[PATCH] sched/fair: prevent using decay_load_missed() with a negative value

[Byungchul Park]

decay_load_missed() cannot handle nagative value. So we need to prevent
using the function with a negative value.

Signed-off-by: Byungchul Park <byungchul.park@xxxxxxx>
---
 kernel/sched/fair.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8dde8b6..3f08d75 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4443,8 +4443,14 @@ static void __update_cpu_load(struct rq *this_rq, unsigned long this_load,
 
 		/* scale is effectively 1 << i now, and >> i divides by scale */
 
-		old_load = this_rq->cpu_load[i] - tickless_load;
+		old_load = this_rq->cpu_load[i];
 		old_load = decay_load_missed(old_load, pending_updates - 1, i);
+		old_load -= decay_load_missed(tickless_load, pending_updates - 1, i);
+		/*
+		 * old_load can never be a negative value because a decayed
+		 * tickless_load cannot be greater than the original
+		 * tickless_load.
+		 */
 		old_load += tickless_load;
 		new_load = this_load;
 		/*
-- 
1.9.1


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