[PATCH} PPC64: revised patch for recursive xmon entry

[Linas Vepstas]

On Wed, Dec 15, 2004 at 10:54:20AM +1100, Paul Mackerras was heard to remark:
> Linas Vepstas writes:
> 
> > I had a recursive call to xmon in linux-2.6.10-rc2 after a crash 
> > to firmware.  The resursion was due to a scrambled value in r1 
> > inherited from firmware.  The following patch prevents the recursion
> > and sets up a usable stack. Unfortunately, it still doesn't get us
> > to an xmon prompt; xmon thinks some other cpu is in control.  
> > I'll see if I can fix that next, if I manage to reproduce.
> 
> I don't think this is the right approach; we should be detecting the
> bogus stack pointer and switching to the emergency stack in the
> exception entry code.  By the time we get to your stack we would have
> already been using the bogus stack for some time.

Yes.

I concluded something like that once I started actually reading the
code I was fixing :, 

This reproduces  every third try (somethings racing somehwere), 
so I'll know more tommorrow.

--linas