sched/fair: Use reweight_entity() for set_user_nice()

Now that we directly change load_avg and propagate that change into
the sums, sys_nice() and co should do the same, otherwise its possible
to confuse load accounting when we migrate near the weight change.

Fixes-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org>
[ Added changelog, fixed the call condition. ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/20170517095045.GA8420@linaro.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

@@ -2776,6 +2776,43 @@ static inline void
 dequeue_load_avg(struct cfs_rq *cfs_rq, struct sched_entity *se) { }
 #endif
 
+static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
+			    unsigned long weight)
+{
+	if (se->on_rq) {
+		/* commit outstanding execution time */
+		if (cfs_rq->curr == se)
+			update_curr(cfs_rq);
+		account_entity_dequeue(cfs_rq, se);
+		dequeue_runnable_load_avg(cfs_rq, se);
+	}
+	dequeue_load_avg(cfs_rq, se);
+
+	update_load_set(&se->load, weight);
+
+#ifdef CONFIG_SMP
+	se->avg.load_avg = div_u64(se_weight(se) * se->avg.load_sum,
+				   LOAD_AVG_MAX - 1024 + se->avg.period_contrib);
+#endif
+
+	enqueue_load_avg(cfs_rq, se);
+	if (se->on_rq) {
+		account_entity_enqueue(cfs_rq, se);
+		enqueue_runnable_load_avg(cfs_rq, se);
+	}
+}
+
+void reweight_task(struct task_struct *p, int prio)
+{
+	struct sched_entity *se = &p->se;
+	struct cfs_rq *cfs_rq = cfs_rq_of(se);
+	struct load_weight *load = &se->load;
+	unsigned long weight = scale_load(sched_prio_to_weight[prio]);
+
+	reweight_entity(cfs_rq, se, weight);
+	load->inv_weight = sched_prio_to_wmult[prio];
+}
+
 #ifdef CONFIG_FAIR_GROUP_SCHED
 # ifdef CONFIG_SMP
 /*
@@ -2878,32 +2915,6 @@ static long calc_cfs_shares(struct cfs_rq *cfs_rq)
 }
 # endif /* CONFIG_SMP */
 
-static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
-			    unsigned long weight)
-{
-	if (se->on_rq) {
-		/* commit outstanding execution time */
-		if (cfs_rq->curr == se)
-			update_curr(cfs_rq);
-		account_entity_dequeue(cfs_rq, se);
-		dequeue_runnable_load_avg(cfs_rq, se);
-	}
-	dequeue_load_avg(cfs_rq, se);
-
-	update_load_set(&se->load, weight);
-
-#ifdef CONFIG_SMP
-	se->avg.load_avg = div_u64(se_weight(se) * se->avg.load_sum,
-				   LOAD_AVG_MAX - 1024 + se->avg.period_contrib);
-#endif
-
-	enqueue_load_avg(cfs_rq, se);
-	if (se->on_rq) {
-		account_entity_enqueue(cfs_rq, se);
-		enqueue_runnable_load_avg(cfs_rq, se);
-	}
-}
-
 static inline int throttled_hierarchy(struct cfs_rq *cfs_rq);
 
 static void update_cfs_shares(struct sched_entity *se)