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=-0.8 required=3.0 tests=BAYES_00, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 D7D2CC4338F for ; Wed, 18 Aug 2021 08:36:28 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4B66060C3E for ; Wed, 18 Aug 2021 08:36:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 4B66060C3E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=sina.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id E501D8D0002; Wed, 18 Aug 2021 04:36:27 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id DFFB66B0072; Wed, 18 Aug 2021 04:36:27 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id D15A58D0002; Wed, 18 Aug 2021 04:36:27 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0171.hostedemail.com [216.40.44.171]) by kanga.kvack.org (Postfix) with ESMTP id B68F16B006C for ; Wed, 18 Aug 2021 04:36:27 -0400 (EDT) Received: from smtpin23.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 613AC8249980 for ; Wed, 18 Aug 2021 08:36:27 +0000 (UTC) X-FDA: 78487544814.23.18A6B99 Received: from r3-18.sinamail.sina.com.cn (r3-18.sinamail.sina.com.cn [202.108.3.18]) by imf17.hostedemail.com (Postfix) with SMTP id D93DDF0011F9 for ; Wed, 18 Aug 2021 08:36:25 +0000 (UTC) Received: from unknown (HELO localhost.localdomain)([222.130.245.194]) by sina.com (172.16.97.35) with ESMTP id 611CC6830002BF1D; Wed, 18 Aug 2021 16:36:22 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 83561915073692 From: Hillf Danton To: Liam Howlett Cc: "maple-tree@lists.infradead.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Peter Zijlstra , Michel Lespinasse , Andrew Morton Subject: [PATCH v2 10/61] kernel/fork: Use maple tree for dup_mmap() during forking Date: Wed, 18 Aug 2021 16:36:10 +0800 Message-Id: <20210818083610.3698-1-hdanton@sina.com> In-Reply-To: <20210817154651.1570984-11-Liam.Howlett@oracle.com> References: <20210817154651.1570984-1-Liam.Howlett@oracle.com> MIME-Version: 1.0 X-Rspamd-Queue-Id: D93DDF0011F9 Authentication-Results: imf17.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf17.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.18 as permitted sender) smtp.mailfrom=hdanton@sina.com X-Rspamd-Server: rspam04 X-Stat-Signature: xth7orzy4bun113rk95e3ypus7iwsp39 X-HE-Tag: 1629275785-627104 Content-Transfer-Encoding: quoted-printable 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 Tue, 17 Aug 2021 15:47:11 +0000 Liam R. Howlett wrote: >=20 > static inline void mmget(struct mm_struct *mm) > { > + mt_set_in_rcu(&mm->mm_mt); > atomic_inc(&mm->mm_users); > } >=20 > static inline bool mmget_not_zero(struct mm_struct *mm) > { > + /* > + * There is a race below during task tear down that can cause the map= le > + * tree to enter rcu mode with only a single user. If this race > + * happens, the result would be that the maple tree nodes would remai= n > + * active for an extra RCU read cycle. > + */ > + mt_set_in_rcu(&mm->mm_mt); > return atomic_inc_not_zero(&mm->mm_users); > } Nit, leave the mm with zero refcount intact. if (atomic_inc_not_zero(&mm->mm_users)) { mt_set_in_rcu(&mm->mm_mt); return true; } return false;