linux-kernel - Re: [PATCH v2] cgroup/cpuset: Move procfs cpuset attribute under cgroup-v1.c

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Message-ID: <b3988753-bd9e-400c-a9ab-a0d54324b9e1@redhat.com>
Date: Fri, 17 Jan 2025 09:39:09 -0500
From: Waiman Long <llong@...hat.com>
To: Michal Koutný <mkoutny@...e.com>,
 Tejun Heo <tj@...nel.org>
Cc: Waiman Long <llong@...hat.com>, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
 Chen Ridong <chenridong@...wei.com>
Subject: Re: [PATCH v2] cgroup/cpuset: Move procfs cpuset attribute under
 cgroup-v1.c

On 1/17/25 5:44 AM, Michal Koutný wrote:
> The cpuset file is a legacy attribute that is bound primarily to cpuset
> v1 hierarchy (equivalent information is available in /proc/$pid/cgroup path
> on the unified hierarchy in conjunction with respective
> cgroup.controllers showing where cpuset controller is enabled).
>
> Followup to commit b0ced9d378d49 ("cgroup/cpuset: move v1 interfaces to
> cpuset-v1.c") and hide CONFIG_PROC_PID_CPUSET under CONFIG_CPUSETS_V1.
> Drop an obsolete comment too.
>
> Signed-off-by: Michal Koutný <mkoutny@...e.com>
> ---
>   init/Kconfig              |  5 +++--
>   kernel/cgroup/cpuset-v1.c | 40 +++++++++++++++++++++++++++++++++++
>   kernel/cgroup/cpuset.c    | 44 ---------------------------------------
>   3 files changed, 43 insertions(+), 46 deletions(-)
>
> v2 changes:
> - explicitly say what's part of CPUSETS_V1
> - commit message wrt effective paths
>
> diff --git a/init/Kconfig b/init/Kconfig
> index a20e6efd3f0fb..2f3121c49ed23 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1182,7 +1182,8 @@ config CPUSETS_V1
>   	help
>   	  Legacy cgroup v1 cpusets controller which has been deprecated by
>   	  cgroup v2 implementation. The v1 is there for legacy applications
> -	  which haven't migrated to the new cgroup v2 interface yet. If you
> +	  which haven't migrated to the new cgroup v2 interface yet. Legacy
> +	  interface includes cpuset filesystem and /proc/<pid>/cpuset. If you
>   	  do not have any such application then you are completely fine leaving
>   	  this option disabled.
>   
> @@ -1190,7 +1191,7 @@ config CPUSETS_V1
>   
>   config PROC_PID_CPUSET
>   	bool "Include legacy /proc/<pid>/cpuset file"
> -	depends on CPUSETS
> +	depends on CPUSETS_V1
>   	default y
>   
>   config CGROUP_DEVICE
> diff --git a/kernel/cgroup/cpuset-v1.c b/kernel/cgroup/cpuset-v1.c
> index 25c1d7b77e2f2..fff1a38f2725f 100644
> --- a/kernel/cgroup/cpuset-v1.c
> +++ b/kernel/cgroup/cpuset-v1.c
> @@ -373,6 +373,46 @@ int cpuset1_validate_change(struct cpuset *cur, struct cpuset *trial)
>   	return ret;
>   }
>   
> +#ifdef CONFIG_PROC_PID_CPUSET
> +/*
> + * proc_cpuset_show()
> + *  - Print tasks cpuset path into seq_file.
> + *  - Used for /proc/<pid>/cpuset.
> + */
> +int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
> +		     struct pid *pid, struct task_struct *tsk)
> +{
> +	char *buf;
> +	struct cgroup_subsys_state *css;
> +	int retval;
> +
> +	retval = -ENOMEM;
> +	buf = kmalloc(PATH_MAX, GFP_KERNEL);
> +	if (!buf)
> +		goto out;
> +
> +	rcu_read_lock();
> +	spin_lock_irq(&css_set_lock);
> +	css = task_css(tsk, cpuset_cgrp_id);
> +	retval = cgroup_path_ns_locked(css->cgroup, buf, PATH_MAX,
> +				       current->nsproxy->cgroup_ns);
> +	spin_unlock_irq(&css_set_lock);
> +	rcu_read_unlock();
> +
> +	if (retval == -E2BIG)
> +		retval = -ENAMETOOLONG;
> +	if (retval < 0)
> +		goto out_free;
> +	seq_puts(m, buf);
> +	seq_putc(m, '\n');
> +	retval = 0;
> +out_free:
> +	kfree(buf);
> +out:
> +	return retval;
> +}
> +#endif /* CONFIG_PROC_PID_CPUSET */
> +
>   static u64 cpuset_read_u64(struct cgroup_subsys_state *css, struct cftype *cft)
>   {
>   	struct cpuset *cs = css_cs(css);
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 0f910c828973a..7d6e8db234290 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -4244,50 +4244,6 @@ void cpuset_print_current_mems_allowed(void)
>   	rcu_read_unlock();
>   }
>   
> -#ifdef CONFIG_PROC_PID_CPUSET
> -/*
> - * proc_cpuset_show()
> - *  - Print tasks cpuset path into seq_file.
> - *  - Used for /proc/<pid>/cpuset.
> - *  - No need to task_lock(tsk) on this tsk->cpuset reference, as it
> - *    doesn't really matter if tsk->cpuset changes after we read it,
> - *    and we take cpuset_mutex, keeping cpuset_attach() from changing it
> - *    anyway.
> - */
> -int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
> -		     struct pid *pid, struct task_struct *tsk)
> -{
> -	char *buf;
> -	struct cgroup_subsys_state *css;
> -	int retval;
> -
> -	retval = -ENOMEM;
> -	buf = kmalloc(PATH_MAX, GFP_KERNEL);
> -	if (!buf)
> -		goto out;
> -
> -	rcu_read_lock();
> -	spin_lock_irq(&css_set_lock);
> -	css = task_css(tsk, cpuset_cgrp_id);
> -	retval = cgroup_path_ns_locked(css->cgroup, buf, PATH_MAX,
> -				       current->nsproxy->cgroup_ns);
> -	spin_unlock_irq(&css_set_lock);
> -	rcu_read_unlock();
> -
> -	if (retval == -E2BIG)
> -		retval = -ENAMETOOLONG;
> -	if (retval < 0)
> -		goto out_free;
> -	seq_puts(m, buf);
> -	seq_putc(m, '\n');
> -	retval = 0;
> -out_free:
> -	kfree(buf);
> -out:
> -	return retval;
> -}
> -#endif /* CONFIG_PROC_PID_CPUSET */
> -
>   /* Display task mems_allowed in /proc/<pid>/status file. */
>   void cpuset_task_status_allowed(struct seq_file *m, struct task_struct *task)
>   {
Acked-by: Waiman Long <longman@...hat.com>