linux-kernel - Re: [PATCH] tcp: fix marked lost packets not being retransmitted

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Message-Id: <20200115.133542.149188857628032129.davem@davemloft.net>
Date:   Wed, 15 Jan 2020 13:35:42 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     yangpc@...gsu.com
Cc:     edumazet@...gle.com, kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        ast@...nel.org, daniel@...earbox.net, kafai@...com,
        songliubraving@...com, yhs@...com, andriin@...com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tcp: fix marked lost packets not being retransmitted

From: Pengcheng Yang <yangpc@...gsu.com>
Date: Tue, 14 Jan 2020 17:23:40 +0800

> When the packet pointed to by retransmit_skb_hint is unlinked by ACK,
> retransmit_skb_hint will be set to NULL in tcp_clean_rtx_queue().
> If packet loss is detected at this time, retransmit_skb_hint will be set
> to point to the current packet loss in tcp_verify_retransmit_hint(),
> then the packets that were previously marked lost but not retransmitted
> due to the restriction of cwnd will be skipped and cannot be
> retransmitted.
> 
> To fix this, when retransmit_skb_hint is NULL, retransmit_skb_hint can
> be reset only after all marked lost packets are retransmitted
> (retrans_out >= lost_out), otherwise we need to traverse from
> tcp_rtx_queue_head in tcp_xmit_retransmit_queue().
> 
> Packetdrill to demonstrate:
 ...
> Signed-off-by: Pengcheng Yang <yangpc@...gsu.com>

Applied, thank you.