Re: [PATCH 04/12] ia64: Replace cpu_down with freeze_secondary_cpus

Thomas Gleixner
2019-11-19T22:59:18Z

On Tue, 19 Nov 2019, Qais Yousef wrote:
> On 11/19/19 23:21, Thomas Gleixner wrote:
> > On Wed, 30 Oct 2019, Qais Yousef wrote:
> > > void machine_shutdown(void)
> > > {
> > > #ifdef CONFIG_HOTPLUG_CPU
> > > - int cpu;
> > > -
> > > - for_each_online_cpu(cpu) {
> > > - if (cpu != smp_processor_id())
> > > - cpu_down(cpu);
> > > - }
> > > + /* TODO: Can we use disable_nonboot_cpus()? */
> > > + freeze_secondary_cpus(smp_processor_id());
> >
> > freeze_secondary_cpus() is only available for CONFIG_PM_SLEEP_SMP=y and
> > disable_nonboot_cpus() is a NOOP for CONFIG_PM_SLEEP_SMP=n :)
>
> I thought I replied to this :-(
>
> My plan was to simply make freeze_secondary_cpus() available and protected by
> CONFIG_SMP only instead.
>
> Good plan?

No. freeze_secondary_cpus() is really for hibernation. Look at the exit
conditions there.

So you really want a seperate function which depends on CONFIG_HOTPLUG_CPU
and provides an inline stub for the CONFIG_HOTPLUG_CPU=n case.

But I have a hard time to see how that stuff works at all on
ia64:

cpu_down() might sleep, i.e. it must be called from preemptible
context. smp_processor_id() is invalid from preemtible context.

As this is obviously broken and ia64 is in keep compile mode only, it
should just go away.

Thanks,

tglx