Re: [PATCH] sched_ext: Print deprecation warnings only once

[Christian Loehle <christian.loehle@arm.com>]

On 6/23/26 15:38, Breno Leitao wrote:
> The deprecation notices for direct p->scx.slice/dsq_vtime writes and for
> ops->cpu_acquire/release() use plain pr_warn(), so they repeat on every
> scheduler (re)load and flood the kernel log.
> > The slice/dsq_vtime notice is emitted from the BPF verifier's
> btf_struct_access callback, which runs once per write access and is
> re-evaluated as the verifier explores paths, so loading a single
> scheduler can print it several times. The cpu_acquire/release notice is
> printed on every scheduler enable.
> 
> Switch both to pr_warn_once() so each deprecation is reported a single
> time, and add the missing newline to the slice/dsq_vtime message.

I guess this should be warned for once per BPF scheduler like
sch->warned_deprecated_rq

> 
> Signed-off-by: Breno Leitao <leitao@debian.org>
> ---
>  kernel/sched/ext/ext.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
> index 691d53fe0f648..708eb9024cb25 100644
> --- a/kernel/sched/ext/ext.c
> +++ b/kernel/sched/ext/ext.c
> @@ -6988,7 +6988,7 @@ static int validate_ops(struct scx_sched *sch, const struct sched_ext_ops *ops)
>  	 * run past the BPF allocation. Skip for cid-form.
>  	 */
>  	if (!sch->is_cid_type && (ops->cpu_acquire || ops->cpu_release))
> -		pr_warn("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n");
> +		pr_warn_once("ops->cpu_acquire/release() are deprecated, use sched_switch TP instead\n");
>  
>  	/*
>  	 * Sub-scheduler support is tied to the cid-form struct_ops. A sub-sched
> @@ -7806,7 +7806,7 @@ static int bpf_scx_btf_struct_access(struct bpf_verifier_log *log,
>  		     off + size <= offsetofend(struct task_struct, scx.slice)) ||
>  		    (off >= offsetof(struct task_struct, scx.dsq_vtime) &&
>  		     off + size <= offsetofend(struct task_struct, scx.dsq_vtime))) {
> -			pr_warn("sched_ext: Writing directly to p->scx.slice/dsq_vtime is deprecated, use scx_bpf_task_set_slice/dsq_vtime()");
> +			pr_warn_once("sched_ext: Writing directly to p->scx.slice/dsq_vtime is deprecated, use scx_bpf_task_set_slice/dsq_vtime()\n");
>  			return SCALAR_VALUE;
>  		}
>  
> 
> ---
> base-commit: 4e5dfb7c84012007c3c7061126491bbc92d71bf1
> change-id: 20260623-scx_warning-0df49c442afb
> 
> Best regards,