[PATCH 06/17] sched_ext: Make scx_enable() take scx_enable_cmd

Tejun Heo
2026-04-24T17:27:29Z

Pass struct scx_enable_cmd to scx_enable() rather than unpacking @ops
at every call site and re-packing into a fresh cmd inside. bpf_scx_reg()
now builds the cmd on its stack and hands it in; scx_enable() just
wires up the kthread work and waits.

Relocate struct scx_enable_cmd above scx_alloc_and_add_sched() so
upcoming patches that also want the cmd can see it.

No behavior change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
---
kernel/sched/ext.c | 46 +++++++++++++++++++++++-----------------------
1 file changed, 23 insertions(+), 23 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index ad255268f207..cd4c235e0c82 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -6425,6 +6425,19 @@ static struct scx_sched_pnode *alloc_pnode(struct scx_sched *sch, int node)
return pnode;
}

+/*
+ * scx_enable() is offloaded to a dedicated system-wide RT kthread to avoid
+ * starvation. During the READY -> ENABLED task switching loop, the calling
+ * thread's sched_class gets switched from fair to ext. As fair has higher
+ * priority than ext, the calling thread can be indefinitely starved under
+ * fair-class saturation, leading to a system hang.
+ */
+struct scx_enable_cmd {
+ struct kthread_work work;
+ struct sched_ext_ops *ops;
+ int ret;
+};
+
/*
* Allocate and initialize a new scx_sched. @cgrp's reference is always
* consumed whether the function succeeds or fails.
@@ -6656,19 +6669,6 @@ static int validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops)
return 0;
}

-/*
- * scx_enable() is offloaded to a dedicated system-wide RT kthread to avoid
- * starvation. During the READY -> ENABLED task switching loop, the calling
- * thread's sched_class gets switched from fair to ext. As fair has higher
- * priority than ext, the calling thread can be indefinitely starved under
- * fair-class saturation, leading to a system hang.
- */
-struct scx_enable_cmd {
- struct kthread_work work;
- struct sched_ext_ops *ops;
- int ret;
-};
-
static void scx_root_enable_workfn(struct kthread_work *work)
{
struct scx_enable_cmd *cmd = container_of(work, struct scx_enable_cmd, work);
@@ -7244,11 +7244,10 @@ static s32 __init scx_cgroup_lifetime_notifier_init(void)
core_initcall(scx_cgroup_lifetime_notifier_init);
#endif /* CONFIG_EXT_SUB_SCHED */

-static s32 scx_enable(struct sched_ext_ops *ops, struct bpf_link *link)
+static s32 scx_enable(struct scx_enable_cmd *cmd, struct bpf_link *link)
{
static struct kthread_worker *helper;
static DEFINE_MUTEX(helper_mutex);
- struct scx_enable_cmd cmd;

if (!cpumask_equal(housekeeping_cpumask(HK_TYPE_DOMAIN),
cpu_possible_mask)) {
@@ -7272,16 +7271,15 @@ static s32 scx_enable(struct sched_ext_ops *ops, struct bpf_link *link)
}

#ifdef CONFIG_EXT_SUB_SCHED
- if (ops->sub_cgroup_id > 1)
- kthread_init_work(&cmd.work, scx_sub_enable_workfn);
+ if (cmd->ops->sub_cgroup_id > 1)
+ kthread_init_work(&cmd->work, scx_sub_enable_workfn);
else
#endif /* CONFIG_EXT_SUB_SCHED */
- kthread_init_work(&cmd.work, scx_root_enable_workfn);
- cmd.ops = ops;
+ kthread_init_work(&cmd->work, scx_root_enable_workfn);

- kthread_queue_work(READ_ONCE(helper), &cmd.work);
- kthread_flush_work(&cmd.work);
- return cmd.ret;
+ kthread_queue_work(READ_ONCE(helper), &cmd->work);
+ kthread_flush_work(&cmd->work);
+ return cmd->ret;
}

@@ -7453,7 +7451,9 @@ static int bpf_scx_check_member(const struct btf_type *t,

static int bpf_scx_reg(void *kdata, struct bpf_link *link)
{
- return scx_enable(kdata, link);
+ struct scx_enable_cmd cmd = { .ops = kdata };
+
+ return scx_enable(&cmd, link);
}

static void bpf_scx_unreg(void *kdata, struct bpf_link *link)
--
2.53.0