[PATCH] swap: Check nrexceptional of swap cache before being freed

[Huang Ying]

To catch the error in updating the swap cache shadow entries or their count.

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>,
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>,
Cc: Vlastimil Babka <vbabka@xxxxxxx>, Hugh Dickins <hughd@xxxxxxxxxx>,
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>,
Cc: Michal Hocko <mhocko@xxxxxxxxxx>,
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>,
Cc: Christoph Hellwig <hch@xxxxxx>, Ilya Dryomov <idryomov@xxxxxxxxx>,
---
 mm/swap_state.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index d0d417efeecc..240a4f97594a 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -703,7 +703,12 @@ int init_swap_address_space(unsigned int type, unsigned long nr_pages)
 
 void exit_swap_address_space(unsigned int type)
 {
-	kvfree(swapper_spaces[type]);
+	int i;
+	struct address_space *spaces = swapper_spaces[type];
+
+	for (i = 0; i < nr_swapper_spaces[type]; i++)
+		VM_BUG_ON(spaces[i].nrexceptional);
+	kvfree(spaces);
 	nr_swapper_spaces[type] = 0;
 	swapper_spaces[type] = NULL;
 }
-- 
2.29.2