[PATCH 1/2] sched_ext: Factor out drain_offline_rq()

[Tejun Heo <tj@kernel.org>]

Factor drain_offline_rq() out of rq_offline_scx() so that the drain can move
to handle_hotplug() in the following patch, which removes the rq_online and
rq_offline hooks. The drain is the rescue flush and the re-enqueue of an
offline cpu's tasks onto its local DSQ. No functional change.

Cc: stable@vger.kernel.org # v6.12+
Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/sched/ext/ext.c | 35 ++++++++++++++++++++---------------
 kernel/sched/sched.h   |  2 +-
 2 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index cd923f9f1f2a..c75df42d8c6f 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -2428,7 +2428,7 @@ static void set_task_runnable(struct rq *rq, struct task_struct *p)
 	}
 
 	/*
-	 * list_add_tail() must be used. scx_bypass() and rq_offline_scx()
+	 * list_add_tail() must be used. scx_bypass() and drain_offline_rq()
 	 * depend on tasks being appended to the runnable_list.
 	 */
 	list_add_tail(&p->scx.runnable_node, &rq->scx.runnable_list);
@@ -4304,6 +4304,24 @@ static void set_cpus_allowed_scx(struct task_struct *p,
 		scx_call_op_set_cpumask(sch, task_rq(p), p, (struct cpumask *)p->cpus_ptr);
 }
 
+static void drain_offline_rq(struct rq *rq)
+{
+	struct task_struct *p, *n;
+
+	scx_rescue_flush(rq);
+
+	/*
+	 * An offline CPU no longer calls ops.dispatch(). Re-enqueue its tasks
+	 * onto the local DSQ so that they run here and balance_push() moves
+	 * them off.
+	 */
+	list_for_each_entry_safe_reverse(p, n, &rq->scx.runnable_list, scx.runnable_node) {
+		if (p->scx.dsq == &rq->scx.local_dsq)
+			continue;
+		guard(sched_change)(p, DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK);
+	}
+}
+
 static void handle_hotplug(struct rq *rq, bool online)
 {
 	struct scx_sched *sch = scx_root_protected();
@@ -4391,26 +4409,13 @@ static void rq_online_scx(struct rq *rq)
 
 static void rq_offline_scx(struct rq *rq)
 {
-	struct task_struct *p, *n;
-
 	rq->scx.flags &= ~SCX_RQ_ONLINE;
 
 	/* sched domain rebuilds call rq_offline with the CPU staying alive */
 	if (cpu_active(cpu_of(rq)))
 		return;
 
-	scx_rescue_flush(rq);
-
-	/*
-	 * An offline CPU no longer calls ops.dispatch(). Re-enqueue its tasks
-	 * onto the local DSQ so that they run here and balance_push() moves
-	 * them off.
-	 */
-	list_for_each_entry_safe_reverse(p, n, &rq->scx.runnable_list, scx.runnable_node) {
-		if (p->scx.dsq == &rq->scx.local_dsq)
-			continue;
-		guard(sched_change)(p, DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK);
-	}
+	drain_offline_rq(rq);
 }
 
 static bool check_rq_for_timeouts(struct rq *rq)
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 6c7c5633524a..2cc16c01b168 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -4294,7 +4294,7 @@ extern void balance_callbacks(struct rq *rq, struct balance_callback *head);
  * Typically this must be called while holding task_rq_lock, since most/all
  * properties are serialized under those locks. There are currently two
  * exceptions to this rule in sched/ext which only hold rq->lock: scx_bypass()
- * and rq_offline_scx().
+ * and drain_offline_rq().
  */
 
 /*
-- 
2.56.0