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

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Date:   Fri, 27 Jan 2017 08:48:54 +0100
From:   "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To:     "Kani, Toshimitsu" <toshi.kani@....com>
Cc:     "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "zhenzhang.zhang@...wei.com" <zhenzhang.zhang@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "arbab@...ux.vnet.ibm.com" <arbab@...ux.vnet.ibm.com>,
        "abanman@....com" <abanman@....com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "rientjes@...gle.com" <rientjes@...gle.com>
Subject: Re: [PATCH 2/2] base/memory, hotplug: fix a kernel oops in
 show_valid_zones()

On Thu, Jan 26, 2017 at 10:26:23PM +0000, Kani, Toshimitsu wrote:
> 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@....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.
> 
> 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.  In particular:
> > under what circumstances will it occur?  On 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.
> 
>  BIOS-e820: [mem 0x0000003240000000-0x000000603fffffff] usable
> 
> I will add the descriptions to the patch.

Should it also be backported to the stable kernels to resolve the issue
there?

thanks,

greg k-h