Re: [PATCH] genirq: Avoid race between cpu hot plug and irq_desc() allocation paths

[pheragu]

On 2018-09-05 11:23, Thomas Gleixner wrote:
> On Wed, 5 Sep 2018, Prakruthi Deepak Heragu wrote:
>
> > One of the cores might have just allocated irq_desc() and other core
> > might be doing irq migration in the hot plug path. In the hot plug 
> > path
> > during the IRQ migration, for_each_active_irq macro is trying to get
> > irqs whose bits are set in allocated_irqs bit map but there is no 
> > return
> > value check after irq_to_desc for desc validity.
>
> Confused. All parts involved, irq allocation/deallocation and the CPU
> hotplug code take sparse_irq_lock to prevent exavtly that.
Removing the NULL pointer check and adding this sparse_irq_lock
that you suggested will solve this issue. The code looks like
this now. Is this okay?
diff --git a/kernel/irq/cpuhotplug.c b/kernel/irq/cpuhotplug.c
index 9409b55..f2ef76e 100644
--- a/kernel/irq/cpuhotplug.c
+++ b/kernel/irq/cpuhotplug.c
@@ -185,14 +185,10 @@ void irq_migrate_all_off_this_cpu(void)
 {
 	struct irq_desc *desc;
 	unsigned int irq;
-
+	irq_lock_sparse();
 	for_each_active_irq(irq) {
 		bool affinity_broken;
-
 		desc = irq_to_desc(irq);
-		if (!desc)
-			continue;
-
 		raw_spin_lock(&desc->lock);
 		affinity_broken = migrate_one_irq(desc);
 		raw_spin_unlock(&desc->lock);
@@ -202,6 +198,7 @@ void irq_migrate_all_off_this_cpu(void)
 					    irq, smp_processor_id());
 		}
 	}
+	irq_unlock_sparse();
 }

 static void irq_restore_affinity_of_irq(struct irq_desc *desc, unsigned 
int cpu)

> Thanks,
>
> 	tglx

Thanks,
Prakruthi Deepak Heragu