On 7/1/22 11:57 AM, Eric Dumazet wrote:
On Fri, Jul 1, 2022 at 11:43 AM Johan Almbladh
<johan.almbladh@xxxxxxxxxxxxxxxxx> wrote:
The byte queue limits (BQL) mechanism is intended to move queuing from
the driver to the network stack in order to reduce latency caused by
excessive queuing in hardware. However, when transmitting or redirecting
a packet with XDP, the qdisc layer is bypassed and there are no
additional queues. Since netif_xmit_stopped() also takes BQL limits into
account, but without having any alternative queuing, packets are
silently dropped.
This patch modifies the drop condition to only consider cases when the
driver itself cannot accept any more packets. This is analogous to the
condition in __dev_direct_xmit(). Dropped packets are also counted on
the device.
This means XDP packets are able to starve other packets going through a qdisc,
DDOS attacks will be more effective.
in-driver-XDP use dedicated TX queues, so they do not have this
starvation issue.
This should be mentioned somewhere I guess.
+1, Johan, could you add this as comment and into commit description in a v2
of your fix? Definitely should be clarified that it's limited to generic XDP.
Thanks,
Daniel
