Re: [PATCH v16 3/8] cpu/hotplug: Add dynamic parallel bringup states before CPUHP_BRINGUP_CPU

[Thomas Gleixner]

On Fri, Mar 24 2023 at 02:16, Thomas Gleixner wrote:
> On Thu, Mar 23 2023 at 23:12, David Woodhouse wrote:
> So surely you could claim that up to #6 (TSC sync) nothing needs to
> synchronize.
>
> But that's simply not true because topology information is implicitely
> serialized by CPU hotplug and your attempt to serialize that in patch
> 7/8 is not cutting it at all because AP #4 (STARTING) callbacks rely
> implicitely on the immutability of the topology information and so do
> some of the later (threaded) AP callbacks too.

It's even worse. Any topology relevant change _must_ be serialized by
holding cpu_hotplug_lock write locked. So this needs fundamentally more
thought than just slapping a few misnomed states into the picture and
pretending that everything else just works.

Thanks,

        tglx