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Message-ID: <20080904145617.GB28095@elte.hu>
Date: Thu, 4 Sep 2008 16:56:17 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Prarit Bhargava <prarit@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>,
linux-kernel@...r.kernel.org, arozansk@...hat.com,
dzickus@...hat.com, Thomas.Mingarelli@...com, ak@...ux.intel.com,
Alan Cox <alan@...rguk.ukuu.org.uk>,
"H. Peter Anvin" <hpa@...or.com>,
Thomas Gleixner <tglx@...utronix.de>,
"Maciej W. Rozycki" <macro@...ux-mips.org>
Subject: Re: [PATCH RFC] NMI Re-introduce un[set]_nmi_callback
* Prarit Bhargava <prarit@...hat.com> wrote:
>> Why is the DIE_NMIWATCHDOG notifier not sufficient for this driver?
>
> Peter -- good question. The HP systems with this HW will use the
> hpwdt driver in place of the default nmi watchdog. When the HW
> detects a problem, the HW will generate a single NMI that the driver
> will handle. The driver doesn't want the NMI to be rejected due to a
> reason code. I'm sure that Thomas Mingarelli, who is cc'd, can
> provide further details.
>
> From our quick conversation as well, you raised an interesting point
> about oprofile, kgdb, and other subsystems that use the NMI notifier
> chains -- they may be impacted by the NMI callback.
>
> Don (dzickus) or Aris, do you have any thoughts on how to get around
> the second issue? We could check to see if anything is registered on
> the notifier chain and the fail to register the callback.
i'd much rather attack this general problem from this angle:
static inline unsigned char get_nmi_reason(void)
{
return inb(0x61);
}
that port 61H read is both arcane (on modern chipsets) and broken on
multiple levels. It's racy and SMP unsafe to begin with, if there's any
mixture of intentional cross-CPU or CPU self-generated NMIs mixed with
chipset generated NMIs.
One possible approach would be to get rid of it, and to perhaps register
a low-priority die notifier on systems where we know port 61
reads+writes to be safe and desired. Modern systems will emit MCEs in
most cases anyway, not NMIs.
Ingo
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