Subject: Re: [PATCH net-next v2 3/4] bpf, mlx5: drop priv->xdp_prog reference on netdev cleanup

From: Daniel Borkmann <[email-masked]>
Date: Wed, 16 Nov 2016 16:45:21 +0100

On 11/16/2016 01:51 PM, Saeed Mahameed wrote:
> On Wed, Nov 16, 2016 at 2:04 AM, Daniel Borkmann <[email-masked]> wrote:
>> mlx5e_xdp_set() is currently the only place where we drop reference on the
>> prog sitting in priv->xdp_prog when it's exchanged by a new one. We also
>> need to make sure that we eventually release that reference, for example,
>> in case the netdev is dismantled.
>>
>> Fixes: 86994156c736 ("net/mlx5e: XDP fast RX drop bpf programs support")
>> Signed-off-by: Daniel Borkmann <[email-masked]>
>> ---
>>   drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>> index cf26672..60fe54c 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
>> @@ -3715,6 +3715,9 @@ static void mlx5e_nic_cleanup(struct mlx5e_priv *priv)
>>
>>          if (MLX5_CAP_GEN(mdev, vport_group_manager))
>>                  mlx5_eswitch_unregister_vport_rep(esw, 0);
>> +
>> +       if (priv->xdp_prog)
>> +               bpf_prog_put(priv->xdp_prog);
>>   }
>
> I thought that on unregister_netdev  ndo_xdp_set will be called with
> NULL prog to cleanup. like any other resources (Vlans/mac_lists/
> etc..), why xdp should be different ?
> Anyway if this is the case, I am ok with this fix, you can even send
> it to net (it looks like a serious leak).

The only interaction with ndo_xdp() right now is dev_change_xdp_fd()
and the currently a bit terse dump via rtnl_xdp_fill(). The latter
only tells whether something is actually attached and will have more
info in near future, but doesn't alter anything.

dev_change_xdp_fd() is only triggered from user side via netlink when
IFLA_XDP container attr is around, so no automatic cleanup here. This
means as per documentation in enum xdp_netdev_command, that the driver
has full ownership, thus needs to bpf_prog_put().