[PATCH] sched: fix load_above_capacity underflow

[Lei Wen]

Apparently we don't want to see sds->busiest_nr_running is small than
sds->busiest_group_capacity, while our load_above_capacity is
an "unsigned long" type.

Signed-off-by: Lei Wen <leiwen@xxxxxxxxxxx>
---
 kernel/sched/fair.c |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c61a614..fd90b17 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4780,12 +4780,17 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
 		/*
 		 * Don't want to pull so many tasks that a group would go idle.
 		 */
-		load_above_capacity = (sds->busiest_nr_running -
-						sds->busiest_group_capacity);
+		if (sds->busiest_has_capacity)
+			load_above_capacity = 0;
+		else {
+			load_above_capacity = (sds->busiest_nr_running -
+					sds->busiest_group_capacity);
 
-		load_above_capacity *= (SCHED_LOAD_SCALE * SCHED_POWER_SCALE);
+			load_above_capacity *=
+				(SCHED_LOAD_SCALE * SCHED_POWER_SCALE);
 
-		load_above_capacity /= sds->busiest->sgp->power;
+			load_above_capacity /= sds->busiest->sgp->power;
+		}
 	}
 
 	/*
-- 
1.7.10.4

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