable

I will add the descriptions to the patch.