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Fri, 30 Jul 2021 03:12:48 +0000 Date: Thu, 29 Jul 2021 20:12:43 -0700 From: Roman Gushchin To: Miaohe Lin CC: , , , , , , , , , , , Subject: Re: [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing in mem_cgroup_init() Message-ID: References: <20210729125755.16871-1-linmiaohe@huawei.com> <20210729125755.16871-5-linmiaohe@huawei.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20210729125755.16871-5-linmiaohe@huawei.com> X-ClientProxiedBy: MWHPR13CA0029.namprd13.prod.outlook.com (2603:10b6:300:95::15) To BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from carbon.lan (2620:10d:c090:400::5:6b55) by MWHPR13CA0029.namprd13.prod.outlook.com (2603:10b6:300:95::15) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4394.10 via Frontend Transport; Fri, 30 Jul 2021 03:12:47 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: ffb8befb-dd05-4529-1cdb-08d95307e875 X-MS-TrafficTypeDiagnostic: SJ0PR15MB4472: X-Microsoft-Antispam-PRVS: X-FB-Source: Internal X-MS-Oob-TLC-OOBClassifiers: OLM:8882; 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dkim=pass header.d=fb.com header.s=facebook header.b=Uy6JsIcY; dmarc=pass (policy=reject) header.from=fb.com; spf=pass (imf20.hostedemail.com: domain of "prvs=78455e497e=guro@fb.com" designates 67.231.145.42 as permitted sender) smtp.mailfrom="prvs=78455e497e=guro@fb.com" X-Stat-Signature: pq51uqj8rt1ttadrre7f5xmx7ap6yz1p X-HE-Tag: 1627614803-246289 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jul 29, 2021 at 08:57:54PM +0800, Miaohe Lin wrote: > 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 > --- > 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; I also really doubt that it makes any sense to continue in this case. If this allocations fails (at the very beginning of the system's life, it's an __init function), something is terribly wrong and panic'ing on a NULL-pointer dereference sounds like a perfect choice. Is this a real world problem? Do I miss something?