netdev - Re: [PATCH bpf 4/4] net/ixgbe: Fix concurrency issues between config flow and XSK

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Date:   Fri, 6 Dec 2019 10:03:09 +0100
From:   Björn Töpel <bjorn.topel@...il.com>
To:     Maxim Mikityanskiy <maximmi@...lanox.com>
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
        "David S. Miller" <davem@...emloft.net>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>
Subject: Re: [PATCH bpf 4/4] net/ixgbe: Fix concurrency issues between config
 flow and XSK

On Thu, 5 Dec 2019 at 16:52, Maxim Mikityanskiy <maximmi@...lanox.com> wrote:
>
> Use synchronize_rcu to wait until the XSK wakeup function finishes
> before destroying the resources it uses:
>
> 1. ixgbe_down already calls synchronize_rcu after setting __IXGBE_DOWN.
>
> 2. After switching the XDP program, call synchronize_rcu to let
> ixgbe_xsk_async_xmit exit before the XDP program is freed.
>
> 3. Changing the number of channels brings the interface down.
>
> 4. Disabling UMEM sets __IXGBE_TX_DISABLED before closing hardware
> resources and resetting xsk_umem. Check that bit in ixgbe_xsk_async_xmit
> to avoid using the XDP ring when it's already destroyed. synchronize_rcu
> is called from ixgbe_txrx_ring_disable.
>
> Signed-off-by: Maxim Mikityanskiy <maximmi@...lanox.com>
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 6 +++++-
>  drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c  | 8 ++++++--
>  2 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index 25c097cd8100..60503318c7e5 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -10273,8 +10273,12 @@ static int ixgbe_xdp_setup(struct net_device *dev, struct bpf_prog *prog)
>                             adapter->xdp_prog);
>         }
>
> -       if (old_prog)
> +       if (old_prog) {
> +               /* Wait until ndo_xsk_async_xmit completes. */
> +               synchronize_rcu();
> +
>                 bpf_prog_put(old_prog);
> +       }
>
>         /* Kick start the NAPI context if there is an AF_XDP socket open
>          * on that queue id. This so that receiving will start.
> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
> index d6feaacfbf89..b43be9f14105 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_xsk.c
> @@ -709,10 +709,14 @@ int ixgbe_xsk_wakeup(struct net_device *dev, u32 qid, u32 flags)
>         if (qid >= adapter->num_xdp_queues)
>                 return -ENXIO;
>
> -       if (!adapter->xdp_ring[qid]->xsk_umem)
> +       ring = adapter->xdp_ring[qid];
> +
> +       if (test_bit(__IXGBE_TX_DISABLED, &ring->state))
> +               return -ENETDOWN;
> +
> +       if (!ring->xsk_umem)

Pretty much same comment as in i40e. The synchronize_rcu() is not
needed, but the additional test is!

>                 return -ENXIO;
>
> -       ring = adapter->xdp_ring[qid];
>         if (!napi_if_scheduled_mark_missed(&ring->q_vector->napi)) {
>                 u64 eics = BIT_ULL(ring->q_vector->v_idx);
>
> --
> 2.20.1
>