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 59165C433EF for ; Mon, 6 Jun 2022 03:12:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352260AbiFFDMP (ORCPT ); Sun, 5 Jun 2022 23:12:15 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54520 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1349220AbiFFDMM (ORCPT ); Sun, 5 Jun 2022 23:12:12 -0400 Received: from szxga01-in.huawei.com (szxga01-in.huawei.com [45.249.212.187]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 12CC019FB9 for ; Sun, 5 Jun 2022 20:12:10 -0700 (PDT) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.56]) by szxga01-in.huawei.com (SkyGuard) with ESMTP id 4LGdmd3vfHzjXQ0; Mon, 6 Jun 2022 11:11:13 +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; Mon, 6 Jun 2022 11:12:08 +0800 Subject: Re: [PATCH v1] mm,hwpoison: set PG_hwpoison for busy hugetlb pages To: =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= CC: Mike Kravetz , Naoya Horiguchi , "linux-mm@kvack.org" , Andrew Morton , zhenwei pi , "linux-kernel@vger.kernel.org" References: <20220511151955.3951352-1-naoya.horiguchi@linux.dev> <20220512043253.GA242760@hori.linux.bs1.fc.nec.co.jp> <7395dbe7-7be6-6ef7-7728-a118471caa5a@huawei.com> <20220602061203.GB1172281@hori.linux.bs1.fc.nec.co.jp> From: Miaohe Lin Message-ID: <95a3c6d3-ae33-580b-9448-bb5d5c356cec@huawei.com> Date: Mon, 6 Jun 2022 11:12:08 +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: <20220602061203.GB1172281@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: 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 2022/6/2 14:12, HORIGUCHI NAOYA(堀口 直也) wrote: > On Thu, May 12, 2022 at 07:18:51PM +0800, Miaohe Lin wrote: >> On 2022/5/12 12:32, HORIGUCHI NAOYA(堀口 直也) wrote: >>> On Wed, May 11, 2022 at 11:35:55AM -0700, Mike Kravetz wrote: >>>> On 5/11/22 08:19, Naoya Horiguchi wrote: >>>>> From: Naoya Horiguchi >>>>> >>>>> If memory_failure() fails to grab page refcount on a hugetlb page >>>>> because it's busy, it returns without setting PG_hwpoison on it. >>>>> This not only loses a chance of error containment, but breaks the rule >>>>> that action_result() should be called only when memory_failure() do >>>>> any of handling work (even if that's just setting PG_hwpoison). >>>>> This inconsistency could harm code maintainability. >>>>> >>>>> So set PG_hwpoison and call hugetlb_set_page_hwpoison() for such a case. >>>>> >>>>> Fixes: 405ce051236c ("mm/hwpoison: fix race between hugetlb free/demotion and memory_failure_hugetlb()") >>>>> Signed-off-by: Naoya Horiguchi >>>>> --- >>>>> include/linux/mm.h | 1 + >>>>> mm/memory-failure.c | 8 ++++---- >>>>> 2 files changed, 5 insertions(+), 4 deletions(-) >>>>> >>>>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>>>> index d446e834a3e5..04de0c3e4f9f 100644 >>>>> --- a/include/linux/mm.h >>>>> +++ b/include/linux/mm.h >>>>> @@ -3187,6 +3187,7 @@ enum mf_flags { >>>>> MF_MUST_KILL = 1 << 2, >>>>> MF_SOFT_OFFLINE = 1 << 3, >>>>> MF_UNPOISON = 1 << 4, >>>>> + MF_NO_RETRY = 1 << 5, >>>>> }; >>>>> extern int memory_failure(unsigned long pfn, int flags); >>>>> extern void memory_failure_queue(unsigned long pfn, int flags); >>>>> diff --git a/mm/memory-failure.c b/mm/memory-failure.c >>>>> index 6a28d020a4da..e3269b991016 100644 >>>>> --- a/mm/memory-failure.c >>>>> +++ b/mm/memory-failure.c >>>>> @@ -1526,7 +1526,8 @@ int __get_huge_page_for_hwpoison(unsigned long pfn, int flags) >>>>> count_increased = true; >>>>> } else { >>>>> ret = -EBUSY; >>>>> - goto out; >>>>> + if (!(flags & MF_NO_RETRY)) >>>>> + goto out; >>>>> } >>>> >>>> Hi Naoya, >>>> >>>> We are in the else block because !HPageFreed() and !HPageMigratable(). >>>> IIUC, this likely means the page is isolated. One common reason for isolation >>>> is migration. So, the page could be isolated and on a list for migration. >>> >>> Yes, and I also detected this issue by testing race between hugepage allocation >>> and memory_failure(). >>> >>>> >>>> I took a quick look at the hugetlb migration code and did not see any checks >>>> for PageHWPoison after a hugetlb page is isolated. I could have missed >>>> something? If there are no checks, we will read the PageHWPoison page >>>> in kernel mode while copying to the migration target. >>> >>> Yes, that could happen. This patch does not affect ongoing hugepage migration. >>> But after the migration source hugepage is freed, the PG_hwpoison should work >>> to prevent reusing. >>> >>>> >>>> Is this an issue? Is is something we need to be concerned with? Memory >>>> errors can happen at any time, and gracefully handling them is best effort. >>> >>> Right, so doing nothing for this case could be OK if doing something causes >>> some issues or makes code too complicated. The motivation of this patch is >>> that now I think memory_failure() should do something (at least setting >>> PG_hwpoison) unless the page is already hwpoisoned or rejected by >>> hwpoison_filter(), because of the effect after free as mentioned above. >>> >>> This is also expected in other case too. For example, slab is a unhandlable >>> type of page, but we do set PG_hwpoison. This flag should not affect any of >>> ongoing slab-related process, but that's OK because it becomes effective >>> after the slab page is freed. >>> >>> So this patch is intended to align to the behavior. Allowing hugepage >>> migration to do something good using PG_hwpoison seems to me an unsolved >>> separate issue. >> >> I tend to agree with Naoya. And could we try to do it better? IMHO, we could do a >> get_page_unless_zero here to ensure that hugetlb page migration will fail due to >> this extra page reference and thus preventing the page content from being accessed. >> Does this work? Or am I miss something? > > Sorry for my missing to answering the question, Never mind. I almost forget it too. ;) > > Taking page refcount to prevent page migration could work. One concern is > how we can distinguish hugepages under migration and those under allocation > from buddy. Maybe this was also mentioned in discussion over > https://github.com/torvalds/linux/commit/405ce051236cc65b30bbfe490b28ce60ae6aed85 > , there's a small window where an allocating compound page is refcounted and > hugepage (having deconstructor COMPOUND_PAGE_DTOR), and not protected by > hugetlb_lock, so simply get_page_unless_zero() might not work (might break > allocation code). > If we have more reliable indicator to ensure that a hugepage is under migration, > that would be helpful. Yes, I agree with you. If we have more reliable indicator to ensure that a hugepage is under migration, we could try to do this then. :) > > Thanks, > Naoya Horiguchi Many thanks for reply! >