ftrace introduces instability into kernel 2.6.27(-rc2,-rc3)

[Benjamin Herrenschmidt]

> Hmm... so whats now?
> 
> Is there a way to prove this scenario is indeed the one that caused the 
> opps?

I've verified in sim that the crash in do_lookup() I was seeing (similar
backtrace) was indeed caused by an interrupt coming between those two
instructions and clobbering the saved GPRs.

So I think it's very likely our problem.

Ben.