[PATCH 3/5] mm/swap_state: fix get_shadow_from_swap_cache() race with swapoff

[Miaohe Lin]

The function get_shadow_from_swap_cache() can race with swapoff, though
it's only called by do_swap_page() now.

Fixes: aae466b0052e ("mm/swap: implement workingset detection for anonymous LRU")
Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
---
 mm/swap_state.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/swap_state.c b/mm/swap_state.c
index 272ea2108c9d..709c260d644a 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -83,11 +83,14 @@ void show_swap_cache_info(void)
 
 void *get_shadow_from_swap_cache(swp_entry_t entry)
 {
-	struct address_space *address_space = swap_address_space(entry);
-	pgoff_t idx = swp_offset(entry);
+	struct swap_info_struct *si;
 	struct page *page;
 
-	page = xa_load(&address_space->i_pages, idx);
+	si = get_swap_device(entry);
+	if (!si)
+		return NULL;
+	page = xa_load(&swap_address_space(entry)->i_pages, swp_offset(entry));
+	put_swap_device(si);
 	if (xa_is_value(page))
 		return page;
 	return NULL;
-- 
2.19.1