From: Shaohua Li <shli@fb.com>
Date: Tue, 3 Oct 2017 16:15:29 -0700
Subject: mm: avoid marking swap cached page as lazyfree
Git-commit: 24c92eb7dce0a299b8e1a8c5fa585844a53bf7f0
Patch-mainline: v4.14-rc4
References: VM Functionality, bsc#1061775

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.  Page reclaim could add
the page to swap cache and unmap the page.  After page reclaim, the page
is added back to lru.  At that time, we probably start draining per-cpu
pagevec and mark the page lazyfree.  So the page could be in a state
with SwapBacked cleared and PG_swapcache set.  Next time there is a
refault in the virtual address, do_swap_page can find the page from swap
cache but the page has PageSwapCache false because SwapBacked isn't set,
so do_swap_page will bail out and do nothing.  The task will keep
running into fault handler.

Fixes: 802a3a92ad7a ("mm: reclaim MADV_FREE pages")
Link: http://lkml.kernel.org/r/6537ef3814398c0073630b03f176263bc81f0902.1506446061.git.shli@fb.com
Signed-off-by: Shaohua Li <shli@fb.com>
Reported-by: Artem Savkov <asavkov@redhat.com>
Tested-by: Artem Savkov <asavkov@redhat.com>
Reviewed-by: Rik van Riel <riel@redhat.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: <stable@vger.kernel.org>	[4.12+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/swap.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

--- a/mm/swap.c
+++ b/mm/swap.c
@@ -575,7 +575,7 @@ static void lru_lazyfree_fn(struct page
 			    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,
@@ -664,7 +664,7 @@ void deactivate_file_page(struct page *p
 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);