[PATCH 6.19 167/311] sched_ext: Fix inconsistent NUMA node lookup in scx_select_cpu_dfl()

Greg Kroah-Hartman
2026-04-08T18:57:01Z

From: Cheng-Yang Chou <yphbchou0911@gmail.com>

commit db08b1940f4beb25460b4a4e9da3446454f2e8fe upstream.

In the WAKE_SYNC path of scx_select_cpu_dfl(), waker_node was computed
with cpu_to_node(), while node (for prev_cpu) was computed with
scx_cpu_node_if_enabled(). When scx_builtin_idle_per_node is disabled,
idle_cpumask(waker_node) is called with a real node ID even though
per-node idle tracking is disabled, resulting in undefined behavior.

Fix by using scx_cpu_node_if_enabled() for waker_node as well, ensuring
both variables are computed consistently.

Fixes: 48849271e6611 ("sched_ext: idle: Per-node idle cpumasks")
Cc: stable@vger.kernel.org # v6.15+
Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/sched/ext_idle.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -543,7 +543,7 @@ s32 scx_select_cpu_dfl(struct task_struc
* piled up on it even if there is an idle core elsewhere on
* the system.
*/
- waker_node = cpu_to_node(cpu);
+ waker_node = scx_cpu_node_if_enabled(cpu);
if (!(current->flags & PF_EXITING) &&
cpu_rq(cpu)->scx.local_dsq.nr == 0 &&
(!(flags & SCX_PICK_IDLE_IN_NODE) || (waker_node == node)) &&