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

Pull scheduler fixes from Ingo Molnar:
 "Four bugfixes and one performance fix"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Avoid integer overflow
  sched: Optimize task_sched_runtime()
  sched/numa: Cure update_numa_stats() vs. hotplug
  sched/numa: Fix NULL pointer dereference in task_numa_migrate()
  sched: Fix endless sync_sched/rcu() loop inside _cpu_down()

1 files changed, 14 insertions, 0 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 1deccd78be98..c1808606ee5f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2253,6 +2253,20 @@ unsigned long long task_sched_runtime(struct task_struct *p)
 	struct rq *rq;
 	u64 ns = 0;
 
+#if defined(CONFIG_64BIT) && defined(CONFIG_SMP)
+	/*
+	 * 64-bit doesn't need locks to atomically read a 64bit value.
+	 * So we have a optimization chance when the task's delta_exec is 0.
+	 * Reading ->on_cpu is racy, but this is ok.
+	 *
+	 * If we race with it leaving cpu, we'll take a lock. So we're correct.
+	 * If we race with it entering cpu, unaccounted time is 0. This is
+	 * indistinguishable from the read occurring a few cycles earlier.
+	 */
+	if (!p->on_cpu)
+		return p->se.sum_exec_runtime;
+#endif
+
 	rq = task_rq_lock(p, &flags);
 	ns = p->se.sum_exec_runtime + do_task_delta_exec(p, rq);
 	task_rq_unlock(rq, p, &flags);