sched/fair: Fix imbalance overflow

[ Upstream commit 91dcf1e8068e9a8823e419a7a34ff4341275fb70 ]

When local group is fully busy but its average load is above system load,
computing the imbalance will overflow and local group is not the best
target for pulling this load.

Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()")
Reported-by: Tingjia Cao <tjcao980311@gmail.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Tingjia Cao <tjcao980311@gmail.com>
Link: https://lore.kernel.org/lkml/CABcWv9_DAhVBOq2=W=2ypKE9dKM5s2DvoV8-U0+GDwwuKZ89jQ@mail.gmail.com/T/
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e046a2bff207b94636ab7409c9b6b25d171fa850..661226e38835d4bd0daf1fb9906a0cc3d456ae36 100644 (file)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -10123,6 +10123,16 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s
 
                sds->avg_load = (sds->total_load * SCHED_CAPACITY_SCALE) /
                                sds->total_capacity;
+
+               /*
+                * If the local group is more loaded than the average system
+                * load, don't try to pull any tasks.
+                */
+               if (local->avg_load >= sds->avg_load) {
+                       env->imbalance = 0;
+                       return;
+               }
+
        }
 
        /*