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From:   Liu Shixin <liushixin2@huawei.com>
To:     Sachin Sant <sachinp@linux.ibm.com>,
        Michael Ellerman <michaele@au1.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Yosry Ahmed <yosryahmed@google.com>,
        Huang Ying <ying.huang@intel.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>
CC:     <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
        Liu Shixin <liushixin2@huawei.com>
Subject: [PATCH] mm: vmscan: fix NULL pointer dereference in can_reclaim_anon_pages
Date:   Fri, 8 Sep 2023 17:31:03 +0800
Message-ID: <20230908093103.2620512-1-liushixin2@huawei.com>
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Precedence: bulk

The variable sc is NULL pointer in can_reclaim_anon_pages() when called
from zone_reclaimable_pages(). Check it before setting swapcache_only.

Reported-by: Sachin Sant <sachinp@linux.ibm.com>
Link: https://lore.kernel.org/linux-mm/F00144DE-2A3F-4463-8203-45E0D57E313E@linux.ibm.com/T/
Fixes: 92039ae85e8d("mm: vmscan: try to reclaim swapcache pages if no swap space")
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
---
 mm/vmscan.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index f1dc0dbf1cdb..5eb85ddf403f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -617,7 +617,7 @@ static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg,
 		if (get_nr_swap_pages() > 0)
 			return true;
 		/* Is there any swapcache pages to reclaim? */
-		if (total_swapcache_pages() > 0) {
+		if (sc && total_swapcache_pages() > 0) {
 			sc->swapcache_only = 1;
 			return true;
 		}
@@ -626,7 +626,7 @@ static inline bool can_reclaim_anon_pages(struct mem_cgroup *memcg,
 		if (mem_cgroup_get_nr_swap_pages(memcg) > 0)
 			return true;
 		/* Is there any swapcache pages in memcg to reclaim? */
-		if (mem_cgroup_get_nr_swapcache_pages(memcg) > 0) {
+		if (sc && mem_cgroup_get_nr_swapcache_pages(memcg) > 0) {
 			sc->swapcache_only = 1;
 			return true;
 		}
-- 
2.25.1