2019-03-11 10:09:09

by Sibi Sankar

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

From: Saravana Kannan <[email protected]>

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 <[email protected]>
Signed-off-by: Saravana Kannan <[email protected]>
Reviewed-by: Chanwoo Choi <[email protected]>
---
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

2019-03-12 07:18:51

by MyungJoo Ham

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

>From: Saravana Kannan <[email protected]>
>
>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 <[email protected]>
>Signed-off-by: Saravana Kannan <[email protected]>
>Reviewed-by: Chanwoo Choi <[email protected]>

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 <[email protected]>


>---
>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(-)
>

2019-03-13 06:03:00

by Sibi Sankar

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

On 2019-03-12 12:47, MyungJoo Ham wrote:
>> From: Saravana Kannan <[email protected]>
>>
>> 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 <[email protected]>
>> Signed-off-by: Saravana Kannan <[email protected]>
>> Reviewed-by: Chanwoo Choi <[email protected]>
>
> 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 <[email protected]>
>
>
>> ---
>> 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.