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

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Date:	Wed, 4 Aug 2010 11:31:22 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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, Hugh Dickins <hughd@...gle.com>
Subject: Re: [BUGFIX][PATCH] fix corruption of hibernation caused by reusing
 swap at saving image

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.
What should be done is stop swap-reuse before hibernation_snapshot().
But, hmm, this one can't.

Maybe what really happens is someone (kswapd?) reuses swap while
swsusp_alloc() is on going.

please allow me to retry..

Thanks,
-Kame


> =
> 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 hibernation. Considering how
> the image is saved, the calls of try_to_reclaim_swap() changes the
> status of memory and there will be inconsitency between saved-memory-image's
> swap_map[] / memmap / swapper_space because memory is saved per page with
> swap-allocation per page.
> 
> This patch is for avoiding bug by not reclaiming swap-entry at hibernation.
> This is a quick fix for backporting.
> 
> Cc: stable@...nel.org
> Cc: Rafael J. Wysocki <rjw@...k.pl>
> Reported-by: Ondreg Zary <linux@...nbow-software.org>
> Tested-by: Andrea Gelmini <andrea.gelmini@...il.com>
> Acked-by: Hugh Dickins <hughd@...gle.com>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
>  mm/swapfile.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6.35.org/mm/swapfile.c
> ===================================================================
> --- linux-2.6.35.org.orig/mm/swapfile.c
> +++ linux-2.6.35.org/mm/swapfile.c
> @@ -318,8 +318,10 @@ checks:
>  	if (offset > si->highest_bit)
>  		scan_base = offset = si->lowest_bit;
>  
> -	/* reuse swap entry of cache-only swap if not busy. */
> -	if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) {
> +	/* reuse swap entry of cache-only swap if not hibernation. */
> +	if (vm_swap_full()
> +		&& usage == SWAP_HAS_CACHE
> +		&& si->swap_map[offset] == SWAP_HAS_CACHE) {
>  		int swap_was_freed;
>  		spin_unlock(&swap_lock);
>  		swap_was_freed = __try_to_reclaim_swap(si, offset);
> 
> 

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