linux-kernel - Re: [PATCH v4 2/4] PM / devfreq: Fix kernel warning with cpufreq passive register fail

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Message-ID: <8ec38d8c-2ece-dfbb-8435-5963d7e80049@gmail.com>
Date:   Sat, 18 Jun 2022 04:08:35 +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 2/4] PM / devfreq: Fix kernel warning with cpufreq
 passive register fail

On 22. 6. 15. 18:20, Ansuel Smith wrote:
> On Wed, Jun 15, 2022 at 04:11:13PM +0900, Chanwoo Choi wrote:
>> On 22. 6. 15. 08:09, Christian 'Ansuel' Marangi wrote:
>>> When the cpufreq passive register path from the passive governor fails,
>>> the cpufreq_passive_unregister is called and a kernel WARNING is always
>>> reported.

>>> This is caused by the fact that the devfreq driver already call the
>>> governor unregister with the GOV_STOP, for this reason the second
>>> cpufreq_passive_unregister always return error and a WARN is printed
>>> from the WARN_ON function.

>>> Remove the unregister call from the error handling of the cpufreq register
>>> notifier as it's fundamentally wrong and already handled by the devfreq
>>> core code.

If possible, could you make the patch description more simply?

>>>
>>> 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 | 1 -
>>>  1 file changed, 1 deletion(-)
>>>
>>> diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
>>> index 95de336f20d5..dcc9dd518197 100644
>>> --- a/drivers/devfreq/governor_passive.c
>>> +++ b/drivers/devfreq/governor_passive.c
>>> @@ -331,7 +331,6 @@ static int cpufreq_passive_register_notifier(struct devfreq *devfreq)
>>>  err_put_policy:
>>>  	cpufreq_cpu_put(policy);
>>>  err:
>>> -	WARN_ON(cpufreq_passive_unregister_notifier(devfreq));
>>>  
>>>  	return ret;
>>>  }
>>
>> I think that it is necessary to free the resource when error happen.
> 
> Thing is that it should not be done in the register. Following the flow
> of the devfreq core code, if a gov fails to START, the gov STOP is
> called and we correctly free our resources. In the current
> implementation we call the free 2 times and the second time will always
> print error as the notifier is already unregistered.
> 
>> Also, after merging the your patch1, I think that cpufreq_passive_unregister_notifier(devfreq)
>> will not return error. Instead, just 0 for success.
> 
> With path1 we removed the error with the parent_cpu_data deletion but
> the unregister error is still there.
> 
>>
>> Instead, 'err_free_cpu_data' and 'err_put_policy' goto statement are wrong exception
>> handling. If fix the exception handling code in cpufreq_passive_register_notifier
>> as following and with your patch1, I'll handle the resource for free/un-registration
>> when error happen during cpufreq_passive_register_notifier.
>>
> 
> Don't know the main problem here is calling unregister 2 times.

Ah. I understood. To fix the error path handling with unregister function
is called twice, I think that need to to fix it as following:


diff --git a/drivers/devfreq/governor_passive.c b/drivers/devfreq/governor_passive.c
index a35b39ac656c..8f38a63beefc 100644
--- a/drivers/devfreq/governor_passive.c
+++ b/drivers/devfreq/governor_passive.c
@@ -289,22 +289,25 @@ static int cpufreq_passive_register_notifier(struct devfreq *devfreq)
                parent_cpu_data = kzalloc(sizeof(*parent_cpu_data),
                                                GFP_KERNEL);
                if (!parent_cpu_data) {
+                       cpufreq_cpu_put(policy);
                        ret = -ENOMEM;
-                       goto err_put_policy;
+                       goto err;
                }
 
                cpu_dev = get_cpu_device(cpu);
                if (!cpu_dev) {
                        dev_err(dev, "failed to get cpu device\n");
+                       cpufreq_cpu_put(policy);
                        ret = -ENODEV;
-                       goto err_free_cpu_data;
+                       goto err;
                }
 
                opp_table = dev_pm_opp_get_opp_table(cpu_dev);
                if (IS_ERR(opp_table)) {
                        dev_err(dev, "failed to get opp_table of cpu%d\n", cpu);
+                       cpufreq_cpu_put(policy);
                        ret = PTR_ERR(opp_table);
-                       goto err_free_cpu_data;
+                       goto err;
                }
 
                parent_cpu_data->dev = cpu_dev;
@@ -324,15 +327,7 @@ static int cpufreq_passive_register_notifier(struct devfreq *devfreq)
        if (ret)
                dev_err(dev, "failed to update the frequency\n");
 
-       return ret;
-
-err_free_cpu_data:
-       kfree(parent_cpu_data);
-err_put_policy:
-       cpufreq_cpu_put(policy);
 err:
-       WARN_ON(cpufreq_passive_unregister_notifier(devfreq));
-
        return ret;
 }


-- 
Best Regards,
Samsung Electronics
Chanwoo Choi