linux-kernel - Re: [PATCH v4] mm/memblock: fix overlapping allocation when doubling reserved array

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Message-ID: <4FE1EA73.2030300@hp.com>
Date:	Wed, 20 Jun 2012 15:21:24 +0000
From:	"Pearson, Greg" <greg.pearson@...com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	"tj@...nel.org" <tj@...nel.org>,
	"hpa@...ux.intel.com" <hpa@...ux.intel.com>,
	"shangw@...ux.vnet.ibm.com" <shangw@...ux.vnet.ibm.com>,
	"mingo@...e.hu" <mingo@...e.hu>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4] mm/memblock: fix overlapping allocation when
 doubling reserved array

On 06/19/2012 05:00 PM, Andrew Morton wrote:
> On Tue, 19 Jun 2012 22:35:08 +0000
> "Pearson, Greg" <greg.pearson@...com> wrote:
>
>> On 06/19/2012 04:14 PM, Andrew Morton wrote:
>>> On Mon, 18 Jun 2012 17:47:58 -0600
>>> Greg Pearson <greg.pearson@...com> wrote:
>>>
>>>> The __alloc_memory_core_early() routine will ask memblock for a range
>>>> of memory then try to reserve it. If the reserved region array lacks
>>>> space for the new range, memblock_double_array() is called to allocate
>>>> more space for the array. If memblock is used to allocate memory for
>>>> the new array it can end up using a range that overlaps with the range
>>>> originally allocated in __alloc_memory_core_early(), leading to possible
>>>> data corruption.
>>> OK, but we have no information about whether it *does* lead to data
>>> corruption.  Are there workloads which trigger this?  End users who are
>>> experiencing problems?
>>>
>>> See, I (and others) need to work out whether this patch should be
>>> included in 3.5 or even earlier kernels.  To do that we often need the
>>> developer to tell us what the impact of the bug is upon users.  Please
>>> always include this info when fixing bugs.
>> Andrew,
>>
>> I'm currently working on a prototype system that exhibits the data
>> corruption problem when doubling the reserved array while booting the
>> system. This system will be a released product in the future.
> OK.  I guess we can slip this fix into 3.5.  Do you think it should be
> backported?  I guess "yes", as you will probably want to run 3.4 or
> earlier kernels on that machine.
>
Having the fix in 3.4 would be good for us, as we do plan to test on the 
latest stable kernel.

If there is anything I can do to help with that please let me know.

Thanks

--
Greg--
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