linux-kernel - [PATCH 1/3] sched/rt: Skip group schedulable check with rt_group

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Message-Id: <20260119-sched-rert_groups-v1-1-80c1e5269910@suse.com>
Date: Mon, 19 Jan 2026 18:41:19 +0100
From: Michal Koutný <mkoutny@...e.com>
To: 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>
Cc: linux-kernel@...r.kernel.org, 
 Michal Koutný <mkoutny@...e.com>
Subject: [PATCH 1/3] sched/rt: Skip group schedulable check with
 rt_group_sched=0

The warning from the commit 87f1fb77d87a6 ("sched: Add RT_GROUP WARN
checks for non-root task_groups") is wrong -- it assumes that only
task_groups with rt_rq are traversed, however, the schedulability check
would iterate all task_groups even when rt_group_sched=0 is disabled at
boot time but some non-root task_groups exist.

The schedulability check is supposed to validate:
  a) that children don't overcommit its parent,
  b) no RT task group overcommits global RT limit.
but with rt_group_sched=0 there is no (non-trivial) hierarchy of RT groups,
therefore skip the validation altogether.

This fix is immaterial with CONFIG_RT_GROUP_SCHED=n.

Fixes: 87f1fb77d87a6 ("sched: Add RT_GROUP WARN checks for non-root task_groups")
Signed-off-by: Michal Koutný <mkoutny@...e.com>
---
 kernel/sched/rt.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index f1867fe8e5c53..2dfdf2d9471be 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -2668,9 +2668,6 @@ 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);
 
 	/*
@@ -2814,6 +2811,8 @@ long sched_group_rt_period(struct task_group *tg)
 static int sched_rt_global_constraints(void)
 {
 	int ret = 0;
+	if (!rt_group_sched_enabled())
+		return ret;
 
 	mutex_lock(&rt_constraints_mutex);
 	ret = __rt_schedulable(NULL, 0, 0);

-- 
2.52.0