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: NMinchan Kim <minchan@kernel.org>
Reported-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>