linux-kernel - Re: [PATCH 4/5] x86, NMI: Allow NMI reason io port (0x61) to be processed on any CPU

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Message-ID: <1287621995.19320.14.camel@yhuang-dev>
Date:	Thu, 21 Oct 2010 08:46:35 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Robert Richter <robert.richter@....com>
Cc:	Don Zickus <dzickus@...hat.com>, "mingo@...e.hu" <mingo@...e.hu>,
	"andi@...stfloor.org" <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"peterz@...radead.org" <peterz@...radead.org>
Subject: Re: [PATCH 4/5] x86, NMI: Allow NMI reason io port (0x61) to be
 processed on any CPU

On Wed, 2010-10-20 at 18:03 +0800, Robert Richter wrote:
> > > > > What about using raw_spin_trylock() instead? We don't have to wait
> > > > > here since we are already processing it by another cpu.
> > > > 
> > > > This would avoid a global lock and also deadlocking in case of a
> > > > potential #gp in the nmi handler.
> > > 
> > > I would feel more comfortable with it too.  I can't find a reason where
> > > trylock would do harm.
> > 
> > One possible issue can be as follow:
> > 
> > - PCI SERR NMI raised on CPU 0
> > - IOCHK NMI raised on CPU 1
> > 
> > If we use try lock, we may get unknown NMI on one CPU. Do you guys think
> > so?
> 
> This could be a valid point. On the other side the former
> implementation to let only handle cpu #0 i/o interrupts didn't trigger
> unknown nmis, so try_lock wouldn't change much compared to this.

Because we want to support BSP hot-remove, these NMIs may be redirected
to other CPUs. I think it may be possible after we hot-remove the BSP
PCI SERR NMI is routed to CPU 1, while IOCHK NMI is routed to CPU 2. The
raw_spin_lock() here is for that.

Best Regards,
Huang Ying

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