Re: [PATCH v3] PM / devfreq: Restart previous governor if new governor fails to start

[Saravana Kannan]

On 10/26/2016 05:06 PM, Chanwoo Choi wrote:
> Hi,
>
> On 2016ë 10ì 27ì 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 <skannan@xxxxxxxxxxxxxx>
> > ---
> > * 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.


Thanks,
Saravana

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