linux-kernel - Re: [PATCH bpf-next v1 08/10] bpf: Add bpf_task_work_schedule_* kfuncs with KF_IMPLICIT

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Message-ID: <CAADnVQ+_AmiwuupkVJTGyKY3KOp68GLuivs2LMEr0M_yaHPUUg@mail.gmail.com>
Date: Fri, 9 Jan 2026 12:47:30 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Ihor Solodrai <ihor.solodrai@...ux.dev>
Cc: Alexei Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Eduard Zingerman <eddyz87@...il.com>, Mykyta Yatsenko <yatsenko@...a.com>, Tejun Heo <tj@...nel.org>, 
	Alan Maguire <alan.maguire@...cle.com>, Benjamin Tissoires <bentiss@...nel.org>, 
	Jiri Kosina <jikos@...nel.org>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, 
	"open list:HID CORE LAYER" <linux-input@...r.kernel.org>, sched-ext@...ts.linux.dev
Subject: Re: [PATCH bpf-next v1 08/10] bpf: Add bpf_task_work_schedule_*
 kfuncs with KF_IMPLICIT_ARGS

On Fri, Jan 9, 2026 at 12:02 PM Ihor Solodrai <ihor.solodrai@...ux.dev> wrote:
>
> On 1/9/26 11:58 AM, Alexei Starovoitov wrote:
> > On Fri, Jan 9, 2026 at 10:50 AM Ihor Solodrai <ihor.solodrai@...ux.dev> wrote:
> >>
> >> +__bpf_kfunc int bpf_task_work_schedule_signal(struct task_struct *task, struct bpf_task_work *tw,
> >> +                                             void *map__map, bpf_task_work_callback_t callback,
> >> +                                             struct bpf_prog_aux *aux)
> >> +{
> >> +       return bpf_task_work_schedule(task, tw, map__map, callback, aux, TWA_SIGNAL);
> >> +}
> >> +
> >>  __bpf_kfunc int bpf_task_work_schedule_signal_impl(struct task_struct *task,
> >>                                                    struct bpf_task_work *tw, void *map__map,
> >>                                                    bpf_task_work_callback_t callback,
> >>                                                    void *aux__prog)
> >>  {
> >> -       return bpf_task_work_schedule(task, tw, map__map, callback, aux__prog, TWA_SIGNAL);
> >> +       return bpf_task_work_schedule_signal(task, tw, map__map, callback, aux__prog);
> >>  }
> >
> > I thought we decided that _impl() will not be marked as __bpf_kfunc
> > and will not be in BTF_ID(func, _impl).
> > We can mark it as __weak noinline and it will be in kallsyms.
> > That's all we need for the verifier and resolve_btfid, no?
> >
> > Sorry, it's been a long time. I must have forgotten something.
>
> For the *generated* _impl kfuncs there is no decl tags and the ids are
> absent from BTF_ID sets, yes.
>
> However for the "legacy" cases it must be there for backwards
> compatibility, as well as relevant verifier checks.

I see.
I feel bpf_task_work_schedule_resume() is ok to break, since it's so new.
We can remove bpf_task_work_schedule_[resume|singal]_impl()
to avoid carrying forward forever.

bpf_stream_vprintk_impl() is not that clear. I would remove it too.