Fix to avoid -1 retval.

Includes fixes from Hillf Danton[off-list ref].

Signed-off-by: Andrea Arcangeli<redacted>
---
  kernel/sched/fair.c |    4 ++++
  1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c099cc6..fa96810 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c

@@ -2789,6 +2789,9 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
  		if (new_cpu == -1 || new_cpu == cpu) {
  			/* Now try balancing at a lower domain level of cpu */
  			sd = sd->child;
+			if (new_cpu<  0)
+				/* Return prev_cpu is find_idlest_cpu failed */
+				new_cpu = prev_cpu;
  			continue;
  		}

@@ -2807,6 +2810,7 @@ select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flags)
  unlock:
  	rcu_read_unlock();

+	BUG_ON(new_cpu<  0);
  	return new_cpu;
  }
  #endif /* CONFIG_SMP */