linux-kernel - Re: [PATCH] NMI watchdog: setup before enabling NMI watchdog

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Date:	Mon, 22 Sep 2008 22:48:54 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Aristeu Rozanski <aris@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	dzickus@...hat.com, prarit@...hat.com, vgoyal@...hat.com
Subject: Re: [PATCH] NMI watchdog: setup before enabling NMI watchdog

[Aristeu Rozanski - Mon, Sep 22, 2008 at 02:35:05PM -0400]
| > Hi Aristeu,
| > 
| > thanks for the patch! I may be _absolutely_ wrong but could you
| > explain me how we reach this site in traps
| > 
| > ---
| > 	if (!(reason & 0xc0)) {
| > 		if (notify_die(DIE_NMI_IPI, "nmi_ipi", regs, reason,
| > 				2, SIGINT) == NOTIFY_STOP)
| > 			return;
| > 		/*
| > 		 * Ok, so this is none of the documented NMI sources,
| > 		 * so it must be the NMI watchdog.
| > 			 ^^^^
| > 		 */
| > 		if (nmi_watchdog_tick(regs, reason))
| > 			return;
| > 		if (!do_nmi_callback(regs, cpu))
| > 			unknown_nmi_error(reason, regs);
| > 
| > 		return;
| > 	}
| > ---
| > 
| > not having masked APIC registers as NMI entry yet (which is done during
| > perfctl initialization)?
| actually the comment is a bit misleading. we can get other "undocumented"
| NMIs from different sources. Notice that if the nmi_watchdog_tick() doesn't
| identifies it as a performance counter generated NMI (if LAPIC based, IOAPIC
| always assume that the NMI is for the NMI watchdog), a default NMI callback
| will be tried and if it fails, unknown_nmi_error() will be called. The first
| case comes to my head is those NMI buttons present on development machines.
| 
| -- 
| Aristeu
| 

Thanks Aristeu!

		- Cyrill -
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