[PATCH net-next] tcp: out_of_order_queue do not use its lock

[PATCH net-next] tcp: out_of_order_queue do not use its lock

[Eric Dumazet]

From: Eric Dumazet <edumazet@google.com>

TCP out_of_order_queue lock is not used, as queue manipulation
happens with socket lock held and we therefore use the lockless
skb queue routines (as __skb_queue_head())

We can use __skb_queue_head_init() instead of skb_queue_head_init()
to make this more consistent.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/linux/tcp.h      |    5 ++++-
 net/ipv4/tcp.c           |    2 +-
 net/ipv4/tcp_minisocks.c |    2 +-
 3 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/tcp.h b/include/linux/tcp.h
index d68633452d9b..4ad0706d40eb 100644
--- a/include/linux/tcp.h
+++ b/include/linux/tcp.h
@@ -248,7 +248,10 @@ struct tcp_sock {
 	struct sk_buff* lost_skb_hint;
 	struct sk_buff *retransmit_skb_hint;
 
-	struct sk_buff_head	out_of_order_queue; /* Out of order segments go here */
+	/* OOO segments go in this list. Note that socket lock must be held,
+	 * as we do not use sk_buff_head lock.
+	 */
+	struct sk_buff_head	out_of_order_queue;
 
 	/* SACKs data, these 2 need to be together (see tcp_options_write) */
 	struct tcp_sack_block duplicate_sack[1]; /* D-SACK block */
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index d099f9a055c6..e2a40515e665 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -381,7 +381,7 @@ void tcp_init_sock(struct sock *sk)
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	skb_queue_head_init(&tp->out_of_order_queue);
+	__skb_queue_head_init(&tp->out_of_order_queue);
 	tcp_init_xmit_timers(sk);
 	tcp_prequeue_init(tp);
 	INIT_LIST_HEAD(&tp->tsq_node);
diff --git a/net/ipv4/tcp_minisocks.c b/net/ipv4/tcp_minisocks.c
index 97b684159861..3aa9e3247991 100644
--- a/net/ipv4/tcp_minisocks.c
+++ b/net/ipv4/tcp_minisocks.c
@@ -425,7 +425,7 @@ struct sock *tcp_create_openreq_child(struct sock *sk, struct request_sock *req,
 
 		tcp_set_ca_state(newsk, TCP_CA_Open);
 		tcp_init_xmit_timers(newsk);
-		skb_queue_head_init(&newtp->out_of_order_queue);
+		__skb_queue_head_init(&newtp->out_of_order_queue);
 		newtp->write_seq = newtp->pushed_seq = treq->snt_isn + 1;
 
 		newtp->rx_opt.saw_tstamp = 0;

Re: [PATCH net-next] tcp: out_of_order_queue do not use its lock

[David Miller]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Mon, 06 Jan 2014 09:36:12 -0800

> From: Eric Dumazet <edumazet@google.com>
> 
> TCP out_of_order_queue lock is not used, as queue manipulation
> happens with socket lock held and we therefore use the lockless
> skb queue routines (as __skb_queue_head())
> 
> We can use __skb_queue_head_init() instead of skb_queue_head_init()
> to make this more consistent.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied, thanks Eric.

We should probably at some point try to make an sk_buff_head_lite
that only has the two pointers, so that we could shrink various
structures which have queues which we use like this.