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=unavailable 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 DFF0AC4338F for ; Sat, 31 Jul 2021 02:07:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AF90160F36 for ; Sat, 31 Jul 2021 02:07:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235192AbhGaCGA (ORCPT ); Fri, 30 Jul 2021 22:06:00 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:12430 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231335AbhGaCF7 (ORCPT ); Fri, 30 Jul 2021 22:05:59 -0400 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > From mboxrd@z Thu Jan 1 00:00:00 1970 From: Miaohe Lin Subject: Re: [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing in mem_cgroup_init() Date: Sat, 31 Jul 2021 10:05:51 +0800 Message-ID: References: <20210729125755.16871-1-linmiaohe@huawei.com> <20210729125755.16871-5-linmiaohe@huawei.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Language: en-US List-ID: Content-Type: text/plain; charset="us-ascii" To: Michal Hocko , Roman Gushchin Cc: hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, shakeelb@google.com, willy@infradead.org, alexs@kernel.org, richard.weiyang@gmail.com, songmuchun@bytedance.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org 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. >