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=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 39A9AC4338F for ; Mon, 2 Aug 2021 10:00:19 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A593960F6D for ; Mon, 2 Aug 2021 10:00:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org A593960F6D 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 DB8E86B0033; Mon, 2 Aug 2021 06:00:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D6A4E6B0036; Mon, 2 Aug 2021 06:00:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C564A6B005D; Mon, 2 Aug 2021 06:00:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0005.hostedemail.com [216.40.44.5]) by kanga.kvack.org (Postfix) with ESMTP id A8C196B0033 for ; Mon, 2 Aug 2021 06:00:17 -0400 (EDT) Received: from smtpin02.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 4845B181AEF23 for ; Mon, 2 Aug 2021 10:00:17 +0000 (UTC) X-FDA: 78429695274.02.01EE01C Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf10.hostedemail.com (Postfix) with ESMTP id 256EA600BF01 for ; Mon, 2 Aug 2021 10:00:14 +0000 (UTC) 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 Authentication-Results: imf10.hostedemail.com; dkim=none; spf=pass (imf10.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=none) header.from=huawei.com X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 256EA600BF01 X-Stat-Signature: ytmgo3jt4f18ucp8hikwn55js3orywzo X-HE-Tag: 1627898414-33892 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 2021/8/2 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);