[Crash-utility] Broken backtrace with nested NMIs

[Dave Anderson]

----- Original Message -----
> Hi all,
> 
> as discovered by my colleagues, the backtrace code has been broken for
> NMI stacks since kernel commit 3f3c8b8c4b2a34776c3470142a7c8baafcda6eb0
> (Linux 3.3).
> 
> I am working on a fix, but it's tricky to get all cases right. For
> example, the copied and saved register locations were swapped with
> kernel commit 28696f434fef0efa97534b59986ad33b9c4df7f8, so we have at
> least 3 possible layouts:
> 
> 1. pre-3.3 (no nesting)
> 2. 3.3 to 3.8 (saved, then copied)
> 3. 3.8+ (copied, then saved)
> 
> I'm writing this mail to tell you I'm working on it. I don't have a fix
> (yet), but want to avoid duplicate efforts if more people start working
> on this.
> 
> Petr T

Thanks Petr, I appreciate your efforts, and won't get in your way...

I was aware of Steven's work in this area, but haven't yet seen any
core dumps that show the changes.  What exactly happens?  Does the
backtrace fumble its way through the top of the NMI stack, but then
successfully make the transition to the original stack, or does it 
just blow up while transitioning through the NMI stack?

Dave