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Howlett" , Mike Rapoport , Michal Hocko , Jason Gunthorpe , Peter Xu , Matthew Wilcox , Usama Arif , Paul Walmsley , Palmer Dabbelt , Albert Ou , Alexandre Ghiti , linux-riscv@lists.infradead.org References: <20260724222934.1463812-1-riel@surriel.com> <20260724222934.1463812-3-riel@surriel.com> Content-Language: en-US From: John Hubbard In-Reply-To: <20260724222934.1463812-3-riel@surriel.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SJ2P220CA0011.NAMP220.PROD.OUTLOOK.COM (2603:10b6:a03:5da::15) To DM3PR12MB9416.namprd12.prod.outlook.com (2603:10b6:0:4b::8) 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: DM3PR12MB9416:EE_|SA5PPFA403A61D8:EE_ X-MS-Office365-Filtering-Correlation-Id: 3397df4c-456d-4618-6bc4-08deec49c89c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|23010399003|7416014|1800799024|4143699003|56012099006|22082099003|18002099003|10067099003|11063799006; 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> > - if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags) && mm->context.pmlen != pmlen) { > - mmap_write_unlock(mm); > - return -EBUSY; > + if (test_bit(MM_CONTEXT_LOCK_PMLEN, &mm->context.flags)) { > + if (READ_ONCE(mm->context.pmlen) != pmlen) { I think you should remove this misleading READ_ONCE, because it implies a race that is not there. The code is happening under mmap_write_lock_*(), and so does the only writer to pmlen (below), so they cannot race with each other. > + mmap_write_unlock(mm); > + return -EBUSY; > + } > } > > envcfg_update_bits(task, ENVCFG_PMM, pmm); > - mm->context.pmlen = pmlen; > + WRITE_ONCE(mm->context.pmlen, pmlen); > > mmap_write_unlock(mm); > > @@ -394,7 +396,7 @@ long get_tagged_addr_ctrl(struct task_struct *task) > break; > } > > - if (task->mm->context.pmlen) > + if (READ_ONCE(task->mm->context.pmlen)) > ret |= PR_TAGGED_ADDR_ENABLE; > > return ret; thanks, -- John Hubbard