netdev - Re: [PATCH net-next 2/3] tcp: allow segment with FIN in tcp_try

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Message-ID: <1410778626.7106.145.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Mon, 15 Sep 2014 03:57:06 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eric Dumazet <edumazet@...gle.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Yuchung Cheng <ycheng@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next 2/3] tcp: allow segment with FIN in
 tcp_try_coalesce()

On Sun, 2014-09-14 at 19:56 -0700, Eric Dumazet wrote:
> There is nothing special with allowing a segment with FIN to be aggregated,
> if we take care to add tcp flags.
> 
> Signed-of-by: Eric Dumazet <edumazet@...gle.com>
> ---
>  net/ipv4/tcp_input.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 8f639a4face9..228bf0c5ff19 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -4143,9 +4143,6 @@ static bool tcp_try_coalesce(struct sock *sk,
>  
>  	*fragstolen = false;
>  
> -	if (tcp_hdr(from)->fin)
> -		return false;
> -
>  	/* Its possible this segment overlaps with prior segment in queue */
>  	if (TCP_SKB_CB(from)->seq != TCP_SKB_CB(to)->end_seq)
>  		return false;
> @@ -4158,6 +4155,7 @@ static bool tcp_try_coalesce(struct sock *sk,
>  	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPRCVCOALESCE);
>  	TCP_SKB_CB(to)->end_seq = TCP_SKB_CB(from)->end_seq;
>  	TCP_SKB_CB(to)->ack_seq = TCP_SKB_CB(from)->ack_seq;
> +	TCP_SKB_CB(to)->tcp_flags |= TCP_SKB_CB(from)->tcp_flags;
>  	return true;
>  }
>  

This patch needs to be refined.

skb_try_coalesce() should not do an unconditional 
BUG_ON(skb_copy_bits(from, 0, skb_put(to, len), len));

And do it only if len is non 0

I will send a v2


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