linux-kernel - Re: [BUGFIX][PATCH] fix corruption of hibernation caused by reusing swap at saving image

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Message-ID: <AANLkTimi7iQbLeAS6DLZKLa7EED_eEc0WymCh-butmhm@mail.gmail.com>
Date:	Thu, 5 Aug 2010 12:12:58 -0700
From:	Hugh Dickins <hughd@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrea Gelmini <andrea.gelmini@...il.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Ondrej Zary <linux@...nbow-software.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ibm.com>, nigel@...onice.net,
	stable@...nel.org
Subject: Re: [BUGFIX][PATCH] fix corruption of hibernation caused by reusing 
	swap at saving image

On Tue, Aug 3, 2010 at 7:46 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Wed, 4 Aug 2010 11:31:22 +0900
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
>
>> On Wed, 4 Aug 2010 10:50:54 +0900
>> KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
>>
>> > This patch is created against 2.6.35. CC'ed stable.
>> > Thank you for all helps.
>> >
>>
>> I'm sorry I now doubt this patch is wrong.
>
> Changed the description.
> Maybe the patch description/my understanding was wrong
> but the patch itself should work.
>
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> Since 2.6.31, swap_map[]'s refcounting was changed to show that
> a used swap entry is just for swap-cache, can be reused.
> Then, while scanning free entry in swap_map[], a swap entry may
> be able to be reclaimed and reused. It was by the commit
> c9e444103b5e7a5a3519f9913f59767f92e33baf.
>
> But this caused deta corruption at resume.
> The scenario is
>        - Assume a clean-swap cache, but mapped.
>        - at hibernation_snapshot[], clean-swap-cache is saved as
>          clean-swap-cache and swap_map[] is marked as SWAP_HAS_CACHE.
>        - then, save_image() is called. And reuse SWAP_HAS_CACHE entry
>          to save image, and break the contents.
>        After resume.
>        - the memory reclaim runs and finds clean-not-referenced-swap-cache
>          and discards it because it's marked as clean.
>          But here, the contents on disk and swap-cache is inconsistent.
>
> Here, memory is corrupted.

Yes, that's the scenario: I thought that was what you meant by your
original description, but this more detailed description is a better
one.

Hugh
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