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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C3263C4332F for ; Thu, 12 May 2022 11:18:58 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 003F26B0074; Thu, 12 May 2022 07:18:58 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id EF6856B0075; Thu, 12 May 2022 07:18:57 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DBF6D6B0078; Thu, 12 May 2022 07:18:57 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id CADE96B0074 for ; Thu, 12 May 2022 07:18:57 -0400 (EDT) Received: from smtpin16.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 95BD1607DF for ; Thu, 12 May 2022 11:18:57 +0000 (UTC) X-FDA: 79456843914.16.390CE56 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by imf13.hostedemail.com (Postfix) with ESMTP id 71FCE200A9 for ; Thu, 12 May 2022 11:18:38 +0000 (UTC) Received: from canpemm500002.china.huawei.com (unknown [172.30.72.53]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4KzTgH6g7nzCsZR; Thu, 12 May 2022 19:14:03 +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 15.1.2375.24; Thu, 12 May 2022 19:18:51 +0800 Subject: Re: [PATCH v1] mm,hwpoison: set PG_hwpoison for busy hugetlb pages To: =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= , Mike Kravetz CC: 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> From: Miaohe Lin Message-ID: <7395dbe7-7be6-6ef7-7728-a118471caa5a@huawei.com> Date: Thu, 12 May 2022 19:18:51 +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: <20220512043253.GA242760@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: dggems704-chm.china.huawei.com (10.3.19.181) To canpemm500002.china.huawei.com (7.192.104.244) X-CFilter-Loop: Reflected X-Stat-Signature: fmxzxtqpaqqkdds4ifscg8dmzee3k3zh X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 71FCE200A9 Authentication-Results: imf13.hostedemail.com; dkim=none; spf=pass (imf13.hostedemail.com: domain of linmiaohe@huawei.com designates 45.249.212.189 as permitted sender) smtp.mailfrom=linmiaohe@huawei.com; dmarc=pass (policy=quarantine) header.from=huawei.com X-Rspam-User: X-HE-Tag: 1652354318-525494 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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? Thanks! > > Thanks, > Naoya Horiguchi >