linux-kernel - [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing in mem_cgroup

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Date:   Thu, 29 Jul 2021 20:57:54 +0800
From:   Miaohe Lin <linmiaohe@...wei.com>
To:     <hannes@...xchg.org>, <mhocko@...nel.org>,
        <vdavydov.dev@...il.com>, <akpm@...ux-foundation.org>
CC:     <shakeelb@...gle.com>, <guro@...com>, <willy@...radead.org>,
        <alexs@...nel.org>, <richard.weiyang@...il.com>,
        <songmuchun@...edance.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
        <linmiaohe@...wei.com>
Subject: [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing in mem_cgroup_init()

rtpn might be NULL in very rare case. We have better to check it before
dereferencing it. Since memcg can live with NULL rb_tree_per_node in
soft_limit_tree, warn this case and continue.

Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
---
 mm/memcontrol.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 5b4592d1e0f2..70a32174e7c4 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -7109,6 +7109,8 @@ static int __init mem_cgroup_init(void)
 		rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL,
 				    node_online(node) ? node : NUMA_NO_NODE);
 
+		if (WARN_ON_ONCE(!rtpn))
+			continue;
 		rtpn->rb_root = RB_ROOT;
 		rtpn->rb_rightmost = NULL;
 		spin_lock_init(&rtpn->lock);
-- 
2.23.0