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Thu, 23 Jan 2025 02:07:29 +0000 Date: Wed, 22 Jan 2025 18:07:27 -0800 From: Dan Williams To: "zhangzekun (A)" , Greg KH CC: , , , , , , Subject: Re: Possible hungtask issue will be introduced with device_lock() in uevent_show() Message-ID: <6791a45f711e2_9b922948@dwillia2-mobl3.amr.corp.intel.com.notmuch> References: <172790598832.1168608.4519484276671503678.stgit@dwillia2-xfh.jf.intel.com> <20241231075608.84009-1-zhangzekun11@huawei.com> <2024123128-monetize-outtakes-3260@gregkh> <7b599394-d1a1-4e13-9c5c-48321172ec65@huawei.com> Content-Type: text/plain; charset="utf-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <7b599394-d1a1-4e13-9c5c-48321172ec65@huawei.com> X-ClientProxiedBy: MW4PR04CA0306.namprd04.prod.outlook.com (2603:10b6:303:82::11) To PH8PR11MB8107.namprd11.prod.outlook.com (2603:10b6:510:256::6) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: PH8PR11MB8107:EE_|PH0PR11MB5093:EE_ X-MS-Office365-Filtering-Correlation-Id: 850114c4-40c6-452b-0b56-08dd3b52b0cf X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014; 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The reproduce procedure is quite simple: > > > > The revert just puts the original logic back in place, so this is not > > anything new that has been introduced, right? It's just that the > > attempted fix didn't work, so a different fix needs to happen. > Hi, Greg, > > Yes, there is nothing new introduced here. We have been testing the rcu > fix (commit 15fffc6a5624 ("driver core: Fix uevent_show() vs driver > detach race")) for monthes but has not obersved problems. Hi Zekun, If you have some cycles to help investigate the replacement fix that would be much appreciated. So far I came up with this: http://lore.kernel.org/172790598832.1168608.4519484276671503678.stgit@dwillia2-xfh.jf.intel.com ...but have not had time to debug the 0day report. My worry is still that Linux has long since shipped the expectation that reading 'uevent' bounces the device_lock() which, among other things, makes sure that any in-flight driver probing has completed. The report of USB devices disappearing is consistent with a udev operation failing due to the driver not being done attaching, or something similar. So even though you have not seen any issues, I suspect small differences in the devices on your system and the reporter's system, or udev rule differences could result in a failure to trigger the regression.