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

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Date:	Fri, 6 Jun 2008 09:41:22 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
	minyard@....org, dvhltc@...ibm.com, niv@...ibm.com
Subject: Re: Recoverable MCA interrupts from NMI handlers?  IPMI and RCU?

On Fri, Jun 06, 2008 at 09:12:44AM -0700, H. Peter Anvin 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).
> 
> In theory, recoverable #MC's can occur anywhere.  It's an exception.

Thank you for the info!  I guess I had better get busy testing the
patch, then.

> >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.
> 
> Not sure about that one.  I clearly need to look carefully into this... 
> SMI is quite "special" in that it sets up an entirely new environment; 
> the concept of executing kernel code at SMI level makes me want to run 
> away and hide.

Well, as long as the SMI handlers don't include calls to rcu_read_lock()
and rcu_read_unlock(), then they don't need to include any calls to
rcu_irq_enter() and rcu_irq_exit().  ;-)

							Thanx, Paul
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