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

[Corey Minyard <minyard@acm.org>]

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.

-corey