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Mon, 7 Apr 2025 18:08:10 +0000 Message-ID: <0b9b1239-8514-4a8d-b991-73f371a6aebf@intel.com> Date: Mon, 7 Apr 2025 11:08:08 -0700 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] x86/resctrl: Fix rdtgroup_mkdir()'s unlocked use of kernfs_node::name To: James Morse , , CC: Tony Luck , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , , "Sebastian Andrzej Siewior" References: <20250213145023.2820193-7-bigeasy@linutronix.de> <20250407124637.2433230-1-james.morse@arm.com> From: Reinette Chatre Content-Language: en-US In-Reply-To: <20250407124637.2433230-1-james.morse@arm.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-ClientProxiedBy: MW4PR04CA0221.namprd04.prod.outlook.com (2603:10b6:303:87::16) 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_|MW4PR11MB5889:EE_ X-MS-Office365-Filtering-Correlation-Id: 65a6915d-2464-4b90-26c6-08dd75ff2792 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|376014|1800799024|7053199007; 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This is done > without holding rdtgroup_mutex, and now triggers the following warning: > | WARNING: suspicious RCU usage > | 6.15.0-rc1 #4465 Tainted: G E > | ----------------------------- > | arch/x86/kernel/cpu/resctrl/internal.h:408 suspicious rcu_dereference_check() usage! > [...] > | Call Trace: > | > | dump_stack_lvl+0x6c/0xa0 > | lockdep_rcu_suspicious.cold+0x4e/0x96 > | is_mon_groups+0xba/0xd0 > | rdtgroup_mkdir+0x118/0x1970 > | kernfs_iop_mkdir+0xfa/0x1a0 > | vfs_mkdir+0x456/0x760 > | do_mkdirat+0x257/0x310 > | __x64_sys_mkdir+0xd4/0x120 > | do_syscall_64+0x6d/0x150 > | entry_SYSCALL_64_after_hwframe+0x76/0x7e > > Creating a control or monitor group calls mkdir_rdt_prepare(), which uses > rdtgroup_kn_lock_live() to take the rdtgroup_mutex. > > To avoid taking and dropping the lock, move the check for the monitor group > name and position into mkdir_rdt_prepare() so that it occurs under > rdtgroup_mutex. Hoist is_mon_groups() earlier in the file. > > CC: Sebastian Andrzej Siewior > Fixes: 741c10b096bc ("kernfs: Use RCU to access kernfs_node::name.") > Signed-off-by: James Morse > --- Thank you very much. Reviewed-by: Reinette Chatre Reinette