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

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Message-Id: <20120619160001.0c58c7be.akpm@linux-foundation.org>
Date:	Tue, 19 Jun 2012 16:00:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Pearson, Greg" <greg.pearson@...com>
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 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.

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