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Wed, 19 Aug 2026 17:55:00 +0000 (GMT) Received: from [9.124.213.40] (unknown [9.124.213.40]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 19 Aug 2026 17:54:59 +0000 (GMT) Message-ID: <3a199af0-a7dd-4ca6-a4ae-3c53fe9bfec7@linux.ibm.com> Date: Wed, 19 Aug 2026 23:24:59 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] sched/topology: Add a cpus_read_lock to rebuild_sched_domains() To: Sebastian Andrzej Siewior , linux-kernel@vger.kernel.org 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" , "Chen, Yu C" References: <20260813073855.ji2UrtVh@linutronix.de> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20260813073855.ji2UrtVh@linutronix.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=LsCiDHdc c=1 sm=1 tr=0 ts=6a85edfc cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VwQbUJbxAAAA:8 a=qlo83hKUyzZydqUxCM8A:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: wVHN-NuvfLS5oLMzaebOj-KAQ7QSnifl X-Proofpoint-Spam-Info: AW1haW4tMjYwODE5MDEzNiBTYWx0ZWRfX3uEyunS1KJEN 7otF2fL/ig/qizud2g9kBa+CfBEtiXyhsxU4WeX228VFybhxhSJ8imAdvffV07CPYyE6734ZSAz /PsdmDFQ1JBtehx/dsB/ozUEbHfocis= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODE5MDEzNiBTYWx0ZWRfXxL9jbT7tvn9n YsPHyBJs9HAcGMWyqZK3w955zY1WjuB6LyvE1HfLsJrHMB3O8hsxff16qRpInRZzbHTl9vC2P2u srJQN2h8DrExlStLResj8gBzVXg1e9nQ83vMmm8jRz3XcuHxcTQT6Gxk22/cMwiR7ZQpNA2Mh24 nrlRanSTJCaNdz5r5zCIns/psgNShmk2PLNJsAJqK/HrsE/Dt5JISeyZDPvmdKcnYDpYfW9RDOy 02AAZFbAfuMmjwIetXKPQB+cU18oNt13GltSgoFcb1meuecDegj7pRi860KkGWCbolCDa/F5AHE 5yd+60VkDmrS8stfynhgWN3ZnmgbvwAEaWWJ4mxX5LISmmzKYKkSfDvOUOJjUuMszu6SC6QVi7r zAFCwFNlO/JBI7i976VVw1dr/0Jia04F4O5xrkxmFb2eJ0NSEKE4IlJFnrPbDX8BfBuc+WVCAZg 6jhprbO+6GcV+nVwmRw== X-Proofpoint-ORIG-GUID: 6G3MwDlHB9UXGsBrWdwf3WyCcWte3_1W X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-19_04,2026-08-19_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 spamscore=0 priorityscore=1501 lowpriorityscore=0 bulkscore=0 adultscore=0 suspectscore=0 impostorscore=0 clxscore=1011 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608190136 Hi Sebastian. On 8/13/26 1:08 PM, Sebastian Andrzej Siewior wrote: > A read from /proc/sys/kernel/sched_rt_runtime_us leads to backtrace due > to missing cpu_hotplug_lock with CONFIG_CPUSETS=n. 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 > before invoking any of the _cpuslocked() functions. > > This is only a problem with CONFIG_CPUSETS=n because in the =y case the > other implementation of rebuild_sched_domains acquires the CPU-hotplug > lock. > > Acquire CPU hotplug lock before in rebuild_sched_domains(), before > partition_sched_domains() is invoked for the CONFIG_CPUSETS=n case. > > Fixes: a7660ce1590fc ("sched/cache: Fix has_multi_llcs iff at least one partition has multiple LLCs") > Signed-off-by: Sebastian Andrzej Siewior > --- > v1…v2: https://lore.kernel.org/all/20260812095800.gl06ANul@linutronix.de/ > - Move the lock from partition_sched_domains() to > rebuild_sched_domains() in the CONFIG_CPUSETS=n since this is the > only affected case. Noticed by Yu C Chen and Tim Chen. > > include/linux/cpuset.h | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h > index 65d76a38974ba..bf3999daa080a 100644 > --- a/include/linux/cpuset.h > +++ b/include/linux/cpuset.h > @@ -273,6 +273,7 @@ static inline void dl_rebuild_rd_accounting(void) > > static inline void rebuild_sched_domains(void) > { > + guard(cpus_read_lock)(); > partition_sched_domains(1, NULL, NULL); > } > Now, both rebuild_sched_domains have the same code. I guess it is worth moving it out of CONFIG_CPUSETS. kernel/cgroup/cpuset.c: void rebuild_sched_domains(void) { cpus_read_lock(); rebuild_sched_domains_cpuslocked(); cpus_read_unlock(); }