Re: [PATCH v3 3/3] sched_ext: Guarantee rq lock on scx_bpf_cpu_rq()

[Tejun Heo <tj@kernel.org>]

Hello,

On Tue, Aug 05, 2025 at 12:10:36PM +0100, Christian Loehle wrote:
> @@ -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();

So, this will break the existing scheduler binaries immediately, which I
don't think is a good way to go about it. Can you add a pr_warn_once() to
print deprecation warning and add e.g. scx_bpf_locked_cpu_rq() instead?

Thanks.

-- 
tejun