linux-kernel - Re: [PATCH] x86, UV: Fix NMI handler for UV platforms

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Date:	Mon, 21 Mar 2011 20:19:09 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Jack Steiner <steiner@....com>
CC:	Ingo Molnar <mingo@...e.hu>, Don Zickus <dzickus@...hat.com>,
	tglx@...utronix.de, hpa@...or.com, x86@...nel.org,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] x86, UV: Fix NMI handler for UV platforms

On 03/21/2011 08:08 PM, Jack Steiner wrote:
> On Mon, Mar 21, 2011 at 08:00:53PM +0300, Cyrill Gorcunov wrote:
>> On 03/21/2011 07:43 PM, Cyrill Gorcunov wrote:
>> ...
>>>
>>> I think Jack might need to setup priority for his notifier, like
>>>
>>> static struct notifier_block uv_dump_stack_nmi_nb = {
>>> 	.notifier_call	= uv_handle_nmi,
>>> 	.priority	= NMI_LOCAL_HIGH_PRIOR+1,
>>> };
>>>
>>> so it would be called before perf nmi. Don, am I right?
>>>
>>> Since for perf nmis we do have
>>>
>>> static __read_mostly struct notifier_block perf_event_nmi_notifier = {
>>> 	.notifier_call		= perf_event_nmi_handler,
>>> 	.next			= NULL,
>>> 	.priority		= NMI_LOCAL_LOW_PRIOR,
>>> };
>>>
>>
>>   I must admit I've missed the fact that Jack has tried NMIs priorities, right?
>> x86_platform_ops seems to be a cleaner indeed (btw I think p4 pmu kgdb issue
>> is exactly the same problem) but same time this might end up in over-swelled
>> ideas behind this small code snippet. Dunno. Probably we need some per-cpu
>> system status for nmi reasons other than unknown nmis...
> 
> We use KDB internally, and yes, it has the same issue. The version of the
> patch that uses KDB OR's the "handled" status for both KDB & the UV NMI handler.
> If either KDB or the UV NMI handler returns "handled", the code in traps.c exits
> after the call to the first die notifier.
> 
> Not particularily pretty but I could not find a better way to do it.
> 
> --- jack

  Another option might be to add pre-nmi notifier chain, which of course
not much differ from platform ops but I guess platform ops stands mostly
for one-shot events while chain might be more flexible. Ie I mean something
like

	if (notify_pre_die(DIE_NMI, "nmi", regs, 0, 2, SIGINT) == NOTIFY_STOP)
		return;

-- 
    Cyrill
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