linux-kernel - Re: [PATCH 2/2] base/memory, hotplug: fix a kernel oops in show_valid

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Date:   Thu, 26 Jan 2017 13:52:54 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Toshi Kani <toshi.kani@....com>
Cc:     gregkh@...uxfoundation.org, linux-mm@...ck.org,
        zhenzhang.zhang@...wei.com, arbab@...ux.vnet.ibm.com,
        dan.j.williams@...el.com, abanman@....com, rientjes@...gle.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] base/memory, hotplug: fix a kernel oops in
 show_valid_zones()

On Thu, 26 Jan 2017 14:44:15 -0700 Toshi Kani <toshi.kani@....com> 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
own?