[PATCH 1/3] genirq/irqdomain: Check for existing mapping in irq_domain_associate()

["Sverdlin, Alexander (Nokia - DE/Ulm)" <alexander.sverdlin@nokia.com>]

From: Alexander Sverdlin <alexander.sverdlin@nokia.com>

irq_domain_associate() is the only place where irq_find_mapping() can be
used reliably (under irq_domain_mutex) to make a decision if the mapping
shall be created or not. Other calls to irq_find_mapping() (not under
any lock) cannot be used for this purpose and lead to race conditions in
particular inside irq_create_mapping().

Give the callers of irq_domain_associate() an ability to detect existing
domain reliably by examining the return value.

Cc: stable@vger.kernel.org
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
---
 kernel/irq/irqdomain.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 3078d0e..7bc07b6 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -532,6 +532,7 @@ int irq_domain_associate(struct irq_domain *domain, unsigned int virq,
 			 irq_hw_number_t hwirq)
 {
 	struct irq_data *irq_data = irq_get_irq_data(virq);
+	unsigned int eirq;
 	int ret;
 
 	if (WARN(hwirq >= domain->hwirq_max,
@@ -543,6 +544,16 @@ int irq_domain_associate(struct irq_domain *domain, unsigned int virq,
 		return -EINVAL;
 
 	mutex_lock(&irq_domain_mutex);
+
+	/* Check if mapping already exists */
+	eirq = irq_find_mapping(domain, hwirq);
+	if (eirq) {
+		mutex_unlock(&irq_domain_mutex);
+		pr_debug("%s: conflicting mapping for hwirq 0x%x\n",
+			 domain->name, (int)hwirq);
+		return -EBUSY;
+	}
+
 	irq_data->hwirq = hwirq;
 	irq_data->domain = domain;
 	if (domain->ops->map) {
-- 
2.4.6