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Commit 4aea39c1 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: tcp_make_synack() consumes dst parameter 



tcp_make_synack() clones the dst, and callers release it.

We can avoid two atomic operations per SYNACK if tcp_make_synack()
consumes dst instead of cloning it.

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 90ba9b19

net/ipv4/tcp_ipv4.c

+0 −1
Original line number Diff line number Diff line
@@ -848,7 +848,6 @@ static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst, 
		err = net_xmit_eval(err);

	}



	dst_release(dst);

	return err;

}

net/ipv4/tcp_output.c

+14 −4
Original line number Diff line number Diff line
@@ -2442,7 +2442,16 @@ int tcp_send_synack(struct sock *sk) 
	return tcp_transmit_skb(sk, skb, 1, GFP_ATOMIC);

}



/* Prepare a SYN-ACK. */

/**

 * tcp_make_synack - Prepare a SYN-ACK.

 * sk: listener socket

 * dst: dst entry attached to the SYNACK

 * req: request_sock pointer

 * rvp: request_values pointer

 *

 * Allocate one skb and build a SYNACK packet.

 * @dst is consumed : Caller should not use it again.

 */

struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst,

				struct request_sock *req,

				struct request_values *rvp)
@@ -2462,13 +2471,14 @@ struct sk_buff *tcp_make_synack(struct sock *sk, struct dst_entry *dst, 
	if (cvp != NULL && cvp->s_data_constant && cvp->s_data_desired)

		s_data_desired = cvp->s_data_desired;

	skb = alloc_skb(MAX_TCP_HEADER + 15 + s_data_desired, GFP_ATOMIC);

	if (skb == NULL)

	if (unlikely(!skb)) {

		dst_release(dst);

		return NULL;



	}

	/* Reserve space for headers. */

	skb_reserve(skb, MAX_TCP_HEADER);



	skb_dst_set(skb, dst_clone(dst));

	skb_dst_set(skb, dst);



	mss = dst_metric_advmss(dst);

	if (tp->rx_opt.user_mss && tp->rx_opt.user_mss < mss)

net/ipv6/tcp_ipv6.c

+0 −1
Original line number Diff line number Diff line
@@ -522,7 +522,6 @@ static int tcp_v6_send_synack(struct sock *sk, struct request_sock *req, 
done:

	if (opt && opt != np->opt)

		sock_kfree_s(sk, opt, opt->tot_len);

	dst_release(dst);

	return err;

}