Patch "sched/eevdf: Fix miscalculation in reweight_entity() when se is not curr" has been added to the 6.8-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    sched/eevdf: Fix miscalculation in reweight_entity() when se is not curr

to the 6.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     sched-eevdf-fix-miscalculation-in-reweight_entity-wh.patch
and it can be found in the queue-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 0de307a494c79d5a1daa5a8b6ab41cb49a3836af
Author: Tianchen Ding <dtcccc@xxxxxxxxxxxxxxxxx>
Date:   Wed Mar 6 10:21:33 2024 +0800

    sched/eevdf: Fix miscalculation in reweight_entity() when se is not curr
    
    [ Upstream commit afae8002b4fd3560c8f5f1567f3c3202c30a70fa ]
    
    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@xxxxxxxxxxxxxxxxx>
    [peterz: flip if() condition for clarity]
    Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
    Reviewed-by: Abel Wu <wuyun.abel@xxxxxxxxxxxxx>
    Link: https://lkml.kernel.org/r/20240306022133.81008-3-dtcccc@xxxxxxxxxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 69d2158873429..b9ee4397b484a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3670,11 +3670,10 @@ 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;
 
 	/*
@@ -3781,24 +3780,26 @@ 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);
 	}
 	dequeue_load_avg(cfs_rq, se);
 
-	if (!se->on_rq) {
+	if (se->on_rq) {
+		reweight_eevdf(se, avruntime, weight);
+	} else {
 		/*
 		 * Because we keep se->vlag = V - v_i, while: lag_i = w_i*(V - v_i),
 		 * we need to scale se->vlag when w_i changes.
 		 */
 		se->vlag = div_s64(se->vlag * se->load.weight, weight);
-	} else {
-		reweight_eevdf(cfs_rq, se, weight);
 	}
 
 	update_load_set(&se->load, weight);