[PATCH v3] sched/eevdf: Fix vprot across reweighting

[Kayra Cizmeci <kayracizmeci@gmail.com>]

Currently in reweighting, while a tasks vruntime changes dead protection
could go alive, or alive protection could decrease, increase and go dead.
Fix it.

Fixes: 80390ead2080 ("sched/fair: Separate se->vlag from se->vprot")
Fixes: bcd74b2ffdd0 ("sched/fair: Only set slice protection at pick time")
Suggested-by: Vincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: Kayra Cizmeci <kayracizmeci@gmail.com>
---

Changes v2->v3:
* Rebase and move the enqueue_task_fair() block to if (!curr) block.


Not tested at all :-(. But I think
This should'a cover the shced_change_begin() path same,
since curr == NULL, so we always enter if (!curr) block.

 kernel/sched/fair.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0feec172fd37..4593d0122d66 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4892,12 +4892,15 @@ static void reweight_eevdf(struct cfs_rq *cfs_rq, struct sched_entity *se,
 	update_load_set(&se->h_load, weight);
 
 	if (on_rq) {
-		if (rel_vprot)
-			se->vprot += avruntime;
 		se->deadline += avruntime;
 		se->rel_deadline = 0;
 		se->vruntime = avruntime - se->vlag;
 
+		if (rel_vprot)
+			se->vprot += avruntime;
+		else if (curr)
+			se->vprot = se->vruntime;
+
 		if (!curr)
 			__enqueue_entity(cfs_rq, se);
 		cfs_rq->h_nr_queued++;
@@ -8155,8 +8158,9 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	int task_new = !(flags & ENQUEUE_WAKEUP);
 	struct sched_entity *se = &p->se;
 	struct cfs_rq *cfs_rq = &rq->cfs;
-	unsigned long weight;
-	bool curr;
+	unsigned long weight, old_weight;
+	bool curr, live, running;
+	s64 dist;
 
 	if (task_is_throttled(p) && enqueue_throttled_task(p))
 		return;
@@ -8200,8 +8204,24 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
 	weight = enqueue_hierarchy(p, flags);
 
 	if (!curr) {
+		running = task_current_donor(rq, p);
+		live = running && protect_slice(se);
+
+		if (live) {
+			old_weight = se->h_load.weight;
+			dist = se->vprot - se->vruntime;
+		}
 		reweight_eevdf(cfs_rq, se, weight, false);
 		place_entity(cfs_rq, se, flags | ENQUEUE_QUEUED);
+
+		if (live) {
+			if (weight != old_weight)
+				dist = div64_long(dist * old_weight, weight);
+			se->vprot = se->vruntime + dist;
+		} else if (running) {
+			cancel_protect_slice(se);
+		}
+
 		__enqueue_entity(cfs_rq, se);
 	}
 
-- 
2.53.0