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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 88A96C433EF for ; Thu, 23 Jun 2022 12:03:50 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7D1E88E0147; Thu, 23 Jun 2022 08:03:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 75A728E0144; Thu, 23 Jun 2022 08:03:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5FC168E0147; Thu, 23 Jun 2022 08:03:49 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0013.hostedemail.com [216.40.44.13]) by kanga.kvack.org (Postfix) with ESMTP id 4B3668E0144 for ; Thu, 23 Jun 2022 08:03:49 -0400 (EDT) Received: from smtpin17.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 0D8EB2038C for ; Thu, 23 Jun 2022 12:03:49 +0000 (UTC) X-FDA: 79609366578.17.6B8407A Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by imf30.hostedemail.com (Postfix) with ESMTP id 4C5E280026 for ; Thu, 23 Jun 2022 12:03:47 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.55]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4LTJlC5c6jzkWLh; Thu, 23 Jun 2022 20:01:59 +0800 (CST) Received: from [10.174.177.76] (10.174.177.76) by canpemm500002.china.huawei.com (7.192.104.244) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2375.24; Thu, 23 Jun 2022 20:03:42 +0800 Subject: Re: [PATCH 02/16] mm/huge_memory: access vm_page_prot with READ_ONCE in remove_migration_pmd To: "Kirill A. Shutemov" CC: , , , , , References: <20220622170627.19786-1-linmiaohe@huawei.com> <20220622170627.19786-3-linmiaohe@huawei.com> <20220623031401.wdyt5ylin4aijzhh@box.shutemov.name> From: Miaohe Lin Message-ID: <7ee4a597-d7cb-f387-5613-f51b17262745@huawei.com> Date: Thu, 23 Jun 2022 20:03:41 +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: <20220623031401.wdyt5ylin4aijzhh@box.shutemov.name> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf30.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1655985828; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=gkpB0jGOEI7SnV/+lvRRUgHmhMpE8i9KGEZecRj1Wpc=; b=tneXPqWFV4SxR3GYiod+/EuUbXIQw7oEHa2m2iavAQBkZMcIlRdUhYVy86qIpb3nSxfJMl UDYFEi2q79CfYXR1e48q2Hsy2txuafd/jEWiQLHPvH9ROnrYKbW9JV1vJOJfsXBu7/TgJK VqBcKLNgZO+HaFjyuSBDg1QdcIcXi2U= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1655985828; a=rsa-sha256; cv=none; b=8D54G1TND7zvaxsgeS7/gWMyXgFiHgGvKld/Xcbk7FA44kh+t6RUNbWjw6VR6LgK1BTbdQ lQ8/YCVX3Bph3fvgSFO+TKvOBWZh3W4WCNDkNxzz4by+spiVa4jm+FKmv1qtH/Psi5wQoq sxUCJAedl9kGWgykBPVXZJb3/DhbONY= X-Rspam-User: Authentication-Results: imf30.hostedemail.com; dkim=none; dmarc=pass (policy=quarantine) header.from=huawei.com; spf=pass (imf30.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.188 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com X-Stat-Signature: pzo951f9jen3ec6b379chhsoyubznrdg X-Rspamd-Queue-Id: 4C5E280026 X-Rspamd-Server: rspam12 X-HE-Tag: 1655985827-506014 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 2022/6/23 11:14, Kirill A. Shutemov wrote: > On Thu, Jun 23, 2022 at 01:06:13AM +0800, Miaohe Lin wrote: >> vma->vm_page_prot is read lockless from the rmap_walk, it may be updated >> concurrently. Using READ_ONCE to prevent the risk of reading intermediate >> values. > > Have you checked all other vm_page_prot reads that they hold mmap_lock? I took a glance when I made this patch. > > I think the right fix would be to provide a helper to read vm_page_prot > which does READ_ONCE() and use it everywhere. This seems more sustainable. > This patch is inspired from the below commit 6d2329f8872f ("mm: vm_page_prot: update with WRITE_ONCE/READ_ONCE") It changed all the places that need to use READ_ONCE. But remove_migration_pmd is missed due to it's introduced later. It looks fine to add a helper to read vm_page_prot which does READ_ONCE() but READ_ONCE is unneeded while under the mmap_lock, so might it be a little overkill to add a helper because the helper is used iff mmap_lock is not held? Thanks.