linux-kernel - Re: Memory corruption during hibernation since 2.6.31

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Date:	Thu, 29 Jul 2010 19:33:18 +0200
From:	Ondrej Zary <linux@...nbow-software.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Balbir Singh <balbir@...ibm.com>
Subject: Re: Memory corruption during hibernation since 2.6.31

On Thursday 29 July 2010 07:24:29 KAMEZAWA Hiroyuki wrote:
> On Thu, 29 Jul 2010 14:23:33 +0900 (JST)
>
> KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> > Can you please add explicit commenting in the code?
>
> How about this ?
> ==
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
>
> At hibernation, all pages-should-be-saved are written into a image (here,
> swap). Then, swap_map[], memmap etcs are also saved into disks.
>
> But, swap allocation happens one by one. So, the final image of swap_map[]
> is different from saved one and the commit
> c9e444103b5e7a5a3519f9913f59767f92e33baf changes page's state while
> assiging swap. Because memory can be modified in hibernation is only
> not-to-be-save memory. it's a breakage.
>
> This patch fixes it by disabling swap entry reuse at hibernation.


Thanks for the patch, I'm going to test it for a few days. It didn't compile 
with 2.6.32 (because of missing "usage" parameter) so I tried 2.6.35-rc6 only 
to find that there's regression since 2.6.34 that causes console font 
corruption with matroxfb. Almost every new kernel means new regressions on 
this machine. Looks like something is wrong with the development process...

So at least the patch compiles with 2.6.33 where the console works - so that's 
going to be tested.


> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> ---
>  mm/swapfile.c |    4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> Index: linux-2.6.34.org/mm/swapfile.c
> ===================================================================
> --- linux-2.6.34.org.orig/mm/swapfile.c
> +++ linux-2.6.34.org/mm/swapfile.c
> @@ -315,8 +315,15 @@ 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 busy &&
> + 	 * when we're called via pageout(). At hibernation, swap-reuse
> + 	 * is harmful because it changes memory status...which may
> + 	 * be saved already.
> + 	 */
> +	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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-- 
Ondrej Zary
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