4 files changed, 19 insertions, 6 deletions
diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 2da3a5f44b4a..151befdc9602 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -4792,7 +4792,7 @@ SCX_ATTR(events);
 
 #ifdef CONFIG_EXT_SUB_SCHED
 static const char *scx_cap_names[__SCX_NR_CAPS] = {
-	[__SCX_CAP_DUMMY]	= "dummy",
+	[__SCX_CAP_ENQ_IMMED]	= "enq_immed",
 };
 
 static ssize_t scx_attr_caps_show(struct kobject *kobj,
diff --git a/kernel/sched/ext/internal.h b/kernel/sched/ext/internal.h
index 079ee941b343..e735812e77a5 100644
--- a/kernel/sched/ext/internal.h
+++ b/kernel/sched/ext/internal.h
@@ -1270,17 +1270,22 @@ struct scx_sched_pnode {
  * topology-aligned and likely to serve as the locality unit when cids are
  * allocated to schedulers, so per-shard lock granularity scales naturally with
  * the allocation pattern.
+ *
+ * ENQ_IMMED  insert an IMMED task onto the cid's local DSQ
  */
 enum scx_cap_flags {
-	__SCX_CAP_DUMMY			= 0,
+	__SCX_CAP_ENQ_IMMED		= 0,
 
 	__SCX_NR_CAPS,
 	__SCX_CAP_ALL			= BIT_U64(__SCX_NR_CAPS) - 1,
 
-	SCX_CAP_DUMMY			= BIT_U64(__SCX_CAP_DUMMY),
+	SCX_CAP_ENQ_IMMED		= BIT_U64(__SCX_CAP_ENQ_IMMED),
+
+	/* alias for minimal cap to make any use of a cpu */
+	SCX_CAP_BASE			= SCX_CAP_ENQ_IMMED,
 
 	/* caps whose loss strands queued tasks, see scx_process_sync_ecaps() */
-	SCX_CAPS_REENQ_ON_LOSS		= 0,
+	SCX_CAPS_REENQ_ON_LOSS		= SCX_CAP_ENQ_IMMED,
 };
 
 #ifdef CONFIG_EXT_SUB_SCHED
diff --git a/kernel/sched/ext/sub.c b/kernel/sched/ext/sub.c
index bbd068bfd86c..11fda1d3828d 100644
--- a/kernel/sched/ext/sub.c
+++ b/kernel/sched/ext/sub.c
@@ -1279,6 +1279,14 @@ __bpf_kfunc bool scx_bpf_sub_dispatch(u64 cgroup_id, const struct bpf_prog_aux *
 		return false;
 	}
 
+	/*
+	 * Skip a child that does not effectively hold the base cap on this cpu:
+	 * its inserts would only be rejected. ecaps are synced at the top of
+	 * balance_one() before dispatch, so this reflects the in-effect state.
+	 */
+	if (scx_missing_caps(child, cpu_of(this_rq), SCX_CAP_BASE))
+		return false;
+
 	return scx_dispatch_sched(child, this_rq, this_rq->scx.sub_dispatch_prev,
 				  true);
 }
diff --git a/kernel/sched/ext/sub.h b/kernel/sched/ext/sub.h
index 3c22ae40349d..13e9dec56a6a 100644
--- a/kernel/sched/ext/sub.h
+++ b/kernel/sched/ext/sub.h
@@ -115,13 +115,13 @@ static inline u64 scx_caps_for_enq(u64 enq_flags)
 	/* a restored task must be put into the local DSQ regardless of caps */
 	if (enq_flags & SCX_ENQ_IGNORE_CAPS)
 		return 0;
-	return 0;
+	return SCX_CAP_ENQ_IMMED;
 }
 
 /* map queued @p to the SCX_CAP_* bit required to stay on its local DSQ */
 static inline u64 scx_caps_for_task(struct task_struct *p)
 {
-	return 0;
+	return SCX_CAP_ENQ_IMMED;
 }
 
 /* caps implied by holding @cap */