[PATCH 1/1] sched/fair: Fix the wrong sched_stat_wait time

[qianjun . kernel]

From: jun qian <qianjun.kernel@xxxxxxxxx>

When the sched_schedstat changes from 0 to 1, some sched se maybe
already in the runqueue, the se->statistics.wait_start will be 0.
So it will let the (rq_of(cfs_rq)) - se->statistics.wait_start)
wrong. We need to avoid this scenario.

Signed-off-by: jun qian <qianjun.kernel@xxxxxxxxx>
Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
 kernel/sched/fair.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 658aa7a..dd7c3bb 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -908,6 +908,14 @@ static void update_curr_fair(struct rq *rq)
 	if (!schedstat_enabled())
 		return;
 
+	/*
+	 * When the sched_schedstat changes from 0 to 1, some sched se maybe
+	 * already in the runqueue, the se->statistics.wait_start will be 0.
+	 * So it will let the delta wrong. We need to avoid this scenario.
+	 */
+	if (unlikely(!schedstat_val(se->statistics.wait_start)))
+		return;
+
 	delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);
 
 	if (entity_is_task(se)) {
-- 
1.8.3.1