Re: [PATCH v6 01/12] cgroup/misc: Add per resource callbacks for CSS events

[Haitao Huang]

On Wed, 15 Nov 2023 14:25:59 -0600, Jarkko Sakkinen <jarkko@xxxxxxxxxx>  
wrote:

> On Mon Oct 30, 2023 at 8:20 PM EET, Haitao Huang wrote:
> > From: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
> >
> > The misc cgroup controller (subsystem) currently does not perform
> > resource type specific action for Cgroups Subsystem State (CSS) events:
> > the 'css_alloc' event when a cgroup is created and the 'css_free' event
> > when a cgroup is destroyed.
> >
> > Define callbacks for those events and allow resource providers to
> > register the callbacks per resource type as needed. This will be
> > utilized later by the EPC misc cgroup support implemented in the SGX
> > driver.
> >
> > Also add per resource type private data for those callbacks to store and
> > access resource specific data.
> >
> > Signed-off-by: Kristen Carlson Accardi <kristen@xxxxxxxxxxxxxxx>
> > Co-developed-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Haitao Huang <haitao.huang@xxxxxxxxxxxxxxx>
> > ---
> > V6:
> > - Create ops struct for per resource callbacks (Jarkko)
> > - Drop max_write callback (Dave, Michal)
> > - Style fixes (Kai)
> > ---
> >  include/linux/misc_cgroup.h | 14 ++++++++++++++
> >  kernel/cgroup/misc.c        | 27 ++++++++++++++++++++++++---
> >  2 files changed, 38 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/misc_cgroup.h b/include/linux/misc_cgroup.h
> > index e799b1f8d05b..5dc509c27c3d 100644
> > --- a/include/linux/misc_cgroup.h
> > +++ b/include/linux/misc_cgroup.h
> > @@ -27,16 +27,30 @@ struct misc_cg;
> >
> >  #include <linux/cgroup.h>
> >
> > +/**
> > + * struct misc_operations_struct: per resource callback ops.
> > + * @alloc: invoked for resource specific initialization when cgroup is  
> > allocated.
> > + * @free: invoked for resource specific cleanup when cgroup is  
> > deallocated.
> > + */
> > +struct misc_operations_struct {
> > +	int (*alloc)(struct misc_cg *cg);
> > +	void (*free)(struct misc_cg *cg);
> > +};
>
> Maybe just misc_operations, or even misc_ops?

With Michal's suggestion to make ops per-resource-type, I'll rename this  
misc_res_ops  (I was following vm_operations_struct as example)

> > +
> >  /**
> >   * struct misc_res: Per cgroup per misc type resource
> >   * @max: Maximum limit on the resource.
> >   * @usage: Current usage of the resource.
> >   * @events: Number of times, the resource limit exceeded.
> > + * @priv: resource specific data.
> > + * @misc_ops: resource specific operations.
> >   */
> >  struct misc_res {
> >  	u64 max;
> >  	atomic64_t usage;
> >  	atomic64_t events;
> > +	void *priv;
>
> priv is the wrong patch, it just confuses the overall picture heere.
> please move it to 04/12. Let's deal with the callbacks here.

Ok

> > +	const struct misc_operations_struct *misc_ops;
> >  };
>
> misc_ops would be at least consistent with this, as misc_res also has an
> acronym.
>
> >  /**
> > diff --git a/kernel/cgroup/misc.c b/kernel/cgroup/misc.c
> > index 79a3717a5803..d971ede44ebf 100644
> > --- a/kernel/cgroup/misc.c
> > +++ b/kernel/cgroup/misc.c
> > @@ -383,23 +383,37 @@ 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, *cg;
> >  	enum misc_res_type i;
> > -	struct misc_cg *cg;
> > +	int ret;
> >
> >  	if (!parent_css) {
> > -		cg = &root_cg;
> > +		parent_cg = 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_ops && parent_cg->res[i].misc_ops->alloc)  
> > {
> > +			ret = parent_cg->res[i].misc_ops->alloc(cg);
> > +			if (ret)
> > +				goto alloc_err;
>
> The patch set only has a use case for both operations defined - any
> partial combinations should never be allowed.
>
> To enforce this invariant you could create a set of operations (written
> out of top of my head):
>
> static int misc_res_init(struct misc_res *res, struct misc_ops *ops)
> {
> 	if (!misc_ops->alloc) {
> 		pr_err("%s: alloc missing\n", __func__);
> 		return -EINVAL;
> 	}
>
> 	if (!misc_ops->free) {
> 		pr_err("%s: free missing\n", __func__);
> 		return -EINVAL;
> 	}
>
> 	res->misc_ops = misc_ops;
> 	return 0;
> }
>
> static inline int misc_res_alloc(struct misc_cg *cg, struct misc_res  
> *res)
> {
> 	int ret;
>
> 	if (!res->misc_ops)
> 		return 0;
> 	
> 	return res->misc_ops->alloc(cg);
> }
>
> static inline void misc_res_free(struct misc_cg *cg, struct misc_res  
> *res)
> {
> 	int ret;
>
> 	if (!res->misc_ops)
> 		return 0;
> 	
> 	return res->misc_ops->alloc(cg);
> }
>
> Now if anything has misc_ops, it will also always have *both* callback,
> and nothing half-baked gets in.
>
> The above loops would be then:
>
> 	for (i = 0; i < MISC_CG_RES_TYPES; i++) {
> 		WRITE_ONCE(cg->res[i].max, MAX_NUM);
> 		atomic64_set(&cg->res[i].usage, 0);
> 		ret = misc_res_alloc(&parent_cg->res[i]);
> 		if (ret)
> 			goto alloc_err;
>
> Cleaner and better guards for state consistency. In 04/12 you need to
> then call misc_res_init() instead of direct assignment.
>
> BR, Jarkko

Will combine these with the use of a static operations array suggested by  
Michal.

Thanks
Haitao