[tip: sched/core] sched: Always initialize rt_rq's task_group

["tip-bot2 for Michal Koutný" <tip-bot2@linutronix.de>]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     a5a25b32c08a31c03258ec4960bec26caaf76e9a
Gitweb:        https://git.kernel.org/tip/a5a25b32c08a31c03258ec4960bec26caaf76e9a
Author:        Michal Koutný <mkoutny@suse.com>
AuthorDate:    Mon, 10 Mar 2025 18:04:35 +01:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Tue, 08 Apr 2025 20:55:53 +02:00

sched: Always initialize rt_rq's task_group

rt_rq->tg may be NULL which denotes the root task_group.
Store the pointer to root_task_group directly so that callers may use
rt_rq->tg homogenously.

root_task_group exists always with CONFIG_CGROUPS_SCHED,
CONFIG_RT_GROUP_SCHED depends on that.

This changes root level rt_rq's default limit from infinity to the
value of (originally) global RT throttling.

Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250310170442.504716-4-mkoutny@suse.com
---
 kernel/sched/rt.c    | 7 ++-----
 kernel/sched/sched.h | 2 ++
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 61ec29b..1af3996 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -89,6 +89,7 @@ void init_rt_rq(struct rt_rq *rt_rq)
 	rt_rq->rt_throttled = 0;
 	rt_rq->rt_runtime = 0;
 	raw_spin_lock_init(&rt_rq->rt_runtime_lock);
+	rt_rq->tg = &root_task_group;
 #endif
 }
 
@@ -482,9 +483,6 @@ static inline bool rt_task_fits_capacity(struct task_struct *p, int cpu)
 
 static inline u64 sched_rt_runtime(struct rt_rq *rt_rq)
 {
-	if (!rt_rq->tg)
-		return RUNTIME_INF;
-
 	return rt_rq->rt_runtime;
 }
 
@@ -1154,8 +1152,7 @@ inc_rt_group(struct sched_rt_entity *rt_se, struct rt_rq *rt_rq)
 	if (rt_se_boosted(rt_se))
 		rt_rq->rt_nr_boosted++;
 
-	if (rt_rq->tg)
-		start_rt_bandwidth(&rt_rq->tg->rt_bandwidth);
+	start_rt_bandwidth(&rt_rq->tg->rt_bandwidth);
 }
 
 static void
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 47972f3..c006348 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -821,6 +821,8 @@ struct rt_rq {
 	unsigned int		rt_nr_boosted;
 
 	struct rq		*rq;
+#endif
+#ifdef CONFIG_CGROUP_SCHED
 	struct task_group	*tg;
 #endif
 };