[PATCH 1/2] mm: avoid marking swap cached page as lazyfree

[Shaohua Li <shli@kernel.org>]

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 the page is added to swap
cache, marking the page lazyfree will confuse page fault if the page is
reclaimed and refault.

Reported-and-tested-y: Artem Savkov <asavkov@redhat.com>
Fix: 802a3a92ad7a(mm: reclaim MADV_FREE pages)
Signed-off-by: Shaohua Li <shli@fb.com>
Cc: stable@vger.kernel.org
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 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

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