Re: [PATCH] mm/bpf_memcontrol: mark BPF memcg kfuncs static

[Alexei Starovoitov]

On Wed, Jun 17, 2026 at 1:22 PM JP Kobryn <jp.kobryn@xxxxxxxxx> wrote:
>
> The kfuncs in bpf_memcontrol.c are not called by in-kernel C code. They are
> only referenced by BPF programs and resolved through BTF.
>
> Since no external linkage is needed, mark these functions static.
>
> Fixes: 5904db9891f8 ("mm: introduce BPF kfuncs to deal with memcg pointers")
> Fixes: 5c7db3239c9f ("mm: introduce bpf_get_root_mem_cgroup() BPF kfunc")
> Fixes: 99430ab8b804 ("mm: introduce BPF kfuncs to access memcg statistics and events")
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> Closes: https://lore.kernel.org/oe-kbuild-all/202606150332.Xy4Egd9s-lkp@xxxxxxxxx/
> Signed-off-by: JP Kobryn <jp.kobryn@xxxxxxxxx>
> ---
>  mm/bpf_memcontrol.c | 21 +++++++++++----------
>  1 file changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/mm/bpf_memcontrol.c b/mm/bpf_memcontrol.c
> index 716df49d7647..eff79bb2c758 100644
> --- a/mm/bpf_memcontrol.c
> +++ b/mm/bpf_memcontrol.c
> @@ -20,7 +20,7 @@ __bpf_kfunc_start_defs();
>   *
>   * Return: A pointer to the root memory cgroup.
>   */
> -__bpf_kfunc struct mem_cgroup *bpf_get_root_mem_cgroup(void)
> +__bpf_kfunc static struct mem_cgroup *bpf_get_root_mem_cgroup(void)

sashiko disappoints. It couldn't notice that kfuncs should not be static.
We have few "__bpf_kfunc static" in net/ipv4/
that work by sort-of "luck", since their addresses are taken.

In general kfuncs cannot be declared static.

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