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

commit fb993fa1 upstream.

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@samsung.com>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Seth Jennings <sjennings@variantweb.net>
Cc: Dan Streetman <ddstreet@ieee.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Bob Liu <bob.liu@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

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 */