On Fri, Oct 5, 2018 at 4:28 AM Björn Töpel <bjorn.to...@gmail.com> wrote:
>
> From: Björn Töpel <bjorn.to...@intel.com>
>
> The AF_XDP socket struct can exist in three different, implicit
> states: setup, bound and released. Setup is prior the socket has been
> bound to a device. Bound is when the socket is active for receive and
> send. Released is when the process/userspace side of the socket is
> released, but the sock object is still lingering, e.g. when there is a
> reference to the socket in an XSKMAP after process termination.
>
> The Rx fast-path code uses the "dev" member of struct xdp_sock to
> check whether a socket is bound or relased, and the Tx code uses the
> struct xdp_umem "xsk_list" member in conjunction with "dev" to
> determine the state of a socket.
>
> However, the transition from bound to released did not tear the socket
> down in correct order.
>
> On the Rx side "dev" was cleared after synchronize_net() making the
> synchronization useless. On the Tx side, the internal queues were
> destroyed prior removing them from the "xsk_list".
>
> This commit corrects the cleanup order, and by doing so
> xdp_del_sk_umem() can be simplified and one synchronize_net() can be
> removed.
>
> Fixes: 965a99098443 ("xsk: add support for bind for Rx")
> Fixes: ac98d8aab61b ("xsk: wire upp Tx zero-copy functions")
> Reported-by: Jesper Dangaard Brouer <bro...@redhat.com>
> Signed-off-by: Björn Töpel <bjorn.to...@intel.com>
Acked-by: Song Liu <songliubrav...@fb.com>
> ---
> net/xdp/xdp_umem.c | 11 +++--------
> net/xdp/xsk.c | 13 ++++++++-----
> 2 files changed, 11 insertions(+), 13 deletions(-)
>
> diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
> index c6007c58231c..a264cf2accd0 100644
> --- a/net/xdp/xdp_umem.c
> +++ b/net/xdp/xdp_umem.c
> @@ -32,14 +32,9 @@ void xdp_del_sk_umem(struct xdp_umem *umem, struct
> xdp_sock *xs)
> {
> unsigned long flags;
>
> - if (xs->dev) {
> - spin_lock_irqsave(&umem->xsk_list_lock, flags);
> - list_del_rcu(&xs->list);
> - spin_unlock_irqrestore(&umem->xsk_list_lock, flags);
> -
> - if (umem->zc)
> - synchronize_net();
> - }
> + spin_lock_irqsave(&umem->xsk_list_lock, flags);
> + list_del_rcu(&xs->list);
> + spin_unlock_irqrestore(&umem->xsk_list_lock, flags);
> }
>
> /* The umem is stored both in the _rx struct and the _tx struct as we do
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index caeddad15b7c..0577cd49aa72 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -355,12 +355,18 @@ static int xsk_release(struct socket *sock)
> local_bh_enable();
>
> if (xs->dev) {
> + struct net_device *dev = xs->dev;
> +
> /* Wait for driver to stop using the xdp socket. */
nit: I guess we should move this comment together with synchronize_net().
> - synchronize_net();
> - dev_put(xs->dev);
> + xdp_del_sk_umem(xs->umem, xs);
> xs->dev = NULL;
> + synchronize_net();
> + dev_put(dev);
> }
>
> + xskq_destroy(xs->rx);
> + xskq_destroy(xs->tx);
> +
> sock_orphan(sk);
> sock->sk = NULL;
>
> @@ -714,9 +720,6 @@ static void xsk_destruct(struct sock *sk)
> if (!sock_flag(sk, SOCK_DEAD))
> return;
>
> - xskq_destroy(xs->rx);
> - xskq_destroy(xs->tx);
> - xdp_del_sk_umem(xs->umem, xs);
> xdp_put_umem(xs->umem);
>
> sk_refcnt_debug_dec(sk);
> --
> 2.17.1
>
