[RFC PATCH v7 24/29] sched/syscalls: Allow unpriviledged tasks to set RT priority inside cgroups.

[Yuri Andriaccio <yurand2000@gmail.com>]

Signed-off-by: Yuri Andriaccio <yurand2000@gmail.com>
---
 kernel/sched/syscalls.c | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/kernel/sched/syscalls.c b/kernel/sched/syscalls.c
index f1e9de478e1d..36bb07b10d41 100644
--- a/kernel/sched/syscalls.c
+++ b/kernel/sched/syscalls.c
@@ -444,15 +444,27 @@ static int user_check_sched_setscheduler(struct task_struct *p,

 	if (rt_policy(policy)) {
 		unsigned long rlim_rtprio = task_rlimit(p, RLIMIT_RTPRIO);
+		struct task_group *active_context;

-		/* Can't set/change the rt policy: */
-		if (policy != p->policy && !rlim_rtprio)
-			goto req_priv;
+		if (!rt_group_sched_enabled())
+			goto root_cgroup_checks;

-		/* Can't increase priority: */
-		if (attr->sched_priority > p->rt_priority &&
-		    attr->sched_priority > rlim_rtprio)
-			goto req_priv;
+		scoped_guard(raw_spinlock_irq, dl_bw_lock_of_tg(p->sched_task_group)) {
+			active_context = dl_bandwidth_read(p->sched_task_group)->active_context;
+		}
+
+		/* Allow changing to the rt policy when not in the root cgroup */
+		if (active_context == &root_task_group) {
+root_cgroup_checks:
+			/* Can't set/change the rt policy: */
+			if (policy != p->policy && !rlim_rtprio)
+				goto req_priv;
+
+			/* Can't increase priority: */
+			if (attr->sched_priority > p->rt_priority &&
+			    attr->sched_priority > rlim_rtprio)
+				goto req_priv;
+		}
 	}

 	/*
--
2.56.0