[PATCH 2/3 resend] TCP_DEFER_ACCEPT updates - dont retxmt synack

[PATCH 2/3 resend] TCP_DEFER_ACCEPT updates - dont retxmt synack

[Patrick McManus]

commit 95dea62ad7004a1de84e1f38c1b5243e1cb0d554
Author: Patrick McManus <mcmanus@ducksong.com>
Date:   Sat Feb 23 15:59:22 2008 -0500

    a socket in LISTEN that had completed its 3 way handshake, but not notified
    userspace because of SO_DEFER_ACCEPT, would retransmit the already
    acked syn-ack during the time it was waiting for the first data byte
    from the peer.
    
    Signed-off-by: Patrick McManus <mcmanus@ducksong.com>
    Acked-by: Eric Dumazet <dada1@cosmosbay.com>

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 03cc323..3380d04 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -461,8 +461,9 @@ void inet_csk_reqsk_queue_prune(struct sock *parent,
 		reqp=&lopt->syn_table[i];
 		while ((req = *reqp) != NULL) {
 			if (time_after_eq(now, req->expires)) {
-				if ((req->retrans < (inet_rsk(req)->acked ? max_retries : thresh))
-				    && !req->rsk_ops->rtx_syn_ack(parent, req, NULL)) {
+				if ((req->retrans < (inet_rsk(req)->acked ? max_retries : thresh)) &&
+				    (inet_rsk(req)->acked ||
+				     !req->rsk_ops->rtx_syn_ack(parent, req, NULL))) {
 					unsigned long timeo;
 
 					if (req->retrans++ == 0)

[PATCH 3/3 (spin 2) resend] TCP_DEFER_ACCEPT updates - process as established

[Patrick McManus]

commit 4a234b7dd1a5144fe5630f1b0739e3c8c28de2ed
Author: Patrick McManus <mcmanus@ducksong.com>
Date:   Sun Mar 2 16:52:37 2008 -0500

    Change TCP_DEFER_ACCEPT implementation so that it transitions a
    connection to ESTABLISHED after handshake is complete instead of
    leaving it in SYN-RECV until some data arrvies. Place connection in
    accept queue when first data packet arrives from slow path.
    
    Benefits:
      - established connection is now reset if it never makes it
       to the accept queue
    
     - diagnostic state of established matches with the packet traces
       showing completed handshake
    
     - TCP_DEFER_ACCEPT timeouts are expressed in seconds and can now be
       enforced with reasonable accuracy instead of rounding up to next
       exponential back-off of syn-ack retry.
    
    Signed-off-by: Patrick McManus <mcmanus@ducksong.com>

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index 08027f1..d96d9b1 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -239,6 +239,11 @@ static inline struct tcp_request_sock *tcp_rsk(const struct request_sock *req)
 	return (struct tcp_request_sock *)req;
 }
 
+struct tcp_deferred_accept_info {
+	struct sock *listen_sk;
+	struct request_sock *request;
+};
+
 struct tcp_sock {
 	/* inet_connection_sock has to be the first member of tcp_sock */
 	struct inet_connection_sock	inet_conn;
@@ -374,6 +379,8 @@ struct tcp_sock {
 	unsigned int		keepalive_intvl;  /* time interval between keep alive probes */
 	int			linger2;
 
+	struct tcp_deferred_accept_info defer_tcp_accept;
+
 	unsigned long last_synq_overflow; 
 
 	u32	tso_deferred;
diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index cff4608..389abc4 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -116,8 +116,8 @@ struct request_sock_queue {
 	struct request_sock	*rskq_accept_head;
 	struct request_sock	*rskq_accept_tail;
 	rwlock_t		syn_wait_lock;
-	u8			rskq_defer_accept;
-	/* 3 bytes hole, try to pack */
+	u16			rskq_defer_accept;
+	/* 2 bytes hole, try to pack */
 	struct listen_sock	*listen_opt;
 };
 
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 7de4ea3..5780f62 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -138,6 +138,7 @@ extern void tcp_time_wait(struct sock *sk, int state, int timeo);
 #define MAX_TCP_KEEPINTVL	32767
 #define MAX_TCP_KEEPCNT		127
 #define MAX_TCP_SYNCNT		127
+#define MAX_TCP_ACCEPT_DEFERRED 65535
 
