[PATCH 1/7] sched_ext: Separate out scx_kick_cpu() and add @sch to it

[Tejun Heo <tj@kernel.org>]

In preparation for multiple scheduler support, separate out scx_kick_cpu()
from scx_bpf_kick_cpu() and add the @sch parameter to it. scx_bpf_kick_cpu()
now acquires an RCU read lock, reads $scx_root, and calls scx_kick_cpu()
with it if non-NULL. The passed in @sch parameter is not used yet.

Internal uses of scx_bpf_kick_cpu() are converted to scx_kick_cpu(). Where
$sch is available, it's used. In the pick_task_scx() path where no
associated scheduler can be identified, $scx_root is used directly. Note
that $scx_root cannot be NULL in this case.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/sched/ext.c | 43 +++++++++++++++++++++++++++----------------
 1 file changed, 27 insertions(+), 16 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index d131e98156ac..560ac5a575bd 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -136,7 +136,7 @@ static struct kset *scx_kset;
 #include <trace/events/sched_ext.h>
 
 static void process_ddsp_deferred_locals(struct rq *rq);
-static void scx_bpf_kick_cpu(s32 cpu, u64 flags);
+static void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags);
 static void scx_vexit(struct scx_sched *sch, enum scx_exit_kind kind,
 		      s64 exit_code, const char *fmt, va_list args);
 
@@ -2125,10 +2125,10 @@ static int balance_one(struct rq *rq, struct task_struct *prev)
 		 * balance(), we want to complete this scheduling cycle and then
 		 * start a new one. IOW, we want to call resched_curr() on the
 		 * next, most likely idle, task, not the current one. Use
-		 * scx_bpf_kick_cpu() for deferred kicking.
+		 * scx_kick_cpu() for deferred kicking.
 		 */
 		if (unlikely(!--nr_loops)) {
-			scx_bpf_kick_cpu(cpu_of(rq), 0);
+			scx_kick_cpu(sch, cpu_of(rq), 0);
 			break;
 		}
 	} while (dspc->nr_tasks);
@@ -2417,7 +2417,8 @@ static struct task_struct *pick_task_scx(struct rq *rq)
 		p = first_local_task(rq);
 		if (!p) {
 			if (kick_idle)
-				scx_bpf_kick_cpu(cpu_of(rq), SCX_KICK_IDLE);
+				scx_kick_cpu(rcu_dereference_sched(scx_root),
+					     cpu_of(rq), SCX_KICK_IDLE);
 			return NULL;
 		}
 
@@ -3721,7 +3722,7 @@ static void scx_clear_softlockup(void)
  *
  * - pick_next_task() suppresses zero slice warning.
  *
- * - scx_bpf_kick_cpu() is disabled to avoid irq_work malfunction during PM
+ * - scx_kick_cpu() is disabled to avoid irq_work malfunction during PM
  *   operations.
  *
  * - scx_prio_less() reverts to the default core_sched_at order.
@@ -5809,17 +5810,7 @@ static const struct btf_kfunc_id_set scx_kfunc_set_unlocked = {
 
 __bpf_kfunc_start_defs();
 
-/**
- * scx_bpf_kick_cpu - Trigger reschedule on a CPU
- * @cpu: cpu to kick
- * @flags: %SCX_KICK_* flags
- *
- * Kick @cpu into rescheduling. This can be used to wake up an idle CPU or
- * trigger rescheduling on a busy CPU. This can be called from any online
- * scx_ops operation and the actual kicking is performed asynchronously through
- * an irq work.
- */
-__bpf_kfunc void scx_bpf_kick_cpu(s32 cpu, u64 flags)
+static void scx_kick_cpu(struct scx_sched *sch, s32 cpu, u64 flags)
 {
 	struct rq *this_rq;
 	unsigned long irq_flags;
@@ -5872,6 +5863,26 @@ __bpf_kfunc void scx_bpf_kick_cpu(s32 cpu, u64 flags)
 	local_irq_restore(irq_flags);
 }
 
+/**
+ * scx_bpf_kick_cpu - Trigger reschedule on a CPU
+ * @cpu: cpu to kick
+ * @flags: %SCX_KICK_* flags
+ *
+ * Kick @cpu into rescheduling. This can be used to wake up an idle CPU or
+ * trigger rescheduling on a busy CPU. This can be called from any online
+ * scx_ops operation and the actual kicking is performed asynchronously through
+ * an irq work.
+ */
+__bpf_kfunc void scx_bpf_kick_cpu(s32 cpu, u64 flags)
+{
+	struct scx_sched *sch;
+
+	guard(rcu)();
+	sch = rcu_dereference(scx_root);
+	if (likely(sch))
+		scx_kick_cpu(sch, cpu, flags);
+}
+
 /**
  * scx_bpf_dsq_nr_queued - Return the number of queued tasks
  * @dsq_id: id of the DSQ
-- 
2.51.0