Re: [PATCH V3 2/2] mm: fix data corruption caused by lazyfree page

[Minchan Kim <minchan@kernel.org>]

On Tue, Sep 26, 2017 at 10:26:26AM -0700, Shaohua Li wrote:
> From: Shaohua Li <shli@fb.com>
> 
> 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 <asavkov@redhat.com>
> Fix: 802a3a92ad7a(mm: reclaim MADV_FREE pages)
> Signed-off-by: Shaohua Li <shli@fb.com>

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

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