[PATCH 6.18 120/122] sched_ext: Dont kick CPUs running higher classes

Greg Kroah-Hartman
2026-02-04T15:34:40Z

From: Tejun Heo <tj@kernel.org>

commit a9c1fbbd6dadbaa38c157a07d5d11005460b86b9 upstream.

When a sched_ext scheduler tries to kick a CPU, the CPU may be running a
higher class task. sched_ext has no control over such CPUs. A sched_ext
scheduler couldn't have expected to get access to the CPU after kicking it
anyway. Skip kicking when the target CPU is running a higher class.

Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/sched/ext.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -5164,18 +5164,23 @@ static bool kick_one_cpu(s32 cpu, struct
{
struct rq *rq = cpu_rq(cpu);
struct scx_rq *this_scx = &this_rq->scx;
+ const struct sched_class *cur_class;
bool should_wait = false;
unsigned long flags;

raw_spin_rq_lock_irqsave(rq, flags);
+ cur_class = rq->curr->sched_class;

/*
* During CPU hotplug, a CPU may depend on kicking itself to make
- * forward progress. Allow kicking self regardless of online state.
+ * forward progress. Allow kicking self regardless of online state. If
+ * @cpu is running a higher class task, we have no control over @cpu.
+ * Skip kicking.
*/
- if (cpu_online(cpu) || cpu == cpu_of(this_rq)) {
+ if ((cpu_online(cpu) || cpu == cpu_of(this_rq)) &&
+ !sched_class_above(cur_class, &ext_sched_class)) {
if (cpumask_test_cpu(cpu, this_scx->cpus_to_preempt)) {
- if (rq->curr->sched_class == &ext_sched_class)
+ if (cur_class == &ext_sched_class)
rq->curr->scx.slice = 0;
cpumask_clear_cpu(cpu, this_scx->cpus_to_preempt);
}