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

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Date:   Wed, 20 Jan 2021 15:27:11 +0800
From:   Huang Ying <ying.huang@...el.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Huang Ying <ying.huang@...el.com>,
        Minchan Kim <minchan@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Christoph Hellwig <hch@....de>
Subject: [PATCH] swap: Check nrexceptional of swap cache before being freed

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

Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
Cc: Minchan Kim <minchan@...nel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@....com>,
Cc: Johannes Weiner <hannes@...xchg.org>,
Cc: Vlastimil Babka <vbabka@...e.cz>, Hugh Dickins <hughd@...gle.com>,
Cc: Mel Gorman <mgorman@...hsingularity.net>,
Cc: Michal Hocko <mhocko@...nel.org>,
Cc: Dan Williams <dan.j.williams@...el.com>,
Cc: Christoph Hellwig <hch@....de>, Ilya Dryomov <idryomov@...il.com>,
---
 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