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? 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.
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.)
--
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according to speedtest.net.
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