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

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Date:	Wed, 29 Jun 2016 05:26:17 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	ncardwell@...gle.com, arjun@...lsio.com, edumazet@...gle.com,
	netdev@...r.kernel.org, hariprasad@...lsio.com, leedom@...lsio.com,
	kumaras@...lsio.com, santosh@...lsio.com, nirranjan@...lsio.com,
	ycheng@...gle.com
Subject: Re: [PATCH net] tcp: do not send too big packets at retransmit time

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Mon, 27 Jun 2016 17:38:50 +0200

> From: Eric Dumazet <edumazet@...gle.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@...gle.com>
> Reported-by: Arjun V <arjun@...lsio.com>
> Tested-by: Arjun V <arjun@...lsio.com>

Applied.