From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH v2 net] fq_codel: fix NET_XMIT_CN behavior
Date: Mon, 06 Jun 2016 07:37:25 -0700
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Cc: Jamal Hadi Salim <jhs@mojatatu.com>,
	Cong Wang <xiyou.wangcong@gmail.com>,
	David Miller <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>,
	Stas Nichiporovich <stasn77@gmail.com>
To: Florian Westphal <fw@strlen.de>
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On Mon, 2016-06-06 at 13:42 +0200, Florian Westphal wrote:
> Jamal Hadi Salim <jhs@mojatatu.com> wrote:
> > BTW, returning NET_XMIT_CN could be confusing to tcp;
> > it does not mean that the packet that we are getting return
> > code for was dropped; it could mean _another_ packet in
> > the queue was dropped.
> 
> Yes, but we currently conceal NET_XMIT_CN from upper layer (tcp)
> via the net_xmit_* macros:
> 
> #define net_xmit_eval(e)       ((e) == NET_XMIT_CN ? 0 : (e))
> #define net_xmit_errno(e)      ((e) != NET_XMIT_CN ? -ENOBUFS : 0)
> 
> Might be worth changing this so tcp reduces cwnd in _CN case too.

It always had been the case.

tcp_transmit_skb() calls tcp_enter_cwr(), unless someone broke this.