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=-15.2 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 4C91CC4338F for ; Mon, 2 Aug 2021 10:00:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 29CD760F50 for ; Mon, 2 Aug 2021 10:00:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233180AbhHBKAY (ORCPT ); Mon, 2 Aug 2021 06:00:24 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:7913 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232973AbhHBKAW (ORCPT ); Mon, 2 Aug 2021 06:00:22 -0400 Received: from dggeme703-chm.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4GdYLF5kG6z82wG; Mon, 2 Aug 2021 17:56:21 +0800 (CST) Received: from [10.174.179.25] (10.174.179.25) 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; Mon, 2 Aug 2021 18:00:10 +0800 Subject: Re: [PATCH 4/5] mm, memcg: avoid possible NULL pointer dereferencing in mem_cgroup_init() To: Michal Hocko CC: Roman Gushchin , , , , , , , , , , , References: <20210729125755.16871-1-linmiaohe@huawei.com> <20210729125755.16871-5-linmiaohe@huawei.com> From: Miaohe Lin Message-ID: <47daf062-f510-edb3-6ec7-f8e7615ad8a0@huawei.com> Date: Mon, 2 Aug 2021 18:00:10 +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: [10.174.179.25] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) 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 2021/8/2 14:43, Michal Hocko wrote: > On Sat 31-07-21 10:05:51, Miaohe Lin wrote: >> 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. > > It is not that I would insist. I just do not see any point in the code > churn. This check is not going to ever trigger and there is nothing you > can do to recover anyway so crashing the kernel is likely the only > choice left. > I hope I get the point now. What you mean is nothing we can do to recover and panic'ing on a NULL-pointer dereference is a perfect choice ? Should we declare that we leave the rtpn without NULL check on purpose like below ? Many thanks. @@ -7109,8 +7109,12 @@ 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; + /* + * If this allocation 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. + */ rtpn->rb_root = RB_ROOT; rtpn->rb_rightmost = NULL; spin_lock_init(&rtpn->lock); 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: Mon, 2 Aug 2021 18:00:10 +0800 Message-ID: <47daf062-f510-edb3-6ec7-f8e7615ad8a0@huawei.com> 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 Cc: Roman Gushchin , 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 2021/8/2 14:43, Michal Hocko wrote: > On Sat 31-07-21 10:05:51, Miaohe Lin wrote: >> 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. > > It is not that I would insist. I just do not see any point in the code > churn. This check is not going to ever trigger and there is nothing you > can do to recover anyway so crashing the kernel is likely the only > choice left. > I hope I get the point now. What you mean is nothing we can do to recover and panic'ing on a NULL-pointer dereference is a perfect choice ? Should we declare that we leave the rtpn without NULL check on purpose like below ? Many thanks. @@ -7109,8 +7109,12 @@ 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; + /* + * If this allocation 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. + */ rtpn->rb_root = RB_ROOT; rtpn->rb_rightmost = NULL; spin_lock_init(&rtpn->lock);