path: root/net
diff options
authorEric Dumazet <>2016-06-27 17:38:50 +0200
committerDavid S. Miller <>2016-06-29 05:25:11 -0400
commita3d2e9f8eb1487f4191ff08ce2d3d63702c65a90 (patch)
tree6bd92ff1c7e9c968a795b73804f7cc2869f68659 /net
parent96183182ad05d1ce31b9048921c12bf4ad621eaf (diff)
tcp: do not send too big packets at retransmit time
Arjun reported a bug in TCP stack and bisected it to a recent commit. In case where we process SACK, we can coalesce multiple skbs into fat ones (tcp_shift_skb_data()), to lower write queue overhead, because we do not expect to retransmit these packets. However, SACK reneging can happen, forcing the sender to retransmit all these packets. If skb->len is above 64KB, we then send buggy IP packets that could hang TSO engine on cxgb4. Neal suggested to use tcp_tso_autosize() instead of tp->gso_segs so that we cook packets of optimal size vs TCP/pacing. Thanks to Arjun for reporting the bug and running the tests ! Fixes: 10d3be569243 ("tcp-tso: do not split TSO packets at retransmit time") Signed-off-by: Eric Dumazet <> Reported-by: Arjun V <> Tested-by: Arjun V <> Acked-by: Neal Cardwell <> Signed-off-by: David S. Miller <>
Diffstat (limited to 'net')
1 files changed, 6 insertions, 1 deletions
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 8bd9911fdd16..e00e972c4e6a 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2751,7 +2751,7 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *skb;
struct sk_buff *hole = NULL;
- u32 last_lost;
+ u32 max_segs, last_lost;
int mib_idx;
int fwd_rexmitting = 0;
@@ -2771,6 +2771,7 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
last_lost = tp->snd_una;
+ max_segs = tcp_tso_autosize(sk, tcp_current_mss(sk));
tcp_for_write_queue_from(skb, sk) {
__u8 sacked = TCP_SKB_CB(skb)->sacked;
int segs;
@@ -2784,6 +2785,10 @@ void tcp_xmit_retransmit_queue(struct sock *sk)
segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
if (segs <= 0)
+ /* In case tcp_shift_skb_data() have aggregated large skbs,
+ * we need to make sure not sending too bigs TSO packets
+ */
+ segs = min_t(int, segs, max_segs);
if (fwd_rexmitting) {