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SubjectRe: [PATCH] cpufreq: Avoid double addition/removal of sysfs links
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On Wednesday, July 22, 2015 01:15:01 AM Rafael J. Wysocki wrote:
> Hi VIresh,
>
> On Mon, Jul 20, 2015 at 11:47 AM, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> > Consider a dual core (0/1) system with two CPUs:
> > - sharing clock/voltage rails and hence cpufreq-policy
> > - CPU1 is offline while the cpufreq driver is registered
> >
> > - cpufreq_add_dev() is called from subsys callback for CPU0 and we
> > create the policy for the CPUs and create link for CPU1.
> > - cpufreq_add_dev() is called from subsys callback for CPU1, we find
> > that the cpu is offline and we try to create a sysfs link for CPU1.
>
> So the problem is that the cpu_is_offline(cpu) check in
> cpufreq_add_dev() matches two distinct cases: (1) the CPU was not
> present before and it is just being hot-added and (2) the CPU is
> initially offline, but present, and this is the first time its device
> is registered. In the first case we can expect that the CPU will
> become online shortly (although that is not guaranteed too), but in
> the second case that very well may not happen.
>
> We need to be able to distinguish between those two cases and your
> patch does that, but I'm not sure if this really is the most
> straightforward way to do it.

It looks like we need a mask of related CPUs that are present. Or,
alternatively, a mask of CPUs that would have been related had they
been present.

That's sort of what your patch is adding, but not quite.

Thanks,
Rafael



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