| Message ID | 1467041930.6850.166.camel@edumazet-glaptop3.roam.corp.google.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On Mon, Jun 27, 2016 at 11:38 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote: > From: Eric Dumazet <edumazet@google.com> > > 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 <edumazet@google.com> > Reported-by: Arjun V <arjun@chelsio.com> > Tested-by: Arjun V <arjun@chelsio.com> > --- > net/ipv4/tcp_output.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) Acked-by: Neal Cardwell <ncardwell@google.com> Thanks, Eric! neal
From: Eric Dumazet <eric.dumazet@gmail.com> Date: Mon, 27 Jun 2016 17:38:50 +0200 > From: Eric Dumazet <edumazet@google.com> > > 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 <edumazet@google.com> > Reported-by: Arjun V <arjun@chelsio.com> > Tested-by: Arjun V <arjun@chelsio.com> Applied.
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) return; + /* 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) { begin_fwd: