Re: [PATCH v5] perf: arm_cspmu: Separate Arm and vendor module

[Robin Murphy]

On 2023-08-19 21:11, Besar Wicaksono wrote:
[...]
> > > +void arm_cspmu_impl_unregister(const struct arm_cspmu_impl_match
> > *impl_match)
> > > +{
> > > +     struct device *dev;
> > > +     struct arm_cspmu_impl_match *match;
> > > +
> > > +     match = arm_cspmu_impl_match_get(impl_match->pmiidr_val);
> > > +
> > > +     WARN_ON(!match);

Nit: do "if (WARN_ON(!match)) return;" rather than indenting almost the 
whole function.

> > > +
> > > +     if (match) {
> > > +             /* Unbind the driver from all matching backend devices. */
> > > +dev_release:
> > > +             dev = driver_find_device(&arm_cspmu_driver.driver, NULL,
> > > +                     match, arm_cspmu_match_device);
> > > +             if (dev) {
> > > +                     device_release_driver(dev);
> > > +                     goto dev_release;
> > > +             }
> >
> > minor nit: We could simply do :
> >
> > static int arm_cspmu_release_driver(struct device *dev, void *data)
> > {
> >          struct arm_cspmu *cspmu =
> > platform_get_drvdata(to_platform_device(dev));
> >
> >          if (cspmu && cspmu->impl.match == match)
> >                  device_release_driver(dev);
> >          return 0;
> > }
> >
> >                  ret = driver_for_each_device(&driver, NULL, match,
> > arm_csmpu_release_driver);
>
> It doesn’t seem to work for me.
> Is it safe to release while iterating via driver_for_each_device ?

Looking at the klist code it doesn't *obviously* appear safe to modify 
the list during iteration, so probably best not to risk it anyway. 
However, please try to write this loop as an actual loop, e.g.:

	while ((dev = driver_find_device()))
		device_release_driver();

At first glance I thought there was a bug here that it's only processing 
a single device, then eventually I saw the goto and my thought changed 
to "Eww..."

Thanks,
Robin.