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b=vKwF0ODPGpEwjDUP3J2bQBCgWPIN2mVLLPI7sOyV7maRUrXW+sjT0/A52KEqOFfyUCe5w2p3xAbRtShHrI05EdIjPS3RZnAU8syqJ2hbSa6aCalFCXHOOh0UnAlWTIQuqXsES+CRikYFjeCYM5vI9WLJK71H90rfVv1BiVIblmE= Received: from BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) by CO1PR10MB4596.namprd10.prod.outlook.com (2603:10b6:303:6f::10) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.5038.14; Fri, 4 Mar 2022 19:32:05 +0000 Received: from BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::51f1:9cb7:a497:f0f7]) by BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::51f1:9cb7:a497:f0f7%5]) with mapi id 15.20.5038.017; Fri, 4 Mar 2022 19:32:05 +0000 Message-ID: <79f79813-bb9a-bfff-0837-a24d14da0b19@oracle.com> Date: Fri, 4 Mar 2022 11:32:02 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH 1/4] mm/memory-failure.c: fix race with changing page compound again Content-Language: en-US To: =?UTF-8?B?SE9SSUdVQ0hJIE5BT1lBKOWggOWPoyDnm7TkuZ8p?= , Miaohe Lin Cc: "akpm@linux-foundation.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" References: <20220228140245.24552-1-linmiaohe@huawei.com> <20220228140245.24552-2-linmiaohe@huawei.com> <20220304082624.GA3778609@hori.linux.bs1.fc.nec.co.jp> From: Mike Kravetz In-Reply-To: <20220304082624.GA3778609@hori.linux.bs1.fc.nec.co.jp> Content-Type: text/plain; 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dkim=pass header.d=oracle.com header.s=corp-2021-07-09 header.b=c+pVeCNW; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=vKwF0ODP; spf=none (imf18.hostedemail.com: domain of mike.kravetz@oracle.com has no SPF policy when checking 205.220.177.32) smtp.mailfrom=mike.kravetz@oracle.com; dmarc=pass (policy=none) header.from=oracle.com X-HE-Tag: 1646422334-789480 Content-Transfer-Encoding: quoted-printable 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 3/4/22 00:26, HORIGUCHI NAOYA(=E5=A0=80=E5=8F=A3 =E7=9B=B4=E4=B9=9F) w= rote: > On Mon, Feb 28, 2022 at 10:02:42PM +0800, Miaohe Lin wrote: >> There is a race window where we got the compound_head, the hugetlb pag= e >> could be freed to buddy, or even changed to another compound page just >> before we try to get hwpoison page. If this happens, just bail out. >=20 > I think that when some hugetlb page is about to change into other type/= size > of compound page, it has to go through buddy allocator because hugetlb = pages > are maintained in separate memory allocator and they never change into = other > normal state directly. memory_failure_hugetlb() takes refcount before > lock_page(), so the hugetlb page seems not change between get_hwpoison_= page() > and lock_page(). So it this new check really necessary? A hugetlb page could change size without going through buddy via the new demote functionality [1]. Only hugetlb pages on the hugetlb free list ca= n be demoted. =20 We should not demote a page if poison is set. However, there is no check= in the demote code. IIUC, poison is set early in the memory error handling process, even before taking ref on page. Demote code needs to be fixed s= o that poisoned pages are not demoted. I can do that. With this change in place, then I think Naoya's statement that hugetlb pa= ges can not change state is correct and this patch is not necessary. Does that sound reasonable? [1] https://lore.kernel.org/linux-mm/20211007181918.136982-1-mike.kravetz= @oracle.com/ --=20 Mike Kravetz