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Tue, 8 Dec 2020 02:35:14 +0000 From: =?iso-2022-jp?B?SE9SSUdVQ0hJIE5BT1lBKBskQktZOH0hIUQ+TGkbKEIp?= To: Oscar Salvador CC: "akpm@linux-foundation.org" , "n-horiguchi@ah.jp.nec.com" , "vbabka@suse.cz" , "dan.j.williams@intel.com" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] mm,memory_failure: Always pin the page in madvise_inject_error Thread-Topic: [PATCH] mm,memory_failure: Always pin the page in madvise_inject_error Thread-Index: AQHWzH4hO9bKFpDJuEiM7pqnWm2hdKnsfIcA Date: Tue, 8 Dec 2020 02:35:14 +0000 Message-ID: <20201208023513.GB10757@hori.linux.bs1.fc.nec.co.jp> References: <20201207094818.8518-1-osalvador@suse.de> In-Reply-To: <20201207094818.8518-1-osalvador@suse.de> Accept-Language: ja-JP, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: suse.de; dkim=none (message not signed) header.d=none;suse.de; dmarc=none action=none header.from=nec.com; x-originating-ip: [165.225.110.205] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: adae0acd-b608-4dbd-ee1d-08d89b21e4a3 x-ms-traffictypediagnostic: TYAPR01MB5930: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:2000; 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charset="iso-2022-jp" Content-ID: <8EA991E89894DB4E83C94B190FAE1487@jpnprd01.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: nec.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: TY1PR01MB1852.jpnprd01.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: adae0acd-b608-4dbd-ee1d-08d89b21e4a3 X-MS-Exchange-CrossTenant-originalarrivaltime: 08 Dec 2020 02:35:14.4879 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: e67df547-9d0d-4f4d-9161-51c6ed1f7d11 X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: lBQbjsaLhz5Jsr1rJKSsvb1cuj2r3mANAMjNzZd5NLif3jGq6QGgP1U0h/++GVgK55b36fhR0m1WjbyIBNaU5Q== X-MS-Exchange-Transport-CrossTenantHeadersStamped: TYAPR01MB5930 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 Mon, Dec 07, 2020 at 10:48:18AM +0100, Oscar Salvador wrote: > madvise_inject_error() uses get_user_pages_fast to translate the > address we specified to a page. > After [1], we drop the extra reference count for memory_failure() path. > That commit says that memory_failure wanted to keep the pin in order > to take the page out of circulation. >=20 > The truth is that we need to keep the page pinned, otherwise the > page might be re-used after the put_page() and we can end up messing > with someone else's memory. >=20 > E.g: >=20 > CPU0 > process X CPU1 > madvise_inject_error > get_user_pages > put_page > page gets reclaimed > process Y allocates the page > memory_failure > // We mess with process Y memory >=20 > madvise() is meant to operate on a self address space, so messing with > pages that do not belong to us seems the wrong thing to do. > To avoid that, let us keep the page pinned for memory_failure as well. >=20 > Pages for DAX mappings will release this extra refcount in > memory_failure_dev_pagemap. >=20 > [1] ("23e7b5c2e271: mm, madvise_inject_error: > Let memory_failure() optionally take a page reference") >=20 > Signed-off-by: Oscar Salvador > Suggested-by: Vlastimil Babka > Fixes: 23e7b5c2e271 ("mm, madvise_inject_error: Let memory_failure() opti= onally take a page reference") Thank you very much. Acked-by: Naoya Horiguchi =