genirq/affinity: Use get/put_online_cpus around cpumask operations

Without locking out CPU mask operations we might end up with an inconsistent
view of the cpumask in the function.

Fixes: 5e385a6ef31f: "genirq: Add a helper to spread an affinity mask for MSI/MSI-X vectors"
Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: http://lkml.kernel.org/r/1470924405-25728-1-git-send-email-hch@lst.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index f68959341c0f..32f6cfcff212 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -39,6 +39,7 @@ struct cpumask *irq_create_affinity_mask(unsigned int *nr_vecs)
                 return NULL;
         }
 
+        get_online_cpus();
         if (max_vecs >= num_online_cpus()) {
                 cpumask_copy(affinity_mask, cpu_online_mask);
                 *nr_vecs = num_online_cpus();
@@ -56,6 +57,7 @@ struct cpumask *irq_create_affinity_mask(unsigned int *nr_vecs)
                 }
                 *nr_vecs = vecs;
         }
+        put_online_cpus();
 
         return affinity_mask;
 }