irqdomain: Protect the linear revmap with RCU

It is pretty odd that the radix tree uses RCU while the linear
portion doesn't, leading to potential surprises for the users,
depending on how the irqdomain has been created.

Fix this by moving the update of the linear revmap under
the mutex, and the lookup under the RCU read-side lock.

The mutex name is updated to reflect that it doesn't only
cover the radix-tree anymore.
Signed-off-by: Marc Zyngier <maz@kernel.org>

include/linux/irqdomain.h

@@ -151,6 +151,7 @@ struct irq_domain_chip_generic;
  * Revmap data, used internally by irq_domain
  * @revmap_size: Size of the linear map table @revmap[]
  * @revmap_tree: Radix map tree for hwirqs that don't fit in the linear map
+ * @revmap_mutex: Lock for the revmap
  * @revmap: Linear table of irq_data pointers
  */
 struct irq_domain {
@@ -173,8 +174,8 @@ struct irq_domain {
 	irq_hw_number_t hwirq_max;
 	unsigned int revmap_size;
 	struct radix_tree_root revmap_tree;
-	struct mutex revmap_tree_mutex;
-	struct irq_data *revmap[];
+	struct mutex revmap_mutex;
+	struct irq_data __rcu *revmap[];
 };
 
 /* Irq domain flags */

kernel/irq/irqdomain.c

@@ -213,7 +213,7 @@ struct irq_domain *__irq_domain_add(struct fwnode_handle *fwnode, int size,
 
 	/* Fill structure */
 	INIT_RADIX_TREE(&domain->revmap_tree, GFP_KERNEL);
-	mutex_init(&domain->revmap_tree_mutex);
+	mutex_init(&domain->revmap_mutex);
 	domain->ops = ops;
 	domain->host_data = host_data;
 	domain->hwirq_max = hwirq_max;
@@ -504,13 +504,12 @@ static void irq_domain_clear_mapping(struct irq_domain *domain,
 	if (irq_domain_is_nomap(domain))
 		return;
 
-	if (hwirq < domain->revmap_size) {
-		domain->revmap[hwirq] = NULL;
-	} else {
-		mutex_lock(&domain->revmap_tree_mutex);
+	mutex_lock(&domain->revmap_mutex);
+	if (hwirq < domain->revmap_size)
+		rcu_assign_pointer(domain->revmap[hwirq], NULL);
+	else
 		radix_tree_delete(&domain->revmap_tree, hwirq);
-		mutex_unlock(&domain->revmap_tree_mutex);
-	}
+	mutex_unlock(&domain->revmap_mutex);
 }
 
 static void irq_domain_set_mapping(struct irq_domain *domain,
@@ -520,13 +519,12 @@ static void irq_domain_set_mapping(struct irq_domain *domain,
 	if (irq_domain_is_nomap(domain))
 		return;
 
-	if (hwirq < domain->revmap_size) {
-		domain->revmap[hwirq] = irq_data;
-	} else {
-		mutex_lock(&domain->revmap_tree_mutex);
+	mutex_lock(&domain->revmap_mutex);
+	if (hwirq < domain->revmap_size)
+		rcu_assign_pointer(domain->revmap[hwirq], irq_data);
+	else
 		radix_tree_insert(&domain->revmap_tree, hwirq, irq_data);
-		mutex_unlock(&domain->revmap_tree_mutex);
-	}
+	mutex_unlock(&domain->revmap_mutex);
 }
 
 static void irq_domain_disassociate(struct irq_domain *domain, unsigned int irq)
@@ -911,12 +909,12 @@ unsigned int irq_find_mapping(struct irq_domain *domain,
 		return 0;
 	}
 
+	rcu_read_lock();
 	/* Check if the hwirq is in the linear revmap. */
 	if (hwirq < domain->revmap_size)
-		return domain->revmap[hwirq]->irq;
-
-	rcu_read_lock();
-	data = radix_tree_lookup(&domain->revmap_tree, hwirq);
+		data = rcu_dereference(domain->revmap[hwirq]);
+	else
+		data = radix_tree_lookup(&domain->revmap_tree, hwirq);
 	rcu_read_unlock();
 	return data ? data->irq : 0;
 }
@@ -1499,18 +1497,17 @@ static void irq_domain_fix_revmap(struct irq_data *d)
 	if (irq_domain_is_nomap(d->domain))
 		return;
 
+	/* Fix up the revmap. */
+	mutex_lock(&d->domain->revmap_mutex);
 	if (d->hwirq < d->domain->revmap_size) {
 		/* Not using radix tree */
-		d->domain->revmap[d->hwirq] = d;
-		return;
+		rcu_assign_pointer(d->domain->revmap[d->hwirq], d);
+	} else {
+		slot = radix_tree_lookup_slot(&d->domain->revmap_tree, d->hwirq);
+		if (slot)
+			radix_tree_replace_slot(&d->domain->revmap_tree, slot, d);
 	}
-
-	/* Fix up the revmap. */
-	mutex_lock(&d->domain->revmap_tree_mutex);
-	slot = radix_tree_lookup_slot(&d->domain->revmap_tree, d->hwirq);
-	if (slot)
-		radix_tree_replace_slot(&d->domain->revmap_tree, slot, d);
-	mutex_unlock(&d->domain->revmap_tree_mutex);
+	mutex_unlock(&d->domain->revmap_mutex);
 }
 
 /**