linux-kernel - [21/67] mm: fix corruption of hibernation caused by reusing swap during image saving

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Date:	Wed, 11 Aug 2010 17:05:36 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Hugh Dickins <hughd@...gle.com>
Subject: [21/67] mm: fix corruption of hibernation caused by reusing swap during image saving

2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

commit 966cca029f739716fbcc8068b8c6dfe381f86fc3 upstream.

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 caused by commit c9e444103b5e7a5 ("mm: reuse unused swap
entry if necessary").

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.

Hance memory is corrupted.

This patch avoids the bug by not reclaiming swap-entry during hibernation.
This is a quick fix for backporting.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Rafael J. Wysocki <rjw@...k.pl>
Reported-by: Ondreg Zary <linux@...nbow-software.org>
Tested-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: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 mm/swapfile.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/mm/swapfile.c
+++ b/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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