linux-kernel - Re: nmi_watchdog suspicious

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Message-ID: <Pine.LNX.4.55.0806181749050.4857@cliff.in.clinika.pl>
Date:	Wed, 18 Jun 2008 17:54:32 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Cyrill Gorcunov <gorcunov@...il.com>
cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: nmi_watchdog suspicious

On Wed, 18 Jun 2008, Cyrill Gorcunov wrote:

> Maciej, it seems we are talking about different code snippets ;)
> I'm talking only about touch_nmi_watchdog(). By now (in -tip tree
> we have)
> 
> void touch_nmi_watchdog(void)
> {
> 	if (nmi_watchdog == NMI_LOCAL_APIC ||
> 		nmi_watchdog == NMI_IO_APIC) {
> 		unsigned cpu;
> 		...
> 
> so we check explicitly the values (so if touch_nmi_watchdog
> was called when nmi_watchdog = 0 or -1U this code will not
> be executed anyway). So I think I'm a bit lost, Maciej... I just
> can't figure out what is wrong with this code, so please help
> me ;). If you're talking about apic code in _general_ design
> then...well, I think I need some time to _understand_ the code
> say byte-by-byte first.

 The value of nmi_watchdog being NMI_IO_APIC or NMI_LOCAL_APIC does not 
mean the watchdog has been set up already.  This observation applies both 
here and elsewhere, e.g. to nmi_watchdog_tick().

  Maciej
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