linux-kernel - Re: [PATCHv6 1/2] cgroup/cpuset: Introduce cpuset_cpus_allowed

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Message-ID: <45bdbbd5-9c82-4f5f-864b-9f01e356d8ef@redhat.com>
Date: Tue, 18 Nov 2025 09:33:53 -0500
From: Waiman Long <llong@...hat.com>
To: Pingfan Liu <piliu@...hat.com>, Waiman Long <llong@...hat.com>
Cc: cgroups@...r.kernel.org, Chen Ridong <chenridong@...weicloud.com>,
 Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
 Pierre Gondois <pierre.gondois@....com>, Ingo Molnar <mingo@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>,
 Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
 Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>,
 mkoutny@...e.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv6 1/2] cgroup/cpuset: Introduce
 cpuset_cpus_allowed_locked()

On 11/18/25 1:30 AM, Pingfan Liu wrote:
> On Tue, Nov 18, 2025 at 4:37 AM Waiman Long <llong@...hat.com> wrote:
>> On 11/17/25 4:27 AM, Pingfan Liu wrote:
>>> cpuset_cpus_allowed() uses a reader lock that is sleepable under RT,
>>> which means it cannot be called inside raw_spin_lock_t context.
>>>
>>> Introduce a new cpuset_cpus_allowed_locked() helper that performs the
>>> same function as cpuset_cpus_allowed() except that the caller must have
>>> acquired the cpuset_mutex so that no further locking will be needed.
>>>
>>> Suggested-by: Waiman Long <longman@...hat.com>
>>> Signed-off-by: Pingfan Liu <piliu@...hat.com>
>>> Cc: Waiman Long <longman@...hat.com>
>>> Cc: Tejun Heo <tj@...nel.org>
>>> Cc: Johannes Weiner <hannes@...xchg.org>
>>> Cc: "Michal Koutný" <mkoutny@...e.com>
>>> Cc: linux-kernel@...r.kernel.org
>>> To: cgroups@...r.kernel.org
>>> ---
>>>    include/linux/cpuset.h |  1 +
>>>    kernel/cgroup/cpuset.c | 51 +++++++++++++++++++++++++++++-------------
>>>    2 files changed, 37 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
>>> index 2ddb256187b51..e057a3123791e 100644
>>> --- a/include/linux/cpuset.h
>>> +++ b/include/linux/cpuset.h
>>> @@ -75,6 +75,7 @@ extern void dec_dl_tasks_cs(struct task_struct *task);
>>>    extern void cpuset_lock(void);
>>>    extern void cpuset_unlock(void);
>>>    extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
>>> +extern void cpuset_cpus_allowed_locked(struct task_struct *p, struct cpumask *mask);
>>>    extern bool cpuset_cpus_allowed_fallback(struct task_struct *p);
>>>    extern bool cpuset_cpu_is_isolated(int cpu);
>>>    extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
>> Ah, the following code should be added to to !CONFIG_CPUSETS section
>> after cpuset_cpus_allowed().
>>
>> #define cpuset_cpus_allowed_locked(p, m)  cpuset_cpus_allowed(p, m)
>>
>> Or you can add another inline function that just calls
>> cpuset_cpus_allowed().
>>
> It may be better to make cpuset_cpus_allowed() call
> cpuset_cpus_allowed_locked(), following the call chain used under
> CONFIG_CPUSETS case.

That is fine too.

Cheers,
Longman

>
> Thanks,
>
> Pingfan
>