Re: [PATCH] devfreq: rk3399_dmc: Don't use OPP structures outside of RCU locks

[Viresh Kumar <viresh.kumar@linaro.org>]

On 02-12-16, 22:26, Chanwoo Choi wrote:
> Hi Viresh,
> 
> I'm sorry. I sent the mail without any message. It is my mistake.
> 
> 2016-12-02 22:21 GMT+09:00 Chanwoo Choi <cwchoi00@gmail.com>:
> > Hi Viresh,
> >
> > 2016-12-02 18:00 GMT+09:00 Viresh Kumar <viresh.kumar@linaro.org>:
> >> Hi Chanwoo,
> >>
> >> Thanks for trying to review all these patches.
> >>
> >> On 02-12-16, 17:42, Chanwoo Choi wrote:
> >>> Hi Viresh,
> >>>
> >>> On 2016년 12월 01일 19:38, Viresh Kumar wrote:
> >>> > The OPP structures are abused to the best here, without understanding
> >>> > how the OPP core and RCU locks work.
> >>> >
> >>> > In short, the OPP pointer saved in 'rk3399_dmcfreq' can become invalid
> >>> > under your nose, as the OPP core may free it.
> >>> >
> >>> > Fix various abuses around OPP structures and calls.
> >>> >
> >>> > Compile tested only.
> >>> >
> >>> > Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
> >>> > ---
> >>> > I would like it to go via the PM tree. Perhaps that's already the
> >>> > default tree for this.
> >>> >
> >>> >  drivers/devfreq/rk3399_dmc.c | 11 +++++------
> >>> >  1 file changed, 5 insertions(+), 6 deletions(-)
> >>> >
> >>> > diff --git a/drivers/devfreq/rk3399_dmc.c b/drivers/devfreq/rk3399_dmc.c
> >>> > index 5063ac1a5939..cf14631b1945 100644
> >>> > --- a/drivers/devfreq/rk3399_dmc.c
> >>> > +++ b/drivers/devfreq/rk3399_dmc.c
> >>> > @@ -80,7 +80,6 @@ struct rk3399_dmcfreq {
> >>> >     struct regulator *vdd_center;
> >>> >     unsigned long rate, target_rate;
> >>> >     unsigned long volt, target_volt;
> >>> > -   struct dev_pm_opp *curr_opp;
> >>> >  };
> >>> >
> >>> >  static int rk3399_dmcfreq_target(struct device *dev, unsigned long *freq,
> >>> > @@ -102,9 +101,6 @@ static int rk3399_dmcfreq_target(struct device *dev, unsigned long *freq,
> >>> >     target_rate = dev_pm_opp_get_freq(opp);
> >>> >     target_volt = dev_pm_opp_get_voltage(opp);
> >>> >
> >>> > -   dmcfreq->rate = dev_pm_opp_get_freq(dmcfreq->curr_opp);
> >>> > -   dmcfreq->volt = dev_pm_opp_get_voltage(dmcfreq->curr_opp);
> >>> > -
> >>> >     rcu_read_unlock();
> >>> >
> >>> >     if (dmcfreq->rate == target_rate)
> >>>
> >>> dmcfreq->rate is used on here.
> >>
> >> Are you trying to say that dmcfreq->rate is required to have the right value as
> >> we will be using it here for comparison? If yes, then ...
> >>
> >>> Maybe struct rk3399_dmcfreq need to add the new 'curr_freq' field.
> >>>
> >>>
> >>> > @@ -165,7 +161,9 @@ static int rk3399_dmcfreq_target(struct device *dev, unsigned long *freq,
> >>> >     if (err)
> >>> >             dev_err(dev, "Cannot to set vol %lu uV\n", target_volt);
> >>> >
> >>> > -   dmcfreq->curr_opp = opp;
> >>> > +   dmcfreq->rate = target_rate;
> >>> > +   dmcfreq->volt = target_volt;
> >>
> >> This takes care of it for all cases except the first call to target()...
> 
> You're right. I could not think of it.
> 
> As you mentioned, except the first call to target(), this patch looks
> good to me.
> On the first call, the target() should change the appropriate freq/voltage
> according to the real utilization.
> 
> I'm sorry for my confusion. Feel free to add my reviewed tag.
> 
> Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>

Perhaps you missed part of my reply. The first call is also taken care of. see
below.

> > @@ -431,8 +429,9 @@ static int rk3399_dmcfreq_probe(struct platform_device *pdev)
> >  		rcu_read_unlock();
> >  		return PTR_ERR(opp);
> >  	}
> > +	dmcfreq->rate = dev_pm_opp_get_freq(opp);
> > +	dmcfreq->volt = dev_pm_opp_get_voltage(opp);

And this takes care of the first call to target().

-- 
viresh