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Tue, 16 Sep 2025 01:11:50 +0000 From: Aaron Tomlin To: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org Cc: dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, shashank.mahadasyam@sony.com, longman@redhat.com, mkoutny@suse.com, tj@kernel.org, atomlin@atomlin.com, linux-kernel@vger.kernel.org Subject: [PATCH] sched/core: Report failed rt migrations to non-root cgroup without rt bandwidth under RT_GROUP_SCHED Date: Mon, 15 Sep 2025 21:11:46 -0400 Message-ID: <20250916011146.4129696-1-atomlin@atomlin.com> X-Mailer: git-send-email 2.49.0 Content-Transfer-Encoding: quoted-printable X-ClientProxiedBy: BLAPR03CA0079.namprd03.prod.outlook.com (2603:10b6:208:329::24) To CWLP123MB3523.GBRP123.PROD.OUTLOOK.COM (2603:10a6:400:70::10) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CWLP123MB3523:EE_|LO6P123MB6721:EE_ X-MS-Office365-Filtering-Correlation-Id: a4ecbca8-eb18-462e-7d7b-08ddf4be03dc X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|1800799024|7416014|376014|366016; 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charset="utf-8" Following on from commit c7461cca91 ("cgroup, docs: Be explicit about independence of RT_GROUP_SCHED and non-cpu controllers"), this patch introduces an explicit error message that informs the user why the task migration failed. Now user-mode has a clear and actionable reason for the failure, greatly assisting with debugging. Signed-off-by: Aaron Tomlin --- kernel/sched/core.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 62b3416f5e43..b9d7689d21e4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -9185,8 +9185,18 @@ static int cpu_cgroup_can_attach(struct cgroup_tasks= et *tset) goto scx_check; =20 cgroup_taskset_for_each(task, css, tset) { - if (!sched_rt_can_attach(css_tg(css), task)) + struct task_group *tg =3D css_tg(css); + + if (!sched_rt_can_attach(tg, task)) { + if (tg !=3D &root_task_group) { + pr_err_ratelimited("cgroup: cannot attach " + "cpu controller. Task " + "%s:%d is not in the root " + "cgroup.", task->comm, + task_pid_nr(task)); + } return -EINVAL; + } } scx_check: #endif /* CONFIG_RT_GROUP_SCHED */ --=20 2.49.0