af_packet / TX_RING not fully non-blocking (w/ MSG_DONTWAIT).

This patch fixes an issue where the send(MSG_DONTWAIT) call
on a TX_RING is not fully non-blocking in cases where the device's sndBuf is
full. We pass nonblock=true to sock_alloc_send_skb() and return any possibly
occuring error code (most likely EGAIN) to the caller. As the fast-path stays
as it is, we keep the unlikely() around skb == NULL.

Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 3 deletions

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 5102c3cc4eec..b5989c6ee551 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2311,11 +2311,14 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
                 tlen = dev->needed_tailroom;
                 skb = sock_alloc_send_skb(&po->sk,
                                 hlen + tlen + sizeof(struct sockaddr_ll),
-                                0, &err);
+                                !need_wait, &err);
 
-                if (unlikely(skb == NULL))
+                if (unlikely(skb == NULL)) {
+                        /* we assume the socket was initially writeable ... */
+                        if (likely(len_sum > 0))
+                                err = len_sum;
                         goto out_status;
-
+                }
                 tp_len = tpacket_fill_skb(po, skb, ph, dev, size_max, proto,
                                           addr, hlen);
                 if (tp_len > dev->mtu + dev->hard_header_len) {