Re: [PATCH bpf-next v2 01/21] bpf: Initialize ftrace_managed in bpf_trampoline_get()

[Jiri Olsa]

On Mon, Oct 12, 2026 at 11:40:03PM +0800, Leon Hwang wrote:
> A trampoline managed by ftrace is determined by its target, that said
> ftrace_managed is already known when the trampoline is initialized. so,
> set 'ftrace_managed = tr->ip != 0' in bpf_trampoline_get() instead of
> relying on the first regular or tracing_multi attachment to set it.
> 
> This makes the backend selection independent of attachment order and keeps
> the registration callbacks focused on installing the trampoline.
> 
> No functional change intended.
> 
> Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx>

Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>

jirka

> ---
>  kernel/bpf/trampoline.c | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)
> 
> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index 24edb59238f3..17f2a8133f61 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -475,18 +475,11 @@ static int register_fentry(struct bpf_trampoline *tr, struct bpf_tramp_image *im
>  			   void *data __maybe_unused)
>  {
>  	void *new_addr = im->image;
> -	void *ip = tr->func.addr;
> -	unsigned long faddr;
>  	int ret;
>  
> -	faddr = ftrace_location((unsigned long)ip);
> -	if (faddr) {
> +	if (tr->func.ftrace_managed) {
>  		if (!tr->fops)
>  			return -ENOTSUPP;
> -		tr->func.ftrace_managed = true;
> -	}
> -
> -	if (tr->func.ftrace_managed) {
>  		ret = direct_ops_add(tr, new_addr);
>  	} else {
>  		ret = bpf_trampoline_update_fentry(tr, 0, NULL, new_addr);
> @@ -1286,6 +1279,7 @@ struct bpf_trampoline *bpf_trampoline_get(u64 key,
>  
>  	memcpy(&tr->func.model, &tgt_info->fmodel, sizeof(tgt_info->fmodel));
>  	tr->func.addr = (void *)tgt_info->tgt_addr;
> +	tr->func.ftrace_managed = tr->ip != 0;
>  out:
>  	trampoline_unlock(tr);
>  	return tr;
> @@ -1649,7 +1643,6 @@ static int register_fentry_multi(struct bpf_trampoline *tr, struct bpf_tramp_ima
>  	if (bpf_trampoline_use_jmp(tr->flags))
>  		addr = ftrace_jmp_set(addr);
>  
> -	tr->func.ftrace_managed = true;
>  	ftrace_hash_add(data->reg, data->entry, ip, addr);
>  	tr->cur_image = im;
>  	return 0;
> -- 
> 2.55.0
>