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

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Date:	Fri, 24 Aug 2012 05:56:48 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Seth Jennings <sjenning@...ux.vnet.ibm.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nitin Gupta <ngupta@...are.org>,
	Minchan Kim <minchan@...nel.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()

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?

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

> 
> Please apply this patchset to 3.6.  This problem didn't exist
> in previous releases so nothing need be done for the stable trees.
> 
> Seth Jennings (2):
>   Revert "staging: zcache: cleanup zcache_do_preload and
>     zcache_put_page"
>   Revert "staging: zcache: optimize zcache_do_preload"
> 
>  drivers/staging/zcache/zcache-main.c |   54 +++++++++++++++++++---------------
>  1 file changed, 31 insertions(+), 23 deletions(-)
> 
> -- 
> 1.7.9.5
> 
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