Re: [PATCH RESEND 3/4] PM / devfreq: Fix governor_store() failing when device has no current governor

[Jie Zhan]

On 3/31/2026 4:02 PM, Yaxiong Tian wrote:
> 
> 在 2026/3/31 15:16, Jie Zhan 写道:
>>
>> On 3/19/2026 5:17 PM, Yaxiong Tian wrote:
>>> Since devfreq_remove_governor() may clear the device's current governor
>>> in certain situations, while governors actually exist independently
>>> of the device, directly returning EINVAL in this case is inaccurate.
>>>
>>> To fix this issue, remove this check and add relevant logic for when
>>> df->governor is NULL.
>>>
>>> Fixes: 483d557ee9a3 ("PM / devfreq: Clean up the devfreq instance name in sysfs attr")
>>> Signed-off-by: Yaxiong Tian <tianyaxiong@xxxxxxxxxx>
>>> ---
>>>   drivers/devfreq/devfreq.c | 15 ++++++++++++---
>>>   1 file changed, 12 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index 0bf320123e3a..4a312f3c2421 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -1425,9 +1425,6 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
>>>       char str_governor[DEVFREQ_NAME_LEN + 1];
>>>       const struct devfreq_governor *governor, *prev_governor;
>>>   -    if (!df->governor)
>>> -        return -EINVAL;
>>> -
>>>       ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor);
>>>       if (ret != 1)
>>>           return -EINVAL;
>>> @@ -1438,6 +1435,18 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
>>>           ret = PTR_ERR(governor);
>>>           goto out;
>>>       }
>>> +
>>> +    if (!df->governor) {
>>> +        df->governor = governor;
>>> +        ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
>>> +        if (ret) {
>>> +            dev_warn(dev, "%s: Governor %s not started(%d)\n",
>>> +                __func__, df->governor->name, ret);
>>> +            df->governor = NULL;
>>> +        }
>>> +        goto out;
>>> +    }
>>> +
>> The sequence that starts the governor, and stops, and then re-starts looks
>> quite weird.
>> Can you do a NULL pointer check before the IMMUTABLE flag check and
>> stopping governor, rather than this?
> 
> This patch only addresses the issue raised in the commit message. As for the original
> 
> start, stop, and then restart sequence, I haven't found any problems with it so far.
> 
You just added the first 'start' here.
Please see the other process in governor_store().
>>>       if (df->governor == governor) {
>>>           ret = 0;
>>>           goto out;