[PATCH] powerpc/irq: Improve/fix migrate_irqs()

[Benjamin Herrenschmidt]

migrate_irqs() is used by some platforms to migrate interrupts
away from a CPU about to be offlined.

The current implementation had various issues such as not taking
the descriptor lock before manipulating it. This refactors it
a bit, fixing that problem at the same time.

Signed-off-by: Benjamin Herrenschmidt <b...@kernel.crashing.org>
---
 arch/powerpc/kernel/irq.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
index a018f5c..52308b4 100644
--- a/arch/powerpc/kernel/irq.c
+++ b/arch/powerpc/kernel/irq.c
@@ -456,22 +456,31 @@ void migrate_irqs(void)
        for_each_irq_desc(irq, desc) {
                struct irq_data *data;
                struct irq_chip *chip;
+               const struct cpumask *affinity;
 
-               data = irq_desc_get_irq_data(desc);
-               if (irqd_is_per_cpu(data))
-                       continue;
+               /* Interrupts are already disabled */
+               raw_spin_lock(&desc->lock);
 
+               data = irq_desc_get_irq_data(desc);
+               affinity = irq_data_get_affinity_mask(data);
                chip = irq_data_get_irq_chip(data);
+               if (!irq_has_action(irq) || irqd_is_per_cpu(data) ||
+                   cpumask_subset(affinity, cpu_online_mask) ||
+                   !chip) {
+                       raw_spin_unlock(&desc->lock);
+                       continue;
+               }
 
-               cpumask_and(mask, irq_data_get_affinity_mask(data), map);
-               if (cpumask_any(mask) >= nr_cpu_ids) {
+               cpumask_and(mask, affinity, map);
+               if (cpumask_empty(mask)) {
                        pr_warn("Breaking affinity for irq %i\n", irq);
                        cpumask_copy(mask, map);
                }
                if (chip->irq_set_affinity)
                        chip->irq_set_affinity(data, mask, true);
                else if (desc->action && !(warned++))
-                       pr_err("Cannot set affinity for irq %i\n", irq);
+                       pr_debug("Cannot set affinity for irq %i\n", irq);
+               raw_spin_unlock(&desc->lock);
        }
 
        free_cpumask_var(mask);