sched: Ensure update_cfs_shares() is called for parents of continuous…

…ly-running tasks

We typically update a task_group's shares within the dequeue/enqueue
path.  However, continuously running tasks sharing a CPU are not
subject to these updates as they are only put/picked.  Unfortunately,
when we reverted f269ae0 (in 17bc14b), we lost the augmenting
periodic update that was supposed to account for this; resulting in a
potential loss of fairness.

To fix this, re-introduce the explicit update in
update_cfs_rq_blocked_load() [called via entity_tick()].

Reported-by: Max Hailperin <max@gustavus.edu>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Paul Turner <pjt@google.com>
Link: http://lkml.kernel.org/n/tip-9545m3apw5d93ubyrotrj31y@git.kernel.org
Cc: <stable@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

@@ -2032,6 +2032,7 @@ entity_tick(struct cfs_rq *cfs_rq, struct sched_entity *curr, int queued)
 	 */
 	update_entity_load_avg(curr, 1);
 	update_cfs_rq_blocked_load(cfs_rq, 1);
+	update_cfs_shares(cfs_rq);
 
 #ifdef CONFIG_SCHED_HRTICK
 	/*