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Date: Tue, 18 Aug 2009 16:45:02 +0300 (EEST)
From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To: Damian Lukowski <damian@....rwth-aachen.de>
cc: David Miller <davem@...emloft.net>, Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] revert TCP retransmission backoff on ICMP destination
unreachable
On Fri, 14 Aug 2009, Damian Lukowski wrote:
>> Longer than 80 columns, and use an inline function instead
>> of a macro in order to get proper type checking.
>> [...]
>> Do not break up the function local variables with spurious new lines
>> like this, please.
>> [...]
>> The indentation and tabbing is messed up in all of the code you are
>> adding, please fix it up to be consistent with the surrounding code
>> and the rest of the TCP stack.
>>
>> Do not use C++ style // comments.
>
> Better?
Please, include the changelog message on resubmits too next time.
> Signed-off-by: Damian Lukowski <damian@....rwth-aachen.de>
> diff -Naur linux-2.6.30.4/include/net/tcp.h linux-2.6.30.4-tcp-icmp/include/net/tcp.h
> --- linux-2.6.30.4/include/net/tcp.h 2009-07-31 00:34:47.000000000 +0200
> +++ linux-2.6.30.4-tcp-icmp/include/net/tcp.h 2009-08-14 12:18:30.846060685 +0200
> @@ -1220,6 +1220,14 @@
> #define tcp_for_write_queue_from_safe(skb, tmp, sk) \
> skb_queue_walk_from_safe(&(sk)->sk_write_queue, skb, tmp)
>
> +static inline bool retrans_overstepped(const struct sock *sk,
> + unsigned int boundary)
> +{
> + return inet_csk(sk)->icsk_retransmits &&
> + (tcp_time_stamp - tcp_sk(sk)->retrans_stamp) >=
> + TCP_RTO_MIN*(2 << boundary);
> +}
> +
> static inline struct sk_buff *tcp_send_head(struct sock *sk)
> {
> return sk->sk_send_head;
> diff -Naur linux-2.6.30.4/net/ipv4/tcp_ipv4.c linux-2.6.30.4-tcp-icmp/net/ipv4/tcp_ipv4.c
> --- linux-2.6.30.4/net/ipv4/tcp_ipv4.c 2009-07-31 00:34:47.000000000 +0200
> +++ linux-2.6.30.4-tcp-icmp/net/ipv4/tcp_ipv4.c 2009-08-14 13:19:48.841598908 +0200
> @@ -332,11 +332,13 @@
> {
> struct iphdr *iph = (struct iphdr *)skb->data;
> struct tcphdr *th = (struct tcphdr *)(skb->data + (iph->ihl << 2));
> + struct inet_connection_sock *icsk;
> struct tcp_sock *tp;
> struct inet_sock *inet;
> const int type = icmp_hdr(skb)->type;
> const int code = icmp_hdr(skb)->code;
> struct sock *sk;
> + struct sk_buff *skb_r;
I'd make this called "skb", and change the old skb to icmp_skb.
> __u32 seq;
> int err;
> struct net *net = dev_net(skb->dev);
> @@ -367,6 +369,7 @@
> if (sk->sk_state == TCP_CLOSE)
> goto out;
>
> + icsk = inet_csk(sk);
> tp = tcp_sk(sk);
> seq = ntohl(th->seq);
> if (sk->sk_state != TCP_LISTEN &&
> @@ -393,6 +396,41 @@
> }
>
> err = icmp_err_convert[code].errno;
> + /* check if ICMP unreachable messages allow revert of backoff */
> + if ((code != ICMP_NET_UNREACH && code != ICMP_HOST_UNREACH) ||
> + seq != tp->snd_una || !icsk->icsk_retransmits ||
> + !icsk->icsk_backoff)
I'd recommend you break this into two if()\nbreak's, one for filtering
other icmps and other for filtering mismatching against the socket's
state.
> + break;
> +
> + icsk->icsk_backoff--;
> + icsk->icsk_rto >>= 1;
Are you absolute sure that we don't go to zero here when phase of the
moon is just right? I'd put a max(..., 1) guard there.
