linux-kernel - RE: [RFC][PATCH v3 2/3] Skip spin_locks in panic case and add WARN

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Date:	Tue, 3 Jan 2012 17:49:13 +0000
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Seiji Aguchi <seiji.aguchi@....com>,
	Don Zickus <dzickus@...hat.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Matthew Garrett <mjg@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>,
	"Chen, Gong" <gong.chen@...el.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"Brown, Len" <len.brown@...el.com>,
	"'ying.huang@...el.com'" <'ying.huang@...el.com'>,
	"'ak@...ux.intel.com'" <'ak@...ux.intel.com'>,
	"'hughd@...omium.org'" <'hughd@...omium.org'>,
	"'mingo@...e.hu'" <'mingo@...e.hu'>,
	"jmorris@...ei.org" <jmorris@...ei.org>,
	"a.p.zijlstra@...llo.nl" <a.p.zijlstra@...llo.nl>,
	"namhyung@...il.com" <namhyung@...il.com>,
	"dle-develop@...ts.sourceforge.net" 
	<dle-develop@...ts.sourceforge.net>,
	Satoru Moriya <satoru.moriya@....com>
Subject: RE: [RFC][PATCH v3 2/3] Skip spin_locks in panic case and add
 WARN_ON()

> I'll ask an Intel EFI guru whether I'm on target.

Got a short note back from the EFI people:

----
The reason the paragraph exists in 7.1.1 is that certain services (as listed
in table 31) are guaranteed to work if you call them a second time when you
have taken an exception in trying to execute them already -- say SetVariable()
face plants with an exception...because of the way our code is designed you
can call it a second time even if the first call that took the exception
didn't succeed.

At any rate, I checked with a couple of the other experts around us and none
of us can see any reason to send yourself an NMI just to preface a call to
a UEFI runtime service.  Thus, our collective opinion is that you are correct
in your interpretation.
----

If you want to discuss this more - they apparently have an external mailing
list some place on TianoCore.org. But this seems pretty clear that we don't
need to self-NMI.

-Tony
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