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

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Date:   Wed, 15 Jun 2022 11:13:06 +0200
From:   Ansuel Smith <ansuelsmth@...il.com>
To:     Chanwoo Choi <cwchoi00@...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 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)

> > +	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

-- 
	Ansuel