On Thu, 27 Apr 2017, Mark Rutland wrote:
> On Thu, Apr 27, 2017 at 10:27:20AM +0200, Sebastian Siewior wrote:
> > On 2017-04-26 11:32:36 [+0100], Mark Rutland wrote:
> > > > So we could end up calling static_branch_enable_cpuslocked()
> > > > without actually holding the lock. Should we do a
> > > > cpu_hotplug_begin/done in
> > > > setup_cpu_feature_capabilities ? I agree it doesn't look that nice.
> > > > Thoughts ?
> > >
> > > I agree that's hideous, but it looks like the only choice given the
> > > hotplug rwsem cahnges. :/
> >
> > would work for you to provide a locked and unlocked version?
>
> Maybe. Today we have:
>
> // rwsem unlocked
> start_kernel()
> ->smp_prepare_boot_cpu()
> -->update_cpu_errata_workarounds()
> --->update_cpu_capabilities()
>
> // rwsem locked (by other CPU)
> secondary_start_kernel()
> ->check_local_cpu_capabilities()
> -->update_cpu_errata_workarounds()
> --->update_cpu_capabilities()
>
> With the common chain:
>
> update_cpu_capabilities()
> ->cpus_set_cap()
> -->static_branch_enable()
>
> ... so we could add a update_cpu_capabilities{,_cpuslocked}(), and say
> that cpus_set_cap() expects the hotplug rswem to be locked, as per the
> below diff.
You just can take the rwsen in smp_prepare_boot_cpu(), so you don't need
that conditional thingy at all. Hmm?
Thanks,
tglx
