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

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Message-Id: <20100729132325.59871484.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 29 Jul 2010 13:23:25 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	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>
Subject: Re: Memory corruption during hibernation since 2.6.31

On Wed, 28 Jul 2010 23:34:07 +0200
"Rafael J. Wysocki" <rjw@...k.pl> wrote:

> On Wednesday, July 28, 2010, Ondrej Zary wrote:
> > Hello,
> > after very long bisection, I finally found what's causing memory corruption 
> > during hibernation on my machine sice 2.6.31:
> > https://bugzilla.kernel.org/show_bug.cgi?id=15753
> > 
> > It's commit c9e444103b5e7a5a3519f9913f59767f92e33baf (mm: reuse unused swap 
> > entry if necessary).
> > 
> > I don't know anything about swapping in Linux so I don't have a clue what's
> > wrong with that commit.
> 
> Thanks for bisecting!
> 
> This looks rather serious.  I'd be grateful from any clues from the mm guys
> involved (CCed).
> 

Considering possible cases...and here is a patch.
but I'm not fully sure. Could you clarify ?

But hmm...status of swap_map[] to be recovered at resume() seems to be just
based on luck. or hibernation has some tricks on swap_map[] ?

==
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.


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
@@ -316,7 +316,9 @@ checks:
 		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) {
+	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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