Thread (262 messages) 262 messages, 17 authors, 2014-09-14

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

From: Russell King - ARM Linux <hidden>
Date: 2014-09-08 16:23:28
Also in: lkml

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.
Keyboard shortcuts
hback out one level
jnext message in thread
kprevious message in thread
ldrill in
Escclose help / fold thread tree
?toggle this help