netdev - Re: [PATCH bpf v3] xdp: fix hang while unregistering device bound to xdp socket

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Message-ID: <CALDO+SYhxw-Y7+i5Su9xz5PPYzgZm4qna+tEmBnXeG=GD7YSpg@mail.gmail.com>
Date:   Mon, 10 Jun 2019 12:45:50 -0700
From:   William Tu <u9012063@...il.com>
To:     Ilya Maximets <i.maximets@...sung.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Xdp <xdp-newbies@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>
Subject: Re: [PATCH bpf v3] xdp: fix hang while unregistering device bound to
 xdp socket

On Mon, Jun 10, 2019 at 9:39 AM Ilya Maximets <i.maximets@...sung.com> wrote:
>
> Device that bound to XDP socket will not have zero refcount until the
> userspace application will not close it. This leads to hang inside
> 'netdev_wait_allrefs()' if device unregistering requested:
>
>   # ip link del p1
>   < hang on recvmsg on netlink socket >
>
>   # ps -x | grep ip
>   5126  pts/0    D+   0:00 ip link del p1
>
>   # journalctl -b
>
>   Jun 05 07:19:16 kernel:
>   unregister_netdevice: waiting for p1 to become free. Usage count = 1
>
>   Jun 05 07:19:27 kernel:
>   unregister_netdevice: waiting for p1 to become free. Usage count = 1
>   ...

Thanks. I hit the same issue quite often when using veth driver to
test AF_XDP.

>
> Fix that by implementing NETDEV_UNREGISTER event notification handler
> to properly clean up all the resources and unref device.
>
> This should also allow socket killing via ss(8) utility.
>
> Fixes: 965a99098443 ("xsk: add support for bind for Rx")
> Signed-off-by: Ilya Maximets <i.maximets@...sung.com>
> ---
Tested-by: William Tu <u9012063@...il.com>