Re: [PATCH v3 5/5] irqchip: gic: Add support for IPI FIQ

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.)