swap: check mapping_empty() for swap cache before being freed

To check whether all pages and shadow entries in swap cache has been
removed before swap cache is freed.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: "Huang, Ying" <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Vlastimil Babka <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Ilya Dryomov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

1 files changed, 6 insertions, 1 deletions

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 4f8a912ff692..c56aa9ac050d 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -693,7 +693,12 @@ 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_WARN_ON_ONCE(!mapping_empty(&spaces[i]));
+	kvfree(spaces);
 	nr_swapper_spaces[type] = 0;
 	swapper_spaces[type] = NULL;
 }