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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 2B3A1C433B4 for ; Wed, 19 May 2021 08:41:52 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A45EF611AD for ; Wed, 19 May 2021 08:41:51 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A45EF611AD Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 238636B0036; Wed, 19 May 2021 04:41:51 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 1C2AE6B006C; Wed, 19 May 2021 04:41:51 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 03B8E6B006E; Wed, 19 May 2021 04:41:50 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0238.hostedemail.com [216.40.44.238]) by kanga.kvack.org (Postfix) with ESMTP id BDC716B0036 for ; Wed, 19 May 2021 04:41:50 -0400 (EDT) Received: from smtpin28.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id 5F1BD180AD804 for ; Wed, 19 May 2021 08:41:50 +0000 (UTC) X-FDA: 78157337580.28.59417E1 Received: from szxga05-in.huawei.com (szxga05-in.huawei.com [45.249.212.191]) by imf22.hostedemail.com (Postfix) with ESMTP id 3DBF1C001C6D for ; Wed, 19 May 2021 08:41:49 +0000 (UTC) Received: from dggems706-chm.china.huawei.com (unknown [172.30.72.58]) by szxga05-in.huawei.com (SkyGuard) with ESMTP id 4FlR8m48phzQpWf; Wed, 19 May 2021 16:38:16 +0800 (CST) Received: from dggeme703-chm.china.huawei.com (10.1.199.99) by dggems706-chm.china.huawei.com (10.3.19.183) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256) id 15.1.2176.2; Wed, 19 May 2021 16:41:46 +0800 Received: from [10.174.176.110] (10.174.176.110) 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; Wed, 19 May 2021 16:41:45 +0800 Subject: Re: [Question] Is there a race window between __anon_vma_prepare() with page_lock_anon_vma_read() ? From: Miaohe Lin To: Linux-MM , linux-kernel CC: Andrew Morton References: <726b53ca-f8a5-c8cb-d704-bcd656afa68e@huawei.com> Message-ID: <6da23315-a00e-4b30-68f4-828b2f66dd47@huawei.com> Date: Wed, 19 May 2021 16:41:45 +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: <726b53ca-f8a5-c8cb-d704-bcd656afa68e@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.176.110] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggeme703-chm.china.huawei.com (10.1.199.99) X-CFilter-Loop: Reflected Authentication-Results: imf22.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=huawei.com; spf=pass (imf22.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.191 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-Stat-Signature: 6gn78hdup576u7j5ps9edu7kw5n7umox X-Rspamd-Queue-Id: 3DBF1C001C6D X-Rspamd-Server: rspam02 X-HE-Tag: 1621413709-145357 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 2021/5/14 17:16, Miaohe Lin wrote: > Hi all, > I am investigating the rmap code, and I found the below possible race window: > > CPU 1 CPU 2 > ----- ----- > page_lock_anon_vma_read > rcu_read_lock > /* We assume anon_vam == root_anon_vma in this case. */ > root_anon_vma = READ_ONCE(anon_vma->root); > root_anon_vma is *released* somewhere unfortunately. > down_read_trylock(&root_anon_vma->rwsem) > __anon_vma_prepare > anon_vma_alloc > root_anon_vma is *allocated* here. > init_rwsem(&anon_vma->rwsem); > !page_mapped(page) > up_read(&root_anon_vma->rwsem); -- *Oops!* > > root_anon_vma->rwsem is reinitialized after locked. And reinitialized anon_vma->rwsem will be > unlocked without lock first. > > I think this could happen due to the subtle SLAB_TYPESAFE_BY_RCU. But only can occur when anon_vma > is root anon_vma or they won't operate on the same rwsem. > Is this will really happen or Am I miss something ? Any reply would be very grateful. > Many Thanks! :) Any reply would be very grateful. Many thanks! >