linux-kernel - Re: [PATCH/for-next v3 3/3] cgroup/cpuset: Call housekeeping_update() without holding cpus_read

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Message-ID: <83d0426d-92ea-4e2b-83bc-62998218b212@redhat.com>
Date: Tue, 3 Feb 2026 23:47:00 -0500
From: Waiman Long <llong@...hat.com>
To: Chen Ridong <chenridong@...weicloud.com>, Tejun Heo <tj@...nel.org>,
 Johannes Weiner <hannes@...xchg.org>, Michal Koutný
 <mkoutny@...e.com>, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 Anna-Maria Behnsen <anna-maria@...utronix.de>,
 Frederic Weisbecker <frederic@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Shuah Khan <shuah@...nel.org>
Cc: cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH/for-next v3 3/3] cgroup/cpuset: Call housekeeping_update()
 without holding cpus_read_lock

On 2/3/26 9:51 PM, Chen Ridong wrote:
>
> On 2026/2/3 4:11, Waiman Long wrote:
>> --- a/kernel/time/timer_migration.c
>> +++ b/kernel/time/timer_migration.c
>> @@ -1559,8 +1559,6 @@ int tmigr_isolated_exclude_cpumask(struct cpumask *exclude_cpumask)
>>   	cpumask_var_t cpumask __free(free_cpumask_var) = CPUMASK_VAR_NULL;
>>   	int cpu;
>>   
>> -	lockdep_assert_cpus_held();
>> -
>>   	if (!works)
>>   		return -ENOMEM;
>>   	if (!alloc_cpumask_var(&cpumask, GFP_KERNEL))
>> @@ -1570,6 +1568,7 @@ int tmigr_isolated_exclude_cpumask(struct cpumask *exclude_cpumask)
>>   	 * First set previously isolated CPUs as available (unisolate).
>>   	 * This cpumask contains only CPUs that switched to available now.
>>   	 */
>> +	guard(cpus_read_lock)();
>>   	cpumask_andnot(cpumask, cpu_online_mask, exclude_cpumask);
>>   	cpumask_andnot(cpumask, cpumask, tmigr_available_cpumask);
>>   
> It may lead to lockdep issue.
>
> tmigr_init_isolation
> 	guard(cpus_read_lock)()
> 	tmigr_isolated_exclude_cpumask(cpumask)
> 		guard(cpus_read_lock)()
>
Good catch. I haven't set up "isolcpus" in my test environment. That is 
why this lockdep splat didn't get triggered. I will fix that in the next 
version.

Cheers,
Longman