From 642e450b6b5955f2059d0ae372183f7c6323f951 Mon Sep 17 00:00:00 2001 From: Magnus Karlsson Date: Wed, 16 Sep 2020 14:00:25 +0200 Subject: 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 Suggested-by: Arkadiusz Zema Suggested-by: Daniel Borkmann Signed-off-by: Magnus Karlsson Signed-off-by: Daniel Borkmann Reviewed-by: Jesse Brandeburg Link: https://lore.kernel.org/bpf/1600257625-2353-1-git-send-email-magnus.karlsson@gmail.com --- net/xdp/xsk.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) (limited to 'net/xdp') diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c index c3231620d210..6c5e09e7440a 100644 --- a/net/xdp/xsk.c +++ b/net/xdp/xsk.c @@ -377,15 +377,30 @@ static int xsk_generic_xmit(struct sock *sk) skb_shinfo(skb)->destructor_arg = (void *)(long)desc.addr; skb->destructor = xsk_destruct_skb; + /* Hinder dev_direct_xmit from freeing the packet and + * therefore completing it in the destructor + */ + refcount_inc(&skb->users); err = dev_direct_xmit(skb, xs->queue_id); + if (err == NETDEV_TX_BUSY) { + /* Tell user-space to retry the send */ + skb->destructor = sock_wfree; + /* Free skb without triggering the perf drop trace */ + consume_skb(skb); + err = -EAGAIN; + goto out; + } + xskq_cons_release(xs->tx); /* Ignore NET_XMIT_CN as packet might have been sent */ - if (err == NET_XMIT_DROP || err == NETDEV_TX_BUSY) { + if (err == NET_XMIT_DROP) { /* SKB completed but not sent */ + kfree_skb(skb); err = -EBUSY; goto out; } + consume_skb(skb); sent_frame = true; } -- cgit v1.2.3