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

["Jarkko Sakkinen" <jarkko@kernel.org>]

On Tue Jan 9, 2024 at 5:37 AM EET, Haitao Huang wrote:
> On Wed, 15 Nov 2023 14:25:59 -0600, Jarkko Sakkinen <jarkko@kernel.org>  
> wrote:
>
> > On Mon Oct 30, 2023 at 8:20 PM EET, Haitao Huang wrote:
> >> From: Kristen Carlson Accardi <kristen@linux.intel.com>
> >>
> >> 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@linux.intel.com>
> >> Co-developed-by: Haitao Huang <haitao.huang@linux.intel.com>
> >> Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
> >> ---
> >> 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.

OK, great, thanks!

BR, Jarkko