ARM: irq migration: ensure migration is handled safely

Ensure appropriate locks are taken to ensure that IRQ migration off
the current CPU is race-free.  We may have a concurrent set_affinity
via procfs running on another CPU in parallel with the IRQ migration,
resulting in unpredictable results.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

diff --git a/arch/arm/kernel/irq.c b/arch/arm/kernel/irq.c
index 2f19aa5f33917f69e742448360fbc347e665787f..3535d3793e65264b1e7ca457f530b4e1be40da95 100644 (file)
--- a/arch/arm/kernel/irq.c
+++ b/arch/arm/kernel/irq.c
@@ -179,14 +179,21 @@ int __init arch_probe_nr_irqs(void)
 
 #ifdef CONFIG_HOTPLUG_CPU
 
-static void route_irq(struct irq_desc *desc, unsigned int irq, unsigned int cpu)
+static bool migrate_one_irq(struct irq_data *d)
 {
-       pr_debug("IRQ%u: moving from cpu%u to cpu%u\n", irq, desc->irq_data.node, cpu);
+       unsigned int cpu = cpumask_any_and(d->affinity, cpu_online_mask);
+       bool ret = false;
 
-       raw_spin_lock_irq(&desc->lock);
-       desc->irq_data.chip->irq_set_affinity(&desc->irq_data,
-                                             cpumask_of(cpu), true);
-       raw_spin_unlock_irq(&desc->lock);
+       if (cpu >= nr_cpu_ids) {
+               cpu = cpumask_any(cpu_online_mask);
+               ret = true;
+       }
+
+       pr_debug("IRQ%u: moving from cpu%u to cpu%u\n", d->irq, d->node, cpu);
+
+       d->chip->irq_set_affinity(d, cpumask_of(cpu), true);
+
+       return ret;
 }
 
 /*
@@ -198,25 +205,30 @@ void migrate_irqs(void)
 {
        unsigned int i, cpu = smp_processor_id();
        struct irq_desc *desc;
+       unsigned long flags;
+
+       local_irq_save(flags);
 
        for_each_irq_desc(i, desc) {
                struct irq_data *d = &desc->irq_data;
+               bool affinity_broken = false;
 
-               if (d->node == cpu) {
-                       unsigned int newcpu = cpumask_any_and(d->affinity,
-                                                             cpu_online_mask);
-                       if (newcpu >= nr_cpu_ids) {
-                               if (printk_ratelimit())
-                                       printk(KERN_INFO "IRQ%u no longer affine to CPU%u\n",
-                                              i, cpu);
+               raw_spin_lock(&desc->lock);
+               do {
+                       if (desc->action == NULL)
+                               break;
 
-                               cpumask_setall(d->affinity);
-                               newcpu = cpumask_any_and(d->affinity,
-                                                        cpu_online_mask);
-                       }
+                       if (d->node != cpu)
+                               break;
 
-                       route_irq(desc, i, newcpu);
-               }
+                       affinity_broken = migrate_one_irq(d);
+               } while (0);
+               raw_spin_unlock(&desc->lock);
+
+               if (affinity_broken && printk_ratelimit())
+                       pr_warning("IRQ%u no longer affine to CPU%u\n", i, cpu);
        }
+
+       local_irq_restore(flags);
 }
 #endif /* CONFIG_HOTPLUG_CPU */