netdev - Re: [PATCH net-next v2] tcp: avoid reducing cwnd when ACK+DSACK is received

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 08 Jan 2015 07:19:56 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Sébastien Barré <sebastien.barre@...ouvain.be>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Gregory Detal <gregory.detal@...ouvain.be>,
	Nandita Dukkipati <nanditad@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next v2] tcp: avoid reducing cwnd when ACK+DSACK is
 received

On Thu, 2015-01-08 at 13:20 +0100, Sébastien Barré wrote:
> When the peer has delayed ack enabled, it may reply to a probe with an
> ACK+D-SACK, with ack value set to tlp_high_seq. In the current code,
> such ACK+DSACK will be missed and only at next, higher ack will the TLP
> episode be considered done. Since the DSACK is not present anymore,
> this will cost a cwnd reduction.
> 
...
>  net/ipv4/tcp_input.c | 30 +++++++++++++-----------------
>  1 file changed, 13 insertions(+), 17 deletions(-)
> 
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 075ab4d..cf63a29 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3363,29 +3363,25 @@ static void tcp_replace_ts_recent(struct tcp_sock *tp, u32 seq)
>  static void tcp_process_tlp_ack(struct sock *sk, u32 ack, int flag)
>  {
>  	struct tcp_sock *tp = tcp_sk(sk);
> -	bool is_tlp_dupack = (ack == tp->tlp_high_seq) &&
> -			     !(flag & (FLAG_SND_UNA_ADVANCED |
> -				       FLAG_NOT_DUP | FLAG_DATA_SACKED));
>  

No idea why you removed this bool, it really helped to understand the
code. This makes your patch looks more complex than needed.

>  	/* Mark the end of TLP episode on receiving TLP dupack or when
>  	 * ack is after tlp_high_seq.
> +	 * With delayed acks, we may also get a regular ACK+DSACK, in which
> +	 * case we don't want to reduce the cwnd either.
>  	 */
> -	if (is_tlp_dupack) {
> +	if (((ack == tp->tlp_high_seq) &&
> +	     !(flag & (FLAG_SND_UNA_ADVANCED |
> +		       FLAG_NOT_DUP | FLAG_DATA_SACKED))) ||
> +	    (!before(ack, tp->tlp_high_seq) && (flag & FLAG_DSACKING_ACK))) {
>  		tp->tlp_high_seq = 0;
> -		return;
> -	}


--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html