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Fri, 3 Jan 2020 17:46:29 +0000 Received: from SN6PR15MB2446.namprd15.prod.outlook.com ([fe80::615e:4236:ddfa:3d10]) by SN6PR15MB2446.namprd15.prod.outlook.com ([fe80::615e:4236:ddfa:3d10%6]) with mapi id 15.20.2602.012; Fri, 3 Jan 2020 17:46:29 +0000 Received: from [172.30.100.156] (2620:10d:c091:480::44f7) by BL0PR02CA0022.namprd02.prod.outlook.com (2603:10b6:207:3c::35) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.2602.12 via Frontend Transport; Fri, 3 Jan 2020 17:46:28 +0000 From: Chris Mason To: "Theodore Y. Ts'o" CC: Linux Filesystem Development List , "linux-mm@kvack.org" , Andrew Morton Subject: Re: [PATCH -v2] memcg: fix a crash in wb_workfn when a device disappears Thread-Topic: [PATCH -v2] memcg: fix a crash in wb_workfn when a device disappears Thread-Index: AQHVvRkX1XTmcfbDL0iuYh1G7ObE/KfZOIqAgAAItAA= Date: Fri, 3 Jan 2020 17:46:29 +0000 Message-ID: <527DCBC3-28D2-4BFE-A99C-8ED65A613A20@fb.com> References: <20191227194829.150110-1-tytso@mit.edu> <20191228005211.163952-1-tytso@mit.edu> <20200103171517.GA4253@mit.edu> In-Reply-To: <20200103171517.GA4253@mit.edu> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-mailer: MailMate (1.13.1r5671) x-clientproxiedby: BL0PR02CA0022.namprd02.prod.outlook.com (2603:10b6:207:3c::35) To SN6PR15MB2446.namprd15.prod.outlook.com (2603:10b6:805:22::25) x-ms-exchange-messagesentrepresentingtype: 1 x-originating-ip: [2620:10d:c091:480::44f7] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: ac6df590-cd59-4fc6-00b5-08d79074dcb0 x-ms-traffictypediagnostic: SN6PR15MB2287: x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:9508; x-forefront-prvs: 0271483E06 x-forefront-antispam-report: SFV:NSPM;SFS:(10019020)(366004)(136003)(346002)(396003)(39860400002)(376002)(199004)(189003)(64756008)(66946007)(66476007)(66556008)(4326008)(66446008)(2616005)(478600001)(316002)(53546011)(71200400001)(36756003)(81166006)(2906002)(81156014)(6916009)(54906003)(5660300002)(966005)(186003)(16526019)(86362001)(8936002)(33656002)(8676002)(52116002)(6486002);DIR:OUT;SFP:1102;SCL:1;SRVR:SN6PR15MB2287;H:SN6PR15MB2446.namprd15.prod.outlook.com;FPR:;SPF:None;LANG:en;PTR:InfoNoRecords;A:1;MX:1; received-spf: None (protection.outlook.com: fb.com does not designate permitted sender hosts) x-ms-exchange-senderadcheck: 1 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: o+5mmyIP8g3FWMm7N3dE+kF2MhRE21wDDhbJIoi8G4dZesBMO0PubdFA859WPMGvT+HEl4J5tohRGwJ47vvhlRE+8U+GMD0Iz22juLUgr+/bOrnWs9jxVy9XeZpmP1okYDWHKV/O+9DjYv7kAFFAaHNSUA+TopCln90WW0/m18CKUjXluwAmLNPHYWHUey+npQerBHgAWilD4n83+CAdPQoAvAltpt/CgXu6woH8ygbb1cHb+zPyXCCyvpEmpwJidIc1tVqd1aAo3LjI3vDcCAkMDjODrCOL/R+capi2mNZF3qPBmfnnTWHwKG2PkF8Mo16HlTIMKh4l61WPi+Q0UoRmjAP3+MceU7AA3dRYwgh6Shh0oH4DF5MCBmX1PFNzucz5zB1xyUWt0iSm58Z8QOijWmwVzIJNxelSquJRTaH/dSW2/qhvdbCrfGvZXjC6RUJ4olaqrxB5MpZp8rObniS7JzTg8RPwja1igLoohtA= x-ms-exchange-transport-forked: True Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: ac6df590-cd59-4fc6-00b5-08d79074dcb0 X-MS-Exchange-CrossTenant-originalarrivaltime: 03 Jan 2020 17:46:29.0352 (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: YmGq2O1AIsoGqFKeXRWJzCbIpbpL4z6tjkmSmHuPDK92O84yoqieTqajmLL0rFny X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN6PR15MB2287 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.95,18.0.572 definitions=2020-01-03_05:2020-01-02,2020-01-03 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 lowpriorityscore=0 mlxscore=0 phishscore=0 clxscore=1015 bulkscore=0 mlxlogscore=907 adultscore=0 malwarescore=0 impostorscore=0 spamscore=0 suspectscore=0 priorityscore=1501 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-1910280000 definitions=main-2001030163 X-FB-Internal: deliver Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 3 Jan 2020, at 12:15, Theodore Y. Ts'o wrote: > On Fri, Dec 27, 2019 at 07:52:11PM -0500, Theodore Ts'o wrote: >> >> Fortunately, it looks like the rest of the writeback path is=20 >> perfectly >> happy with bdi->dev and bdi->owner being NULL, so the simplest fix is >> to create a bdi_dev_name() function which can handle bdi->dev being >> NULL. This also allows us to bulletproof the writeback tracepoints=20 >> to >> prevent them from dereferencing a NULL pointer and crashing the=20 >> kernel >> if one is tracing with memcg's enabled, and an iSCSI device dies or a >> USB storage stick is pulled. >> >> Previous-Version-Link:=20 >> https://lore.kernel.org/r/20191227194829.150110-1-tytso@mit.edu >> Google-Bug-Id: 145475544 >> Tested: fs smoke test >> Signed-off-by: Theodore Ts'o >> --- >> >> Notes: >> v2: add #include for linux/device.h >> >> fs/fs-writeback.c | 2 +- >> include/linux/backing-dev.h | 10 +++++++++ >> include/trace/events/writeback.h | 37=20 >> +++++++++++++++----------------- >> mm/backing-dev.c | 1 + >> 4 files changed, 29 insertions(+), 21 deletions(-) > > Ping? > > Any comments? Any objections if I carry this patch[1] in the ext4 > tree? Or would it be better for Andrew to carry it in the linux-mm > tree? > > [1] https://lore.kernel.org/k/20191227203117.152399-1-tytso@mit.edu Seems sane to me, and we probably want this even if del_gendisk()=20 embraces the brave new memcg world because synchronizing all of this is=20 going to get messy. -chris