[PATCH 2/3] genirq/irqdomain: Re-check mapping after associate in irq_create_mapping()

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

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

If two irq_create_mapping() calls perform a mapping of the same hwirq on
two CPU cores in parallel they both will get 0 from irq_find_mapping(),
both will allocate unique virq using irq_domain_alloc_descs() and both
will finally irq_domain_associate() it. Giving different virq numbers
to their callers.

In practice the first caller is usually an interrupt controller driver and
the seconds is some device requesting the interrupt providede by the above
interrupt controller.

In this case either the interrupt controller driver configures virq which
is not the one being "associated" with hwirq, or the "slave" device
requests the virq which is never being triggered.

Cc: stable@vger.kernel.org
Signed-off-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
---
 kernel/irq/irqdomain.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 7bc07b6..176f2cc 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -675,13 +675,6 @@ unsigned int irq_create_mapping(struct irq_domain *domain,
 
 	of_node = irq_domain_get_of_node(domain);
 
-	/* Check if mapping already exists */
-	virq = irq_find_mapping(domain, hwirq);
-	if (virq) {
-		pr_debug("-> existing mapping on virq %d\n", virq);
-		return virq;
-	}
-
 	/* Allocate a virtual interrupt number */
 	virq = irq_domain_alloc_descs(-1, 1, hwirq, of_node_to_nid(of_node), NULL);
 	if (virq <= 0) {
@@ -691,7 +684,11 @@ unsigned int irq_create_mapping(struct irq_domain *domain,
 
 	if (irq_domain_associate(domain, virq, hwirq)) {
 		irq_free_desc(virq);
-		return 0;
+
+		virq = irq_find_mapping(domain, hwirq);
+		if (virq)
+			pr_debug("-> existing mapping on virq %d\n", virq);
+		return virq;
 	}
 
 	pr_debug("irq %lu on domain %s mapped to virtual irq %u\n",
-- 
2.4.6