From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.4 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DE00BC4338F for ; Sat, 31 Jul 2021 02:05:59 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 309A46069E for ; Sat, 31 Jul 2021 02:05:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 309A46069E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 34A096B0033; Fri, 30 Jul 2021 22:05:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2D3658D0001; Fri, 30 Jul 2021 22:05:58 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 19B686B005D; Fri, 30 Jul 2021 22:05:58 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0247.hostedemail.com [216.40.44.247]) by kanga.kvack.org (Postfix) with ESMTP id EFEB56B0033 for ; Fri, 30 Jul 2021 22:05:57 -0400 (EDT) Received: from smtpin32.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 8636D10FAC for ; Sat, 31 Jul 2021 02:05:57 +0000 (UTC) X-FDA: 78421242354.32.59350D4 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf06.hostedemail.com (Postfix) with ESMTP id A405580250EF for ; Sat, 31 Jul 2021 02:05:56 +0000 (UTC) Received: from dggeme703-chm.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4Gc6wG0PjJzchv1; Sat, 31 Jul 2021 10:02:22 +0800 (CST) Received: from [10.174.178.209] (10.174.178.209) by dggeme703-chm.china.huawei.com (10.1.199.99) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2176.2; Sat, 31 Jul 2021 10:05:51 +0800 Subject: Re: [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing in mem_cgroup_init() To: Michal Hocko , Roman Gushchin CC: , , , , , , , , , , References: <20210729125755.16871-1-linmiaohe@huawei.com> <20210729125755.16871-5-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: Date: Sat, 31 Jul 2021 10:05:51 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.209] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To dggeme703-chm.china.huawei.com (10.1.199.99) X-CFilter-Loop: Reflected Authentication-Results: imf06.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=huawei.com; spf=pass (imf06.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-Stat-Signature: narn11yprwwnwr7wzota3mjdqaks4ogu X-Rspamd-Queue-Id: A405580250EF X-Rspamd-Server: rspam01 X-HE-Tag: 1627697156-543914 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 2021/7/30 14:44, Michal Hocko wrote: > On Thu 29-07-21 20:12:43, Roman Gushchin wrote: >> 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. > > Moreover this is 24B allocation during early boot. Kernel will OOM and > panic when not being able to find any victim. I do not think we need to Agree with you. But IMO it may not be a good idea to leave the rtpn without NULL check. We should defend it though it could hardly happen. But I'm not insist on this check. I will drop this patch if you insist. Thanks both of you. > do any special handling here. >