diff mbox series

[kernel,v4,6/8] genirq/irqdomain: Move hierarchical IRQ cleanup to kobject_release

Message ID 20201124061720.86766-7-aik@ozlabs.ru
State Rejected
Headers show
Series genirq/irqdomain: Add reference counting to IRQs | expand

Checks

Context Check Description
snowpatch_ozlabs/needsstable success Patch has no Fixes tags
snowpatch_ozlabs/checkpatch success total: 0 errors, 0 warnings, 0 checks, 70 lines checked
snowpatch_ozlabs/apply_patch success Successfully applied on branch powerpc/merge (7c94b5d4e9d328a69d43a11d7e3dfd7a6d762cb6)

Commit Message

Alexey Kardashevskiy Nov. 24, 2020, 6:17 a.m. UTC
This moves hierarchical domain's irqs cleanup into the kobject release
hook to make irq_domain_free_irqs() as simple as kobject_put.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 kernel/irq/irqdomain.c | 43 +++++++++++++++++++++---------------------
 1 file changed, 22 insertions(+), 21 deletions(-)

Comments

Thomas Gleixner Nov. 30, 2020, 11:13 p.m. UTC | #1
Alexey,

On Tue, Nov 24 2020 at 17:17, Alexey Kardashevskiy wrote:
> This moves hierarchical domain's irqs cleanup into the kobject release
> hook to make irq_domain_free_irqs() as simple as kobject_put.

Truly simple: Simply broken in multiple ways.

CONFIG_SPARSE_IRQ=n is now completely buggered. It does not even compile
anymore. Running core code changes through a larger set of cross
compilers is neither rocket science nor optional.

For CONFIG_SPARSE_IRQ=y, see below.

> @@ -1675,14 +1679,11 @@ void irq_domain_free_irqs(unsigned int virq, unsigned int nr_irqs)
>  		 "NULL pointer, cannot free irq\n"))
>  		return;
>  
> -	mutex_lock(&irq_domain_mutex);
> -	for (i = 0; i < nr_irqs; i++)
> -		irq_domain_remove_irq(virq + i);
> -	irq_domain_free_irqs_hierarchy(data->domain, virq, nr_irqs);
> -	mutex_unlock(&irq_domain_mutex);
> +	for (i = 0; i < nr_irqs; i++) {
> +		struct irq_desc *desc = irq_to_desc(virq + i);
>  
> -	irq_domain_free_irq_data(virq, nr_irqs);
> -	irq_free_descs(virq, nr_irqs);
> +		kobject_put(&desc->kobj);

So up to this point both irq_dispose_mapping() _and_
irq_domain_free_irqs() invoked irq_free_descs().

Let's look at the call chains:

   irq_domain_free_irqs()
     irq_free_descs()
       mutex_lock(&sparse_irq_lock);
         for (i...)
           free_desc(from + i)
             irq_remove_debugfs_entry();
             unregister_irq_proc();
             irq_sysfs_del();
             delete_irq_desc();
             call_rcu();
       bitmap_clear(allocated_irqs, ...);
       mutex_unlock(&sparse_irq_lock);

with your modifications it does:

   irq_domain_free_irqs()
     for (i...)
          kobject_put(&desc->kobj)
            irq_kobj_release()
              if (desc->free_irq)
                desc->free_irq(desc);
              irq_remove_debugfs_entry();
              unregister_irq_proc();
              delete_irq_desc();
              call_rcu();

Can you spot the wreckage? It's not even subtle, it's more than obvious.

    1) None of the operations in irq_kobj_release() is protected by
       sparse_irq_lock anymore. There was a comment in free_desc() which
       explained what is protected. You removed parts of that comment
       and just left the sysfs portion of it above delete_irq_desc()
       which is completely bogus because you removed the irq_sysfs_del()
       call.

    2) Nothing removes the freed interrupts from the allocation
       bitmap. Run this often enough and you exhausted the interrupt
       space.

And no, you cannot just go and invoke irq_free_descs() instead of
kobject_put(), simply because you'd create lock order inversion vs. the
free_irq() callback.

So no, it's not that simple and I'm not at all interested in another
respin of this with some more duct tape applied.

It can be done, but that needs way more thought, a proper design which
preserves the existing semantics completely and wants to be a fine
grained series where each patch does exactly ONE small thing which is
reviewable and testable on _ALL_ users of this code, i.e. _ALL_
architectures and irq chip implementations.  

Thanks,

        tglx
diff mbox series

Patch

diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 4779d912bb86..a0a81cc6c524 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -863,21 +863,9 @@  EXPORT_SYMBOL_GPL(irq_create_of_mapping);
  */
 void irq_dispose_mapping(unsigned int virq)
 {
-	struct irq_data *irq_data = irq_get_irq_data(virq);
-	struct irq_domain *domain;
+	struct irq_desc *desc = irq_to_desc(virq);
 
-	if (!virq || !irq_data)
-		return;
-
-	domain = irq_data->domain;
-	if (WARN_ON(domain == NULL))
-		return;
-
-	if (irq_domain_is_hierarchy(domain)) {
-		irq_domain_free_irqs(virq, 1);
-	} else {
-		irq_free_desc(virq);
-	}
+	kobject_put(&desc->kobj);
 }
 EXPORT_SYMBOL_GPL(irq_dispose_mapping);
 
@@ -1396,6 +1384,19 @@  int irq_domain_alloc_irqs_hierarchy(struct irq_domain *domain,
 	return domain->ops->alloc(domain, irq_base, nr_irqs, arg);
 }
 
+static void irq_domain_hierarchy_free_desc(struct irq_desc *desc)
+{
+	unsigned int virq = desc->irq_data.irq;
+	struct irq_data *data = irq_get_irq_data(virq);
+
+	mutex_lock(&irq_domain_mutex);
+	irq_domain_remove_irq(virq);
+	irq_domain_free_irqs_hierarchy(data->domain, virq, 1);
+	mutex_unlock(&irq_domain_mutex);
+
+	irq_domain_free_irq_data(virq, 1);
+}
+
 int __irq_domain_alloc_irqs_data(struct irq_domain *domain, int virq,
 				 unsigned int nr_irqs, int node, void *arg,
 				 const struct irq_affinity_desc *affinity)
@@ -1430,7 +1431,10 @@  int __irq_domain_alloc_irqs_data(struct irq_domain *domain, int virq,
 	}
 
 	for (i = 0; i < nr_irqs; i++) {
+		struct irq_desc *desc = irq_to_desc(virq + i);
+
 		irq_domain_insert_irq(virq + i);
+		desc->free_irq = irq_domain_hierarchy_free_desc;
 	}
 	mutex_unlock(&irq_domain_mutex);
 
@@ -1675,14 +1679,11 @@  void irq_domain_free_irqs(unsigned int virq, unsigned int nr_irqs)
 		 "NULL pointer, cannot free irq\n"))
 		return;
 
-	mutex_lock(&irq_domain_mutex);
-	for (i = 0; i < nr_irqs; i++)
-		irq_domain_remove_irq(virq + i);
-	irq_domain_free_irqs_hierarchy(data->domain, virq, nr_irqs);
-	mutex_unlock(&irq_domain_mutex);
+	for (i = 0; i < nr_irqs; i++) {
+		struct irq_desc *desc = irq_to_desc(virq + i);
 
-	irq_domain_free_irq_data(virq, nr_irqs);
-	irq_free_descs(virq, nr_irqs);
+		kobject_put(&desc->kobj);
+	}
 }
 
 /**