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Mon, 3 Jun 2019 13:30:28 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=fb.onmicrosoft.com; s=selector1-fb-onmicrosoft-com; h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck; bh=Cm7ryaXuFUYiWgw+pjH9SnNqXBRoDlGHD9r3IrqhOtk=; b=Mb3ec1DCQWQC69evhHHRH7NmLyoUrjgg534+Z6jo7IagfIdtcn6l0HARgsp0LXIUN+Vzt2zhU+SvLwsim9m8FW9mZx3vAdbLxl34t5XjB579YLvoGvvrg8zi1X7a2m/3AHr9OxP7cibOu86Gkq9XLMylgCIr3Gdn++0qzI3yXJ4= Received: from BYAPR15MB2631.namprd15.prod.outlook.com (20.179.156.24) by BYAPR15MB2856.namprd15.prod.outlook.com (20.178.206.85) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.1943.22; Mon, 3 Jun 2019 20:30:26 +0000 Received: from BYAPR15MB2631.namprd15.prod.outlook.com ([fe80::d4f6:b485:69ee:fd9a]) by BYAPR15MB2631.namprd15.prod.outlook.com ([fe80::d4f6:b485:69ee:fd9a%7]) with mapi id 15.20.1943.018; Mon, 3 Jun 2019 20:30:26 +0000 From: Roman Gushchin To: Uladzislau Rezki CC: Andrew Morton , "linux-mm@kvack.org" , Hillf Danton , Michal Hocko , Matthew Wilcox , LKML , Thomas Garnier , Oleksiy Avramchenko , Steven Rostedt , Joel Fernandes , Thomas Gleixner , Ingo Molnar , Tejun Heo Subject: Re: [PATCH v3 4/4] mm/vmap: move BUG_ON() check to the unlink_va() Thread-Topic: [PATCH v3 4/4] mm/vmap: move BUG_ON() check to the unlink_va() Thread-Index: AQHVFHAFBgyZ0nJ640yaup+zuj/dD6aAsSSAgAFzHYD//7QaAIAIZDwAgAAw3YA= Date: Mon, 3 Jun 2019 20:30:26 +0000 Message-ID: <20190603203021.GB14526@tower.DHCP.thefacebook.com> References: <20190527093842.10701-1-urezki@gmail.com> <20190527093842.10701-5-urezki@gmail.com> <20190528225001.GI27847@tower.DHCP.thefacebook.com> <20190529135817.tr7usoi2xwx5zl2s@pc636> <20190529162638.GB3228@tower.DHCP.thefacebook.com> <20190603173528.7ukfgznmiypzfyze@pc636> In-Reply-To: <20190603173528.7ukfgznmiypzfyze@pc636> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-clientproxiedby: MWHPR22CA0047.namprd22.prod.outlook.com (2603:10b6:300:69::33) To BYAPR15MB2631.namprd15.prod.outlook.com (2603:10b6:a03:152::24) x-ms-exchange-messagesentrepresentingtype: 1 x-originating-ip: [2620:10d:c090:200::5409] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: a0540a03-11a9-44f2-6b64-08d6e8624f77 x-microsoft-antispam: BCL:0;PCL:0;RULEID:(2390118)(7020095)(4652040)(8989299)(4534185)(4627221)(201703031133081)(201702281549075)(8990200)(5600148)(711020)(4605104)(1401327)(2017052603328)(7193020);SRVR:BYAPR15MB2856; 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charset="us-ascii" Content-ID: <624474166666AE4E9974023247D462FF@namprd15.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-MS-Exchange-CrossTenant-Network-Message-Id: a0540a03-11a9-44f2-6b64-08d6e8624f77 X-MS-Exchange-CrossTenant-originalarrivaltime: 03 Jun 2019 20:30:26.0957 (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: guro@fb.com X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB2856 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-06-03_16:,, signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1906030137 X-FB-Internal: deliver 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, Jun 03, 2019 at 07:35:28PM +0200, Uladzislau Rezki wrote: > Hello, Roman! >=20 > On Wed, May 29, 2019 at 04:26:43PM +0000, Roman Gushchin wrote: > > On Wed, May 29, 2019 at 03:58:17PM +0200, Uladzislau Rezki wrote: > > > Hello, Roman! > > >=20 > > > > > Move the BUG_ON()/RB_EMPTY_NODE() check under unlink_va() > > > > > function, it means if an empty node gets freed it is a BUG > > > > > thus is considered as faulty behaviour. > > > >=20 > > > > It's not exactly clear from the description, why it's better. > > > >=20 > > > It is rather about if "unlink" happens on unhandled node it is > > > faulty behavior. Something that clearly written in stone. We used > > > to call "unlink" on detached node during merge, but after: > > >=20 > > > [PATCH v3 3/4] mm/vmap: get rid of one single unlink_va() when merge > > >=20 > > > it is not supposed to be ever happened across the logic. > > >=20 > > > > > > > > Also, do we really need a BUG_ON() in either place? > > > >=20 > > > Historically we used to have the BUG_ON there. We can get rid of it > > > for sure. But in this case, it would be harder to find a head or tail > > > of it when the crash occurs, soon or later. > > >=20 > > > > Isn't something like this better? > > > >=20 > > > > diff --git a/mm/vmalloc.c b/mm/vmalloc.c > > > > index c42872ed82ac..2df0e86d6aff 100644 > > > > --- a/mm/vmalloc.c > > > > +++ b/mm/vmalloc.c > > > > @@ -1118,7 +1118,8 @@ EXPORT_SYMBOL_GPL(unregister_vmap_purge_notif= ier); > > > > =20 > > > > static void __free_vmap_area(struct vmap_area *va) > > > > { > > > > - BUG_ON(RB_EMPTY_NODE(&va->rb_node)); > > > > + if (WARN_ON_ONCE(RB_EMPTY_NODE(&va->rb_node))) > > > > + return; > > > > > > > I was thinking about WARN_ON_ONCE. The concern was about if the > > > message gets lost due to kernel ring buffer. Therefore i used that. > > > I am not sure if we have something like WARN_ONE_RATELIMIT that > > > would be the best i think. At least it would indicate if a warning > > > happens periodically or not. > > >=20 > > > Any thoughts? > >=20 > > Hello, Uladzislau! > >=20 > > I don't have a strong opinion here. If you're worried about losing the = message, > > WARN_ON() should be fine here. I don't think that this event will happe= n often, > > if at all. > > >=20 >=20 > If it happens then we are in trouble :) I prefer to keep it here as of no= w, > later on will see. Anyway, let's keep it and i will update it with: >=20 > > if (WARN_ON(RB_EMPTY_NODE(&va->rb_node))) > return; > Works for me. Thank you! >=20 > Thank you for the comments! You're welcome! Roman