sched: Add RT_GROUP WARN checks for non-root task_groups

With CONFIG_RT_GROUP_SCHED but runtime disabling of RT_GROUPs we expect
the existence of the root task_group only and all rt_sched_entity'ies
should be queued on root's rt_rq.

If we get a non-root RT_GROUP something went wrong.

Signed-off-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20250310170442.504716-9-mkoutny@suse.com

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index b6119341f0e24716b7befcf2b3124bf2e2de7974..778911bebacbcb0c7065cc45e1d8f54a5a8fe126 100644 (file)
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -176,11 +176,14 @@ static inline struct task_struct *rt_task_of(struct sched_rt_entity *rt_se)
 
 static inline struct rq *rq_of_rt_rq(struct rt_rq *rt_rq)
 {
+       /* Cannot fold with non-CONFIG_RT_GROUP_SCHED version, layout */
+       WARN_ON(!rt_group_sched_enabled() && rt_rq->tg != &root_task_group);
        return rt_rq->rq;
 }
 
 static inline struct rt_rq *rt_rq_of_se(struct sched_rt_entity *rt_se)
 {
+       WARN_ON(!rt_group_sched_enabled() && rt_se->rt_rq->tg != &root_task_group);
        return rt_se->rt_rq;
 }
 
@@ -188,6 +191,7 @@ static inline struct rq *rq_of_rt_se(struct sched_rt_entity *rt_se)
 {
        struct rt_rq *rt_rq = rt_se->rt_rq;
 
+       WARN_ON(!rt_group_sched_enabled() && rt_rq->tg != &root_task_group);
        return rt_rq->rq;
 }
 
@@ -504,8 +508,10 @@ typedef struct task_group *rt_rq_iter_t;
 
 static inline struct task_group *next_task_group(struct task_group *tg)
 {
-       if (!rt_group_sched_enabled())
+       if (!rt_group_sched_enabled()) {
+               WARN_ON(tg != &root_task_group);
                return NULL;
+       }
 
        do {
                tg = list_entry_rcu(tg->list.next,
@@ -2607,8 +2613,9 @@ static int task_is_throttled_rt(struct task_struct *p, int cpu)
 {
        struct rt_rq *rt_rq;
 
-#ifdef CONFIG_RT_GROUP_SCHED
+#ifdef CONFIG_RT_GROUP_SCHED // XXX maybe add task_rt_rq(), see also sched_rt_period_rt_rq
        rt_rq = task_group(p)->rt_rq[cpu];
+       WARN_ON(!rt_group_sched_enabled() && rt_rq->tg != &root_task_group);
 #else
        rt_rq = &cpu_rq(cpu)->rt;
 #endif
@@ -2718,6 +2725,9 @@ static int tg_rt_schedulable(struct task_group *tg, void *data)
            tg->rt_bandwidth.rt_runtime && tg_has_rt_tasks(tg))
                return -EBUSY;
 
+       if (WARN_ON(!rt_group_sched_enabled() && tg != &root_task_group))
+               return -EBUSY;
+
        total = to_ratio(period, runtime);
 
        /*