diff options
authorEric Dumazet <edumazet@google.com>2019-12-12 12:55:29 -0800
committerJakub Kicinski <jakub.kicinski@netronome.com>2019-12-13 21:58:40 -0800
commit1f85e6267caca44b30c54711652b0726fadbb131 (patch)
parent6pack,mkiss: fix possible deadlock (diff)
tcp: do not send empty skb from tcp_write_xmit()
Backport of commit fdfc5c8594c2 ("tcp: remove empty skb from write queue in error cases") in linux-4.14 stable triggered various bugs. One of them has been fixed in commit ba2ddb43f270 ("tcp: Don't dequeue SYN/FIN-segments from write-queue"), but we still have crashes in some occasions. Root-cause is that when tcp_sendmsg() has allocated a fresh skb and could not append a fragment before being blocked in sk_stream_wait_memory(), tcp_write_xmit() might be called and decide to send this fresh and empty skb. Sending an empty packet is not only silly, it might have caused many issues we had in the past with tp->packets_out being out of sync. Fixes: c65f7f00c587 ("[TCP]: Simplify SKB data portion allocation with NETIF_F_SG.") Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Christoph Paasch <cpaasch@apple.com> Acked-by: Neal Cardwell <ncardwell@google.com> Cc: Jason Baron <jbaron@akamai.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Diffstat (limited to '')
1 files changed, 8 insertions, 0 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index b184f03d7437..57f434a8e41f 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2438,6 +2438,14 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int mss_now, int nonagle,
if (tcp_small_queue_check(sk, skb, 0))
+ /* Argh, we hit an empty skb(), presumably a thread
+ * is sleeping in sendmsg()/sk_stream_wait_memory().
+ * We do not want to send a pure-ack packet and have
+ * a strange looking rtx queue with empty packet(s).
+ */
+ if (TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq)
+ break;
if (unlikely(tcp_transmit_skb(sk, skb, 1, gfp)))