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Mon, 22 Jun 2020 03:07:32 +0000 Date: Sun, 21 Jun 2020 20:07:29 -0700 From: Roman Gushchin To: Qian Cai CC: Andrew Morton , Christoph Lameter , Johannes Weiner , Michal Hocko , Shakeel Butt , , Vlastimil Babka , , , Subject: Re: [PATCH v6 00/19] The new cgroup slab memory controller Message-ID: <20200622030729.GB293939@carbon.DHCP.thefacebook.com> References: <20200621233429.GA293939@carbon.DHCP.thefacebook.com> <7DEA68BC-3B9A-46FA-8103-AE6B72324591@lca.pw> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <7DEA68BC-3B9A-46FA-8103-AE6B72324591@lca.pw> X-ClientProxiedBy: BYAPR08CA0027.namprd08.prod.outlook.com (2603:10b6:a03:100::40) To BYAPR15MB4136.namprd15.prod.outlook.com (2603:10b6:a03:96::24) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from carbon.DHCP.thefacebook.com (2620:10d:c090:400::5:b541) by BYAPR08CA0027.namprd08.prod.outlook.com (2603:10b6:a03:100::40) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3109.22 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 93485ce1-bfc1-489c-c771-08d8165967fc X-MS-Exchange-CrossTenant-OriginalArrivalTime: 22 Jun 2020 03:07:32.7890 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: 3tGvrCHNdAPVOcw0MKFfqvtk+zUiuJYlDSD/rR89wav/5Q1vaueLsSwmprp9S87v X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2663 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.687 definitions=2020-06-21_14:2020-06-19,2020-06-21 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 mlxscore=0 bulkscore=0 malwarescore=0 adultscore=0 mlxlogscore=801 lowpriorityscore=0 phishscore=0 spamscore=0 clxscore=1015 priorityscore=1501 suspectscore=56 impostorscore=0 cotscore=-2147483648 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2004280000 definitions=main-2006220023 X-FB-Internal: deliver X-Rspamd-Queue-Id: 232D7100EDBFB X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 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 Sun, Jun 21, 2020 at 07:53:23PM -0400, Qian Cai wrote: >=20 >=20 > > On Jun 21, 2020, at 7:34 PM, Roman Gushchin wrote: > >=20 > > My wild guess is that kmemleak is getting confused by modifying the l= owest > > bit of page->mem_cgroup/obhj_cgroups pointer: > >=20 > > struct page { > > ... > > union { > > struct mem_cgroup *mem_cgroup; > > struct obj_cgroup **obj_cgroups; > > }; > > ... > > } > >=20 > > We're using the lowest bit to distinguish between a "normal" mem_cgro= up > > pointer and a vector of obj_cgroup pointers. > >=20 > > This pointer to obj_cgroup vector is saved only here, so if we're mod= ifying > > the address, I guess it's what makes kmemleak think that there is a l= eak. > >=20 > > Or do you have a real leak? >=20 > The point is that we can=E2=80=99t have a patchset in the current form = to totally render kmemleak useless with so many even false positives. >=20 > Anyway, this is rather easy to reproduce where I am able to reproduce o= n multiple bare-metal machines by just booting it. >=20 > # echo scan > /sys/kernel/debug/kmemleak > # cat /sys/kernel/debug/kmemleak Ok, thank you for the report, I'll take care of it. It's easy to mark these vectors to be ignored by kmemleak, but I guess it= 's better to explicitly add an additional reference, so we can track actual leaks. I'll send a patch with fix soon-ish. Thanks!