linux-kernel - Re: [RFC PATCH bpf-next 2/8] sched_ext: Add filter for scx_kfunc_ids_select

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Message-ID: <Z6U7H2nzJzmMixdZ@gpd3>
Date: Thu, 6 Feb 2025 23:43:43 +0100
From: Andrea Righi <arighi@...dia.com>
To: Juntong Deng <juntong.deng@...look.com>
Cc: ast@...nel.org, daniel@...earbox.net, john.fastabend@...il.com,
	andrii@...nel.org, martin.lau@...ux.dev, eddyz87@...il.com,
	song@...nel.org, yonghong.song@...ux.dev, kpsingh@...nel.org,
	sdf@...ichev.me, haoluo@...gle.com, jolsa@...nel.org,
	memxor@...il.com, tj@...nel.org, void@...ifault.com,
	changwoo@...lia.com, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH bpf-next 2/8] sched_ext: Add filter for
 scx_kfunc_ids_select_cpu

Hi Juntong,

On Wed, Feb 05, 2025 at 07:30:14PM +0000, Juntong Deng wrote:
> This patch adds filter for scx_kfunc_ids_select_cpu.
> 
> The kfuncs in the scx_kfunc_ids_select_cpu set can be used in select_cpu
> and other rq-locked operations.

The only function in scx_kfunc_ids_select_cpu is scx_bpf_select_cpu_dfl(),
which should be called exclusively from ops.select_cpu() and not from any
rq-locked ops.

> 
> Signed-off-by: Juntong Deng <juntong.deng@...look.com>
> ---
>  kernel/sched/ext.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 8857c0709bdd..c92949aa23f6 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -6401,9 +6401,51 @@ BTF_KFUNCS_START(scx_kfunc_ids_select_cpu)
>  BTF_ID_FLAGS(func, scx_bpf_select_cpu_dfl, KF_RCU)
>  BTF_KFUNCS_END(scx_kfunc_ids_select_cpu)
>  
> +static int scx_kfunc_ids_other_rqlocked_filter(const struct bpf_prog *prog, u32 kfunc_id)
> +{
> +	u32 moff = prog->aux->attach_st_ops_member_off;
> +
> +	if (moff == offsetof(struct sched_ext_ops, runnable) ||
> +	    moff == offsetof(struct sched_ext_ops, dequeue) ||
> +	    moff == offsetof(struct sched_ext_ops, stopping) ||
> +	    moff == offsetof(struct sched_ext_ops, quiescent) ||
> +	    moff == offsetof(struct sched_ext_ops, yield) ||
> +	    moff == offsetof(struct sched_ext_ops, cpu_acquire) ||
> +	    moff == offsetof(struct sched_ext_ops, running) ||
> +	    moff == offsetof(struct sched_ext_ops, core_sched_before) ||
> +	    moff == offsetof(struct sched_ext_ops, set_cpumask) ||
> +	    moff == offsetof(struct sched_ext_ops, update_idle) ||
> +	    moff == offsetof(struct sched_ext_ops, tick) ||
> +	    moff == offsetof(struct sched_ext_ops, enable) ||
> +	    moff == offsetof(struct sched_ext_ops, set_weight) ||
> +	    moff == offsetof(struct sched_ext_ops, disable) ||
> +	    moff == offsetof(struct sched_ext_ops, exit_task) ||
> +	    moff == offsetof(struct sched_ext_ops, dump_task) ||
> +	    moff == offsetof(struct sched_ext_ops, dump_cpu))
> +		return 0;
> +
> +	return -EACCES;
> +}
> +
> +static int scx_kfunc_ids_select_cpu_filter(const struct bpf_prog *prog, u32 kfunc_id)
> +{
> +	u32 moff;
> +
> +	if (!btf_id_set8_contains(&scx_kfunc_ids_select_cpu, kfunc_id) ||
> +	    prog->aux->st_ops != &bpf_sched_ext_ops)
> +		return 0;
> +
> +	moff = prog->aux->attach_st_ops_member_off;
> +	if (moff == offsetof(struct sched_ext_ops, select_cpu))
> +		return 0;
> +
> +	return scx_kfunc_ids_other_rqlocked_filter(prog, kfunc_id);

So, I think we just need to return -EACCES here.

> +}
> +
>  static const struct btf_kfunc_id_set scx_kfunc_set_select_cpu = {
>  	.owner			= THIS_MODULE,
>  	.set			= &scx_kfunc_ids_select_cpu,
> +	.filter			= scx_kfunc_ids_select_cpu_filter,
>  };
>  
>  static bool scx_dsq_insert_preamble(struct task_struct *p, u64 enq_flags)
> -- 
> 2.39.5
> 

Thanks,
-Andrea