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From:   Jiang Biao <benbjiang@gmail.com>
To:     mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
        vincent.guittot@linaro.org
Cc:     dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com,
        mgorman@suse.de, bristot@redhat.com, linux-kernel@vger.kernel.org,
        Jiang Biao <benbjiang@tencent.com>
Subject: [PATCH] sched/fair: add protection for delta of wait time
Date:   Sun, 17 Jan 2021 20:31:04 +0800
Message-Id: <20210117123104.27589-1-benbjiang@tencent.com>
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From: Jiang Biao <benbjiang@tencent.com>

delta in update_stats_wait_end() might be negative, which would
make following statistics go wrong.

Add protection for delta of wait time, like what have been done in
update_stats_enqueue_sleeper() for deltas of sleep/block time.

Signed-off-by: Jiang Biao <benbjiang@tencent.com>
---
 kernel/sched/fair.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c0374c1152e0..ac950ac950bc 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -917,6 +917,9 @@ update_stats_wait_end(struct cfs_rq *cfs_rq, struct sched_entity *se)
 
 	delta = rq_clock(rq_of(cfs_rq)) - schedstat_val(se->statistics.wait_start);
 
+	if ((s64)delta < 0)
+		delta = 0;
+
 	if (entity_is_task(se)) {
 		p = task_of(se);
 		if (task_on_rq_migrating(p)) {
-- 
2.21.0