[PATCH] ppc32: handle Book E debug exceptions on kernel stack

[Josh Boyer]

On Wed, 2006-02-22 at 22:19 -0600, Kumar Gala wrote:
> On Tue, 14 Feb 2006, Dale Farnsworth wrote:
> 
> > From: Dale Farnsworth <dale at farnsworth.org>
> > 
> > On PPC Book E processsors, we currently handle debug
> > exceptions on the critical exception stack (debug stack
> > for E200).  This causes problems with the kgdb single
> > step handler, which calls smp_processor_id() and spin_lock(),
> > which reference current_thread_info(), which only works when
> > we are on the kernel stack.
> > 
> > We address this by switching to the kernel stack early while
> > handling debug exceptions.  Note that the entry values of r10
> > and r11 are still saved on the critical exception (or debug) stack.
> > 
> > Signed-off-by: Dale Farnsworth <dale at farnsworth.org>
> > 
> 
> Paul,
> 
> We were wondering if you or David remember why a specific critical
> exception stack was added in the 40x port from 2.4 to 2.6?

I think Matt did that.  And if I remember correctly, it was to avoid
corruption if you were in the middle of handling a normal interrupt and
a critical interrupt came in.

josh