 #define TCP_SYNQ_INTERVAL	(HZ/5)	/* Period of SYNACK timer */
 
diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 3380d04..9323405 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -414,8 +414,7 @@ void inet_csk_reqsk_queue_prune(struct sock *parent,
 	struct inet_connection_sock *icsk = inet_csk(parent);
 	struct request_sock_queue *queue = &icsk->icsk_accept_queue;
 	struct listen_sock *lopt = queue->listen_opt;
-	int max_retries = icsk->icsk_syn_retries ? : sysctl_tcp_synack_retries;
-	int thresh = max_retries;
+	int thresh = icsk->icsk_syn_retries ? : sysctl_tcp_synack_retries;
 	unsigned long now = jiffies;
 	struct request_sock **reqp, *req;
 	int i, budget;
@@ -451,9 +450,6 @@ void inet_csk_reqsk_queue_prune(struct sock *parent,
 		}
 	}
 
-	if (queue->rskq_defer_accept)
-		max_retries = queue->rskq_defer_accept;
-
 	budget = 2 * (lopt->nr_table_entries / (timeout / interval));
 	i = lopt->clock_hand;
 
@@ -461,9 +457,8 @@ void inet_csk_reqsk_queue_prune(struct sock *parent,
 		reqp=&lopt->syn_table[i];
 		while ((req = *reqp) != NULL) {
 			if (time_after_eq(now, req->expires)) {
-				if ((req->retrans < (inet_rsk(req)->acked ? max_retries : thresh)) &&
-				    (inet_rsk(req)->acked ||
-				     !req->rsk_ops->rtx_syn_ack(parent, req, NULL))) {
+				if (req->retrans < thresh &&
+				    !req->rsk_ops->rtx_syn_ack(parent, req, NULL)) {
 					unsigned long timeo;
 
 					if (req->retrans++ == 0)
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index 071e83a..e0fbc25 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -2105,15 +2105,12 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
 		break;
 
 	case TCP_DEFER_ACCEPT:
-		icsk->icsk_accept_queue.rskq_defer_accept = 0;
-		if (val > 0) {
-			/* Translate value in seconds to number of
-			 * retransmits */
-			while (icsk->icsk_accept_queue.rskq_defer_accept < 32 &&
-			       val > ((TCP_TIMEOUT_INIT / HZ) <<
-				       icsk->icsk_accept_queue.rskq_defer_accept))
-				icsk->icsk_accept_queue.rskq_defer_accept++;
-			icsk->icsk_accept_queue.rskq_defer_accept++;
+		if (val < 0) {
+			err = -EINVAL;
+		} else {
+			if (val > MAX_TCP_ACCEPT_DEFERRED)
+				val = MAX_TCP_ACCEPT_DEFERRED;
+			icsk->icsk_accept_queue.rskq_defer_accept = val;
 		}
 		break;
 
@@ -2295,8 +2292,7 @@ static int do_tcp_getsockopt(struct sock *sk, int level,
 			val = (val ? : sysctl_tcp_fin_timeout) / HZ;
 		break;
 	case TCP_DEFER_ACCEPT:
-		val = !icsk->icsk_accept_queue.rskq_defer_accept ? 0 :
-			((TCP_TIMEOUT_INIT / HZ) << (icsk->icsk_accept_queue.rskq_defer_accept - 1));
+		val = icsk->icsk_accept_queue.rskq_defer_accept;
 		break;
 	case TCP_WINDOW_CLAMP:
 		val = tp->window_clamp;
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 7facdb0..b16714f 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4451,6 +4451,49 @@ static void tcp_urg(struct sock *sk, struct sk_buff *skb, struct tcphdr *th)
 	}
 }
 
