sched: Make the rt throtting disabled tunable valid globally

[Dhaval Giani <dhaval@retis.sssup.it>]

On setting /proc/sys/kernel/sched_rt_runtime_us to -1, the intended
behavior is that rt-group throttling is disabled throughout. This
could be confirmed by trying to launch a real time task in a cgroup
which had zero rt runtime allotted to it.

This though was not happening when one tried to move a rt task into
a rt cgroup which had zero rt runtime. Ensure that this
tunable is honoured globally.

Signed-off-by: Dhaval Giani <dhaval.giani@gmail.com>

---
 kernel/sched.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Index: master/kernel/sched.c
===================================================================
--- master.orig/kernel/sched.c
+++ master/kernel/sched.c
@@ -8542,7 +8542,8 @@ static int sched_rt_global_constraints(v
 int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk)
 {
 	/* Don't accept realtime tasks when there is no way for them to run */
-	if (rt_task(tsk) && tg->rt_bandwidth.rt_runtime == 0)
+	if (rt_task(tsk) && rt_bandwidth_enabled() &&
+				tg->rt_bandwidth.rt_runtime == 0)
 		return 0;
 
 	return 1;