Commit a3d2e9f8 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller

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: 10d3be56 ("tcp-tso: do not split TSO packets at retransmit time")
Signed-off-by: default avatarEric Dumazet <>
Reported-by: default avatarArjun V <>
Tested-by: default avatarArjun V <>
Acked-by: default avatarNeal Cardwell <>
Signed-off-by: default avatarDavid S. Miller <>
parent 96183182
......@@ -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) {
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