linux-kernel - Re: [PATCH v3] PM / devfreq: Fix devfreq_add_device() when drivers are built as modules.

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Date:   Tue, 3 Jul 2018 15:16:35 +0200
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     myungjoo.ham@...sung.com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Cc:     "kernel@...labora.com" <kernel@...labora.com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [PATCH v3] PM / devfreq: Fix devfreq_add_device() when drivers
 are built as modules.

Hi MyungJoo

On 03/07/18 12:57, MyungJoo Ham wrote:
>> @@ -988,12 +1030,13 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
>> 	if (ret != 1)
>> 		return -EINVAL;
>>
>> -	mutex_lock(&devfreq_list_lock);
>> -	governor = find_devfreq_governor(str_governor);
>> +	governor = try_then_request_governor(str_governor);
>> 	if (IS_ERR(governor)) {
>> -		ret = PTR_ERR(governor);
>> -		goto out;
>> +		return PTR_ERR(governor);
>> 	}
>> +
>> +	mutex_lock(&devfreq_list_lock);
>> +
>> 	if (df->governor == governor) {
>> 		ret = 0;
>> 		goto out;
>> -- 
> 
> The possibility that the result of try_then_request_governor is
> not kept protected until the line of
> "if (df->governor == governor)" is itching.
> 
> Can you make it kept "locked" from the return of
> find_devfreq_governor() (either in try_then... or in this function)
> to the unlock of governor_store()?
> 

Sure, I'll send v4 in a minute.

Thanks,
 Enric

> 
> Cheers,
> MyungJoo
>