Commit e994b2f0 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

tcp: do not lock listener to process SYN packets 



Everything should now be ready to finally allow SYN
packets processing without holding listener lock.

Tested:

3.5 Mpps SYNFLOOD. Plenty of cpu cycles available.

Next bottleneck is the refcount taken on listener,
that could be avoided if we remove SLAB_DESTROY_BY_RCU
strict semantic for listeners, and use regular RCU.

    13.18%  [kernel]  [k] __inet_lookup_listener
     9.61%  [kernel]  [k] tcp_conn_request
     8.16%  [kernel]  [k] sha_transform
     5.30%  [kernel]  [k] inet_reqsk_alloc
     4.22%  [kernel]  [k] sock_put
     3.74%  [kernel]  [k] tcp_make_synack
     2.88%  [kernel]  [k] ipt_do_table
     2.56%  [kernel]  [k] memcpy_erms
     2.53%  [kernel]  [k] sock_wfree
     2.40%  [kernel]  [k] tcp_v4_rcv
     2.08%  [kernel]  [k] fib_table_lookup
     1.84%  [kernel]  [k] tcp_openreq_init_rwin

Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 92d6f176

net/ipv4/tcp_ipv4.c

+9 −2
Original line number Diff line number Diff line
@@ -1355,7 +1355,7 @@ static struct sock *tcp_v4_cookie_check(struct sock *sk, struct sk_buff *skb) 
}



/* The socket must have it's spinlock held when we get

 * here.

 * here, unless it is a TCP_LISTEN socket.

 *

 * We have a potential double-lock case here, so even when

 * doing backlog processing we use the BH locking scheme.
@@ -1619,9 +1619,15 @@ process: 
	if (sk_filter(sk, skb))

		goto discard_and_relse;



	sk_incoming_cpu_update(sk);

	skb->dev = NULL;



	if (sk->sk_state == TCP_LISTEN) {

		ret = tcp_v4_do_rcv(sk, skb);

		goto put_and_return;

	}



	sk_incoming_cpu_update(sk);



	bh_lock_sock_nested(sk);

	tcp_sk(sk)->segs_in += max_t(u16, 1, skb_shinfo(skb)->gso_segs);

	ret = 0;
@@ -1636,6 +1642,7 @@ process: 
	}

	bh_unlock_sock(sk);



put_and_return:

	sock_put(sk);



	return ret;

net/ipv6/tcp_ipv6.c

+9 −2
Original line number Diff line number Diff line
@@ -1161,7 +1161,7 @@ out: 
}



/* The socket must have it's spinlock held when we get

 * here.

 * here, unless it is a TCP_LISTEN socket.

 *

 * We have a potential double-lock case here, so even when

 * doing backlog processing we use the BH locking scheme.
@@ -1415,9 +1415,15 @@ process: 
	if (sk_filter(sk, skb))

		goto discard_and_relse;



	sk_incoming_cpu_update(sk);

	skb->dev = NULL;



	if (sk->sk_state == TCP_LISTEN) {

		ret = tcp_v6_do_rcv(sk, skb);

		goto put_and_return;

	}



	sk_incoming_cpu_update(sk);



	bh_lock_sock_nested(sk);

	tcp_sk(sk)->segs_in += max_t(u16, 1, skb_shinfo(skb)->gso_segs);

	ret = 0;
@@ -1432,6 +1438,7 @@ process: 
	}

	bh_unlock_sock(sk);



put_and_return:

	sock_put(sk);

	return ret ? -1 : 0;

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