linux-kernel - Re: nmi_watchdog suspicious

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Message-ID: <20080618172316.GA10431@cvg>
Date:	Wed, 18 Jun 2008 21:23:16 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	"Maciej W. Rozycki" <macro@...ux-mips.org>
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

[Maciej W. Rozycki - Wed, Jun 18, 2008 at 05:54:32PM +0100]
| 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
|

If you mean the case we get NMI physical line assetred while configuring APIC
(ie nmi watchdog is not properly configured yet) then I wonder why we has
this checking at all...

		- Cyrill -
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