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Wed, 12 Aug 2026 12:54:59 +0000 Message-ID: <8c36c744-973a-4e33-a72a-eed0cffc05da@intel.com> Date: Wed, 12 Aug 2026 20:54:49 +0800 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched/topology: Add a cpus_read_lock to partition_sched_domains() To: Sebastian Andrzej Siewior CC: Ben Segall , Dietmar Eggemann , Ingo Molnar , Juri Lelli , K Prateek Nayak , Mel Gorman , Peter Zijlstra , Steven Rostedt , Tim Chen , "Valentin Schneider" , Vincent Guittot , , "chen.yu@linux.dev" References: <20260812095800.gl06ANul@linutronix.de> Content-Language: en-US From: "Chen, Yu C" In-Reply-To: <20260812095800.gl06ANul@linutronix.de> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-ClientProxiedBy: SI2P153CA0008.APCP153.PROD.OUTLOOK.COM (2603:1096:4:140::19) To DM4PR11MB6020.namprd11.prod.outlook.com (2603:10b6:8:61::19) 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: DM4PR11MB6020:EE_|SJ0PR11MB5007:EE_ X-MS-Office365-Filtering-Correlation-Id: ecbe41c6-cedd-4718-a414-08def870eae9 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|23010399003|1800799024|366016|7416014|376014|6133799003|56012099006|22082099003|10067099003|5023799004|11063799006|18002099003; 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The callchain is sched_rt_handler() -> > partition_sched_domains() -> sched_cache_set() -> > static_key_enable_cpuslocked(&sched_cache_present). > > sched_cache_set() itself is also invoked from sched_init_domains() which > is early during the boot, holding just the sched_domains_mutex_lock(). > Here is no warning because it happens before user space is running (and > hotplug operations are not possible). > > There is also sched_cache_active_set() which acquires the hotplug lock > via before invoking any of the _cpuslocked() functions. > > Acquire CPU hotplug lock before in partition_sched_domains(), before > sched_domains_mutex before the _cpuslocked() functions are invoked. > > Fixes: a7660ce1590fc ("sched/cache: Fix has_multi_llcs iff at least one partition has multiple LLCs") > Signed-off-by: Sebastian Andrzej Siewior > --- > kernel/sched/topology.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c > index 622e2e01974c4..ef037d6664d98 100644 > --- a/kernel/sched/topology.c > +++ b/kernel/sched/topology.c > @@ -3498,6 +3498,7 @@ static void partition_sched_domains_locked(int ndoms_new, cpumask_var_t doms_new > void partition_sched_domains(int ndoms_new, cpumask_var_t doms_new[], > struct sched_domain_attr *dattr_new) > { > + guard(cpus_read_lock)(); > sched_domains_mutex_lock(); > partition_sched_domains_locked(ndoms_new, doms_new, dattr_new); > sched_domains_mutex_unlock(); Thanks for taking a look at this issue. I found that there is a comment around partition_sched_domains() says: "Call with hotplug lock held" Not sure if the caller of partition_sched_domains() rather than partition_sched_domains() should grab the cpuhotplug lock? I guess the issue is triggered when CONFIG_CPUSETS=n, in this case rebuild_sched_domains() will not grab cpuhotplug lock, should we add guard(cpus_read_lock) in rebuild_sched_domains() instead? thanks, Chenyu