[PATCH 3/4] sched_ext: Gate sub_dispatch_prev with CONFIG_EXT_SUB_SCHED

[Tejun Heo <tj@kernel.org>]

rq->scx.sub_dispatch_prev is sub-sched-only but was left unconditional. Move
it into the CONFIG_EXT_SUB_SCHED block next to ecaps_to_sync and gate its
updates.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/sched/ext/internal.h | 19 +++++++++++--------
 kernel/sched/sched.h        |  3 +--
 2 files changed, 12 insertions(+), 10 deletions(-)

diff --git a/kernel/sched/ext/internal.h b/kernel/sched/ext/internal.h
index 88b2a9b5d3ab..8c940be9278d 100644
--- a/kernel/sched/ext/internal.h
+++ b/kernel/sched/ext/internal.h
@@ -2352,16 +2352,19 @@ scx_dispatch_sched(struct scx_sched *sch, struct rq *rq,
 	do {
 		dspc->nr_tasks = 0;
 
-		if (nested) {
-			SCX_CALL_OP(sch, dispatch, rq, scx_cpu_arg(cpu),
-				    prev_on_sch ? prev : NULL);
-		} else {
-			/* stash @prev so that nested invocations can access it */
+#ifdef CONFIG_EXT_SUB_SCHED
+		/* stash @prev so that nested invocations can access it */
+		if (!nested)
 			rq->scx.sub_dispatch_prev = prev;
-			SCX_CALL_OP(sch, dispatch, rq, scx_cpu_arg(cpu),
-				    prev_on_sch ? prev : NULL);
+#endif
+
+		SCX_CALL_OP(sch, dispatch, rq, scx_cpu_arg(cpu),
+			    prev_on_sch ? prev : NULL);
+
+#ifdef CONFIG_EXT_SUB_SCHED
+		if (!nested)
 			rq->scx.sub_dispatch_prev = NULL;
-		}
+#endif
 
 		scx_flush_dispatch_buf(sch, rq);
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 54cff94556c0..64d79e9efc3d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -814,6 +814,7 @@ struct scx_rq {
 	u64			clock;			/* current per-rq clock -- see scx_bpf_now() */
 #ifdef CONFIG_EXT_SUB_SCHED
 	struct llist_head	ecaps_to_sync;		/* pending ecaps syncs */
+	struct task_struct	*sub_dispatch_prev;
 #endif
 	cpumask_var_t		cpus_to_sync;
 	bool			kick_sync_pending;
@@ -821,8 +822,6 @@ struct scx_rq {
 
 	struct list_head	sched_pcpus_to_kick;	/* see kick_cpus_irq_workfn() */
 
-	struct task_struct	*sub_dispatch_prev;
-
 	raw_spinlock_t		deferred_reenq_lock;
 	u64			deferred_reenq_locals_seq;
 	struct list_head	deferred_reenq_locals;	/* scheds requesting reenq of local DSQ */
-- 
2.55.0