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

From: Andrew Morton
Date: Thu Jan 26 2017 - 16:53:23 EST

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().
> BUG: unable to handle kernel paging request at ffffea017a000000
> IP: 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(). Please redo and resend.

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