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Date: Fri, 7 Jun 2019 08:58:00 +0200 From: Björn Töpel <bjorn.topel@...el.com> To: Ilya Maximets <i.maximets@...sung.com>, Jonathan Lemon <jonathan.lemon@...il.com> Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, bpf@...r.kernel.org, xdp-newbies@...r.kernel.org, "David S. Miller" <davem@...emloft.net>, Magnus Karlsson <magnus.karlsson@...el.com> Subject: Re: [PATCH] net: Fix hang while unregistering device bound to xdp socket On 2019-06-07 08:36, Ilya Maximets wrote: > On 06.06.2019 21:03, Jonathan Lemon wrote: >> On 6 Jun 2019, at 5:40, Ilya Maximets 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 >>> ... >>> >>> Fix that by counting XDP references for the device and failing >>> RTM_DELLINK with EBUSY if device is still in use by any XDP socket. >>> >>> With this change: >>> >>> # ip link del p1 >>> RTNETLINK answers: Device or resource busy >>> >>> Fixes: 965a99098443 ("xsk: add support for bind for Rx") >>> Signed-off-by: Ilya Maximets <i.maximets@...sung.com> >>> --- >>> >>> Another option could be to force closing all the corresponding AF_XDP >>> sockets, but I didn't figure out how to do this properly yet. >>> >>> include/linux/netdevice.h | 25 +++++++++++++++++++++++++ >>> net/core/dev.c | 10 ++++++++++ >>> net/core/rtnetlink.c | 6 ++++++ >>> net/xdp/xsk.c | 7 ++++++- >>> 4 files changed, 47 insertions(+), 1 deletion(-) >>> >>> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h >>> index 44b47e9df94a..24451cfc5590 100644 >>> --- a/include/linux/netdevice.h >>> +++ b/include/linux/netdevice.h >>> @@ -1705,6 +1705,7 @@ enum netdev_priv_flags { >>> * @watchdog_timer: List of timers >>> * >>> * @pcpu_refcnt: Number of references to this device >>> + * @pcpu_xdp_refcnt: Number of XDP socket references to this device >>> * @todo_list: Delayed register/unregister >>> * @link_watch_list: XXX: need comments on this one >>> * >>> @@ -1966,6 +1967,7 @@ struct net_device { >>> struct timer_list watchdog_timer; >>> >>> int __percpu *pcpu_refcnt; >>> + int __percpu *pcpu_xdp_refcnt; >>> struct list_head todo_list; >> >> >> I understand the intention here, but don't think that putting a XDP reference >> into the generic netdev structure is the right way of doing this. Likely the >> NETDEV_UNREGISTER notifier should be used so the socket and umem unbinds from >> the device. >> > > Thanks for the pointer! That is exactly what I looked for. > I'll make a new version that will unbind resources using netdevice notifier. > > Best regards, Ilya Maximets. > Thanks for working on this. This would open up for supporting killing sockets via ss(8) (-K, --kill), as well! Björn
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