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@xxxxxxxxxxx>
>> ---
>>
>> 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.
