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 B5703C433F5 for ; Tue, 15 Mar 2022 14:00:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348900AbiCOOBs (ORCPT ); Tue, 15 Mar 2022 10:01:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58336 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348896AbiCOOBp (ORCPT ); Tue, 15 Mar 2022 10:01:45 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5CBA354183 for ; Tue, 15 Mar 2022 07:00:32 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.54]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4KHw4R3Bw9zfYq8; Tue, 15 Mar 2022 21:59:03 +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 22:00:30 +0800 Subject: Re: [PATCH v2] mm/hwpoison: set PageHWPoison after taking page lock in memory_failure_hugetlb() To: =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= CC: Naoya Horiguchi , Andrew Morton , Mike Kravetz , Yang Shi , "linux-kernel@vger.kernel.org" , Linux-MM References: <20220314021337.333781-1-naoya.horiguchi@linux.dev> <58732610-36a4-1f05-c09d-a5536013772d@huawei.com> <20220315054935.GA3454497@hori.linux.bs1.fc.nec.co.jp> From: Miaohe Lin Message-ID: <1770029b-fd59-4eb1-c891-5a2ba4beef9c@huawei.com> Date: Tue, 15 Mar 2022 22:00:29 +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: <20220315054935.GA3454497@hori.linux.bs1.fc.nec.co.jp> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-Originating-IP: [10.174.177.76] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) 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 2022/3/15 13:49, HORIGUCHI NAOYA(堀口 直也) wrote: > On Mon, Mar 14, 2022 at 03:10:25PM +0800, Miaohe Lin wrote: >> On 2022/3/14 10:13, Naoya Horiguchi wrote: >>> From: Naoya Horiguchi >>> >>> There is a race condition between memory_failure_hugetlb() and hugetlb >>> free/demotion, which causes setting PageHWPoison flag on the wrong page >>> (which was a hugetlb when memory_failure() was called, but was removed >>> or demoted when memory_failure_hugetlb() is called). This results in >>> killing wrong processes. So set PageHWPoison flag with holding page lock, >> >> It seems hold page lock could not help solve this race condition as hugetlb >> page demotion is not required to hold the page lock. Could you please explain >> this a bit more? > > Sorry, the last line in the paragraph need change. What prevents the current > race is hugetlb_lock, not page lock. The page lock is here to prevent the > race with hugepage allocation (not directly related to the current issue, > but it's still necessary). Many thanks for clarifying this. > >> >> BTW:Is there some words missing or here should be 'page lock.' instead of 'page lock,' ? > > I should use a period here, I'll fix it. > > [...] > >>> @@ -1503,24 +1502,11 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags) >>> int res; >>> unsigned long page_flags; >>> >>> - if (TestSetPageHWPoison(head)) { >>> - pr_err("Memory failure: %#lx: already hardware poisoned\n", >>> - pfn); >>> - res = -EHWPOISON; >>> - if (flags & MF_ACTION_REQUIRED) >>> - res = kill_accessing_process(current, page_to_pfn(head), flags); >>> - return res; >>> - } >>> - >>> - num_poisoned_pages_inc(); >>> - >>> if (!(flags & MF_COUNT_INCREASED)) { >>> res = get_hwpoison_page(p, flags); >>> if (!res) { >> >> In this (res == 0) case, hugetlb page could be dissolved via __page_handle_poison. >> But since PageHWPoison is not set yet, we can't set the PageHWPoison to the correct >> page. Think about the below code in dissolve_free_huge_page: >> /* >> * Move PageHWPoison flag from head page to the raw >> * error page, which makes any subpages rather than >> * the error page reusable. >> */ >> if (PageHWPoison(head) && page != head) { >> SetPageHWPoison(page); >> ClearPageHWPoison(head); >> } >> >> SetPageHWPoison won't be called for the error page. Or am I miss something? > > No, you're right. We need call page_handle_poison() instead of > __page_handle_poison(). > > @@ -1512,7 +1512,7 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags) > } > unlock_page(head); > res = MF_FAILED; > - if (__page_handle_poison(p)) { > + if (page_handle_poison(p, true, false)) { > page_ref_inc(p); > res = MF_RECOVERED; > } > This one looks good to me. > > >> >>> lock_page(head); >>> if (hwpoison_filter(p)) { >>> - if (TestClearPageHWPoison(head)) >>> - num_poisoned_pages_dec(); >>> unlock_page(head); >>> return -EOPNOTSUPP; >>> } >>> @@ -1553,13 +1539,16 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags) >>> page_flags = head->flags; >>> >>> if (hwpoison_filter(p)) { >>> - if (TestClearPageHWPoison(head)) >>> - num_poisoned_pages_dec(); >>> put_page(p); >>> res = -EOPNOTSUPP; >>> goto out; >>> } >>> >>> + if (TestSetPageHWPoison(head)) >>> + goto already_hwpoisoned; >>> + >>> + num_poisoned_pages_inc(); >>> + >>> /* >>> * TODO: hwpoison for pud-sized hugetlb doesn't work right now, so >>> * simply disable it. In order to make it work properly, we need >>> @@ -1585,6 +1574,14 @@ static int memory_failure_hugetlb(unsigned long pfn, int flags) >>> out: >>> unlock_page(head); >>> return res; >>> +already_hwpoisoned: >>> + put_page(p); >>> + unlock_page(head); >> >> Generally speaking, we should do unlock_page before put_page or page might be disappeared >> before we unlock the page. This should be ok when memory_failure succeeds to handle the >> page previously as it holds one extra page refcnt. But it might be problematic when >> memory_failure failed to handle the page last time. We might be the last user here. > > OK, so another code path in "if (hwpoison_filter)@ block seems to need > the same change in the order. You're right. > > Thanks, > Naoya Horiguchi > Many thanks for your patch.