> +
> + skb_r = skb_peek(&sk->sk_write_queue);
tcp_write_queue_head(sk)
> + BUG_ON(!skb_r);
> +
> + if (sock_owned_by_user(sk)) {
> + /* Deferring retransmission clocked by ICMP
> + * due to locked socket. */
> + inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
> + min(icsk->icsk_rto, TCP_RESOURCE_PROBE_INTERVAL),
??? (besides having indent wrong). What makes you think HZ/2 is right
value if icsk_rto is large?
> + TCP_RTO_MAX);
Perhaps you lack here something to exit?
> + }
> +
> + if (tcp_time_stamp - TCP_SKB_CB(skb_r)->when >
> + inet_csk(sk)->icsk_rto) {
icsk->icsk_rto !?!
> + /* RTO revert clocked out retransmission. */
> + tcp_retransmit_skb(sk, skb_r);
This is plain wrong, tcp_sock counters will get messed up if
TCPCB_SACKED_RETRANS is already set while calling tcp_retransmit_skb. As a
sidenote, it would be probably useful to move the check + clear of that
bit before doing the retransmission to some common place one day.
> + inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
> + icsk->icsk_rto, TCP_RTO_MAX);
RFC 2988, step 5.5 missing? Have you verified this patch for real?
> + } else {
> + /* RTO revert shortened timer. */
> + inet_csk_reset_xmit_timer(
> + sk, ICSK_TIME_RETRANS,
> + icsk->icsk_rto-
> + (tcp_time_stamp-TCP_SKB_CB(skb_r)->when),
Spacing.
> + TCP_RTO_MAX);
> + }
> +
How about:
u32 remaining;
remaining = icsk->icsk_rto - min(icsk->icsk_rto,
tcp_time_stamp - TCP_SKB_CB(skb_r)->when));
if (!remaining) {
tcp_retransmit_skb(...);
remaining = icsk->icsk_rto;
}
inet_csk_reset_xmit_timer(..., remaining);
But check my note about step 5.5 (see above) to get remaining set right in
the if branch.
> break;
> case ICMP_TIME_EXCEEDED:
> err = EHOSTUNREACH;
> diff -Naur linux-2.6.30.4/net/ipv4/tcp_timer.c linux-2.6.30.4-tcp-icmp/net/ipv4/tcp_timer.c
> --- linux-2.6.30.4/net/ipv4/tcp_timer.c 2009-07-31 00:34:47.000000000 +0200
> +++ linux-2.6.30.4-tcp-icmp/net/ipv4/tcp_timer.c 2009-08-14 13:22:18.068666329 +0200
> @@ -143,7 +143,7 @@
> dst_negative_advice(&sk->sk_dst_cache);
> retry_until = icsk->icsk_syn_retries ? : sysctl_tcp_syn_retries;
> } else {
> - if (icsk->icsk_retransmits >= sysctl_tcp_retries1) {
> + if (retrans_overstepped(sk, sysctl_tcp_retries1)) {
??? Could you justify these changes and explain their relation to the
draft and icmp messages? If not, please drop them and try with proper
description and description for them in a separate patch. I fail to see
what you're trying to achieve here. You just ended up redefining the
sysctl meaning too I think...
> /* Black hole detection */
> tcp_mtu_probing(icsk, sk);
>
> @@ -156,12 +156,14 @@
>
> retry_until = tcp_orphan_retries(sk, alive);
>
> - if (tcp_out_of_resources(sk, alive || icsk->icsk_retransmits < retry_until))
> + if (tcp_out_of_resources(
> + sk, alive ||
> + !retrans_overstepped(sk, retry_until)))
???
> return 1;
> }
> }
>
> - if (icsk->icsk_retransmits >= retry_until) {
> + if (retrans_overstepped(sk, retry_until)) {
...
> /* Has it gone just too far? */
> tcp_write_err(sk);
> return 1;
> @@ -385,7 +387,7 @@
> out_reset_timer:
> icsk->icsk_rto = min(icsk->icsk_rto << 1, TCP_RTO_MAX);
> inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto, TCP_RTO_MAX);
> - if (icsk->icsk_retransmits > sysctl_tcp_retries1)
> + if (retrans_overstepped(sk, sysctl_tcp_retries1))
...I guess none of these retrans_overstepped are related to the icmp stuff
at all?
> __sk_dst_reset(sk);
>
> out:;
--
i.
--
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