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Date:   Sat, 7 Sep 2019 22:12:52 +0200 (CEST)
From:   Thomas Gleixner <tglx@linutronix.de>
To:     Chris Wilson <chris@chris-wilson.co.uk>
cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Bandan Das <bsd@redhat.com>
Subject: Re: Linux 5.3-rc7
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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