Re: [PATCH] powerpc/mpic: Disable preemption when calling mpic_processor_id()

[Scott Wood <scottwood@freescale.com>]

On Fri, 2013-09-27 at 10:52 -0500, Kumar Gala wrote:
> On Sep 26, 2013, at 7:18 PM, Scott Wood wrote:
> 
> > Otherwise, we get a debug traceback due to the use of
> > smp_processor_id() (or get_paca()) inside hard_smp_processor_id().
> > mpic_host_map() is just looking for a default CPU, so it doesn't matter
> > if we migrate after getting the CPU ID.
> > 
> > Signed-off-by: Scott Wood <scottwood@freescale.com>
> > ---
> > arch/powerpc/sysdev/mpic.c | 8 +++++++-
> > 1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/powerpc/sysdev/mpic.c b/arch/powerpc/sysdev/mpic.c
> > index 1be54fa..bdcb858 100644
> > --- a/arch/powerpc/sysdev/mpic.c
> > +++ b/arch/powerpc/sysdev/mpic.c
> > @@ -1088,8 +1088,14 @@ static int mpic_host_map(struct irq_domain *h, unsigned int virq,
> > 	 * is done here.
> > 	 */
> > 	if (!mpic_is_ipi(mpic, hw) && (mpic->flags & MPIC_NO_RESET)) {
> > +		int cpu;
> > +
> > +		preempt_disable();
> > +		cpu = mpic_processor_id(mpic);
> > +		preempt_enable();
> > +
> 
> Any reason you didn't stick this inside of mpic_processor_id() ?

Because the debug check might be valid for other callers and we don't
want to defeat it.  In this caller it's used only as a heuristic and
thus it doesn't matter if we re-enable preemption before using the
result.

-Scott