1 files changed, 18 insertions, 7 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 7982faf7223b..a3a41c61a2c9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6788,6 +6788,11 @@ out_unlock:
         return 0;
 }
 
+static inline int on_null_domain(struct rq *rq)
+{
+        return unlikely(!rcu_dereference_sched(rq->sd));
+}
+
 #ifdef CONFIG_NO_HZ_COMMON
 /*
  * idle load balancing details
@@ -6842,8 +6847,13 @@ static void nohz_balancer_kick(void)
 static inline void nohz_balance_exit_idle(int cpu)
 {
         if (unlikely(test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))) {
-                cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
-                atomic_dec(&nohz.nr_cpus);
+                /*
+                 * Completely isolated CPUs don't ever set, so we must test.
+                 */
+                if (likely(cpumask_test_cpu(cpu, nohz.idle_cpus_mask))) {
+                        cpumask_clear_cpu(cpu, nohz.idle_cpus_mask);
+                        atomic_dec(&nohz.nr_cpus);
+                }
                 clear_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
         }
 }
@@ -6897,6 +6907,12 @@ void nohz_balance_enter_idle(int cpu)
         if (test_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu)))
                 return;
 
+        /*
+         * If we're a completely isolated CPU, we don't play.
+         */
+        if (on_null_domain(cpu_rq(cpu)))
+                return;
+
         cpumask_set_cpu(cpu, nohz.idle_cpus_mask);
         atomic_inc(&nohz.nr_cpus);
         set_bit(NOHZ_TICK_STOPPED, nohz_flags(cpu));
@@ -7159,11 +7175,6 @@ static void run_rebalance_domains(struct softirq_action *h)
         nohz_idle_balance(this_rq, idle);
 }
 
-static inline int on_null_domain(struct rq *rq)
-{
-        return !rcu_dereference_sched(rq->sd);
-}
-
 /*
  * Trigger the SCHED_SOFTIRQ if it is time to do periodic load balancing.
  */