On Fri, Sep 22, 2017 at 11:46:30AM -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 the page is added to swap > cache, marking the page lazyfree will confuse page fault if the page is > reclaimed and refault. If page is added to swapcache while it stays lru_lazyfree_pvec, it ends up having !PG_swapbacked, PG_swapcache and !PG_dirty. Most important thing is PG_dirty. Without it, VM will reclaim the page without *writeback* so we lose the data. Although we prevent the page adding to swapcache, we lose the data unless we apply [2/2] so this patch alone doesn't fix the problem. That's why I said to you we don't need to separate patches. > > Reported-and-tested-by: Artem Savkov <asavkov@xxxxxxxxxx> > Fix: 802a3a92ad7a(mm: reclaim MADV_FREE pages) > Signed-off-by: Shaohua Li <shli@xxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > Cc: Johannes Weiner <hannes@xxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx> > Cc: Minchan Kim <minchan@xxxxxxxxxx> > Cc: Hugh Dickins <hughd@xxxxxxxxxx> > Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Reviewed-by: Rik van Riel <riel@xxxxxxxxxx> > --- > mm/swap.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/swap.c b/mm/swap.c > index 9295ae9..a77d68f 100644 > --- a/mm/swap.c > +++ b/mm/swap.c > @@ -575,7 +575,7 @@ static void lru_lazyfree_fn(struct page *page, struct lruvec *lruvec, > void *arg) > { > if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) && > - !PageUnevictable(page)) { > + !PageSwapCache(page) && !PageUnevictable(page)) { > bool active = PageActive(page); > > del_page_from_lru_list(page, lruvec, > @@ -665,7 +665,7 @@ void deactivate_file_page(struct page *page) > void mark_page_lazyfree(struct page *page) > { > if (PageLRU(page) && PageAnon(page) && PageSwapBacked(page) && > - !PageUnevictable(page)) { > + !PageSwapCache(page) && !PageUnevictable(page)) { > struct pagevec *pvec = &get_cpu_var(lru_lazyfree_pvecs); > > get_page(page); > -- > 2.9.5 >