On Fri, 2023-03-24 at 10:46 +0100, Thomas Gleixner wrote: > > It's even worse. Any topology relevant change _must_ be serialized by > holding cpu_hotplug_lock write locked. So this needs fundamentally more > thought Yes. Yes, it does. Which is why it isn't being done in parallel in this patch series. The topology update happens from smp_callin() which happens from do_wait_cpu_initialized(), which is still in the CPUHP_BRINGUP_CPU stage for now, being done one at a time. When we come to look at the next stage, doing do_wait_cpu_initialized() in parallel for multiple APs too, we will be happy to hear specifics of why this "must" be serialized by the cpu_hotplug_lock and no other. It will be great to check that we haven't missed anything. But we aren't there yet.
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