On 08/09/14 17:23, Russell King - ARM Linux wrote:
> On Mon, Sep 08, 2014 at 04:28:35PM +0100, Daniel Thompson wrote:
>> @@ -604,8 +731,19 @@ static void gic_raise_softirq(const struct cpumask
>> *mask, unsigned int irq)
>> {
>> int cpu;
>> unsigned long flags, map = 0;
>> + unsigned long softint;
>>
>> - raw_spin_lock_irqsave(&irq_controller_lock, flags);
>> + /*
>> + * The locking in this function ensures we don't use stale cpu mappings
>> + * and thus we never route an IPI to the wrong physical core during a
>> + * big.LITTLE switch. The switch code takes both of these locks meaning
>> + * we can choose whichever lock is safe to use from our current calling
>> + * context.
>> + */
>> + if (in_nmi())
>> + raw_spin_lock(&fiq_safe_migration_lock);
>> + else
>> + raw_spin_lock_irqsave(&irq_controller_lock, flags);
>
> Firstly, why would gic_raise_softirq() be called in FIQ context?
Oops.
This code should have been removed. It *is* required for kgdb (which
needs to send FIQ to other processors via IPI and may itself be running
from FIQ) but it not needed for the currently targeted use case.
> Secondly,
> this doesn't save you. If you were in the middle of gic_migrate_target()
> when the FIQ happened that (for some reason prompted you to call this),
> you would immediately deadlock trying to that this IRQ.
This cannot happen because gic_migrate_target() runs with FIQ disabled.
> I suggest not even trying to solve this "race" which I don't think is
> one which needs to even be considered (due to the first point.)
As mentioned above I believe it eventually needs to be addressed by some
means but it certainly doesn't belong in the current patchset.
I will remove it.
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