Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fix from Ingo Molnar:
 "Fix a crash that can trigger when racing with CPU hotplug: we didn't
  use sched-domains data structures carefully enough in select_idle_cpu()"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Fix sched domains NULL dereference in select_idle_sibling()

1 files changed, 8 insertions, 3 deletions

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2d4ad72f8f3c..76ee7de1859d 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5471,13 +5471,18 @@ static inline int select_idle_smt(struct task_struct *p, struct sched_domain *sd
  */
 static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target)
 {
-        struct sched_domain *this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
-        u64 avg_idle = this_rq()->avg_idle;
-        u64 avg_cost = this_sd->avg_scan_cost;
+        struct sched_domain *this_sd;
+        u64 avg_cost, avg_idle = this_rq()->avg_idle;
         u64 time, cost;
         s64 delta;
         int cpu, wrap;
 
+        this_sd = rcu_dereference(*this_cpu_ptr(&sd_llc));
+        if (!this_sd)
+                return -1;
+
+        avg_cost = this_sd->avg_scan_cost;
+
         /*
          * Due to large variance we need a large fuzz factor; hackbench in
          * particularly is sensitive here.