[Crash-utility] Broken backtrace with nested NMIs

[Petr Tesarik]

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