linux-kernel - Re: Recoverable MCA interrupts from NMI handlers? IPMI and RCU?

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Date:	Fri, 6 Jun 2008 14:33:45 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Corey Minyard <minyard@....org>
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, dvhltc@...ibm.com, niv@...ibm.com
Subject: Re: Recoverable MCA interrupts from NMI handlers?  IPMI and RCU?

On Fri, Jun 06, 2008 at 03:53:00PM -0500, Corey Minyard wrote:
> Paul E. McKenney wrote:
> >Hello!
> >
> >A couple of questions about the x86 architecture...
> >
> >1.	Can recoverable machine-check exceptions occur from within
> >	NMI handlers?  If so, there is a bug in preemptable RCU's
> >	CONFIG_NO_HZ handling that could be fixed by a patch something
> >	like the one shown below (untested, probably does not even
> >	compile).
> >
> >2.	Does the IPMI subsystem make use of RCU read-side primitives
> >	from within SMI handlers?  If so, we need the SMI handlers to
> >	invoke rcu_irq_enter() upon entry and rcu_irq_exit() upon exit
> >	when they are invoked from dynticks idle state.  Or something
> >	similar, depending on restrictions on code within SMI handlers.
> >  
> If you mean the IPMI driver, it does not tie into any SMI.  It 
> theoretically could since there's a bit for that in the watchdog timer, 
> but there's been no demand and I haven't looked at it.  I guess it would 
> be better than an NMI.
> 
> If it did tie in, it would most likely just panic to get useful 
> information out before the watchdog reset the system.

Thanks for the info!  I will stop worrying about SMIs and RCU, then.

						Thanx, Paul
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