linux-kernel - Re: [PATCH AUTOSEL for 3.18 40/40] tcp: fix under-evaluated ssthresh in TCP Vegas

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Date:   Thu, 21 Dec 2017 10:54:34 +0100
From:   Greg KH <greg@...ah.com>
To:     alexander.levin@...izon.com
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Hoang Tran <tranviethoang.vn@...il.com>,
        Hoang Tran <hoang.tran@...ouvain.be>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH AUTOSEL for 3.18 40/40] tcp: fix under-evaluated ssthresh
 in TCP Vegas

On Wed, Dec 13, 2017 at 01:59:21AM +0000, alexander.levin@...izon.com wrote:
> From: Hoang Tran <tranviethoang.vn@...il.com>
> 
> [ Upstream commit cf5d74b85ef40c202c76d90959db4d850f301b95 ]
> 
> With the commit 76174004a0f19785 (tcp: do not slow start when cwnd equals
> ssthresh), the comparison to the reduced cwnd in tcp_vegas_ssthresh() would
> under-evaluate the ssthresh.
> 
> Signed-off-by: Hoang Tran <hoang.tran@...ouvain.be>
> Signed-off-by: David S. Miller <davem@...emloft.net>
> Signed-off-by: Sasha Levin <alexander.levin@...izon.com>
> ---
>  net/ipv4/tcp_vegas.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

76174004a0f19785 did not show up until 4.3-rc1, so this isn't needed for
3.18-stable, so I'm going to drop it from that set of patches.

thanks,

greg k-h

> 
> diff --git a/net/ipv4/tcp_vegas.c b/net/ipv4/tcp_vegas.c
> index a6afde666ab1..28b2728a06c4 100644
> --- a/net/ipv4/tcp_vegas.c
> +++ b/net/ipv4/tcp_vegas.c
> @@ -158,7 +158,7 @@ EXPORT_SYMBOL_GPL(tcp_vegas_cwnd_event);
>  
>  static inline u32 tcp_vegas_ssthresh(struct tcp_sock *tp)
>  {
> -	return  min(tp->snd_ssthresh, tp->snd_cwnd-1);
> +	return  min(tp->snd_ssthresh, tp->snd_cwnd);
>  }
>  
>  static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 acked)
> -- 
> 2.11.0