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Tue, 18 Aug 2026 01:01:34 +0000 Message-ID: <8ec67bca-1f21-4489-8601-3dfd91aa5b2a@intel.com> Date: Mon, 17 Aug 2026 18:01:32 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v10 12/17] x86/resctrl: Prepare to handle nested mount requests To: Tony Luck , Fenghua Yu , "Maciej Wieczor-Retman" , Peter Newman , James Morse , Babu Moger , Drew Fustini , Dave Martin , Chen Yu , David E Box , CC: Christoph Hellwig , , References: <20260729172752.11561-1-tony.luck@intel.com> <20260729172752.11561-13-tony.luck@intel.com> Content-Language: en-US From: Reinette Chatre In-Reply-To: <20260729172752.11561-13-tony.luck@intel.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0092.namprd04.prod.outlook.com (2603:10b6:303:83::7) To SJ2PR11MB8370.namprd11.prod.outlook.com (2603:10b6:a03:540::20) 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: SJ2PR11MB8370:EE_|SJ2PR11MB8345:EE_ X-MS-Office365-Filtering-Correlation-Id: 8653ad6b-b6c1-4957-c71b-08defcc43fb0 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|376014|23010399003|7416014|1800799024|366016|22082099003|18002099003|56012099006|4143699003|11063799006|10067099003|921020; 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Please describe how these locks are used to achieve this protection (more below). > > Signed-off-by: Tony Luck > --- > v10: > New patch > > include/linux/resctrl.h | 2 +- > arch/x86/kernel/cpu/resctrl/core.c | 40 ++++++++++++++++++++++++------ > drivers/resctrl/mpam_resctrl.c | 3 ++- > 3 files changed, 35 insertions(+), 10 deletions(-) > > diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h > index 568a650c0224..65245f2fdad0 100644 > --- a/include/linux/resctrl.h > +++ b/include/linux/resctrl.h > @@ -579,7 +579,7 @@ void resctrl_offline_cpu(unsigned int cpu); > * Architecture hook called at beginning of first file system mount attempt. > * No locks are held. > */ > -void resctrl_arch_pre_mount(void); > +int resctrl_arch_pre_mount(void); There is no mention in changelog why this change is needed. > > /* > * Architecture hook called when mount fails, or on unmount. > diff --git a/arch/x86/kernel/cpu/resctrl/core.c b/arch/x86/kernel/cpu/resctrl/core.c > index e335a143f3e5..906aa4dfc363 100644 > --- a/arch/x86/kernel/cpu/resctrl/core.c > +++ b/arch/x86/kernel/cpu/resctrl/core.c > @@ -16,7 +16,6 @@ > > #define pr_fmt(fmt) "resctrl: " fmt > > -#include > #include > #include > #include > @@ -807,25 +806,47 @@ static int resctrl_arch_offline_cpu(unsigned int cpu) > return 0; > } > > -void resctrl_arch_pre_mount(void) > +/* > + * Linux provides no synchronization for mount(2) system calls. > + * resctrl_arch_pre_mount() and resctrl_arch_unmount() are called > + * with no locks held. Mount/unmount may also race with CPU hotplug > + * events that add/remove per-domain files and directories. > + * > + * Use cpus_read_lock() plus domain_list_lock to protect operations. "protect operations"? Which operations? I expect it to protect concurrent changes to data expected to be protected by the lock. domain_list_lock is understood to protect the architecture managed domain list. It looks to me as though what this actually does is add new architecture state, arch_mounted, and let this new state fall under protection of domain_list_lock to protect it from concurrent changes. The reason why cpus_read_lock() is needed is the locking order requires it. I find "protect operations" to be too vague description to use as motivation and documentation of locking behavior. For completeness I expect arch_mounted to be added to the comments above the original definition of domain_list_lock to make it clear that the lock now has expanded scope. Reinette