linux-kernel - [PATCH v3 3/3] sched_ext: Guarantee rq lock on scx_bpf_cpu

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Message-Id: <20250805111036.130121-4-christian.loehle@arm.com>
Date: Tue,  5 Aug 2025 12:10:36 +0100
From: Christian Loehle <christian.loehle@....com>
To: tj@...nel.org,
	arighi@...dia.com,
	void@...ifault.com
Cc: linux-kernel@...r.kernel.org,
	sched-ext@...ts.linux.dev,
	changwoo@...lia.com,
	hodgesd@...a.com,
	mingo@...hat.com,
	peterz@...radead.org,
	Christian Loehle <christian.loehle@....com>
Subject: [PATCH v3 3/3] sched_ext: Guarantee rq lock on scx_bpf_cpu_rq()

Most fields in scx_bpf_cpu_rq() assume that its rq_lock is held.
Furthermore they become meaningless without rq lock, too.
Only return scx_bpf_cpu_rq() if we hold rq lock of that rq.

All upstream scx schedulers can be converted into the new
scx_bpf_task_acquire_remote_curr() instead.

Signed-off-by: Christian Loehle <christian.loehle@....com>
---
 kernel/sched/ext.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 3e2fa0b1eb57..a66cf654f33e 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -7420,10 +7420,20 @@ __bpf_kfunc s32 scx_bpf_task_cpu(const struct task_struct *p)
  */
 __bpf_kfunc struct rq *scx_bpf_cpu_rq(s32 cpu)
 {
+	struct rq *rq;
+
 	if (!kf_cpu_valid(cpu, NULL))
 		return NULL;
 
-	return cpu_rq(cpu);
+	preempt_disable();
+	rq = cpu_rq(cpu);
+	if (rq != scx_locked_rq()) {
+		scx_kf_error("Accessing not locked rq %d", cpu);
+		rq = NULL;
+	}
+	preempt_enable();
+
+	return rq;
 }
 
 /**
-- 
2.34.1