linux-kernel - Re: [PATCH 0/2] revert changes to zcache_do

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Message-ID: <5036AA38.6010400@linux.vnet.ibm.com>
Date:	Thu, 23 Aug 2012 17:10:00 -0500
From:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	devel@...verdev.osuosl.org, xiaoguangrong@...ux.vnet.ibm.com
Subject: Re: [PATCH 0/2] revert changes to zcache_do_preload()

On 08/23/2012 03:56 PM, Minchan Kim wrote:
> Hi Seth,
> 
> On Thu, Aug 23, 2012 at 10:33:09AM -0500, Seth Jennings wrote:
>> This patchset fixes a regression in 3.6 by reverting two dependent
>> commits that made changes to zcache_do_preload().
>>
>> The commits undermine an assumption made by tmem_put() in
>> the cleancache path that preemption is disabled.  This change
>> introduces a race condition that can result in the wrong page
>> being returned by tmem_get(), causing assorted errors (segfaults,
>> apparent file corruption, etc) in userspace.
>>
>> The corruption was discussed in this thread:
>> https://lkml.org/lkml/2012/8/17/494
> 
> I think changelog isn't enough to explain what's the race.
> Could you write it down in detail?

I didn't come upon this solution via code inspection, but
rather through discovering that the issue didn't exist in
v3.5 and just looking at the changes since then.

> And you should Cc'ed Xiao who is author of reverted patch.

Thanks for adding Xiao.  I meant to do this. For some reason
I thought that you submitted that patchset :-/
My bad.

Seth

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