linux-kernel - [PATCH v2 2/2] sched/eevdf: Fix miscalculation in reweight

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Message-Id: <20240306022133.81008-3-dtcccc@linux.alibaba.com>
Date: Wed,  6 Mar 2024 10:21:33 +0800
From: Tianchen Ding <dtcccc@...ux.alibaba.com>
To: linux-kernel@...r.kernel.org
Cc: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	Abel Wu <wuyun.abel@...edance.com>
Subject: [PATCH v2 2/2] sched/eevdf: Fix miscalculation in reweight_entity() when se is not curr

reweight_eevdf() only keeps V unchanged inside itself. When se !=
cfs_rq->curr, it would be dequeued from rb tree first. So that V is
changed and the result is wrong. Pass the original V to reweight_eevdf()
to fix this issue.

Fixes: eab03c23c2a1 ("sched/eevdf: Fix vruntime adjustment on reweight")
Signed-off-by: Tianchen Ding <dtcccc@...ux.alibaba.com>
Reviewed-by: Abel Wu <wuyun.abel@...edance.com>
---
 kernel/sched/fair.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 5551ce2af73e..091a1a750638 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3676,11 +3676,10 @@ static inline void
 dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
 #endif
 
-static void reweight_eevdf(struct cfs_rq *cfs_rq, struct sched_entity *se,
+static void reweight_eevdf(struct sched_entity *se, u64 avruntime,
 			   unsigned long weight)
 {
 	unsigned long old_weight = se->load.weight;
-	u64 avruntime = avg_vruntime(cfs_rq);
 	s64 vlag, vslice;
 
 	/*
@@ -3787,10 +3786,12 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 			    unsigned long weight)
 {
 	bool curr = cfs_rq->curr == se;
+	u64 avruntime;
 
 	if (se->on_rq) {
 		/* commit outstanding execution time */
 		update_curr(cfs_rq);
+		avruntime = avg_vruntime(cfs_rq);
 		if (!curr)
 			__dequeue_entity(cfs_rq, se);
 		update_load_sub(&cfs_rq->load, se->load.weight);
@@ -3804,7 +3805,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 		 */
 		se->vlag = div_s64(se->vlag * se->load.weight, weight);
 	} else {
-		reweight_eevdf(cfs_rq, se, weight);
+		reweight_eevdf(se, avruntime, weight);
 	}
 
 	update_load_set(&se->load, weight);
-- 
2.39.3