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Fri, 25 Sep 2020 02:22:15 +0000 From: =?iso-2022-jp?B?SE9SSUdVQ0hJIE5BT1lBKBskQktZOH0hIUQ+TGkbKEIp?= To: Oscar Salvador CC: "akpm@linux-foundation.org" , "aris@ruivo.org" , "mhocko@kernel.org" , "tony.luck@intel.com" , "cai@lca.pw" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" Subject: Re: [PATCH v4 1/7] mm,hwpoison: take free pages off the buddy freelists Thread-Topic: [PATCH v4 1/7] mm,hwpoison: take free pages off the buddy freelists Thread-Index: AQHWjMx3crVad5fTGEWr4+KBqX/ffal4q8WA Date: Fri, 25 Sep 2020 02:22:15 +0000 Message-ID: <20200925022214.GA31132@hori.linux.bs1.fc.nec.co.jp> References: <20200917081049.27428-1-osalvador@suse.de> <20200917081049.27428-2-osalvador@suse.de> In-Reply-To: <20200917081049.27428-2-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: 9a89d541-fde7-472f-6cd9-08d860f9d204 x-ms-traffictypediagnostic: TYBPR01MB5486: x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:6430; 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x-ms-exchange-antispam-messagedata: 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 Content-Type: text/plain; charset="iso-2022-jp" Content-ID: Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: nec.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: TY2PR01MB3210.jpnprd01.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: 9a89d541-fde7-472f-6cd9-08d860f9d204 X-MS-Exchange-CrossTenant-originalarrivaltime: 25 Sep 2020 02:22:15.6175 (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: 0oAEh7cduqO+vKSvVetXWopyVBhOkKdBFD5xJmc7iHvAHrrygd0Wn+mAYqyA6Ao7RW9NcryC/f1sRrX7wKWDYA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: TYBPR01MB5486 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 Thu, Sep 17, 2020 at 10:10:43AM +0200, Oscar Salvador wrote: > The crux of the matter is that historically we left poisoned pages in the > buddy system because we have some checks in place when allocating a page > that a gatekeeper for poisoned pages. Unfortunately, we do have other > users (e.g: compaction [1]) that scan buddy freelists and try to get a > page from there without checking whether the page is HWPoison. >=20 > As I stated already, I think it is fundamentally wrong to keep HWPoison > pages within the buddy systems, checks in place or not. >=20 > Let us fix this we same way we did for soft_offline [2], and take the pag= e > off the buddy freelist, so it is completely unreachable. >=20 > Note that this is fairly simple to trigger, as we only need to poison fre= e > buddy pages (madvise MADV_HWPOISON) and then we need to run some sort of > memory stress system. >=20 > Just for a matter of reference, I put a dump_page in compaction_alloc to > trigger for HWPoison patches: >=20 > kernel: page:0000000012b2982b refcount:1 mapcount:0 mapping:0000000000000= 000 index:0x1 pfn:0x1d5db > kernel: flags: 0xfffffc0800000(hwpoison) > kernel: raw: 000fffffc0800000 ffffea00007573c8 ffffc90000857de0 000000000= 0000000 > kernel: raw: 0000000000000001 0000000000000000 00000001ffffffff 000000000= 0000000 > kernel: page dumped because: compaction_alloc >=20 > kernel: CPU: 4 PID: 123 Comm: kcompactd0 Tainted: G E 5.9.= 0-rc2-mm1-1-default+ #5 > kernel: Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1= .10.2-0-g5f4c7b1-prebuilt.qemu-project.org 04/01/2014 > kernel: Call Trace: > kernel: dump_stack+0x6d/0x8b > kernel: compaction_alloc+0xb2/0xc0 > kernel: migrate_pages+0x2a6/0x12a0 > kernel: ? isolate_freepages+0xc80/0xc80 > kernel: ? __ClearPageMovable+0xb0/0xb0 > kernel: compact_zone+0x5eb/0x11c0 > kernel: ? finish_task_switch+0x74/0x300 > kernel: ? lock_timer_base+0xa8/0x170 > kernel: proactive_compact_node+0x89/0xf0 > kernel: ? kcompactd+0x2d0/0x3a0 > kernel: kcompactd+0x2d0/0x3a0 > kernel: ? finish_wait+0x80/0x80 > kernel: ? kcompactd_do_work+0x350/0x350 > kernel: kthread+0x118/0x130 > kernel: ? kthread_associate_blkcg+0xa0/0xa0 > kernel: ret_from_fork+0x22/0x30 >=20 > After that, if e.g: someone faults in the page, that someone will get > killed unexpectedly. >=20 > While we are at it, I also changed the action result for such cases. > I think that MF_DELAYED is a bit misleading, because in case we could > contain the page and take it off the buddy, such a page is not to be used > again unless it is unpoisoned, so we fixed the situation. >=20 > So unless I am missing something, I strongly think that we should report > MF_RECOVERED. >=20 > [1] https://lore.kernel.org/linux-mm/20190826104144.GA7849@linux/T/#u > [2] https://patchwork.kernel.org/patch/11694847/ >=20 > Signed-off-by: Oscar Salvador Acked-by: Naoya Horiguchi =