From: <sjpark@amazon.com>
To: Eric Dumazet <edumazet@google.com>
Cc: <sjpark@amazon.com>, David Miller <davem@davemloft.net>,
Shuah Khan <shuah@kernel.org>, netdev <netdev@vger.kernel.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>, <sj38.park@gmail.com>,
<aams@amazon.com>, SeongJae Park <sjpark@amazon.de>
Subject: Re: Re: Re: [PATCH 2/3] tcp: Reduce SYN resend delay if a suspicous ACK is received
Date: Fri, 31 Jan 2020 18:05:08 +0100 [thread overview]
Message-ID: <20200131170508.21323-1-sjpark@amazon.com> (raw)
In-Reply-To: <CANn89iJjZdoTKnnHNAByp7euDWo0aW9bL8ngw78vx4z7pwBJiw@mail.gmail.com>
On Fri, 31 Jan 2020 08:55:08 -0800 Eric Dumazet <edumazet@google.com> wrote:
> On Fri, Jan 31, 2020 at 8:12 AM <sjpark@amazon.com> wrote:
> >
> > On Fri, 31 Jan 2020 07:01:21 -0800 Eric Dumazet <edumazet@google.com> wrote:
> >
> > > On Fri, Jan 31, 2020 at 4:25 AM <sjpark@amazon.com> wrote:
> > >
> > > > Signed-off-by: SeongJae Park <sjpark@amazon.de>
> > > > ---
> > > > net/ipv4/tcp_input.c | 6 +++++-
> > > > 1 file changed, 5 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> > > > index 2a976f57f7e7..b168e29e1ad1 100644
> > > > --- a/net/ipv4/tcp_input.c
> > > > +++ b/net/ipv4/tcp_input.c
> > > > @@ -5893,8 +5893,12 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
> > > > * the segment and return)"
> > > > */
> > > > if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
> > > > - after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
> > > > + after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
> > > > + /* Previous FIN/ACK or RST/ACK might be ignore. */
> > > > + inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
> > > > + TCP_ATO_MIN, TCP_RTO_MAX);
> > >
> > > This is not what I suggested.
> > >
> > > I suggested implementing a strategy where only the _first_ retransmit
> > > would be done earlier.
> > >
> > > So you need to look at the current counter of retransmit attempts,
> > > then reset the timer if this SYN_SENT
> > > socket never resent a SYN.
> > >
> > > We do not want to trigger packet storms, if for some reason the remote
> > > peer constantly sends
> > > us the same packet.
> >
> > You're right, I missed the important point, thank you for pointing it. Among
> > retransmission related fields of 'tcp_sock', I think '->total_retrans' would
> > fit for this check. How about below change?
> >
> > ```
> > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> > index 2a976f57f7e7..29fc0e4da931 100644
> > --- a/net/ipv4/tcp_input.c
> > +++ b/net/ipv4/tcp_input.c
> > @@ -5893,8 +5893,14 @@ static int tcp_rcv_synsent_state_process(struct sock *sk, struct sk_buff *skb,
> > * the segment and return)"
> > */
> > if (!after(TCP_SKB_CB(skb)->ack_seq, tp->snd_una) ||
> > - after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt))
> > + after(TCP_SKB_CB(skb)->ack_seq, tp->snd_nxt)) {
> > + /* Previous FIN/ACK or RST/ACK might be ignored. */
> > + if (tp->total_retrans == 0)
>
> canonical fied would be icsk->icsk_retransmits (look in net/ipv4/tcp_timer.c )
>
> AFAIK, it seems we forget to clear tp->total_retrans in tcp_disconnect()
> I will send a patch for this tp->total_retrans thing.
Oh, then I will use 'tcsk->icsk_retransmits' instead of 'tp->total_retrans', in
next spin. May I also ask you to Cc me for your 'tp->total_retrans' fix patch?
Thanks,
SeongJae Park
>
> > + inet_csk_reset_xmit_timer(sk,
> > + ICSK_TIME_RETRANS, TCP_ATO_MIN,
> > + TCP_RTO_MAX);
> > goto reset_and_undo;
> > + }
> >
> > if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
> > !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
> > ```
> >
> > Thanks,
> > SeongJae Park
> >
> > >
> > > Thanks.
> > >
> > > > goto reset_and_undo;
> > > > + }
> > > >
> > > > if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
> > > > !between(tp->rx_opt.rcv_tsecr, tp->retrans_stamp,
> > > > --
> > > > 2.17.1
> > > >
> > >
>
next prev parent reply other threads:[~2020-01-31 17:05 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-31 12:24 [PATCH 0/3] Fix reconnection latency caused by FIN/ACK handling race sjpark
2020-01-31 12:24 ` [PATCH 1/3] net/ipv4/inet_timewait_sock: Fix inconsistent comments sjpark
2020-01-31 14:54 ` Eric Dumazet
2020-01-31 15:09 ` sjpark
2020-01-31 12:24 ` [PATCH 2/3] tcp: Reduce SYN resend delay if a suspicous ACK is received sjpark
2020-01-31 15:01 ` Eric Dumazet
2020-01-31 16:12 ` sjpark
2020-01-31 16:55 ` Eric Dumazet
2020-01-31 17:05 ` sjpark [this message]
2020-01-31 17:08 ` Eric Dumazet
2020-01-31 15:10 ` Neal Cardwell
2020-01-31 18:12 ` Eric Dumazet
2020-01-31 22:11 ` Neal Cardwell
2020-01-31 22:17 ` SeongJae Park
2020-02-01 3:55 ` Neal Cardwell
2020-02-01 6:08 ` SeongJae Park
2020-02-01 13:30 ` Neal Cardwell
2020-01-31 22:53 ` Eric Dumazet
2020-02-03 15:40 ` David Laight
2020-02-03 15:54 ` Eric Dumazet
2020-01-31 12:24 ` [PATCH 3/3] selftests: net: Add FIN_ACK processing order related latency spike test sjpark
2020-01-31 14:56 ` Eric Dumazet
2020-01-31 15:13 ` sjpark
2020-01-31 14:00 ` [PATCH 0/3] Fix reconnection latency caused by FIN/ACK handling race David Laight
2020-01-31 15:05 ` sjpark
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