[RFC PATCH] irqchip: arm-gic: take gic_lock when updating irq type

[Aniruddha Banerjee <aniruddhab@nvidia.com>]

The kernel documentation states that the irq-chip driver should
handle the locking of the irq-chip registers. In the irq-gic,
the accesses to the irqchip are seemingly not protected and multiple
writes to SPIs from different irq descriptors do RMW requests without
taking the irq-chip lock. When multiple irqs call the request_irq at
the same time, there can be a simultaneous write at the gic
distributor, leading to a race. Acquire the irq_controller lock when the
irq_type is updated.

This patch is only for GICv2; however, I have noticed a similar
implementation in GICv3. This patch is sent as an RFC in case I am
missing anything.

Signed-off-by: Aniruddha Banerjee <aniruddhab@nvidia.com>
---
 drivers/irqchip/irq-gic.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/irqchip/irq-gic.c b/drivers/irqchip/irq-gic.c
index 4c797b43614d..61380f5a2254 100644
--- a/drivers/irqchip/irq-gic.c
+++ b/drivers/irqchip/irq-gic.c
@@ -67,6 +67,8 @@ static void gic_check_cpu_features(void)
 #define gic_check_cpu_features()       do { } while(0)
 #endif

+static DEFINE_RAW_SPINLOCK(irq_controller_lock);
+
 union gic_base {
        void __iomem *common_base;
        void __percpu * __iomem *percpu_base;
@@ -529,6 +531,7 @@ static int gic_set_type(struct irq_data *d, unsigned int type)
 {
        void __iomem *base = gic_dist_base(d);
        unsigned int gicirq = gic_irq(d);
+       int ret;

        /* Interrupt configuration for SGIs can't be changed */
        if (gicirq < 16)
@@ -539,7 +542,11 @@ static int gic_set_type(struct irq_data *d, unsigned int type)
                            type != IRQ_TYPE_EDGE_RISING)
                return -EINVAL;

-       return gic_configure_irq(gicirq, type, base, NULL);
+       raw_spin_lock(&irq_controller_lock);
+       ret = gic_configure_irq(gicirq, type, base, NULL);
+       raw_spin_unlock(&irq_controller_lock);
+
+       return ret;
 }

 static int gic_irq_set_vcpu_affinity(struct irq_data *d, void *vcpu)
--
2.15.1