Re: [PATCH] sched_ext: Remove deprecated scx_bpf_cpu_rq()

[Andrea Righi <arighi@nvidia.com>]

Hi Christian,

On Fri, Jun 19, 2026 at 04:59:20PM +0100, Christian Loehle wrote:
> scx_bpf_cpu_rq() exposes rq pointers without requiring the rq lock and
> has emitted a deprecation warning since commit
> 5c48d88fe004 ("sched_ext: deprecation warn for scx_bpf_cpu_rq()").
> The supported replacements cover the intended uses:
> scx_bpf_locked_rq() for locked rq access and
> scx_bpf_cpu_curr() for remote curr lookup.
> 
> Remove the kfunc, its BTF registrations, the deprecation warning
> state, and the BPF-side prototype and compat fallback.
> 
> Signed-off-by: Christian Loehle <christian.loehle@arm.com>

It looks like none of the schedulers in the scx repo are using scx_bpf_cpu_rq()
anymore, so I think we can safely remove it.

Reviewed-by: Andrea Righi <arighi@nvidia.com>

Thanks,
-Andrea

> ---
>  kernel/sched/ext.c                       | 30 ------------------------
>  kernel/sched/ext_internal.h              |  1 -
>  tools/sched_ext/include/scx/common.bpf.h |  5 ++--
>  tools/sched_ext/include/scx/compat.bpf.h | 17 --------------
>  4 files changed, 2 insertions(+), 51 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 0db6fa2daea3..72d99dd3fe89 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -10222,34 +10222,6 @@ __bpf_kfunc s32 scx_bpf_task_cid(const struct task_struct *p)
>  	return tbl[task_cpu(p)];
>  }
>  
> -/**
> - * scx_bpf_cpu_rq - Fetch the rq of a CPU
> - * @cpu: CPU of the rq
> - * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs
> - */
> -__bpf_kfunc struct rq *scx_bpf_cpu_rq(s32 cpu, const struct bpf_prog_aux *aux)
> -{
> -	struct scx_sched *sch;
> -
> -	guard(rcu)();
> -
> -	sch = scx_prog_sched(aux);
> -	if (unlikely(!sch))
> -		return NULL;
> -
> -	if (!scx_cpu_valid(sch, cpu, NULL))
> -		return NULL;
> -
> -	if (!sch->warned_deprecated_rq) {
> -		printk_deferred(KERN_WARNING "sched_ext: %s() is deprecated; "
> -				"use scx_bpf_locked_rq() when holding rq lock "
> -				"or scx_bpf_cpu_curr() to read remote curr safely.\n", __func__);
> -		sch->warned_deprecated_rq = true;
> -	}
> -
> -	return cpu_rq(cpu);
> -}
> -
>  /**
>   * scx_bpf_locked_rq - Return the rq currently locked by SCX
>   * @aux: implicit BPF argument to access bpf_prog_aux hidden from BPF progs
> @@ -10540,7 +10512,6 @@ BTF_ID_FLAGS(func, scx_bpf_put_cpumask, KF_RELEASE)
>  BTF_ID_FLAGS(func, scx_bpf_task_running, KF_RCU)
>  BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU)
>  BTF_ID_FLAGS(func, scx_bpf_task_cid, KF_RCU)
> -BTF_ID_FLAGS(func, scx_bpf_cpu_rq, KF_IMPLICIT_ARGS)
>  BTF_ID_FLAGS(func, scx_bpf_locked_rq, KF_IMPLICIT_ARGS | KF_RET_NULL)
>  BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED)
>  BTF_ID_FLAGS(func, scx_bpf_cid_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED)
> @@ -10575,7 +10546,6 @@ static const struct btf_kfunc_id_set scx_kfunc_set_any = {
>  BTF_KFUNCS_START(scx_kfunc_ids_cpu_only)
>  BTF_ID_FLAGS(func, scx_bpf_kick_cpu, KF_IMPLICIT_ARGS)
