linux-kernel - Re: WARNING: at arch/x86/kernel/apic/apic.c:1239 setup_local

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Date:	Mon, 17 Oct 2011 08:23:04 +0100
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Borislav Petkov" <bp@...64.org>, "Tejun Heo" <tj@...nel.org>
Cc:	"Andreas Herrmann3" <Andreas.Herrmann3@....com>,
	"Conny Seidel" <Conny.Seidel@....com>,
	"Ingo Molnar" <mingo@...e.hu>,
	"LKML" <linux-kernel@...r.kernel.org>
Subject: Re: WARNING: at arch/x86/kernel/apic/apic.c:1239
	 setup_local_APIC+...

>>> On 14.10.11 at 19:55, Tejun Heo <tj@...nel.org> wrote:
> Hello,
> 
> (cc'ing Jan Beulich)
> 
> On Fri, Oct 14, 2011 at 06:56:04PM +0200, Borislav Petkov wrote:
>> On Fri, Oct 14, 2011 at 09:55:16AM -0400, Borislav Petkov wrote:
>> > So, in the end, and AFAICR, the warning triggers because we're comparing
>> > logical APIC IDs from the APIC Logical Destination Register (0xD0) which
>> > have been assigned by BIOS with "1 << cpu" shifted values which wrap on
>> > 32-bit.
>> > 
>> > I'd very much like to know why?
>> 
>> Update: upon a second thought, we think we know why: The WARN_ON
>> cannot stomach the switch to bigsmp apic because, on the one hand,
>> bigsmp_init_apic_ldr() "normalizes" the APIC ids by using the BIOS
>> values (x86_bios_cpu_apicid) but OTOH, x86_cpu_to_logical_apicid
>> contains the early percpu value which got assigned by the default apic,
>> i.e. the shifting thing as it is spec'ed for the LDR register.
>> 
>> So, the way we see it, the WARN_ON should know whether we switched apics
>> or should be removed completely. Btw, why was it added in the first
>> place, the commit message doesn't quite explain why.
> 
> Jan hit similar problem a while back.
> 
>   http://thread.gmane.org/gmane.linux.kernel/1180954 
> 
> I can't seem to find the patch in mainline.

Ingo let me know at the end of September that v2 got applied to -tip;
at that point, I took it that it would make only 3.2 (and perhaps then
earlier ones via -stable).

Jan

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