+static int tcp_defer_accept_check(struct sock *sk)
+{
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	if (tp->defer_tcp_accept.request) {
+		int queued_data =  tp->rcv_nxt - tp->copied_seq;
+		int hasfin =  !skb_queue_empty(&sk->sk_receive_queue) ?
+			tcp_hdr((struct sk_buff *)
+				sk->sk_receive_queue.prev)->fin : 0;
+
+		if (queued_data && hasfin)
+			queued_data--;
+
+		if (queued_data &&
+		    tp->defer_tcp_accept.listen_sk->sk_state == TCP_LISTEN) {
+			if (sock_flag(sk, SOCK_KEEPOPEN)) {
+				inet_csk_reset_keepalive_timer(sk,
+							       keepalive_time_when(tp));
+			} else {
+				inet_csk_delete_keepalive_timer(sk);
+			}
+
+			inet_csk_reqsk_queue_add(
+				tp->defer_tcp_accept.listen_sk,
+				tp->defer_tcp_accept.request,
+				sk);
+
+			tp->defer_tcp_accept.listen_sk->sk_data_ready(
+				tp->defer_tcp_accept.listen_sk, 0);
+
+			sock_put(tp->defer_tcp_accept.listen_sk);
+			sock_put(sk);
+			tp->defer_tcp_accept.listen_sk = NULL;
+			tp->defer_tcp_accept.request = NULL;
+		} else if (hasfin ||
+			   tp->defer_tcp_accept.listen_sk->sk_state != TCP_LISTEN) {
+			tcp_reset(sk);
+			return -1;
+		}
+	}
+	return 0;
+}
+
 static int tcp_copy_to_iovec(struct sock *sk, struct sk_buff *skb, int hlen)
 {
 	struct tcp_sock *tp = tcp_sk(sk);
@@ -4811,6 +4854,9 @@ step5:
 
 	tcp_data_snd_check(sk);
 	tcp_ack_snd_check(sk);
+
+	if (tcp_defer_accept_check(sk))
+		return -1;
 	return 0;
 
 csum_error:
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 00156bf..d4c9d03 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1921,6 +1921,14 @@ int tcp_v4_destroy_sock(struct sock *sk)
 		sk->sk_sndmsg_page = NULL;
 	}
 
+	if (tp->defer_tcp_accept.request) {
+		reqsk_free(tp->defer_tcp_accept.request);
+		sock_put(tp->defer_tcp_accept.listen_sk);
+		sock_put(sk);
+		tp->defer_tcp_accept.listen_sk = NULL;
+		tp->defer_tcp_accept.request = NULL;
+	}
+
 	atomic_dec(&tcp_sockets_allocated);
 
 	return 0;
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index b61b768..ab519d8 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -569,10 +569,8 @@ struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb,
 	   does sequence test, SYN is truncated, and thus we consider
 	   it a bare ACK.
 
-	   If icsk->icsk_accept_queue.rskq_defer_accept, we silently drop this
-	   bare ACK.  Otherwise, we create an established connection.  Both
-	   ends (listening sockets) accept the new incoming connection and try
-	   to talk to each other. 8-)
+	   Both ends (listening sockets) accept the new incoming
+	   connection and try to talk to each other. 8-)
 
 	   Note: This case is both harmless, and rare.  Possibility is about the
 	   same as us discovering intelligent life on another plant tomorrow.
@@ -640,13 +638,6 @@ struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb,
 		if (!(flg & TCP_FLAG_ACK))
 			return NULL;
 
-		/* If TCP_DEFER_ACCEPT is set, drop bare ACK. */
-		if (inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
-		    TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
-			inet_rsk(req)->acked = 1;
-			return NULL;
-		}
-
 		/* OK, ACK is valid, create big socket and
 		 * feed this segment to it. It will repeat all
 		 * the tests. THIS SEGMENT MUST MOVE SOCKET TO
@@ -685,7 +676,24 @@ struct sock *tcp_check_req(struct sock *sk,struct sk_buff *skb,
 		inet_csk_reqsk_queue_unlink(sk, req, prev);
 		inet_csk_reqsk_queue_removed(sk, req);
 