>  BTF_ID_FLAGS(func, scx_bpf_task_cpu, KF_RCU)
> -BTF_ID_FLAGS(func, scx_bpf_cpu_rq, KF_IMPLICIT_ARGS)
>  BTF_ID_FLAGS(func, scx_bpf_cpu_curr, KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED)
>  BTF_ID_FLAGS(func, scx_bpf_cpu_node, KF_IMPLICIT_ARGS)
>  BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap, KF_IMPLICIT_ARGS)
> diff --git a/kernel/sched/ext_internal.h b/kernel/sched/ext_internal.h
> index b04701190b23..38f099ccd24f 100644
> --- a/kernel/sched/ext_internal.h
> +++ b/kernel/sched/ext_internal.h
> @@ -1165,7 +1165,6 @@ struct scx_sched {
>  	 * but it doesn't really matter.
>  	 */
>  	bool			warned_zero_slice:1;
> -	bool			warned_deprecated_rq:1;
>  	bool			warned_unassoc_progs:1;
>  
>  	struct list_head	all;
> diff --git a/tools/sched_ext/include/scx/common.bpf.h b/tools/sched_ext/include/scx/common.bpf.h
> index 9591a6e778ce..bd51986c4c42 100644
> --- a/tools/sched_ext/include/scx/common.bpf.h
> +++ b/tools/sched_ext/include/scx/common.bpf.h
> @@ -96,7 +96,6 @@ s32 scx_bpf_pick_any_cpu_node(const cpumask_t *cpus_allowed, int node, u64 flags
>  s32 scx_bpf_pick_any_cpu(const cpumask_t *cpus_allowed, u64 flags) __ksym;
>  bool scx_bpf_task_running(const struct task_struct *p) __ksym;
>  s32 scx_bpf_task_cpu(const struct task_struct *p) __ksym;
> -struct rq *scx_bpf_cpu_rq(s32 cpu) __ksym;
>  struct rq *scx_bpf_locked_rq(void) __ksym;
>  struct task_struct *scx_bpf_cpu_curr(s32 cpu) __ksym __weak;
>  struct task_struct *scx_bpf_tid_to_task(u64 tid) __ksym __weak;
> @@ -983,8 +982,8 @@ extern struct irqtime___local cpu_irqtime __ksym __weak;
>  static inline struct rq___local *get_current_rq(u32 cpu)
>  {
>  	/*
> -	 * This is a workaround to get an rq pointer since we decided to
> -	 * deprecate scx_bpf_cpu_rq().
> +	 * This is a workaround to get an rq pointer now that
> +	 * scx_bpf_cpu_rq() has been removed.
>  	 *
>  	 * WARNING: The caller must hold the rq lock for @cpu. This is
>  	 * guaranteed when called from scheduling callbacks (ops.running,
> diff --git a/tools/sched_ext/include/scx/compat.bpf.h b/tools/sched_ext/include/scx/compat.bpf.h
> index 87f15f296234..133058578668 100644
> --- a/tools/sched_ext/include/scx/compat.bpf.h
> +++ b/tools/sched_ext/include/scx/compat.bpf.h
> @@ -233,23 +233,6 @@ static inline bool __COMPAT_is_enq_cpu_selected(u64 enq_flags)
>  	 scx_bpf_pick_any_cpu_node(cpus_allowed, node, flags) :			\
>  	 scx_bpf_pick_any_cpu(cpus_allowed, flags))
>  
> -/*
> - * v6.18: Add a helper to retrieve the current task running on a CPU.
> - *
> - * Keep this helper available until v6.20 for compatibility.
> - */
> -static inline struct task_struct *__COMPAT_scx_bpf_cpu_curr(int cpu)
> -{
> -	struct rq *rq;
> -
> -	if (bpf_ksym_exists(scx_bpf_cpu_curr))
> -		return scx_bpf_cpu_curr(cpu);
> -
> -	rq = scx_bpf_cpu_rq(cpu);
> -
> -	return rq ? rq->curr : NULL;
> -}
> -
>  /*
>   * v6.19: To work around BPF maximum parameter limit, the following kfuncs are
>   * replaced with variants that pack scalar arguments in a struct. Wrappers are
> -- 
> 2.34.1
>