On Tue, Sep 26, 2017 at 10:26:26AM -0700, Shaohua Li wrote:

From: Shaohua Li <redacted>

MADV_FREE clears pte dirty bit and then marks the page lazyfree (clear
SwapBacked). There is no lock to prevent the page is added to swap cache
between these two steps by page reclaim. If page reclaim finds such
page, it will simply add the page to swap cache without pageout the page
to swap because the page is marked as clean. Next time, page fault will
read data from the swap slot which doesn't have the original data, so we
have a data corruption. To fix issue, we mark the page dirty and pageout
the page.

However, we shouldn't dirty all pages which is clean and in swap cache.
swapin page is swap cache and clean too. So we only dirty page which is
added into swap cache in page reclaim, which shouldn't be swapin page.
As Minchan suggested, simply dirty the page in add_to_swap can do the
job.

Reported-by: Artem Savkov <redacted>
Fix: 802a3a92ad7a(mm: reclaim MADV_FREE pages)
Signed-off-by: Shaohua Li <redacted>

Acked-by: Minchan Kim <minchan@kernel.org>

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