linux-kernel - [PATCH] sched/core: Report failed rt migrations to non-root cgroup without rt bandwidth under RT_GROUP

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <20250916011146.4129696-1-atomlin@atomlin.com>
Date: Mon, 15 Sep 2025 21:11:46 -0400
From: Aaron Tomlin <atomlin@...mlin.com>
To: mingo@...hat.com,
	peterz@...radead.org,
	juri.lelli@...hat.com,
	vincent.guittot@...aro.org
Cc: dietmar.eggemann@....com,
	rostedt@...dmis.org,
	bsegall@...gle.com,
	mgorman@...e.de,
	vschneid@...hat.com,
	shashank.mahadasyam@...y.com,
	longman@...hat.com,
	mkoutny@...e.com,
	tj@...nel.org,
	atomlin@...mlin.com,
	linux-kernel@...r.kernel.org
Subject: [PATCH] sched/core: Report failed rt migrations to non-root cgroup without rt bandwidth under RT_GROUP_SCHED

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 <atomlin@...mlin.com>
---
 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_taskset *tset)
 		goto scx_check;
 
 	cgroup_taskset_for_each(task, css, tset) {
-		if (!sched_rt_can_attach(css_tg(css), task))
+		struct task_group *tg = css_tg(css);
+
+		if (!sched_rt_can_attach(tg, task)) {
+			if (tg != &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 */
-- 
2.49.0