[PATCH v5] PM / devfreq: Restart previous governor if new governor fails to start

[PATCH v5] PM / devfreq: Restart previous governor if new governor fails to start

[Sibi Sankar]

From: Saravana Kannan <skannan@codeaurora.org>

If the new governor fails to start, switch back to old governor so that the
devfreq state is not left in some weird limbo.

[Mjungjoo: assume fatal on revert failure and set df->governor to NULL]
Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
---
V5:
* assume fatal on revert failure and set df->governor to NULL

V4:
* Removed prev_governor check.

V3:
* Fix NULL deref for real this time.
* Addressed some style preferences.

V2:
* Fixed typo in commit text
* Fixed potential NULL deref

 drivers/devfreq/devfreq.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 428a1de81008..37490235ec34 100644
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -1124,7 +1124,7 @@ 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)
@@ -1153,12 +1153,24 @@ 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);
+		df->governor = prev_governor;
+		strncpy(df->governor_name, prev_governor->name,
+			DEVFREQ_NAME_LEN);
+		ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
+		if (ret) {
+			dev_warn(dev,
+				 "%s: reverting to Governor %s failed (%d)\n",
+				 __func__, df->governor_name, ret);
+			df->governor = NULL;
+		}
+	}
 out:
 	mutex_unlock(&devfreq_list_lock);
 
-- 
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
a Linux Foundation Collaborative Project

RE: [PATCH v5] PM / devfreq: Restart previous governor if new governor fails to start

[MyungJoo Ham]

>From: Saravana Kannan <skannan@codeaurora.org>
>
>If the new governor fails to start, switch back to old governor so that the
>devfreq state is not left in some weird limbo.
>
>[Mjungjoo: assume fatal on revert failure and set df->governor to NULL]
>Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
>Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
>Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>

I'll modify WARN->ERROR for the case when it's fatal:

>+		if (ret) {
>+			dev_warn(dev,
>+				 "%s: reverting to Governor %s failed (%d)\n",
>+				 __func__, df->governor_name, ret);
>+			df->governor = NULL;
>+		}

Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>


>---
>V5:
>* assume fatal on revert failure and set df->governor to NULL
>
>V4:
>* Removed prev_governor check.
>
>V3:
>* Fix NULL deref for real this time.
>* Addressed some style preferences.
>
>V2:
>* Fixed typo in commit text
>* Fixed potential NULL deref
>
> drivers/devfreq/devfreq.c | 16 ++++++++++++++--
> 1 file changed, 14 insertions(+), 2 deletions(-)
>

Re: [PATCH v5] PM / devfreq: Restart previous governor if new governor fails to start

[Sibi Sankar]

On 2019-03-12 12:47, MyungJoo Ham wrote:
>> From: Saravana Kannan <skannan@codeaurora.org>
>> 
>> If the new governor fails to start, switch back to old governor so 
>> that the
>> devfreq state is not left in some weird limbo.
>> 
>> [Mjungjoo: assume fatal on revert failure and set df->governor to 
>> NULL]
>> Signed-off-by: Sibi Sankar <sibis@codeaurora.org>
>> Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
>> Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
> 
> I'll modify WARN->ERROR for the case when it's fatal:

Sure, thanks.

> 
>> +		if (ret) {
>> +			dev_warn(dev,
>> +				 "%s: reverting to Governor %s failed (%d)\n",
>> +				 __func__, df->governor_name, ret);
>> +			df->governor = NULL;
>> +		}
> 
> Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
> 
> 
>> ---
>> V5:
>> * assume fatal on revert failure and set df->governor to NULL
>> 
>> V4:
>> * Removed prev_governor check.
>> 
>> V3:
>> * Fix NULL deref for real this time.
>> * Addressed some style preferences.
>> 
>> V2:
>> * Fixed typo in commit text
>> * Fixed potential NULL deref
>> 
>> drivers/devfreq/devfreq.c | 16 ++++++++++++++--
>> 1 file changed, 14 insertions(+), 2 deletions(-)
>> 

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