[PATCH v2] PM / devfreq: Restart previous governor if new governor fails to start

[PATCH v2] PM / devfreq: Restart previous governor if new governor fails to start

[Saravana Kannan]

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 <skannan@codeaurora.org>
---
* Fixed typo in commit text
* Fixed potential NULL deref

 drivers/devfreq/devfreq.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index bf3ea76..243253e 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_gov;
 
 	ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor);
 	if (ret != 1)
@@ -944,12 +944,17 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
 			goto out;
 		}
 	}
+	prev_gov = 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);
+		df->governor = prev_gov;
+		strncpy(df->governor_name, prev_gov->name, DEVFREQ_NAME_LEN);
+		df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
+	}
 out:
 	mutex_unlock(&devfreq_list_lock);
 
-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

Re: [PATCH v2] PM / devfreq: Restart previous governor if new governor fails to start

[Chanwoo Choi]

Hi,

On 2016년 10월 26일 10:25, 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 <skannan@codeaurora.org>
> ---
> * Fixed typo in commit text
> * Fixed potential NULL deref
> 
>  drivers/devfreq/devfreq.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index bf3ea76..243253e 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_gov;
>  
>  	ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor);
>  	if (ret != 1)
> @@ -944,12 +944,17 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
>  			goto out;
>  		}
>  	}
> +	prev_gov = 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);
> +		df->governor = prev_gov;
> +		strncpy(df->governor_name, prev_gov->name, DEVFREQ_NAME_LEN);
> +		df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
> +	}
>  out:
>  	mutex_unlock(&devfreq_list_lock);
>  
> 

Looks good to me.
But, how about using the 'prev_governor' instead of 'prev_gov'?
because the variable name of current governor is 'governor' instead of 'gov'.

Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>

-- 
Best Regards,
Chanwoo Choi

Re: [PATCH v2] PM / devfreq: Restart previous governor if new governor fails to start

[Saravana Kannan]

On 10/26/2016 12:22 AM, Chanwoo Choi wrote:
> Hi,
>
> On 2016년 10월 26일 10:25, 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 <skannan@codeaurora.org>
>> ---
>> * Fixed typo in commit text
>> * Fixed potential NULL deref
>>
>>   drivers/devfreq/devfreq.c | 9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index bf3ea76..243253e 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_gov;
>>
>>   	ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor);
>>   	if (ret != 1)
>> @@ -944,12 +944,17 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
>>   			goto out;
>>   		}
>>   	}
>> +	prev_gov = 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);
>> +		df->governor = prev_gov;
>> +		strncpy(df->governor_name, prev_gov->name, DEVFREQ_NAME_LEN);
>> +		df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
>> +	}

Sigh... looks like I added the changes to the index but forgot to commit 
it before I sent the patch. Will send v3.

>>   out:
>>   	mutex_unlock(&devfreq_list_lock);
>>
>>
>
> Looks good to me.
> But, how about using the 'prev_governor' instead of 'prev_gov'?
> because the variable name of current governor is 'governor' instead of 'gov'.

I was trying to avoid wrapping lines too much. But this doesn't cause 
any additional wraps. Done.

>
> Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
>

Can you please review v3?

Thanks,
Saravana

-- 
Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project