On Tue, Sep 26, 2017 at 10:26:26AM -0700, Shaohua Li wrote: > From: Shaohua Li <shli@xxxxxx> > > 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. Reclaim and MADV_FREE hold the page lock when manipulating the dirty and the swapcache state. Instead of undoing a racing MADV_FREE in reclaim, wouldn't it be safe to check the dirty bit before add_to_swap() and skip clean pages?