Messages in this thread Patch in this message | | | Date | Wed, 4 Aug 2010 11:46:31 +0900 | From | KAMEZAWA Hiroyuki <> | Subject | Re: [BUGFIX][PATCH] fix corruption of hibernation caused by reusing swap at saving image |
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On Wed, 4 Aug 2010 11:31:22 +0900 KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:
> On Wed, 4 Aug 2010 10:50:54 +0900 > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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@jp.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.
This patch is for avoiding bug by not reclaiming swap-entry at hibernation. This is a quick fix for backporting.
Cc: stable@kernel.org Cc: Rafael J. Wysocki <rjw@sisk.pl> Reported-by: Ondreg Zary <linux@rainbow-software.org> Tested-by: Andrea Gelmini <andrea.gelmini@gmail.com> Acked-by: Hugh Dickins <hughd@google.com> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.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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