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

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Message-ID: <20070324191112.GA1626@elte.hu>
Date:	Sat, 24 Mar 2007 20:11:12 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Ray Lee <ray-lk@...rabbit.org>
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

* 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)

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?

	Ingo
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