Hi,
On 2016년 11월 08일 03:57, Saravana Kannan wrote:
> On 10/26/2016 05:06 PM, Chanwoo Choi wrote:
>> Hi,
>>
>> On 2016년 10월 27일 04:17, Saravana Kannan wrote:
>>> If the new governor fails to start, switch back to old governor so that the
>>> devfreq state is not left in some weird limbo.
>>>
>>> Signed-off-by: Saravana Kannan <skan...@codeaurora.org>
>>> ---
>>> * Fix NULL deref for real this time.
>>> * Addressed some style preferences.
>>>
>>> drivers/devfreq/devfreq.c | 13 +++++++++++--
>>> 1 file changed, 11 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>>> index bf3ea76..77c41a5 100644
>>> --- a/drivers/devfreq/devfreq.c
>>> +++ b/drivers/devfreq/devfreq.c
>>> @@ -919,7 +919,7 @@ static ssize_t governor_store(struct device *dev,
>>> struct device_attribute *attr,
>>> struct devfreq *df = to_devfreq(dev);
>>> int ret;
>>> char str_governor[DEVFREQ_NAME_LEN + 1];
>>> - struct devfreq_governor *governor;
>>> + const struct devfreq_governor *governor, *prev_governor;
>>>
>>> ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s",
>>> str_governor);
>>> if (ret != 1)
>>> @@ -944,12 +944,21 @@ static ssize_t governor_store(struct device *dev,
>>> struct device_attribute *attr,
>>> goto out;
>>> }
>>> }
>>> + prev_governor = df->governor;
>>> df->governor = governor;
>>> strncpy(df->governor_name, governor->name, DEVFREQ_NAME_LEN);
>>> ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
>>> - if (ret)
>>> + if (ret) {
>>> dev_warn(dev, "%s: Governor %s not started(%d)\n",
>>> __func__, df->governor->name, ret);
>>> + if (prev_governor) {
>>
>> I think that prev_governor is always set. You don't need to check it.
>> Why do check it?
>
> Not true. Even higher up in this function, we check if df->governor != NULL.
> Simple example would be that the default governor passed in while adding the
> device isn't compiled in.
I don't understand. If device is not registered by devfreq_add_device(),
you don't change the governor by using governor_store().
If you can change the governor through governor_store(),
it means that the devfreq instance was added without any problem.
The added devfreq instance must have the sepecific governor
on df->governor variable.
So, I think that df->governor is always set and then prev_governor is always
set.
Best Regards,
Chanwoo Choi
