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Sun, 31 May 2026 08:41:54 +0000 Message-ID: <34aa2c9a-8247-4599-8c9c-ce6dc94f354e@intel.com> Date: Sun, 31 May 2026 16:41:43 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 4/9] fs/resctrl: Fix deadlock for errors during mount To: Reinette Chatre CC: , , , , , , , , , , , , , , References: <2e44b91263f1ccc4403a969524594800bead95c4.1779476724.git.reinette.chatre@intel.com> <6140c3f9-b172-4552-b96f-1b8514b0e75b@intel.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: KU0P306CA0053.MYSP306.PROD.OUTLOOK.COM (2603:1096:d10:28::6) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) 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: DM4PR11MB6020:EE_|DS0PR11MB7360:EE_ X-MS-Office365-Filtering-Correlation-Id: 95a6bd34-7c0a-496b-c2b1-08debef077ee X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014|7416014|22082099003|18002099003|56012099006|11063799006|4143699003; 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>>>       } >>>   -    goto out; >>> +    /* >>> +     * Ensure root kn remains accessible after mutex is unlocked so that >> >> Maybe a little more accurate to say "Ensure rdt_root remains accessible"? >> Here we increase reference for rdtgroup_default.kn, and protect >> against UAF of >> kernfs_kill_sb(sb) -> >>   info = kernfs_info(sb) -> >>     kernfs_put(info->root->kn) >> >> where the info->root is UAF rather than the kn. > > Right. The UAF is indeed on the root self while its lifetime is controlled by references > to its kn (root->kn). Dropping the last reference on root->kn causes root to be freed. > > rdt_root is the name of a variable though and its value can actually change in the flow > involved here so I'd prefer not to phrase it exactly like that. How about just > "Ensure root remains accessible ..."? Yes, this looks good to me. thanks, Chenyu