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Message-ID: <aN_7iDbWQq3HXvd3@gpd4>
Date: Fri, 3 Oct 2025 18:36:24 +0200
From: Andrea Righi <arighi@...dia.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...nel.org>, Juri Lelli <juri.lelli@...hat.com>,
Vincent Guittot <vincent.guittot@...aro.org>,
Waiman Long <longman@...hat.com>, Tejun Heo <tj@...nel.org>,
Johannes Weiner <hannes@...xchg.org>,
Michal Koutný <mkoutny@...e.com>,
Julia Lawall <Julia.Lawall@...ia.fr>,
"Luis Claudio R. Goncalves" <lgoncalv@...hat.com>,
Joseph Salisbury <joseph.salisbury@...cle.com>
Subject: Re: [PATCH] sched: cgroup: Move task_can_attach() to cpuset.c
Hi Steven,
On Fri, Oct 03, 2025 at 12:14:21PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <rostedt@...dmis.org>
>
> At our monthly stable meeting, we were talking about documenting non
> static functions and randomly picked a function to look at. That was
> task_can_attach(). It was then noticed that it's only used by
> cgroup/cpuset.c and nothing else. It's a simple function that doesn't
> reference anything unique to sched/core.c, hence there's no reason that
> function should be there.
>
> Move it to cgroup/cpuset.c as that's the only place it is used. Also make
> it a static inline as it is so small.
>
> Signed-off-by: Steven Rostedt (Google) <rostedt@...dmis.org>
Nice cleanup. :)
Apparently it became that small with commit 2ef269ef1ac00 ("cgroup/cpuset:
Free DL BW in case can_attach() fails"), maybe we can mention that in the
commit message?
> ---
> include/linux/sched.h | 1 -
> kernel/cgroup/cpuset.c | 19 +++++++++++++++++++
> kernel/sched/core.c | 19 -------------------
> 3 files changed, 19 insertions(+), 20 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index e4ce0a76831e..4ee4fa973eda 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -1849,7 +1849,6 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
> }
>
> extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
> -extern int task_can_attach(struct task_struct *p);
> extern int dl_bw_alloc(int cpu, u64 dl_bw);
> extern void dl_bw_free(int cpu, u64 dl_bw);
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 27adb04df675..21fe872803e8 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -3009,6 +3009,25 @@ static void reset_migrate_dl_data(struct cpuset *cs)
> cs->sum_migrate_dl_bw = 0;
> }
>
> +static inline int task_can_attach(struct task_struct *p)
> +{
> + int ret = 0;
> +
> + /*
> + * Kthreads which disallow setaffinity shouldn't be moved
> + * to a new cpuset; we don't want to change their CPU
> + * affinity and isolating such threads by their set of
> + * allowed nodes is unnecessary. Thus, cpusets are not
> + * applicable for such threads. This prevents checking for
> + * success of set_cpus_allowed_ptr() on all attached tasks
> + * before cpus_mask may be changed.
> + */
> + if (p->flags & PF_NO_SETAFFINITY)
> + ret = -EINVAL;
> +
> + return ret;
As we're cleaning up, we could just return -EINVAL and 0 directly and get
rid of that ret variable.
> +}
> +
> /* Called by cgroups to determine if a cpuset is usable; cpuset_mutex held */
> static int cpuset_can_attach(struct cgroup_taskset *tset)
> {
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index ccba6fc3c3fe..a195c4b25475 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -8070,25 +8070,6 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,
> return ret;
> }
>
> -int task_can_attach(struct task_struct *p)
> -{
> - int ret = 0;
> -
> - /*
> - * Kthreads which disallow setaffinity shouldn't be moved
> - * to a new cpuset; we don't want to change their CPU
> - * affinity and isolating such threads by their set of
> - * allowed nodes is unnecessary. Thus, cpusets are not
> - * applicable for such threads. This prevents checking for
> - * success of set_cpus_allowed_ptr() on all attached tasks
> - * before cpus_mask may be changed.
> - */
> - if (p->flags & PF_NO_SETAFFINITY)
> - ret = -EINVAL;
> -
> - return ret;
> -}
> -
> bool sched_smp_initialized __read_mostly;
>
> #ifdef CONFIG_NUMA_BALANCING
> --
> 2.50.1
>
Thanks,
-Andrea
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