Re: [PATCH bpf-next v3 04/15] bpf: Remove unnecessary prog_list_prog() check

["Emil Tsalapatis" <emil@etsalapatis.com>]

On Mon Jul 6, 2026 at 1:19 PM EDT, Amery Hung wrote:
> From: Martin KaFai Lau <martin.lau@kernel.org>
>
> effective_prog_pos(), called from replace_effective_prog() and
> purge_effective_progs(), tests "!prog_list_prog(pl)" to skip a
> 'detaching' pl.
>
> When detaching a pl, pl->prog and pl->link are set to NULL in case
> the update_effective_progs() failed.
>
> However, replace_effective_prog() is not detaching a pl,
> so the case "!prog_list_prog()" will not happen.
>
> In purge_effective_prog(), the pl->prog and pl->link are restored
> before calling purge_effective_progs(), so the case "!prog_list_prog()"
> will not happen either.
>
> This patch removes them as a prep work for the upcoming work
> in attaching struct_ops to cgroup. When attaching a struct_ops
> to cgroup, there is a link->map case and the prog_list_prog()
> will not consider the link->map. The replace_effective_prog()
> and purge_effective_progs() will then incorrectly skip a pl
> with struct_ops map attached to it.
>
> Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
> Signed-off-by: Amery Hung <ameryhung@gmail.com>

Reviewed-by: Emil Tsalapatis <emil@etsalapatis.com>

> ---
>  kernel/bpf/cgroup.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/bpf/cgroup.c b/kernel/bpf/cgroup.c
> index 4355ccb78a9c..b64f6757096c 100644
> --- a/kernel/bpf/cgroup.c
> +++ b/kernel/bpf/cgroup.c
> @@ -965,9 +965,10 @@ static int effective_prog_pos(struct cgroup *cgrp,
>  
>  		init_bstart = bstart;
>  		hlist_for_each_entry(pl, &p->bpf.progs[atype], node) {
> -			if (!prog_list_prog(pl))
> -				continue;
> -
> +			/*
> +			 * No detaching pl (NULL prog and link) is visible to the callers,
> +			 * so skip the check compute_effective_progs() needs.
> +			 */
>  			if (pl->flags & BPF_F_PREORDER) {
>  				if (pl == target_pl)
>  					pos = bstart;