Re: [PATCH] cpufreq: vexpress-spc: Fix wrong alternation of policy->related_cpus during CPU hp

[Sudeep Holla <sudeep.holla@arm.com>]

On Wed, Nov 27, 2019 at 05:37:44PM +0530, Viresh Kumar wrote:
> On 27-11-19, 12:48, Dietmar Eggemann wrote:
> > Since commit ca74b316df96 ("arm: Use common cpu_topology structure and
> > functions.") the core cpumask has to be modified during cpu hotplug
> > operations.
> >
> > ("arm: Fix topology setup in case of CPU hotplug for CONFIG_SCHED_MC")
> > [1] fixed that but revealed another issue on TC2, i.e in its cpufreq
> > driver.
> >
> > During CPU hp stress operations on multiple CPUs, policy->related_cpus
> > can be altered. This is wrong since this cpumask should contain the
> > online and offline CPUs.
> >
> > The WARN_ON(!cpumask_test_cpu(cpu, policy->related_cpus)) in
> > cpufreq_online() triggers in this case.
> >
> > The core cpumask can't be used to set the policy->cpus in
> > ve_spc_cpufreq_init() anymore in case it is called via
> > cpuhp_cpufreq_online()->cpufreq_online()->cpufreq_driver->init().
> >
> > An empty online() callback can be used to avoid that the init()
> > driver function is called during CPU hotplug in so that
> > policy->related_cpus will not be changed.
> >
> > Implementing an online() also requires an offline() callback.
> >
> > Tested on TC2 with CPU hp stress test (CPU hp from multiple CPUs at
> > the same time).
> >
> > [1]
> > https://lore.kernel.org/r/20191127103353.12417-1-dietmar.eggemann@arm.com
> >
> > Signed-off-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
>
> Wanna provide any fixes tag ?
>
> > ---
> >  drivers/cpufreq/vexpress-spc-cpufreq.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
>
> This is 5.5 material or 5.6 ?
>

v5.5 for sure, broken even on v5.4 but unless someone really cares for
stable on TC2, I am happy to skip it.

--
Regards,
Sudeep