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

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Message-id: <000001d0030d$0505aaa0$0f10ffe0$%yang@samsung.com>
Date:	Tue, 18 Nov 2014 16:51:36 +0800
From:	Weijie Yang <weijie.yang@...sung.com>
To:	konrad.wilk@...cle.com
Cc:	'Andrew Morton' <akpm@...ux-foundation.org>,
	'Seth Jennings' <sjennings@...iantweb.net>,
	'Dan Streetman' <ddstreet@...e.org>,
	'Minchan Kim' <minchan@...nel.org>,
	'Bob Liu' <bob.liu@...cle.com>, xfishcoder@...il.com,
	'Weijie Yang' <weijie.yang.kh@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] mm: frontswap: invalidate expired data on a dup-store failure

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@...sung.com>
---
 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
 		 */
 		inc_frontswap_failed_stores();
-		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 */
-- 
1.7.0.4


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