[PATCH v3 5/5] irqchip: gic: Add support for IPI FIQ
From: Russell King - ARM Linux <hidden>
Date: 2014-09-08 16:23:28
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On Mon, Sep 08, 2014 at 04:28:35PM +0100, Daniel Thompson wrote:
quoted hunk ↗ jump to hunk
@@ -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.) -- FTTC broadband for 0.8mile line: currently at 9.5Mbps down 400kbps up according to speedtest.net.