[PATCH] mm: frontswap: invalidate expired data on a dup-store failure

From: Weijie Yang
Date: Tue Nov 18 2014 - 03:52:53 EST

If a frontswap dup-store failed, it should invalidate the expired page
in the backend, or it could trigger some data corruption issue.
Such as:
1. use zswap as the frontswap backend with writeback feature
2. store a swap page(version_1) to entry A, success
3. dup-store a newer page(version_2) to the same entry A, fail
4. use __swap_writepage() write version_2 page to swapfile, success
5. zswap do shrink, writeback version_1 page to swapfile
6. version_2 page is overwrited by version_1, data corrupt.

This patch fixes this issue by invalidating expired data immediately
when meet a dup-store failure.

Signed-off-by: Weijie Yang <weijie.yang@xxxxxxxxxxx>
mm/frontswap.c | 4 +++-
1 files changed, 3 insertions(+), 1 deletions(-)

diff --git a/mm/frontswap.c b/mm/frontswap.c
index c30eec5..f2a3571 100644
--- a/mm/frontswap.c
+++ b/mm/frontswap.c
@@ -244,8 +244,10 @@ int __frontswap_store(struct page *page)
the (older) page from frontswap
- if (dup)
+ if (dup) {
__frontswap_clear(sis, offset);
+ frontswap_ops->invalidate_page(type, offset);
+ }
if (frontswap_writethrough_enabled)
/* report failure so swap also writes to swap device */

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