Re: [PATCH net] tcp: do not send too big packets at retransmit time

On Mon, Jun 27, 2016 at 11:38 AM, Eric Dumazet [off-list ref] 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 <redacted>
Tested-by: Arjun V <redacted>
---
 net/ipv4/tcp_output.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

Acked-by: Neal Cardwell <ncardwell@google.com>

Thanks, Eric!

neal