linux-kernel - Re: [PATCH v4 1/4] PM / devfreq: Fix cpufreq passive unregister erroring on PROBE

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Message-ID: <6502dfdc-3e35-db24-2be5-15eca026d193@gmail.com>
Date:   Sat, 18 Jun 2022 03:35:08 +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 v4 1/4] PM / devfreq: Fix cpufreq passive unregister
 erroring on PROBE_DEFER

On 22. 6. 15. 18:13, Ansuel Smith wrote:
> On Wed, Jun 15, 2022 at 03:48:03PM +0900, Chanwoo Choi wrote:
>> On 22. 6. 15. 08:09, 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 | 39 +++++++++++++-----------------
>>>  1 file changed, 17 insertions(+), 22 deletions(-)
>>>
>>> diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
>>> index 72c67979ebe1..95de336f20d5 100644
>>> --- a/drivers/devfreq/governor_passive.c
>>> +++ b/drivers/devfreq/governor_passive.c
>>> @@ -34,6 +34,20 @@ get_parent_cpu_data(struct devfreq_passive_data *p_data,
>>>  	return NULL;
>>>  }
>>>  
>>> +static void delete_parent_cpu_data(struct devfreq_passive_data *p_data)
>>> +{
>>> +	struct devfreq_cpu_data *parent_cpu_data, *tmp;
>>> +
>>
>> Need to add the validation checking of argument as following:
>>
>> 	if (!p_data)
>> 		return;
>>
> 
> Considering this is called only by cpufreq_passive_unregister_notifier
> and cpufreq_passive_unregister_notifier is called only by devfreq_passive_event_handler
> where the check is already done, isn't that redundant.
> We should never reach delete_parent_cpu_data with no p_data.
> (Unless you want to use that function somewhere else)

Actually, right as you mentioned. I'd like to check the parameter validation
on each function. But, I agree to keep this path without checking p_data.
If needed on later, I'll do that.

Applied it. Thanks.

> 
>>> +	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);
>>> +	}
>>> +}
>>> +
>>>  static unsigned long get_target_freq_by_required_opp(struct device *p_dev,
>>>  						struct opp_table *p_opp_table,
>>>  						struct opp_table *opp_table,
>>> @@ -222,8 +236,7 @@ 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;
>>> +	int ret;
>>>  
>>>  	if (p_data->nb.notifier_call) {
>>>  		ret = cpufreq_unregister_notifier(&p_data->nb,
>>> @@ -232,27 +245,9 @@ 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_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);
>>> -	}
>>> +	delete_parent_cpu_data(p_data);
>>>  
>>> -	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