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Tue, 30 Mar 2021 05:17:42 +0000 Received: from [10.2.63.109] (172.20.145.6) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1497.2; Tue, 30 Mar 2021 05:17:41 +0000 Subject: Re: [PATCH v3] kernel/resource: Fix locking in request_free_mem_region To: Alistair Popple CC: , , , , , , , , , kernel test robot References: <20210330003842.18948-1-apopple@nvidia.com> <801cd23e-9ac0-adb6-88ba-63ad18d4664c@nvidia.com> <7635785.yHxt4vaozm@nvdebian> From: John Hubbard Message-ID: <4738a7e1-ec62-0b11-28df-e81c0f904f84@nvidia.com> Date: Mon, 29 Mar 2021 22:17:41 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <7635785.yHxt4vaozm@nvdebian> Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [172.20.145.6] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To HQMAIL107.nvidia.com (172.20.187.13) X-EOPAttributedMessage: 0 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: c1d18322-b3a8-4c68-bbb1-08d8f33b2551 X-MS-TrafficTypeDiagnostic: MN2PR12MB3936: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:3276; 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X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 30 Mar 2021 05:17:42.6589 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: c1d18322-b3a8-4c68-bbb1-08d8f33b2551 X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=43083d15-7273-40c1-b7db-39efd9ccc17a;Ip=[216.228.112.34];Helo=[mail.nvidia.com] X-MS-Exchange-CrossTenant-AuthSource: DM6NAM11FT067.eop-nam11.prod.protection.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: MN2PR12MB3936 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 5588640002C2 X-Stat-Signature: 1a5gzp1cmu6dw8nuwm35ithogrrmkqm3 Received-SPF: none (nvidia.com>: No applicable sender policy available) receiver=imf17; identity=mailfrom; envelope-from=""; helo=NAM10-DM6-obe.outbound.protection.outlook.com; client-ip=40.107.93.46 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1617081463-916684 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 3/29/21 9:59 PM, Alistair Popple wrote: ... >>> res->desc = IORES_DESC_DEVICE_PRIVATE_MEMORY; >>> + if (dev) { >>> + dr->parent = &iomem_resource; >>> + dr->start = addr; >>> + dr->n = size; >>> + devres_add(dev, dr); >>> + } >>> + >>> + write_unlock(&resource_lock); >>> + revoke_iomem(res); >> >> This is new, and not mentioned in the commit log, and therefore quite >> surprising. It seems like the right thing to do but it also seems like a >> different fix! I'm not saying that it should be a separate patch, but it >> does seem worth loudly mentioning in the commit log, yes? > > This isn't a different fix though, it is just about maintaining the original > behaviour which called revoke_iomem() after dropping the lock. I inadvertently > switched this around in the initial patch such that revoke_iomem() got called > with the lock, leading to deadlock on x86 with CONFIG_IO_STRICT_DEVMEM=y. > > This does change the order of revoke_iomem() and devres_add() slightly, but as > far as I can tell that shouldn't be an issue. Can call that out in the commit > log. Maybe that's why it looked like a change to me. I do think it's worth mentioning. thanks, -- John Hubbard NVIDIA