[PATCH] irqdomain: Fix irqdomain->revmap race

[Mark-PK Tsai]

The irqdomain->revmap(_tree) of a shared irq can be race updated
as following, which result in an unexpected irq mapping:

---------------------------------------------------------------
(2 threads parse the same hwirq fwspec in the same time.)

Thread A 			Thread B
irq_create_fwspec_mapping
irq_find_mapping						Thread A: virq = 0, alloc a new irq_desc
				irq_create_fwspec_mapping
				irq_find_mapping		Thread B: virq = 0, alloc a new irq_desc
irq_domain_alloc_irqs
irq_domain_insert_irq						domain->revmap[hwirq] = irq_data(virq x)
				irq_domain_alloc_irqs
				irq_domain_insert_irq		domain->revmap[hwirq] = irq_data(virq x + 1)

virq = x			virq = x + 1
---------------------------------------------------------------

The virq x can't work because the revmap[hwirq] was
overridden by thread B.

It seems both hierarchy and non-hierarchy irq domain have the same
problem because the code from irq_find_mapping to revmap update are
not protected by a same lock.

Do you have any suggestion about how to fix it properly?

Signed-off-by: Mark-PK Tsai <mark-pk.tsai@xxxxxxxxxxxx>
---
 kernel/irq/irqdomain.c | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 8fe1da9614ee..21d317b26220 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -22,6 +22,7 @@
 
 static LIST_HEAD(irq_domain_list);
 static DEFINE_MUTEX(irq_domain_mutex);
+static DEFINE_MUTEX(irq_revmaps_mutex);
 
 static struct irq_domain *irq_default_domain;
 
@@ -793,6 +794,7 @@ unsigned int irq_create_fwspec_mapping(struct irq_fwspec *fwspec)
 	 * If we've already configured this interrupt,
 	 * don't do it again, or hell will break loose.
 	 */
+	mutex_lock(&irq_revmaps_mutex);
 	virq = irq_find_mapping(domain, hwirq);
 	if (virq) {
 		/*
@@ -801,7 +803,7 @@ unsigned int irq_create_fwspec_mapping(struct irq_fwspec *fwspec)
 		 * interrupt number.
 		 */
 		if (type == IRQ_TYPE_NONE || type == irq_get_trigger_type(virq))
-			return virq;
+			goto unlock;
 
 		/*
 		 * If the trigger type has not been set yet, then set
@@ -809,27 +811,32 @@ unsigned int irq_create_fwspec_mapping(struct irq_fwspec *fwspec)
 		 */
 		if (irq_get_trigger_type(virq) == IRQ_TYPE_NONE) {
 			irq_data = irq_get_irq_data(virq);
-			if (!irq_data)
-				return 0;
+			if (!irq_data) {
+				virq = 0;
+				goto unlock;
+			}
 
 			irqd_set_trigger_type(irq_data, type);
-			return virq;
+			goto unlock;
 		}
 
 		pr_warn("type mismatch, failed to map hwirq-%lu for %s!\n",
 			hwirq, of_node_full_name(to_of_node(fwspec->fwnode)));
-		return 0;
+		virq = 0;
+		goto unlock;
 	}
 
 	if (irq_domain_is_hierarchy(domain)) {
 		virq = irq_domain_alloc_irqs(domain, 1, NUMA_NO_NODE, fwspec);
-		if (virq <= 0)
-			return 0;
+		if (virq <= 0) {
+			virq = 0;
+			goto unlock;
+		}
 	} else {
 		/* Create mapping */
 		virq = irq_create_mapping(domain, hwirq);
 		if (!virq)
-			return virq;
+			goto unlock;
 	}
 
 	irq_data = irq_get_irq_data(virq);
@@ -838,12 +845,15 @@ unsigned int irq_create_fwspec_mapping(struct irq_fwspec *fwspec)
 			irq_domain_free_irqs(virq, 1);
 		else
 			irq_dispose_mapping(virq);
-		return 0;
+		virq = 0;
+		goto unlock;
 	}
 
 	/* Store trigger type */
 	irqd_set_trigger_type(irq_data, type);
 
+unlock:
+	mutex_unlock(&irq_revmaps_mutex);
 	return virq;
 }
 EXPORT_SYMBOL_GPL(irq_create_fwspec_mapping);
-- 
2.18.0