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[2a02:3100:a16a:7801:fd8c:4b37:36b4:e53a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49cdce089c2sm64755395e9.2.2026.09.01.05.26.52 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 01 Sep 2026 05:26:53 -0700 (PDT) From: Karl Mehltretter To: stable@vger.kernel.org Cc: Waiman Long , Ridong Chen , Tejun Heo , Johannes Weiner , =?UTF-8?q?Michal=20Koutn=C3=BD?= , Guopeng Zhang , Chen Ridong , Greg Kroah-Hartman , Sasha Levin , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Karl Mehltretter Subject: [PATCH 6.6.y] cgroup/cpuset: Fix misplaced DL migration reset Date: Tue, 1 Sep 2026 14:26:42 +0200 Message-Id: <20260901122642.11571-1-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Mainline commit 4a39eda5fdd8 ("cgroup/cpuset: Reset DL migration state on can_attach() failure") puts the common error cleanup in cpuset_can_attach(). The 6.6.y backport instead placed that hunk at cpuset_can_fork()'s similarly named out_unlock label, while removing cpuset_can_attach()'s two existing targeted resets. If cpuset_can_attach() fails after accounting a SCHED_DEADLINE task, cgroup_migrate_execute() does not call cpuset_cancel_attach() for the failing subsystem. The temporary migration fields remain set, and a later successful migration can consume the stale state and corrupt deadline-task and pending-bandwidth accounting. Move the reset to cpuset_can_attach()'s common error exit. It is not needed in cpuset_can_fork(), which never accumulates migration DL state. Fixes: 14897ef9341c ("cgroup/cpuset: Reset DL migration state on can_attach() failure") Assisted-by: LLM Signed-off-by: Karl Mehltretter --- Applies to Linux 6.6.155 and 6.6.156-rc1. A controlled QEMU A/B on 6.6.155 forced an attach error after accounting a real SCHED_DEADLINE task. The affected kernel returned with nr_migrate_dl_tasks=1 and sum_migrate_dl_bw=104857; both fields were zero with this patch. The equivalent 6.1.y correction is submitted separately. kernel/cgroup/cpuset.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index f9c7178f51ada..bb413045d1744 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -2630,6 +2630,8 @@ static int cpuset_can_attach(struct cgroup_taskset *tset) */ cs->attach_in_progress++; out_unlock: + if (ret) + reset_migrate_dl_data(cs); mutex_unlock(&cpuset_mutex); return ret; } @@ -3462,8 +3464,6 @@ static int cpuset_can_fork(struct task_struct *task, struct css_set *cset) cs->attach_in_progress++; out_unlock: - if (ret) - reset_migrate_dl_data(cs); mutex_unlock(&cpuset_mutex); return ret; } -- 2.53.0