Re: [PATCH v7 01/15] cgroup/misc: Add per resource callbacks for CSS events

["Haitao Huang" <haitao.huang@linux.intel.com>]

On Mon, 22 Jan 2024 14:14:01 -0600, Jarkko Sakkinen <jarkko@kernel.org>  
wrote:

> On Mon Jan 22, 2024 at 7:20 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.
>>
>> 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>
>> ---
>> V7:
>> - Make ops one per resource type and store them in array (Michal)
>> - Rename the ops struct to misc_res_ops, and enforce the constraints of  
>> required callback
>> functions (Jarkko)
>> - Moved addition of priv field to patch 4 where it was used first.  
>> (Jarkko)
>>
>> V6:
>> - Create ops struct for per resource callbacks (Jarkko)
>> - Drop max_write callback (Dave, Michal)
>> - Style fixes (Kai)
>> ---
>>  include/linux/misc_cgroup.h | 11 +++++++
>>  kernel/cgroup/misc.c        | 60 +++++++++++++++++++++++++++++++++++--
>>  2 files changed, 68 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/misc_cgroup.h b/include/linux/misc_cgroup.h
>> index e799b1f8d05b..0806d4436208 100644
>> --- a/include/linux/misc_cgroup.h
>> +++ b/include/linux/misc_cgroup.h
>> @@ -27,6 +27,16 @@ struct misc_cg;
>>
>>  #include <linux/cgroup.h>
>>
>> +/**
>> + * struct misc_res_ops: per resource type callback ops.
>> + * @alloc: invoked for resource specific initialization when cgroup is  
>> allocated.
>> + * @free: invoked for resource specific cleanup when cgroup is  
>> deallocated.
>> + */
>> +struct misc_res_ops {
>> +	int (*alloc)(struct misc_cg *cg);
>> +	void (*free)(struct misc_cg *cg);
>> +};
>> +
>>  /**
>>   * struct misc_res: Per cgroup per misc type resource
>>   * @max: Maximum limit on the resource.
>> @@ -56,6 +66,7 @@ struct misc_cg {
>>
>>  u64 misc_cg_res_total_usage(enum misc_res_type type);
>>  int misc_cg_set_capacity(enum misc_res_type type, u64 capacity);
>> +int misc_cg_set_ops(enum misc_res_type type, const struct misc_res_ops  
>> *ops);
>>  int misc_cg_try_charge(enum misc_res_type type, struct misc_cg *cg,  
>> u64 amount);
>>  void misc_cg_uncharge(enum misc_res_type type, struct misc_cg *cg, u64  
>> amount);
>>
>> diff --git a/kernel/cgroup/misc.c b/kernel/cgroup/misc.c
>> index 79a3717a5803..b8c32791334c 100644
>> --- a/kernel/cgroup/misc.c
>> +++ b/kernel/cgroup/misc.c
>> @@ -39,6 +39,9 @@ static struct misc_cg root_cg;
>>   */
>>  static u64 misc_res_capacity[MISC_CG_RES_TYPES];
>>
>> +/* Resource type specific operations */
>> +static const struct misc_res_ops *misc_res_ops[MISC_CG_RES_TYPES];
>> +
>>  /**
>>   * parent_misc() - Get the parent of the passed misc cgroup.
>>   * @cgroup: cgroup whose parent needs to be fetched.
>> @@ -105,6 +108,36 @@ int misc_cg_set_capacity(enum misc_res_type type,  
>> u64 capacity)
>>  }
>>  EXPORT_SYMBOL_GPL(misc_cg_set_capacity);
>>
>> +/**
>> + * misc_cg_set_ops() - set resource specific operations.
>> + * @type: Type of the misc res.
>> + * @ops: Operations for the given type.
>> + *
>> + * Context: Any context.
>> + * Return:
>> + * * %0 - Successfully registered the operations.
>> + * * %-EINVAL - If @type is invalid, or the operations missing any  
>> required callbacks.
>> + */
>> +int misc_cg_set_ops(enum misc_res_type type, const struct misc_res_ops  
>> *ops)
>> +{
>> +	if (!valid_type(type))
>> +		return -EINVAL;
>> +
>> +	if (!ops->alloc) {
>> +		pr_err("%s: alloc missing\n", __func__);
>> +		return -EINVAL;
>> +	}
>> +
>> +	if (!ops->free) {
>> +		pr_err("%s: free missing\n", __func__);
>> +		return -EINVAL;
>> +	}
>> +
>> +	misc_res_ops[type] = ops;
>> +	return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(misc_cg_set_ops);
>> +
>>  /**
>>   * misc_cg_cancel_charge() - Cancel the charge from the misc cgroup.
>>   * @type: Misc res type in misc cg to cancel the charge from.
>> @@ -383,23 +416,37 @@ 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 (misc_res_ops[i]) {
>> +			ret = misc_res_ops[i]->alloc(cg);
>> +			if (ret)
>> +				goto alloc_err;
>
> So I'd consider pattern like this to avoid repetition:
>
> 			if (ret) {
> 				__misc_cg_free(cg);
> 				return PERR_PTR(ret);
> 			}
>
> and call __misc_cg_free() also in misc_cg_free().
>
Will change to do that.
Thanks
Haitao