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 3C482C433F5 for ; Tue, 15 Mar 2022 14:19:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349133AbiCOOUr (ORCPT ); Tue, 15 Mar 2022 10:20:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45766 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349165AbiCOOUo (ORCPT ); Tue, 15 Mar 2022 10:20:44 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4235354FAD; Tue, 15 Mar 2022 07:19:29 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4KHwQF2QPLzcb9X; Tue, 15 Mar 2022 22:14:29 +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; Tue, 15 Mar 2022 22:19:25 +0800 Subject: Re: [PATCH v2 1/3] mm/memory-failure.c: fix race with changing page compound again To: Mike Kravetz , CC: , , , , , , References: <20220312074613.4798-1-linmiaohe@huawei.com> <20220312074613.4798-2-linmiaohe@huawei.com> <91661cd4-e9be-959f-8b6a-da257a00a879@oracle.com> From: Miaohe Lin Message-ID: <9826152a-8a83-76a8-ded8-47d185aac0a8@huawei.com> Date: Tue, 15 Mar 2022 22:19:25 +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: <91661cd4-e9be-959f-8b6a-da257a00a879@oracle.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems703-chm.china.huawei.com (10.3.19.180) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-edac@vger.kernel.org On 2022/3/15 2:20, Mike Kravetz wrote: > On 3/11/22 23:46, 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. Think about the below race window: >> CPU 1 CPU 2 >> memory_failure_hugetlb >> struct page *head = compound_head(p); >> hugetlb page might be freed to >> buddy, or even changed to another >> compound page. >> >> get_hwpoison_page -- page is not what we want now... >> >> If this race happens, just bail out. Also MF_MSG_DIFFERENT_PAGE_SIZE is >> introduced to record this event. >> >> Signed-off-by: Miaohe Lin >> --- >> include/linux/mm.h | 1 + >> include/ras/ras_event.h | 1 + >> mm/memory-failure.c | 12 ++++++++++++ >> 3 files changed, 14 insertions(+) >> >> diff --git a/include/linux/mm.h b/include/linux/mm.h >> index c9bada4096ac..ef98cff2b253 100644 >> --- a/include/linux/mm.h >> +++ b/include/linux/mm.h >> @@ -3253,6 +3253,7 @@ enum mf_action_page_type { >> MF_MSG_BUDDY, >> MF_MSG_DAX, >> MF_MSG_UNSPLIT_THP, >> + MF_MSG_DIFFERENT_PAGE_SIZE, >> MF_MSG_UNKNOWN, >> }; >> >> diff --git a/include/ras/ras_event.h b/include/ras/ras_event.h >> index d0337a41141c..1e694fd239b9 100644 >> --- a/include/ras/ras_event.h >> +++ b/include/ras/ras_event.h >> @@ -374,6 +374,7 @@ TRACE_EVENT(aer_event, >> EM ( MF_MSG_BUDDY, "free buddy page" ) \ >> EM ( MF_MSG_DAX, "dax page" ) \ >> EM ( MF_MSG_UNSPLIT_THP, "unsplit thp" ) \ >> + EM ( MF_MSG_DIFFERENT_PAGE_SIZE, "different page size" ) \ >> EMe ( MF_MSG_UNKNOWN, "unknown page" ) >> >> /* >> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >> index 5444a8ef4867..dabecd87ad3f 100644 >> --- a/mm/memory-failure.c >> +++ b/mm/memory-failure.c >> @@ -733,6 +733,7 @@ static const char * const action_page_types[] = { >> [MF_MSG_BUDDY] = "free buddy page", >> [MF_MSG_DAX] = "dax page", >> [MF_MSG_UNSPLIT_THP] = "unsplit thp", >> + [MF_MSG_DIFFERENT_PAGE_SIZE] = "different page size", >> [MF_MSG_UNKNOWN] = "unknown page", >> }; >> >> @@ -1534,6 +1535,17 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags) >> } >> >> lock_page(head); >> + >> + /** >> + * The page could have changed compound pages due to race window. >> + * If this happens just bail out. >> + */ >> + if (!PageHuge(p) || compound_head(p) != head) { >> + action_result(pfn, MF_MSG_DIFFERENT_PAGE_SIZE, MF_IGNORED); >> + res = -EBUSY; > > We have discussed this race in other versions of the patch. When we encounter > the race, we have likely marked poison on the wrong page. Correct? > Many thanks for comment. I assume that Naoya's patch "mm/hwpoison: set PageHWPoison after taking page lock in memory_failure_hugetlb()" would set the PageHWPoison after the above check. So I think the below operation is not needed as PageHWPoison is not set yet. Does this makes sense for you? Thanks. > Instead of printing a "different page size", would it be better to perhaps: > - Print a message that wrong page may be marked for poison? > - Clear the poison flag in the "head page" previously set? >