Commit d44fd4a7 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: set TCP_SYNCNT locklessly 



icsk->icsk_syn_retries can safely be set without locking the socket.

We have to add READ_ONCE() annotations in tcp_fastopen_synack_timer()
and tcp_write_timeout().

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 81083076

net/ipv4/tcp.c

+6 −9
Original line number Diff line number Diff line
@@ -3291,9 +3291,7 @@ int tcp_sock_set_syncnt(struct sock *sk, int val) 
	if (val < 1 || val > MAX_TCP_SYNCNT)

		return -EINVAL;



	lock_sock(sk);

	WRITE_ONCE(inet_csk(sk)->icsk_syn_retries, val);

	release_sock(sk);

	return 0;

}

EXPORT_SYMBOL(tcp_sock_set_syncnt);
@@ -3462,6 +3460,12 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname, 
	if (copy_from_sockptr(&val, optval, sizeof(val)))

		return -EFAULT;



	/* Handle options that can be set without locking the socket. */

	switch (optname) {

	case TCP_SYNCNT:

		return tcp_sock_set_syncnt(sk, val);

	}



	sockopt_lock_sock(sk);



	switch (optname) {
@@ -3569,13 +3573,6 @@ int do_tcp_setsockopt(struct sock *sk, int level, int optname, 
		else

			WRITE_ONCE(tp->keepalive_probes, val);

		break;

	case TCP_SYNCNT:

		if (val < 1 || val > MAX_TCP_SYNCNT)

			err = -EINVAL;

		else

			WRITE_ONCE(icsk->icsk_syn_retries, val);

		break;



	case TCP_SAVE_SYN:

		/* 0: disable, 1: enable, 2: start from ether_header */

		if (val < 0 || val > 2)

net/ipv4/tcp_timer.c

+6 −3
Original line number Diff line number Diff line
@@ -239,7 +239,8 @@ static int tcp_write_timeout(struct sock *sk) 
	if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {

		if (icsk->icsk_retransmits)

			__dst_negative_advice(sk);

		retry_until = icsk->icsk_syn_retries ? :

		/* Paired with WRITE_ONCE() in tcp_sock_set_syncnt() */

		retry_until = READ_ONCE(icsk->icsk_syn_retries) ? :

			READ_ONCE(net->ipv4.sysctl_tcp_syn_retries);



		max_retransmits = retry_until;
@@ -421,8 +422,10 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req) 


	req->rsk_ops->syn_ack_timeout(req);



	/* add one more retry for fastopen */

	max_retries = icsk->icsk_syn_retries ? :

	/* Add one more retry for fastopen.

	 * Paired with WRITE_ONCE() in tcp_sock_set_syncnt()

	 */

	max_retries = READ_ONCE(icsk->icsk_syn_retries) ? :

		READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_synack_retries) + 1;



	if (req->num_timeout >= max_retries) {