linux-kernel - [RFC PATCH 8/9] sched: Add RT_GROUP WARN checks for non-root task

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Message-ID: <20241216201305.19761-9-mkoutny@suse.com>
Date: Mon, 16 Dec 2024 21:13:04 +0100
From: Michal Koutný <mkoutny@...e.com>
To: cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Frederic Weisbecker <fweisbecker@...e.com>
Subject: [RFC PATCH 8/9] 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@...e.com>
---
 kernel/sched/rt.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index db7cdc82003bd..deacd46e27823 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -178,11 +178,14 @@ 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;
 }
 
@@ -190,6 +193,7 @@ 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;
 }
 
@@ -506,8 +510,10 @@ 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,
@@ -2609,8 +2615,9 @@ 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
@@ -2720,6 +2727,9 @@ 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);
 
 	/*
-- 
2.47.1