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Wed, 23 Oct 2024 23:50:12 +0000 Message-ID: <93fe977c-e5c4-407e-ad84-dec7f81e6b87@intel.com> Date: Wed, 23 Oct 2024 16:50:09 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 32/40] x86/resctrl: resctrl_exit() teardown resctrl but leave the mount point To: James Morse , , CC: Fenghua Yu , Thomas Gleixner , Ingo Molnar , Borislav Petkov , H Peter Anvin , Babu Moger , , D Scott Phillips OS , , , , , , Jamie Iles , Xin Hao , , , , David Hildenbrand , Rex Nie , "Dave Martin" , Shaopeng Tan References: <20241004180347.19985-1-james.morse@arm.com> <20241004180347.19985-33-james.morse@arm.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: <20241004180347.19985-33-james.morse@arm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0279.namprd04.prod.outlook.com (2603:10b6:303:89::14) To SJ2PR11MB7573.namprd11.prod.outlook.com (2603:10b6:a03:4d2::10) 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: SJ2PR11MB7573:EE_|BN9PR11MB5227:EE_ X-MS-Office365-Filtering-Correlation-Id: 5d233b8f-f4fa-42fc-da73-08dcf3bd6f9c X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|7416014|376014|1800799024; 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MPAM has an error interrupt which indicates > the MPAM driver has gone haywire. Should this occur tasks could run with > the wrong control values, leading to bad performance for important tasks. > The MPAM driver needs a way to tell resctrl that no further configuration > should be attempted. > > Using resctrl_exit() for this leaves the system in a funny state as > resctrl is still mounted, but cannot be un-mounted because the sysfs > directory that is typically used has been removed. Dave Martin suggests > this may cause systemd trouble in the future as not all filesystems > can be unmounted. > > Add calls to remove all the files and directories in resctrl, and > remove the sysfs_remove_mount_point() call that leaves the system > in a funny state. When triggered, this causes all the resctrl files > to disappear. resctrl can be unmounted, but not mounted again. > > Signed-off-by: James Morse > Tested-by: Carl Worth # arm64 > Tested-by: Shaopeng Tan > Reviewed-by: Shaopeng Tan > --- > arch/x86/kernel/cpu/resctrl/rdtgroup.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > index f77fab859c35..bb5aadaf99b6 100644 > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c > @@ -4319,9 +4319,9 @@ int __init resctrl_init(void) > > void __exit resctrl_exit(void) > { > + rdtgroup_destroy_root(); If I understand correctly, rdtgroup_destroy_root() can now be called twice, first during the error interrupt and then on unmount. Would the second call be safe? I am not familiar with this code but I see kernfs_destroy_root() and __kernfs_remove() dereferencing pointers without checks. I wonder if this needs to be made safer with a: rdtgroup_destroy_root() { if (rdtgroup_default.kn) { kernfs_destroy_root(); rdtgroup_default.kn = NULL; } } > debugfs_remove_recursive(debugfs_resctrl); > unregister_filesystem(&rdt_fs_type); > - sysfs_remove_mount_point(fs_kobj, "resctrl"); > This breaks symmetry with resctrl_init(). The changelog describes the motivation clearly but once this line is removed it will be difficult to get back to this motivation. Could this function get a comment to explain why the mount point is not removed? This will be helpful to anybody following this work that may attempt to "fix" the asymmetry by cleaning up the mount point created during init. > resctrl_mon_resource_exit(); > } Reinette