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SubjectRe: [PATCH] net: Fix hang while unregistering device bound to xdp socket
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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@samsung.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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