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

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Message-ID: <97ec2e86-cb4f-4467-8930-d390519f12a6@redhat.com>
Date: Mon, 17 Nov 2025 15:37:17 -0500
From: Waiman Long <llong@...hat.com>
To: Pingfan Liu <piliu@...hat.com>, cgroups@...r.kernel.org
Cc: 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 11/17/25 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().

Cheers,
Longman