Re: [PATCH 12/16] sched_ext: Forbid cpu-form kfuncs from cid-form schedulers

[Cheng-Yang Chou]

Hi Zhao,

On Thu, Apr 23, 2026 at 05:03:23PM +0800, Zhao Mengmeng wrote:
> non_scx_kfunc_deny.bpf.c:17:6: error: conflicting types for 'scx_bpf_kick_cpu'
> 17 | void scx_bpf_kick_cpu(s32 cpu, u64 flags) __ksym;
> |      ^
> /root/work/source-code/linux-next/tools/testing/selftests/sched_ext/build/include/vmlinux.h:136300:13: note: previous declaration is here
> 136300 | extern void scx_bpf_kick_cpu(s32 cpu, u64 flags, const struct bpf_prog_aux *aux) __weak __ksym;
> |             ^
> non_scx_kfunc_deny.bpf.c:26:23: error: too few arguments to function call, expected 3, have 2
> 26 |         scx_bpf_kick_cpu(0, 0);
> |         ~~~~~~~~~~~~~~~~     ^
> /root/work/source-code/linux-next/tools/testing/selftests/sched_ext/build/include/vmlinux.h:136300:13: note: 'scx_bpf_kick_cpu' declared here
> 136300 | extern void scx_bpf_kick_cpu(s32 cpu, u64 flags, const struct bpf_prog_aux *aux) __weak __ksym;
> 
> On the one hand, non_scx_kfunc_deny.bpf.c has it own problem, it should
> not declare scx_bpf_kick_cpu(), on the other hand, the root cause is after

If your point is that a TCP program shouldn't declare scx_bpf_kick_cpu(),
you are correct. The main goal of non_scx_kfunc_deny is to ensure that,
witch commit 2d2b026c3ea7, no non-SCX programs can use SCX func.

> this commit, the signature of scx_bpf_kick_cpu() changes from
> 
> `extern void scx_bpf_kick_cpu(s32 cpu, u64 flags) __weak __ksym;` to
> `extern void scx_bpf_kick_cpu(s32 cpu, u64 flags, const struct bpf_prog_aux *aux) __weak __ksym` 

Regarding the non_scx_kfunc_deny.bpf.c build failure, I'll fix it. If
needed, we can test with another SCX function that doesn't require the
*aux parameter.

Thanks.

> 
> After code analysis and test, I believe scx_bpf_kick_cpu miss the 
> KF_IMPILCIT_ARGS, just like the defination in scx_kfunc_ids_any.
> 
> So here misses  KF_IMPLICIT_ARGS 
> > +BTF_ID_FLAGS(func, scx_bpf_task_cpu)
> Missing KF_RCU.
> > +BTF_ID_FLAGS(func, scx_bpf_cpu_rq)
> Missing KF_IMPLICIT_ARGS
> > +BTF_ID_FLAGS(func, scx_bpf_cpu_curr)
> Missing KF_IMPLICIT_ARGS | KF_RET_NULL | KF_RCU_PROTECTED
> > +BTF_ID_FLAGS(func, scx_bpf_cpu_node)
> > +BTF_ID_FLAGS(func, scx_bpf_cpuperf_cap)
> Missing KF_IMPLICIT_ARGS
> > +BTF_ID_FLAGS(func, scx_bpf_cpuperf_cur)
> Missing KF_IMPLICIT_ARGS
> > +BTF_ID_FLAGS(func, scx_bpf_cpuperf_set)
> Missing KF_IMPLICIT_ARGS
> > +BTF_ID_FLAGS(func, scx_bpf_get_possible_cpumask)
> Missing KF_ACQUIRE
> > +BTF_ID_FLAGS(func, scx_bpf_get_online_cpumask)
> Missing KF_ACQUIRE
> > +BTF_ID_FLAGS(func, scx_bpf_put_cpumask)
> Missing KF_RELEASE
> > +BTF_ID_FLAGS(func, scx_bpf_select_cpu_dfl)
> Missing KF_IMPLICIT_ARGS | KF_RCU
> > +BTF_ID_FLAGS(func, __scx_bpf_select_cpu_and)
> Missing KF_IMPLICIT_ARGS | KF_RCU
> > +BTF_ID_FLAGS(func, scx_bpf_select_cpu_and)
> Missing KF_RCU
> 
> Please correct me if I miss something.
> > +BTF_ID_FLAGS(func, scx_bpf_get_idle_cpumask)
> > +BTF_ID_FLAGS(func, scx_bpf_get_idle_cpumask_node)
> > +BTF_ID_FLAGS(func, scx_bpf_get_idle_smtmask)
> > +BTF_ID_FLAGS(func, scx_bpf_get_idle_smtmask_node)
> > +BTF_ID_FLAGS(func, scx_bpf_put_idle_cpumask)
> > +BTF_ID_FLAGS(func, scx_bpf_test_and_clear_cpu_idle)
> > +BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu)
> > +BTF_ID_FLAGS(func, scx_bpf_pick_idle_cpu_node)
> > +BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu)
> > +BTF_ID_FLAGS(func, scx_bpf_pick_any_cpu_node)
> > +BTF_KFUNCS_END(scx_kfunc_ids_cpu_only)
> > +
> >  /*
> >   * Per-op kfunc allow flags. Each bit corresponds to a context-sensitive kfunc
> >   * group; an op may permit zero or more groups, with the union expressed in
> > @@ -10031,6 +10067,7 @@ int scx_kfunc_context_filter(const struct bpf_prog *prog, u32 kfunc_id)
> >  	bool in_cpu_release = btf_id_set8_contains(&scx_kfunc_ids_cpu_release, kfunc_id);
> >  	bool in_idle = btf_id_set8_contains(&scx_kfunc_ids_idle, kfunc_id);
> >  	bool in_any = btf_id_set8_contains(&scx_kfunc_ids_any, kfunc_id);
> > +	bool in_cpu_only = btf_id_set8_contains(&scx_kfunc_ids_cpu_only, kfunc_id);
> >  	u32 moff, flags;
> >  
> >  	/* Not an SCX kfunc - allow. */
> > @@ -10068,6 +10105,15 @@ int scx_kfunc_context_filter(const struct bpf_prog *prog, u32 kfunc_id)
> >  	    prog->aux->st_ops != &bpf_sched_ext_ops_cid)
> >  		return -EACCES;
> >  
> > +	/*
> > +	 * cid-form schedulers must use cid/cmask kfuncs. cid and cpu are both
> > +	 * small s32s and trivially confused, so cpu-only kfuncs are rejected at
> > +	 * load time. The reverse (cpu-form calling cid-form kfuncs) is
> > +	 * intentionally permissive to ease gradual cpumask -> cid migration.
> > +	 */
> > +	if (prog->aux->st_ops == &bpf_sched_ext_ops_cid && in_cpu_only)
> > +		return -EACCES;
> > +
> >  	/* SCX struct_ops: check the per-op allow list. */
> >  	if (in_any || in_idle)
> >  		return 0;
> > -- 
> > 2.53.0
> > 
> > 
> 
> 
> 

-- 
Cheers,
Cheng-Yang