-		inet_csk_reqsk_queue_add(sk, req, child);
+		if (inet_csk(sk)->icsk_accept_queue.rskq_defer_accept &&
+		    TCP_SKB_CB(skb)->end_seq == tcp_rsk(req)->rcv_isn + 1) {
+
+			/* the accept queue handling is done is est recv slow
+			 * path so lets make sure to start there
+			 */
+			tcp_sk(child)->pred_flags = 0;
+			sock_hold(sk);
+			sock_hold(child);
+			tcp_sk(child)->defer_tcp_accept.listen_sk = sk;
+			tcp_sk(child)->defer_tcp_accept.request = req;
+
+			inet_csk_reset_keepalive_timer(child,
+						       inet_csk(sk)->icsk_accept_queue.rskq_defer_accept * HZ);
+		} else {
+			inet_csk_reqsk_queue_add(sk, req, child);
+		}
+
 		return child;
 
 	listen_overflow:
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 803d758..160d16f 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -481,6 +481,11 @@ static void tcp_keepalive_timer (unsigned long data)
 		goto death;
 	}
 
+	if (tp->defer_tcp_accept.request && sk->sk_state == TCP_ESTABLISHED) {
+		tcp_send_active_reset(sk, GFP_ATOMIC);
+		goto death;
+	}
+
 	if (!sock_flag(sk, SOCK_KEEPOPEN) || sk->sk_state == TCP_CLOSE)
 		goto out;
 

Re: [PATCH 3/3 (spin 2) resend] TCP_DEFER_ACCEPT updates - process as established

[David Miller]

This looks wrong.  Are you sure you're resending the
correct patch?

The most uptodate version was "spin 3" in which you
incorporated coding style and checkpatch.pl fixes
as recommended by Ilpo.

Re: [PATCH 3/3 (spin 2) resend] TCP_DEFER_ACCEPT updates - process as established

[Patrick McManus]

David,

Thanks for the note - it can be hard to tell patch latency apart from
the drops.

You caught a mistake with the subject line - that patch was indeed spin
#3 - it was the exact same diff as I sent on March 6. 


-Patrick


On Thu, 2008-03-20 at 16:18 -0700, David Miller wrote:
> This looks wrong.  Are you sure you're resending the
> correct patch?
> 
> The most uptodate version was "spin 3" in which you
> incorporated coding style and checkpatch.pl fixes
> as recommended by Ilpo.

Re: [PATCH 2/3 resend] TCP_DEFER_ACCEPT updates - dont retxmt synack

[David Miller]

From: Patrick McManus <mcmanus@ducksong.com>
Date: Thu, 20 Mar 2008 18:55:55 -0400

> commit 95dea62ad7004a1de84e1f38c1b5243e1cb0d554
> Author: Patrick McManus <mcmanus@ducksong.com>
> Date:   Sat Feb 23 15:59:22 2008 -0500
> 
>     a socket in LISTEN that had completed its 3 way handshake, but not notified
>     userspace because of SO_DEFER_ACCEPT, would retransmit the already
>     acked syn-ack during the time it was waiting for the first data byte
>     from the peer.
>     
>     Signed-off-by: Patrick McManus <mcmanus@ducksong.com>
>     Acked-by: Eric Dumazet <dada1@cosmosbay.com>

Applied to net-2.6.26

Re: [PATCH 3/3 (spin 2) resend] TCP_DEFER_ACCEPT updates - process as established

[David Miller]

From: Patrick McManus <mcmanus@ducksong.com>
Date: Thu, 20 Mar 2008 18:55:58 -0400

> commit 4a234b7dd1a5144fe5630f1b0739e3c8c28de2ed
> Author: Patrick McManus <mcmanus@ducksong.com>
> Date:   Sun Mar 2 16:52:37 2008 -0500
> 
>     Change TCP_DEFER_ACCEPT implementation so that it transitions a
>     connection to ESTABLISHED after handshake is complete instead of
>     leaving it in SYN-RECV until some data arrvies. Place connection in
>     accept queue when first data packet arrives from slow path.
>     
>     Benefits:
>       - established connection is now reset if it never makes it
>        to the accept queue
>     
>      - diagnostic state of established matches with the packet traces
>        showing completed handshake
>     
>      - TCP_DEFER_ACCEPT timeouts are expressed in seconds and can now be
>        enforced with reasonable accuracy instead of rounding up to next
>        exponential back-off of syn-ack retry.
>     
>     Signed-off-by: Patrick McManus <mcmanus@ducksong.com>

Applied and pushed to net-2.6.26, thanks.