linux-kernel - Re: [PATCH V3 2/3] thermal/drivers/cpu_cooling: Unregister with the policy

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Date:   Wed, 26 Jun 2019 13:28:19 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Daniel Lezcano <daniel.lezcano@...aro.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Eduardo Valentin <edubezval@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Amit Daniel Kachhap <amit.kachhap@...il.com>,
        Javi Merino <javi.merino@...nel.org>,
        Zhang Rui <rui.zhang@...el.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Keerthy <j-keerthy@...com>,
        "open list:CPU FREQUENCY DRIVERS - ARM BIG LITTLE" 
        <linux-pm@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:TI BANDGAP AND THERMAL DRIVER" 
        <linux-omap@...r.kernel.org>
Subject: Re: [PATCH V3 2/3] thermal/drivers/cpu_cooling: Unregister with the policy

On Wed, Jun 26, 2019 at 12:19 PM Daniel Lezcano
<daniel.lezcano@...aro.org> wrote:
>
> On 26/06/2019 11:06, Rafael J. Wysocki wrote:
> > On Wed, Jun 26, 2019 at 8:37 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >>
> >> On 26-06-19, 08:02, Daniel Lezcano wrote:
> >>> On 26/06/2019 04:58, Viresh Kumar wrote:
> >>>> On 25-06-19, 13:32, Daniel Lezcano wrote:
> >>>>> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> >>>>> index aee024e42618..f07454249fbc 100644
> >>>>> --- a/drivers/cpufreq/cpufreq.c
> >>>>> +++ b/drivers/cpufreq/cpufreq.c
> >>>>> @@ -1379,8 +1379,8 @@ static int cpufreq_online(unsigned int cpu)
> >>>>>            cpufreq_driver->ready(policy);
> >>>>>
> >>>>>    if (cpufreq_thermal_control_enabled(cpufreq_driver))
> >>>>> -          policy->cdev = of_cpufreq_cooling_register(policy);
> >>>>> -
> >>>>> +          of_cpufreq_cooling_register(policy);
> >>>>> +
> >>>>
> >>>> We don't need any error checking here anymore ?
> >>>
> >>> There was no error checking initially. This comment and the others below
> >>> are for an additional patch IMO, not a change in this one.
> >>
> >> right, but ...
> >>
> >>>>> -void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev)
> >>>>> +void cpufreq_cooling_unregister(struct cpufreq_policy *policy)
> >>>>>  {
> >>>>>    struct cpufreq_cooling_device *cpufreq_cdev;
> >>>>>    bool last;
> >>>>>
> >>>>> -  if (!cdev)
> >>>>> -          return;
> >>
> >> we used to return without any errors from here. Now we will have
> >> problems if regsitering fails for some reason.
> >
> > Specifically, the last cpufreq_cdev in the list will be unregistered
> > AFAICS, and without removing it from the list for that matter, which
> > isn't what the caller wants.
>
> Indeed,
>
> What about the resulting code above:
>
> void __cpufreq_cooling_unregister(struct cpufreq_cooling_device
> *cpufreq_cdev, int last)
> {
>         /* Unregister the notifier for the last cpufreq cooling device */
>         if (last)
>                 cpufreq_unregister_notifier(&thermal_cpufreq_notifier_block,
>                                             CPUFREQ_POLICY_NOTIFIER);
>

Doesn't the notifier need to be unregistered under cooling_list_lock ?

>         thermal_cooling_device_unregister(cpufreq_cdev->cdev);
>         ida_simple_remove(&cpufreq_ida, cpufreq_cdev->id);
>         kfree(cpufreq_cdev->idle_time);
>         kfree(cpufreq_cdev);
> }
>
> /**
>
>  * cpufreq_cooling_unregister - function to remove cpufreq cooling
> device.
>  * @cdev: thermal cooling device pointer.
>
>  *
>
>  * This interface function unregisters the "thermal-cpufreq-%x" cooling
> device.
>  */
> void cpufreq_cooling_unregister(struct cpufreq_policy *policy)
> {
>         struct cpufreq_cooling_device *cpufreq_cdev;
>         bool last;
>
>         mutex_lock(&cooling_list_lock);
>         list_for_each_entry(cpufreq_cdev, &cpufreq_cdev_list, node) {
>                 if (cpufreq_cdev->policy == policy) {
>                         list_del(&cpufreq_cdev->node);
>                         last = list_empty(&cpufreq_cdev_list);
>                         break;
>                 }
>         }
>         mutex_unlock(&cooling_list_lock);
>
>         if (cpufreq_cdev->policy == policy)
>                 __cpufreq_cooling_unregister(cpufreq_cdev, last);
> }
> EXPORT_SYMBOL_GPL(cpufreq_cooling_unregister);
>
>
>
>
> --
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