linux-kernel - Re: [PATCH] x86_64: avoid sending LOCAL_TIMER

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Date:	Sun, 25 Mar 2007 12:24:18 -0700
From:	Ray Lee <ray-lk@...rabbit.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	tglx@...utronix.de, Adrian Bunk <bunk@...sta.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>
Subject: Re: [PATCH] x86_64: avoid sending LOCAL_TIMER_VECTOR IPI to itself

Ingo Molnar wrote:
> * Ray Lee <ray-lk@...rabbit.org> wrote:
> 
>> Subject: [PATCH] x86_64: avoid sending LOCAL_TIMER_VECTOR IPI to 
>> itself
>>
>> Ray Lee reported, that on an UP kernel with "noapic" command line 
>> option set, the box locks hard during boot.
> 
> i think this bug deserves a bit more attention, because similar problems 
> could be in other codepaths too.
> 
> the problem here is that we tried to send an IPI to ourselves - which 
> confused Ray's system which has an IO-APIC, but where due to noapic we 
> keep the IO-APIC in its BIOS default.
> 
> this isnt a new problem: the new time code just exposed it more 
> prominently that it was visible before. (the SMP kernel probably would 
> hang in a similar way on Ray's system)

Taking the hint, yes it does. (I'd never had a reason to test it before.)
Booting an SMP kernel without NOAPIC works, with NOAPIC hangs fairly early
on, implying a real fix to my problem belongs down at the arch level, I
suppose.

> i dont see any clear debugging in the IPI code that excludes self-IPIs. 
> I think the only valid way to do that is to use DEST_SELF. Andi?

Ray
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