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Date: Fri, 18 Mar 2016 14:32:36 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Mike Galbraith <umgwanakikbuti@gmail.com>
Cc: Xiong Zhou <jencce.kernel@gmail.com>, Thomas Gleixner <tglx@linutronix.de>,
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        Ingo Molnar <mingo@kernel.org>, Borislav Petkov <bp@alien8.de>,
        Andreas Herrmann <aherrmann@suse.com>
Subject: Re: 4.5.0+ panic when setup loop device
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On Fri, Mar 18, 2016 at 01:39:16PM +0100, Mike Galbraith wrote:
> On Fri, 2016-03-18 at 11:15 +0100, Peter Zijlstra wrote:

> > Ah, did you actually disable HT in the BIOS, or just skip the HT
> > enumeration by saying nr_cpus=64 (knowing that all the siblings are
> > last)?
> 
> It's disabled in BIOS.

OK, so I disabled HT in the BIOS too, on my IVB-EX

> > In any case, Thomas has a clue and I'm going to test, but 4 socket
> > machine takes forever to boot, so might be a few minutes :/
> 
> His one-liner made my DL980 all better.

My machine is profoundly unhappy though; and since I have no nr_cpus=
nr_cpu_ids == total_cpus and his patch wouldn't do anything anyway.

[    0.286838] max_cores: 15, cpu_ids: 60, num_siblings: 2, coreid_bits: 5
[    0.293463] smpboot: Max logical packages: 2
[    0.297733] smpboot: APIC(0) Converting physical 0 to logical package 0
[    0.304346] smpboot: APIC(20) Converting physical 1 to logical package 1
[    0.311047] smpboot: APIC(40) Package 2 exceeds logical package map
[    0.317309] smpboot: CPU 30 APICId 40 disabled
[    0.321757] smpboot: APIC(60) Package 3 exceeds logical package map
[    0.328022] smpboot: CPU 45 APICId 60 disabled

This machine does exactly what I suspected yours did.