mm/hwpoison: fix wrong num_poisoned_pages accounting

Currently, migration code increses num_poisoned_pages on *failed*
migration page as well as successfully migrated one at the trial of
memory-failure.  It will make the stat wrong.  As well, it marks the
page as PG_HWPoison even if the migration trial failed.  It would mean
we cannot recover the corrupted page using memory-failure facility.

This patches fixes it.

Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index 6c822a7b27e0..f9dfb18a4eba 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -975,7 +975,13 @@ out:
                 dec_zone_page_state(page, NR_ISOLATED_ANON +
                                 page_is_file_cache(page));
                 /* Soft-offlined page shouldn't go through lru cache list */
-                if (reason == MR_MEMORY_FAILURE) {
+                if (reason == MR_MEMORY_FAILURE && rc == MIGRATEPAGE_SUCCESS) {
+                        /*
+                         * With this release, we free successfully migrated
+                         * page and set PG_HWPoison on just freed page
+                         * intentionally. Although it's rather weird, it's how
+                         * HWPoison flag works at the moment.
+                         */
                         put_page(page);
                         if (!test_set_page_hwpoison(page))
                                 num_poisoned_pages_inc();