linux-kernel - Re: [PATCH bpf] xsk: inherit need

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Date:   Tue, 20 Sep 2022 08:27:34 +0200
From:   Magnus Karlsson <magnus.karlsson@...il.com>
To:     Jalal Mostafa <jalal.a.mostapha@...il.com>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org, bjorn@...nel.org,
        magnus.karlsson@...el.com, maciej.fijalkowski@...el.com,
        jonathan.lemon@...il.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, ast@...nel.org,
        daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
        linux-kernel@...r.kernel.org, jalal.mostafa@....edu
Subject: Re: [PATCH bpf] xsk: inherit need_wakeup flag for shared sockets

On Mon, Sep 19, 2022 at 9:27 PM Jalal Mostafa
<jalal.a.mostapha@...il.com> wrote:
>
> The flag for need_wakeup is not set for xsks with `XDP_SHARED_UMEM`
> flag and of different queue ids and/or devices. They should inherit
> the flag from the first socket buffer pool since no flags can be
> specified once `XDP_SHARED_UMEM` is specified. The issue is fixed
> by creating a new function `xp_create_and_assign_umem_shared` to
> create xsk_buff_pool for xsks with the shared umem flag set.

Thanks for spotting this Jalal. Though I think we should aim for a
simpler fix. The uses_need_wakeup flag is set by xp_assign_dev(). The
problem here is the function xp_assign_dev_shared() that prepares the
flag parameter for xp_assign_dev().

if (pool->uses_need_wakeup)
                flags |= XDP_USE_NEED_WAKEUP;

Should really be:

if (umem_xs->pool->uses_need_wakeup)
                flags |= XDP_USE_NEED_WAKEUP;

So change the function parameter *umem to *umem_xs, use that in the
function call and do:

flags = umem_xs->umem->zc ? XDP_ZEROCOPY : XDP_COPY;
if (umem_xs->pool->uses_need_wakeup)
          flags |= XDP_USE_NEED_WAKEUP;

What do you think?

> Signed-off-by: Jalal Mostafa <jalal.a.mostapha@...il.com>
> ---
>  include/net/xsk_buff_pool.h |  2 ++
>  net/xdp/xsk.c               |  3 +--
>  net/xdp/xsk_buff_pool.c     | 15 +++++++++++++++
>  3 files changed, 18 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h
> index 647722e847b4..917cfef9d355 100644
> --- a/include/net/xsk_buff_pool.h
> +++ b/include/net/xsk_buff_pool.h
> @@ -93,6 +93,8 @@ struct xsk_buff_pool {
>  /* AF_XDP core. */
>  struct xsk_buff_pool *xp_create_and_assign_umem(struct xdp_sock *xs,
>                                                 struct xdp_umem *umem);
> +struct xsk_buff_pool *xp_create_and_assign_umem_shared(struct xdp_sock *xs,
> +                                                      struct xdp_sock *umem_xs);
>  int xp_assign_dev(struct xsk_buff_pool *pool, struct net_device *dev,
>                   u16 queue_id, u16 flags);
>  int xp_assign_dev_shared(struct xsk_buff_pool *pool, struct xdp_umem *umem,
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index 5b4ce6ba1bc7..a415db88e8e5 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -946,8 +946,7 @@ static int xsk_bind(struct socket *sock, struct sockaddr *addr, int addr_len)
>                         /* Share the umem with another socket on another qid
>                          * and/or device.
>                          */
> -                       xs->pool = xp_create_and_assign_umem(xs,
> -                                                            umem_xs->umem);
> +                       xs->pool = xp_create_and_assign_umem_shared(xs, umem_xs);
>                         if (!xs->pool) {
>                                 err = -ENOMEM;
>                                 sockfd_put(sock);
> diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
> index a71a8c6edf55..7d5b0bd8d953 100644
> --- a/net/xdp/xsk_buff_pool.c
> +++ b/net/xdp/xsk_buff_pool.c
> @@ -112,6 +112,21 @@ struct xsk_buff_pool *xp_create_and_assign_umem(struct xdp_sock *xs,
>         return NULL;
>  }
>
> +struct xsk_buff_pool *xp_create_and_assign_umem_shared(struct xdp_sock *xs,
> +                                                      struct xdp_sock *umem_xs)
> +{
> +       struct xdp_umem *umem = umem_xs->umem;
> +       struct xsk_buff_pool *pool = xp_create_and_assign_umem(xs, umem);
> +
> +       if (!pool)
> +               goto out;
> +
> +       pool->uses_need_wakeup = umem_xs->pool->uses_need_wakeup;
> +
> +out:
> +       return pool;
> +}
> +
>  void xp_set_rxq_info(struct xsk_buff_pool *pool, struct xdp_rxq_info *rxq)
>  {
>         u32 i;
> --
> 2.34.1
>