Re: [PATCH RESEND bpf-next v10 5/8] bpf: Add bpf_list_add to insert node after a given list node

[Eduard Zingerman]

On Tue, 2026-05-12 at 13:59 +0800, Kaitao cheng wrote:
> From: Kaitao Cheng <chengkaitao@xxxxxxxxxx>
> 
> Add a new kfunc bpf_list_add(head, new, prev, meta, off) that
> inserts 'new' after 'prev' in the BPF linked list. Both must be in
> the same list; 'prev' must already be in the list. The new node must
> be an owning reference (e.g. from bpf_obj_new); the kfunc consumes
> that reference and the node becomes non-owning once inserted.
> 
> We have added an additional parameter bpf_list_head *head to
> bpf_list_add, as the verifier requires the head parameter to
> check whether the lock is being held.
> 
> Returns 0 on success, -EINVAL if 'prev' is not in a list or 'new'
> is already in a list (or duplicate insertion). On failure, the
> kernel drops the passed-in node.
> 
> Signed-off-by: Kaitao Cheng <chengkaitao@xxxxxxxxxx>
> ---

Reviewed-by: Eduard Zingerman <eddyz87@xxxxxxxxx>

[...]

> @@ -19228,8 +19231,11 @@ int bpf_fixup_kfunc_call(struct bpf_verifier_env *env, struct bpf_insn *insn,
>  		int struct_meta_reg = BPF_REG_3;
>  		int node_offset_reg = BPF_REG_4;
>  
> -		/* rbtree_add has extra 'less' arg, so args-to-fixup are in diff regs */
> -		if (is_bpf_rbtree_add_kfunc(desc->func_id)) {
> +		/* list_add/rbtree_add have an extra arg (prev/less),
> +		 * so args-to-fixup are in diff regs.
> +		 */
> +		if (desc->func_id == special_kfunc_list[KF_bpf_list_add] ||

Nit: same nit here, maybe add is_bpf_list_add_kfunc().

> +		    is_bpf_rbtree_add_kfunc(desc->func_id)) {
>  			struct_meta_reg = BPF_REG_4;
>  			node_offset_reg = BPF_REG_5;
>  		}