0009-Allow-deeper-hierarchies-of-RT-cgroups.patch

From bb5741e9231b0e6399544a6c9c51f2abd67771c5 Mon Sep 17 00:00:00 2001
From: luca abeni <luca.abeni@santannapisa.it>
Date: Thu, 25 Jan 2018 12:22:21 +0100
Subject: [PATCH 9/9] Allow deeper hierarchies of RT cgroups

The basic rule is that:
- if a cgroup contains RT tasks than it cannot have other cgroups
  with RT tasks as children.
- if a cgroup has children with RT tasks, then it cannot contain RT tasks
---
 kernel/sched/core.c | 10 ++++------
 kernel/sched/rt.c   | 23 ++++++++++++++++++++++-
 2 files changed, 26 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4ea58406ec4a..f8b70c56fb9e 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4202,6 +4202,10 @@ static int __sched_setscheduler(struct task_struct *p,
 
 	if (user) {
 #ifdef CONFIG_RT_GROUP_SCHED
+		if (dl_bandwidth_enabled() && rt_policy(policy) && !sched_rt_can_attach(task_group(p), p)) {
+			task_rq_unlock(rq, p, &rf);
+			return -EPERM;
+		}
 		/*
 		 * Do not allow realtime tasks into groups that have no runtime
 		 * assigned.
@@ -6356,12 +6360,6 @@ cpu_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 		return &root_task_group.css;
 	}
 
-	/* Do not allow cpu_cgroup hierachies with depth greater than 2. */
-#ifdef CONFIG_RT_GROUP_SCHED
-	if (parent != &root_task_group)
-		return ERR_PTR(-EINVAL);
-#endif
-
 	tg = sched_create_group(parent);
 	if (IS_ERR(tg))
 		return ERR_PTR(-ENOMEM);
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 69c2a83560ab..3c622c9e443c 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2036,6 +2036,14 @@ static int tg_set_rt_bandwidth(struct task_group *tg,
 	if (tg == &root_task_group && rt_runtime == 0)
 		return -EINVAL;
 
+	/*
+	 * Do not allow to set a RT runtime > 0 if the parent has RT tasks
+	 * (and is not the root group)
+	 */
+	if (rt_runtime && (tg != &root_task_group) && (tg->parent != &root_task_group) && tg_has_rt_tasks(tg->parent)) {
+		return -EINVAL;
+	}
+
 	/* No period doesn't make any sense. */
 	if (rt_period == 0)
 		return -EINVAL;
@@ -2123,11 +2131,24 @@ static int sched_rt_global_constraints(void)
 
 int sched_rt_can_attach(struct task_group *tg, struct task_struct *tsk)
 {
+	int can_attach = 1;
+
 	/* Don't accept realtime tasks when there is no way for them to run */
 	if (rt_task(tsk) && tg->dl_bandwidth.dl_runtime == 0)
 		return 0;
 
-	return 1;
+	/* If one of the children has runtime > 0, cannot attach RT tasks! */
+	if ((tg != &root_task_group) && rt_task(tsk)) {
+		struct task_group *child;
+
+		list_for_each_entry_rcu(child, &tg->children, siblings) {
+			if (child->dl_bandwidth.dl_runtime) {
+				can_attach = 0;
+			}
+		}
+	}
+
+	return can_attach;
 }
 
 #else /* !CONFIG_RT_GROUP_SCHED */
-- 
2.14.1