On Sat, 7 Sep 2019, Chris Wilson wrote:
> Quoting Thomas Gleixner (2019-09-07 16:00:17)
> > Does this only happen with that CPU0 hotplug stuff enabled or on CPUs other
> > than CPU0 as well? That hotplug CPU0 stuff is a bandaid so I wouldn't be
> > surprised if we broke that somehow.
>
> If I ignore cpu0 in that test and so use
>
> [ 133.847187] smpboot: CPU 1 is now offline
> [ 134.861861] x86: Booting SMP configuration:
> [ 134.861875] smpboot: Booting Node 0 Processor 1 APIC 0x2
> [ 134.880218] smpboot: CPU 2 is now offline
> [ 135.893806] smpboot: Booting Node 0 Processor 2 APIC 0x1
> [ 135.935115] smpboot: CPU 3 is now offline
> [ 136.949760] smpboot: Booting Node 0 Processor 3 APIC 0x3
>
> that has run for 10 minutes without failure, so it seems confined to
> cpu0 hotplugging. All we are doing in the test to generate the hotplugs
> is:
Right, but you also have that config bit enabled which allows CPU0 hotplug
which usually is off even in testing and that's why nobody noticed so far.
So I looked at that code and I know why it's broken. I guess we'll end up
reverting that commit for now as fixing it proper will be not just a one
liner.
Thanks for providing all the information!
tglx
