Messages in this thread | | | Date | Fri, 6 Feb 2009 12:22:10 -0500 (EST) | From | Steven Rostedt <> | Subject | Re: [PATCH 2/4] nmi: add generic nmi tracking state |
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On Fri, 6 Feb 2009, Andrew Morton wrote: > > > > That would be fun to implement. Not the in_nmi code, but the handling of > > nested NMIs. How would you be able to save the state when the NMI occurred > > without being preempted by another NMI? > > Like with normal interrupts?
Normal interrupts can enable interrupts again, while in the handler, as well as disable them.
> > As long as the number of sources is finite, nested NMIs could work OK.
I guess you would need a mechanism to enable and disable NMIs.
> > > I think the arch that has nested NMIs will have many more issues to solve > > in the kernel than this one. > > I have a vague memory that x86 can do this. > > <googles a bit> > > What's all this about? > https://www.x86-64.org/pipermail/discuss/2005-October/007010.html
Yuck, masking Non Maskable Interrupts?
> http://kerneltrap.org/index.php?q=mailarchive/linux-kernel/2008/2/12/830704/thread
It looks like it calls nmi_exit, so the code would dec it.
> > I expect that even if it is possible, we can live without it. > > And if I'm wrong, it'll be easy to accommodate by adding a new counter > into the task_struct or thread_struct.
Yeah, the bug on would trigger as soon as we do that, and we could easily update the code when that time comes.
> > Does your above implementation make in_interrupt() return true if > in_nmi()? I think it doesn't, but should?
The "in_nmi()" is set when we do nmi_enter, and nmi_enter also calls irq_enter which makes in_interrupt() true. I thought adding the in_nmi condition to in_interrupt would be redundant.
-- Steve
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