linux-kernel - Re: [PATCH v3 1/5] PM / devfreq: Fix cpufreq passive unregister erroring on PROBE

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Date:   Wed, 15 Jun 2022 08:12:06 +0900
From:   Chanwoo Choi <cwchoi00@...il.com>
To:     Ansuel Smith <ansuelsmth@...il.com>
Cc:     MyungJoo Ham <myungjoo.ham@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Sibi Sankar <sibis@...eaurora.org>,
        Saravana Kannan <skannan@...eaurora.org>,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 1/5] PM / devfreq: Fix cpufreq passive unregister
 erroring on PROBE_DEFER

On 22. 6. 15. 07:07, Ansuel Smith wrote:
> On Wed, Jun 15, 2022 at 07:58:16AM +0900, Chanwoo Choi wrote:
>> On 22. 6. 14. 20:06, Christian 'Ansuel' Marangi wrote:
>>> With the passive governor, the cpu based scaling can PROBE_DEFER due to
>>> the fact that CPU policy are not ready.
>>> The cpufreq passive unregister notifier is called both from the
>>> GOV_START errors and for the GOV_STOP and assume the notifier is
>>> successfully registred every time. With GOV_START failing it's wrong to
>>> loop over each possible CPU since the register path has failed for
>>> some CPU policy not ready. Change the logic and unregister the notifer
>>> based on the current allocated parent_cpu_data list to correctly handle
>>> errors and the governor unregister path.
>>>
>>> Fixes: a03dacb0316f ("PM / devfreq: Add cpu based scaling support to passive governor")
>>> Signed-off-by: Christian 'Ansuel' Marangi <ansuelsmth@...il.com>
>>> ---
>>>  drivers/devfreq/governor_passive.c | 23 ++++++-----------------
>>>  1 file changed, 6 insertions(+), 17 deletions(-)
>>>
>>> diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
>>> index 72c67979ebe1..0188c32f5198 100644
>>> --- a/drivers/devfreq/governor_passive.c
>>> +++ b/drivers/devfreq/governor_passive.c
>>> @@ -222,8 +222,8 @@ static int cpufreq_passive_unregister_notifier(struct devfreq *devfreq)
>>>  {
>>>  	struct devfreq_passive_data *p_data
>>>  			= (struct devfreq_passive_data *)devfreq->data;
>>> -	struct devfreq_cpu_data *parent_cpu_data;
>>> -	int cpu, ret = 0;
>>> +	struct devfreq_cpu_data *parent_cpu_data, *tmp;
>>> +	int ret;
>>>  
>>>  	if (p_data->nb.notifier_call) {
>>>  		ret = cpufreq_unregister_notifier(&p_data->nb,
>>> @@ -232,27 +232,16 @@ static int cpufreq_passive_unregister_notifier(struct devfreq *devfreq)
>>>  			return ret;
>>>  	}
>>>  
>>> -	for_each_possible_cpu(cpu) {
>>> -		struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);
>>> -		if (!policy) {
>>> -			ret = -EINVAL;
>>> -			continue;
>>> -		}
>>> -
>>> -		parent_cpu_data = get_parent_cpu_data(p_data, policy);
>>> -		if (!parent_cpu_data) {
>>> -			cpufreq_cpu_put(policy);
>>> -			continue;
>>> -		}
>>> -
>>> +	list_for_each_entry_safe(parent_cpu_data, tmp, &p_data->cpu_data_list, node) {
>>>  		list_del(&parent_cpu_data->node);
>>> +
>>>  		if (parent_cpu_data->opp_table)
>>>  			dev_pm_opp_put_opp_table(parent_cpu_data->opp_table);
>>> +
>>>  		kfree(parent_cpu_data);
>>> -		cpufreq_cpu_put(policy);
>>>  	}
>>
>> I agree this patch. Just, I'd like to make the separate function
>> to handle the removing of parent_cpu_data.
>>
>> Please add new delete_parent_cpu_data() function under get_parent_cpu_data()
>> implementation and then call delete_parent_cpu_data()
>> in cpufreq_passive_unregister_notifier().
>>
> 
> Ok just to make sure I understand this correctly.
> A dedicated function with just the list_for_each_entry_safe function
> correct?

Yes to remove the parent_cpu_data with list_for_each_entry_safe.

> 
>>>  
>>> -	return ret;
>>> +	return 0;
>>>  }
>>>  
>>>  static int cpufreq_passive_register_notifier(struct devfreq *devfreq)
>>
>>
>> -- 
>> Best Regards,
>> Samsung Electronics
>> Chanwoo Choi
> 


-- 
Best Regards,
Samsung Electronics
Chanwoo Choi