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 6181BEB64DC for ; Wed, 12 Jul 2023 02:25:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231228AbjGLCZs (ORCPT ); Tue, 11 Jul 2023 22:25:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40606 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229521AbjGLCZq (ORCPT ); Tue, 11 Jul 2023 22:25:46 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CDB4D1722 for ; Tue, 11 Jul 2023 19:25:44 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.56]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4R11jF5LJGzMn13; Wed, 12 Jul 2023 10:22:25 +0800 (CST) Received: from [10.174.151.185] (10.174.151.185) 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 15.1.2507.27; Wed, 12 Jul 2023 10:25:42 +0800 Subject: Re: [PATCH v3 2/4] mm/hwpoison: check if a subpage of a hugetlb folio is raw HWPOISON To: Mike Kravetz , Jiaqi Yan CC: , , , , , , , , References: <20230707201904.953262-1-jiaqiyan@google.com> <20230707201904.953262-3-jiaqiyan@google.com> <6682284d-7ad3-9b59-687d-899f4d08d911@huawei.com> <20230711180159.GA3887@monkey> From: Miaohe Lin Message-ID: Date: Wed, 12 Jul 2023 10:25:41 +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: <20230711180159.GA3887@monkey> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.151.185] X-ClientProxiedBy: dggems701-chm.china.huawei.com (10.3.19.178) 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 2023/7/12 2:01, Mike Kravetz wrote: > On 07/11/23 10:05, Jiaqi Yan wrote: >> On Mon, Jul 10, 2023 at 8:16 AM Jiaqi Yan wrote: >>> On Fri, Jul 7, 2023 at 7:57 PM Miaohe Lin wrote: >>>> On 2023/7/8 4:19, Jiaqi Yan wrote: >>>> >>>>> + if (subpage == p->page) { >>>>> + ret = true; >>>>> + break; >>>>> + } >>>>> + } >>>>> + >>>>> + return ret; >>>>> } >>>> >>>> It seems there's a race between __is_raw_hwp_subpage and unpoison_memory: >>>> unpoison_memory __is_raw_hwp_subpage >>>> if (!folio_test_hwpoison(folio)) -- hwpoison is set >>>> folio_free_raw_hwp llist_for_each_entry_safe raw_hwp_list >>>> llist_del_all .. >>>> folio_test_clear_hwpoison >>>> >>> >>> Thanks Miaohe for raising this concern. >>> >>>> But __is_raw_hwp_subpage is used in hugetlbfs, unpoison_memory couldn't reach here because there's a >>>> folio_mapping == NULL check before folio_free_raw_hwp. >>> >>> I agree. But in near future I do want to make __is_raw_hwp_subpage >>> work for shared-mapping hugetlb, so it would be nice to work with >>> unpoison_memory. It doesn't seem to me that holding mf_mutex in >>> __is_raw_hwp_subpage is nice or even absolutely correct. Let me think >>> if I can come up with something in v4. >> >> At my 2nd thought, if __is_raw_hwp_subpage simply takes mf_mutex >> before llist_for_each_entry, it will introduce a deadlock: >> >> unpoison_memory __is_raw_hwp_subpage >> held mf_mutex held hugetlb_lock >> get_hwpoison_hugetlb_folio attempts mf_mutex >> attempts hugetlb lock >> >> Not for this patch series, but for future, is it a good idea to make >> mf_mutex available to hugetlb code? Then enforce the order of locking >> to be mf_mutex first, hugetlb_lock second? I believe this is the >> current locking pattern / order for try_memory_failure_hugetlb. > > I think only holding mf_mutex in __is_raw_hwp_subpage would be sufficient > to prevent races with unpoison_memory. memory failure code needs to take Since soft_offline_page, memory_failure and unpoison_memory both holds mf_mutex, I think this should be enough to prevent races between them too. Thanks.