[PATCH] sched/cgroup: allow rt tasks in cpu cgroup without group rt scheduler

[Konstantin Khlebnikov]

Without group rt scheduler rt tasks works in cpu cgroup perfectly fine.
This artificial restriction blocks attaching rt threads to cpu cgroup.

Moreover __sched_setscheduler() never had such check and allow changing
policy to rt for threads which are already in non-root cpu cgroup.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
---
 kernel/sched/core.c  |    8 +++-----
 kernel/sched/rt.c    |    9 ---------
 kernel/sched/sched.h |    1 -
 3 files changed, 3 insertions(+), 15 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d17c5da523a0..ceb7df51d448 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6338,11 +6338,9 @@ static int cpu_cgroup_can_attach(struct cgroup_taskset *tset)
 
 	cgroup_taskset_for_each(task, css, tset) {
 #ifdef CONFIG_RT_GROUP_SCHED
-		if (!sched_rt_can_attach(css_tg(css), task))
-			return -EINVAL;
-#else
-		/* We don't support RT-tasks being in separate groups */
-		if (task->sched_class != &fair_sched_class)
+		/* Don't accept rt tasks when there is no way for them to run */
+		if (rt_bandwidth_enabled() && rt_task(task) &&
+		    css_tg(css)->rt_bandwidth.rt_runtime == 0)
 			return -EINVAL;
 #endif
 		/*
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 0af5ca9e3e3f..e25b460d051f 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2650,15 +2650,6 @@ static int sched_rt_global_constraints(void)
 	return ret;
 }
 
-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)
-		return 0;
-
-	return 1;
-}
-
 #else /* !CONFIG_RT_GROUP_SCHED */
 static int sched_rt_global_constraints(void)
 {
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 14db76cd496f..266c5a16ccda 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -387,7 +387,6 @@ extern int sched_group_set_rt_runtime(struct task_group *tg, long rt_runtime_us)
 extern int sched_group_set_rt_period(struct task_group *tg, u64 rt_period_us);
 extern long sched_group_rt_runtime(struct task_group *tg);
 extern long sched_group_rt_period(struct task_group *tg);
-extern int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk);
 
 extern struct task_group *sched_create_group(struct task_group *parent);
 extern void sched_online_group(struct task_group *tg,