[PATCH 4/5] sched_ext: Factor out scx_cpuperf_set()

Factor the cpuperf target write out of scx_bpf_cpuperf_set() into
scx_cpuperf_set() which takes the acting sched and returns 0 or -errno, and
flatten the nested validation into early returns. No functional change.
Prep for gating the write behind a cap and reporting the outcome from the
cid-form kfunc.

Signed-off-by: Tejun Heo <[email protected]>
---
 kernel/sched/ext/ext.c | 77 ++++++++++++++++++++++++------------------
 1 file changed, 44 insertions(+), 33 deletions(-)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 5d02bb99c09d..366245daab68 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -9796,49 +9796,60 @@ __bpf_kfunc u32 scx_bpf_cidperf_cur(s32 cid, const struct bpf_prog_aux *aux)
  * use. Consult hardware and cpufreq documentation for more information. The
  * current performance level can be monitored using scx_bpf_cpuperf_cur().
  */
-__bpf_kfunc void scx_bpf_cpuperf_set(s32 cpu, u32 perf, const struct bpf_prog_aux *aux)
+static s32 scx_cpuperf_set(struct scx_sched *sch, s32 cpu, u32 perf)
 {
-	struct scx_sched *sch;
-
-	guard(rcu)();
-
-	sch = scx_prog_sched(aux);
-	if (unlikely(!sch))
-		return;
+	struct rq *rq, *locked_rq;
+	struct rq_flags rf;
 
 	if (unlikely(perf > SCX_CPUPERF_ONE)) {
 		scx_error(sch, "Invalid cpuperf target %u for CPU %d", perf, cpu);
-		return;
+		return -EINVAL;
 	}
 
-	if (scx_cpu_valid(sch, cpu, NULL)) {
-		struct rq *rq = cpu_rq(cpu), *locked_rq = scx_locked_rq();
-		struct rq_flags rf;
-
-		/*
-		 * When called with an rq lock held, restrict the operation
-		 * to the corresponding CPU to prevent ABBA deadlocks.
-		 */
-		if (locked_rq && rq != locked_rq) {
-			scx_error(sch, "Invalid target CPU %d", cpu);
-			return;
-		}
+	if (!scx_cpu_valid(sch, cpu, NULL))
+		return -EINVAL;
 
-		/*
-		 * If no rq lock is held, allow to operate on any CPU by
-		 * acquiring the corresponding rq lock.
-		 */
-		if (!locked_rq) {
-			rq_lock_irqsave(rq, &rf);
-			update_rq_clock(rq);
-		}
+	rq = cpu_rq(cpu);
+	locked_rq = scx_locked_rq();
 
-		rq->scx.cpuperf_target = perf;
-		cpufreq_update_util(rq, 0);
+	/*
+	 * When called with an rq lock held, restrict the operation to the
+	 * corresponding CPU to prevent ABBA deadlocks.
+	 */
+	if (locked_rq && rq != locked_rq) {
+		scx_error(sch, "Invalid target CPU %d", cpu);
+		return -EINVAL;
+	}
 
-		if (!locked_rq)
-			rq_unlock_irqrestore(rq, &rf);
+	/*
+	 * If no rq lock is held, allow to operate on any CPU by acquiring
+	 * the corresponding rq lock.
+	 */
+	if (!locked_rq) {
+		rq_lock_irqsave(rq, &rf);
+		update_rq_clock(rq);
 	}
+
+	rq->scx.cpuperf_target = perf;
+	cpufreq_update_util(rq, 0);
+
+	if (!locked_rq)
+		rq_unlock_irqrestore(rq, &rf);
+
+	return 0;
+}
+
+__bpf_kfunc void scx_bpf_cpuperf_set(s32 cpu, u32 perf, const struct bpf_prog_aux *aux)
+{
+	struct scx_sched *sch;
+
+	guard(rcu)();
+
+	sch = scx_prog_sched(aux);
+	if (unlikely(!sch))
+		return;
+
+	scx_cpuperf_set(sch, cpu, perf);
 }
 
 /**
-- 
2.55.0