Re: [PATCH bpf] libbpf: unmap rings when umem deleted

[Magnus Karlsson]

On Tue, Mar 1, 2022 at 6:57 PM lic121 <lic121@xxxxxxxxxxxxxxx> wrote:
>
> xsk_umem__create() does mmap for fill/comp rings, but xsk_umem__delete()
> doesn't do the unmap. This works fine for regular cases, because
> xsk_socket__delete() does unmap for the rings. But for the case that
> xsk_socket__create_shared() fails, umem rings are not unmapped.
>
> fill_save/comp_save are checked to determine if rings have already be
> unmapped by xsk. If fill_save and comp_save are NULL, it means that the
> rings have already been used by xsk. Then they are supposed to be
> unmapped by xsk_socket__delete(). Otherwise, xsk_umem__delete() does the
> unmap.

Thanks for the fix. Please note that the AF_XDP support in libbpf has
been deprecated and moved to libxdp
(https://github.com/xdp-project/xdp-tools). The code will be
completely removed in the libbpf 1.0 release. Could I take your patch
and apply it to libxdp instead and fix the bug there? I have not
checked, but it is likely present there as well. And that is the code
base we will be using going forward.

> Fixes: 2f6324a3937f ("libbpf: Support shared umems between queues and devices")
> Signed-off-by: lic121 <lic121@xxxxxxxxxxxxxxx>
> ---
>  tools/lib/bpf/xsk.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/tools/lib/bpf/xsk.c b/tools/lib/bpf/xsk.c
> index edafe56..32a2f57 100644
> --- a/tools/lib/bpf/xsk.c
> +++ b/tools/lib/bpf/xsk.c
> @@ -1193,12 +1193,23 @@ int xsk_socket__create(struct xsk_socket **xsk_ptr, const char *ifname,
>
>  int xsk_umem__delete(struct xsk_umem *umem)
>  {
> +       struct xdp_mmap_offsets off;
> +       int err;
> +
>         if (!umem)
>                 return 0;
>
>         if (umem->refcount)
>                 return -EBUSY;
>
> +       err = xsk_get_mmap_offsets(umem->fd, &off);
> +       if (!err && umem->fill_save && umem->comp_save) {
> +               munmap(umem->fill_save->ring - off.fr.desc,
> +                      off.fr.desc + umem->config.fill_size * sizeof(__u64));
> +               munmap(umem->comp_save->ring - off.cr.desc,
> +                      off.cr.desc + umem->config.comp_size * sizeof(__u64));
> +       }
> +
>         close(umem->fd);
>         free(umem);
>
> --
> 1.8.3.1
>