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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 89D10C433F5 for ; Mon, 7 Mar 2022 03:44:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233585AbiCGDpT (ORCPT ); Sun, 6 Mar 2022 22:45:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48978 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232328AbiCGDpR (ORCPT ); Sun, 6 Mar 2022 22:45:17 -0500 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B74F05D5CE for ; Sun, 6 Mar 2022 19:44:23 -0800 (PST) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.57]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4KBknJ70F0zdZwS; Mon, 7 Mar 2022 11:43:00 +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 15.1.2308.21; Mon, 7 Mar 2022 11:44:21 +0800 Subject: Re: [PATCH 1/4] mm/memory-failure.c: fix race with changing page compound again To: Mike Kravetz , =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= CC: "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" References: <20220228140245.24552-1-linmiaohe@huawei.com> <20220228140245.24552-2-linmiaohe@huawei.com> <20220304082624.GA3778609@hori.linux.bs1.fc.nec.co.jp> <79f79813-bb9a-bfff-0837-a24d14da0b19@oracle.com> From: Miaohe Lin Message-ID: <999a0f88-9465-0c93-e922-8aa80fa64f81@huawei.com> Date: Mon, 7 Mar 2022 11:44:20 +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: <79f79813-bb9a-bfff-0837-a24d14da0b19@oracle.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/3/5 3:32, Mike Kravetz wrote: > On 3/4/22 00:26, HORIGUCHI NAOYA(堀口 直也) wrote: >> On Mon, Feb 28, 2022 at 10:02:42PM +0800, Miaohe Lin wrote: >>> There is a race window where we got the compound_head, the hugetlb page >>> could be freed to buddy, or even changed to another compound page just >>> before we try to get hwpoison page. If this happens, just bail out. >> >> I think that when some hugetlb page is about to change into other type/size >> of compound page, it has to go through buddy allocator because hugetlb pages >> are maintained in separate memory allocator and they never change into other >> normal state directly. memory_failure_hugetlb() takes refcount before >> lock_page(), so the hugetlb page seems not change between get_hwpoison_page() >> and lock_page(). So it this new check really necessary? > > A hugetlb page could change size without going through buddy via the new > demote functionality [1]. Only hugetlb pages on the hugetlb free list can > be demoted. > > We should not demote a page if poison is set. However, there is no check in > the demote code. IIUC, poison is set early in the memory error handling > process, even before taking ref on page. Demote code needs to be fixed so > that poisoned pages are not demoted. I can do that. > > With this change in place, then I think Naoya's statement that hugetlb pages > can not change state is correct and this patch is not necessary. > Sorry for my confusing commit words. What I mean to tell is indeed the below race: CPU 1 CPU 2 memory_failure_hugetlb struct page *head = compound_head(p); hugetlb page is freed to buddy, or even changed to another compound page as we haven't held the page refcnt now get_hwpoison_page -- page is not what we want now... Does this make sense for both of you? Many thanks for comment and reply! :) > Does that sound reasonable? > > [1] https://lore.kernel.org/linux-mm/20211007181918.136982-1-mike.kravetz@oracle.com/ This is really a nice feature. Thanks. >