xsk: Do not discard packet when NETDEV_TX_BUSY
authorMagnus Karlsson <magnus.karlsson@intel.com>
Wed, 16 Sep 2020 12:00:25 +0000 (14:00 +0200)
committerDaniel Borkmann <daniel@iogearbox.net>
Wed, 16 Sep 2020 21:36:58 +0000 (23:36 +0200)
commit642e450b6b5955f2059d0ae372183f7c6323f951
tree68ee2df78dae105e2f652f7e475fe2e11a352404
parentd5d325eae7823c85eedabf05f78f9cd574fe832b
xsk: Do not discard packet when NETDEV_TX_BUSY

In the skb Tx path, transmission of a packet is performed with
dev_direct_xmit(). When NETDEV_TX_BUSY is set in the drivers, it
signifies that it was not possible to send the packet right now,
please try later. Unfortunately, the xsk transmit code discarded the
packet and returned EBUSY to the application. Fix this unnecessary
packet loss, by not discarding the packet in the Tx ring and return
EAGAIN. As EAGAIN is returned to the application, it can then retry
the send operation later and the packet will then likely be sent as
the driver will then likely have space/resources to send the packet.

In summary, EAGAIN tells the application that the packet was not
discarded from the Tx ring and that it needs to call send()
again. EBUSY, on the other hand, signifies that the packet was not
sent and discarded from the Tx ring. The application needs to put
the packet on the Tx ring again if it wants it to be sent.

Fixes: 35fcde7f8deb ("xsk: support for Tx")
Reported-by: Arkadiusz Zema <A.Zema@falconvsystems.com>
Suggested-by: Arkadiusz Zema <A.Zema@falconvsystems.com>
Suggested-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Link: https://lore.kernel.org/bpf/1600257625-2353-1-git-send-email-magnus.karlsson@gmail.com
net/xdp/xsk.c