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

[Kumar Gala <galak@kernel.crashing.org>]

On Sep 27, 2013, at 11:15 AM, Scott Wood wrote:

> On Fri, 2013-09-27 at 10:52 -0500, Kumar Gala wrote:
>> On Sep 26, 2013, at 7:18 PM, Scott Wood wrote:
>>=20
>>> 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.
>>>=20
>>> Signed-off-by: Scott Wood <scottwood@freescale.com>
>>> ---
>>> arch/powerpc/sysdev/mpic.c | 8 +++++++-
>>> 1 file changed, 7 insertions(+), 1 deletion(-)
>>>=20
>>> 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 =3D mpic_processor_id(mpic);
>>> +		preempt_enable();
>>> +
>>=20
>> Any reason you didn't stick this inside of mpic_processor_id() ?
>=20
> 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.

Gotcha, I think you should reword the commit message.  Reading it makes =
me think that preemption should be disabled for all mpic_processor_id() =
calls.

- k=