linux-kernel - Re: nmi_watchdog fix for x86

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Date:	Mon, 1 Oct 2007 21:27:39 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Andi Kleen <ak@...e.de>
cc:	David Bahi <dbahi@...ell.com>, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org,
	Gregory Haskins <GHaskins@...ell.com>
Subject: Re: nmi_watchdog fix for x86_64 to be more like i386

On Mon, 1 Oct 2007, Andi Kleen wrote:
> On Monday 01 October 2007 20:54:21 Thomas Gleixner wrote:
> > On Mon, 1 Oct 2007, Andi Kleen wrote:
> > 
> > > On Wednesday 26 September 2007 20:03:12 David Bahi wrote:
> > > > Thanks to tglx and ghaskins for all the help in tracking down a very
> > > > early nmi_watchdog crash on certain x86_64 machines.
> > > 
> > > The patch is totally bogus. irq 0 doesn't say anything about whether
> > > the current CPU still works or not. You always need some local
> > > interrupt. This basically disables the NMI watchdog for the non boot CPUs.
> > > 
> > > It's even wrong on i386 -- i wonder how that broken patch
> > > made it in there. I'll remove it there.
> > 
> > Right, it's wrong for the broadcast case, but simply removing it will
> > trigger false positives on the CPU which runs the broadcast timer. I
> > fix this proper.
> 
> I already did this here by checking for cpu != 0. But it also needs either tracking
> or forbidding migrations of irq 0. I can take care of the patch.

I was thinking about the same fix. On i386 we already have the irq 
migration / balancing of irq 0 disabled. That's why we setup IRQ0 with
IRQ_NOBALANCING.

	tglx




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