Re: [PATCH v4 01/18] cgroup/misc: Add per resource callbacks for CSS events

[Jarkko Sakkinen]

On Wed Sep 13, 2023 at 7:06 AM EEST, Haitao Huang wrote:
> From: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
>
> Consumers of the misc cgroup controller might need to perform separate
> actions for Cgroups Subsystem State(CSS) events: cgroup alloc and free.

nit: s/State(CSS)/State (CSS)/

"cgroup alloc" and "cgroup free" mean absolutely nothing.


> In addition, writes to the max value may also need separate action. Add

What "the max value"?

> the ability to allow downstream users to setup callbacks for these
> operations, and call the corresponding per-resource-type callback when
> appropriate.

Who are "the downstream users" and what sort of callbacks they setup?

>
> This code will be utilized by the SGX driver in a future patch.
>
> Signed-off-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
> Signed-off-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>
> ---
> V4:
> - Moved this to the front of the series.
> - Applies on cgroup/for-6.6 with the overflow fix for misc.
>
> V3:
> - Removed the released() callback
> ---
>  include/linux/misc_cgroup.h |  5 +++++
>  kernel/cgroup/misc.c        | 32 +++++++++++++++++++++++++++++---
>  2 files changed, 34 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/misc_cgroup.h b/include/linux/misc_cgroup.h
> index e799b1f8d05b..e1bcd176c2de 100644
> --- a/include/linux/misc_cgroup.h
> +++ b/include/linux/misc_cgroup.h
> @@ -37,6 +37,11 @@ struct misc_res {
>  	u64 max;
>  	atomic64_t usage;
>  	atomic64_t events;
> +
> +	/* per resource callback ops */
> +	int (*misc_cg_alloc)(struct misc_cg *cg);
> +	void (*misc_cg_free)(struct misc_cg *cg);
> +	void (*misc_cg_max_write)(struct misc_cg *cg);
>  };
>  
>  /**
> diff --git a/kernel/cgroup/misc.c b/kernel/cgroup/misc.c
> index 79a3717a5803..e0092170d0dd 100644
> --- a/kernel/cgroup/misc.c
> +++ b/kernel/cgroup/misc.c
> @@ -276,10 +276,13 @@ static ssize_t misc_cg_max_write(struct kernfs_open_file *of, char *buf,
>  
>  	cg = css_misc(of_css(of));
>  
> -	if (READ_ONCE(misc_res_capacity[type]))
> +	if (READ_ONCE(misc_res_capacity[type])) {
>  		WRITE_ONCE(cg->res[type].max, max);
> -	else
> +		if (cg->res[type].misc_cg_max_write)
> +			cg->res[type].misc_cg_max_write(cg);
> +	} else {
>  		ret = -EINVAL;
> +	}
>  
>  	return ret ? ret : nbytes;
>  }
> @@ -383,23 +386,39 @@ static struct cftype misc_cg_files[] = {
>  static struct cgroup_subsys_state *
>  misc_cg_alloc(struct cgroup_subsys_state *parent_css)
>  {
> +	struct misc_cg *parent_cg;
>  	enum misc_res_type i;
>  	struct misc_cg *cg;
> +	int ret;
>  
>  	if (!parent_css) {
>  		cg = &root_cg;
> +		parent_cg = &root_cg;
>  	} else {
>  		cg = kzalloc(sizeof(*cg), GFP_KERNEL);
>  		if (!cg)
>  			return ERR_PTR(-ENOMEM);
> +		parent_cg = css_misc(parent_css);
>  	}
>  
>  	for (i = 0; i < MISC_CG_RES_TYPES; i++) {
>  		WRITE_ONCE(cg->res[i].max, MAX_NUM);
>  		atomic64_set(&cg->res[i].usage, 0);
> +		if (parent_cg->res[i].misc_cg_alloc) {
> +			ret = parent_cg->res[i].misc_cg_alloc(cg);
> +			if (ret)
> +				goto alloc_err;
> +		}
>  	}
>  
>  	return &cg->css;
> +
> +alloc_err:
> +	for (i = 0; i < MISC_CG_RES_TYPES; i++)
> +		if (parent_cg->res[i].misc_cg_free)
> +			cg->res[i].misc_cg_free(cg);
> +	kfree(cg);
> +	return ERR_PTR(ret);
>  }
>  
>  /**
> @@ -410,7 +429,14 @@ misc_cg_alloc(struct cgroup_subsys_state *parent_css)
>   */
>  static void misc_cg_free(struct cgroup_subsys_state *css)
>  {
> -	kfree(css_misc(css));
> +	struct misc_cg *cg = css_misc(css);
> +	enum misc_res_type i;
> +
> +	for (i = 0; i < MISC_CG_RES_TYPES; i++)
> +		if (cg->res[i].misc_cg_free)
> +			cg->res[i].misc_cg_free(cg);
> +
> +	kfree(cg);
>  }
>  
>  /* Cgroup controller callbacks */
> -- 
> 2.25.1

BR, Jarkko