Messages in this thread | | | Date | Mon, 8 Sep 2014 17:23:16 +0100 | From | Russell King - ARM Linux <> | Subject | Re: [PATCH v3 5/5] irqchip: gic: Add support for IPI FIQ |
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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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