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Mon, 14 Sep 2026 14:47:45 +0000 Date: Mon, 14 Sep 2026 22:34:20 +0800 From: Chen Yu To: Tim Chen , Peter Zijlstra CC: Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Kees Cook , Christian Brauner , Alexander Viro , Jan Kara , Shrikanth Hegde , Qais Yousef , Aaron Lu , Srikar Dronamraju , "Vineeth Remanan Pillai" , Ricardo Neri-Calderon , Lu Wang , Hyunwoo Kim , Zhan Xusheng , "Zhan Xusheng" , Yi Lai , , , Subject: Re: [PATCH 4/4] sched/cache: Introduce task_struct->sched_cache_grp Message-ID: References: <4532ec4fd5beb829bccb85822a19360fa4191fe6.1789061845.git.tim.c.chen@linux.intel.com> <20260910191901.GW776954@noisy.programming.kicks-ass.net> <72bd9014ee83d5833bc1c78379ead84458045867.camel@linux.intel.com> Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <72bd9014ee83d5833bc1c78379ead84458045867.camel@linux.intel.com> X-ClientProxiedBy: SI2P153CA0035.APCP153.PROD.OUTLOOK.COM (2603:1096:4:190::14) 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_|CH0PR11MB5266:EE_ X-MS-Office365-Filtering-Correlation-Id: 3fcf6317-e225-4843-42a7-08df126f2348 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|7416014|376014|1800799024|366016|22082099003|18002099003|4143699003|10067099003|56012099006|11063799006; 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> > > + > > > > Also: rcu_dereference_protected(.c = true) is another offence, that's > > just wrong. Got it, will fix it. If I understand correctly, the "c" should never pass an explicit const value? The original idea was that, in exec_mmap(), the current running task is the only writer to change tsk->sched_cache_grp, so the condition is true, To fix it, it might be turned into the following for now: rcu_dereference_protected(tsk->sched_cache_grp, tsk == current); like deref_curr_numa_group(). In the future if task tagging is supported, the race condition of multiple updates would require a pi_lock for this task, and it will become: rcu_dereference_protected(tsk->sched_cache_grp, lockdep_is_held(&p->pi_lock)); like what we have done in the prctl based cache aware scheduling patch set: https://lore.kernel.org/lkml/50fe2db1a62ea2376a87d0c14778b1ff456d11ec.1787955777.git.tim.c.chen@linux.intel.com/ thanks, Chenyu