sched_ext: Require cid-form struct_ops for sub-sched support

Sub-scheduler support is tied to the cid-form struct_ops: sub_attach /
sub_detach will communicate allocation via cmask, and the hierarchy assumes
all participants share a single topological cid space. A cpu-form root that
accepts sub-scheds would need cpu <-> cid translation on every cross-sched
interaction, defeating the purpose.

Enforce this at validate_ops():
- A sub-scheduler (scx_parent(sch) non-NULL) must be cid-form.
- A root that exposes sub_attach / sub_detach must be cid-form.

scx_qmap, which is currently the only scheduler demoing sub-sched support,
was converted to cid-form in the preceding patch, so this doesn't cause
breakage.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
Reviewed-by: Changwoo Min <changwoo@igalia.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 65a00c9796915d773778ecabae6e128a9a8b66ff..f3a585e32db36bece0d8fdd5987ca728e09795ad 100644 (file)
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -6869,6 +6869,23 @@ static int validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops)
        if (!sch->is_cid_type && (ops->cpu_acquire || ops->cpu_release))
                pr_warn("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n");
 
+       /*
+        * Sub-scheduler support is tied to the cid-form struct_ops. A sub-sched
+        * attaches through a cid-form-only interface (sub_attach/sub_detach),
+        * and a root that accepts sub-scheds must expose cid-form state to
+        * them. Reject cpu-form schedulers on either side.
+        */
+       if (!sch->is_cid_type) {
+               if (scx_parent(sch)) {
+                       scx_error(sch, "sub-sched requires cid-form struct_ops");
+                       return -EINVAL;
+               }
+               if (ops->sub_attach || ops->sub_detach) {
+                       scx_error(sch, "sub_attach/sub_detach requires cid-form struct_ops");
+                       return -EINVAL;
+               }
+       }
+
        return 0;
 }