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Sun, 31 May 2026 08:37:48 +0000 Message-ID: <8d76c93f-7780-4fdd-a3b2-9faa8eeddf57@intel.com> Date: Sun, 31 May 2026 16:37:37 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 8/9] x86/resctrl: Ensure domain fully initialized before placed on RCU list To: Reinette Chatre CC: , , , , , , , , , , , , , , References: <3ba2959b1cd3596e1e340eaee6b43487edaec0a4.1779476724.git.reinette.chatre@intel.com> <4053bd27-bca3-4745-9f34-65843e250f12@intel.com> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <4053bd27-bca3-4745-9f34-65843e250f12@intel.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: KU0P306CA0050.MYSP306.PROD.OUTLOOK.COM (2603:1096:d10:28::7) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: DM4PR11MB6020:EE_|SJ2PR11MB8422:EE_ X-MS-Office365-Filtering-Correlation-Id: 7b3f996f-cf4d-4203-fd0b-08debeefe4f1 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|7416014|1800799024|6133799003|11063799006|4143699003|18002099003|22082099003|56012099006; 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>> } >> >> - list_add_tail_rcu(&d->hdr.list, add_pos); >> - >> err = resctrl_online_mon_domain(r, &d->hdr); >> if (err) { >> - list_del_rcu(&d->hdr.list); >> - synchronize_rcu(); >> l3_mon_domain_free(hw_dom); >> + return; >> } >> + list_add_tail_rcu(&d->hdr.list, add_pos); >> } >> >> static void domain_add_cpu_mon(int cpu, struct rdt_resource *r) > > I resubmitted the last three patches of series to obtain Sashiko review [1] and > respond to that feedback here: > > a) Sashiko: "Does this reordering expose the monitor directories to userspace before the > domain is actually added to the RCU list?" > > Yes. As pointed out by Sashiko there is a short time where the monitoring data files > may be exposed to user space before the monitoring domain is added to the RCU list. > Also pointed out by Sashiko, if user attempts to read from such file it will return > -ENOENT. > > This behavior looks correct and acceptable to me. It might not return -ENOENT because the read will be blocked by cpus_read_lock() and after the reader has grabed the cpus_read_lock(), the reader will see the newly added domain on the list: CPU 0 (writer) CPU 1 (reader) ========================== ========================== cpus_write_lock held cpus_read_lock() **BLOCKED** mkdir mondata files list_add_tail_rcu() cpus_write_unlock cpus_read_lock() returns lock(rdtgroup_mutex) resctrl_find_domain() **see a new complete domain** unlock(rdtgroup_mutex) cpus_read_unlock() Reviewed-by: Chen Yu thanks, Chenyu