Commit 9c30ae83 authored by Yuchung Cheng's avatar Yuchung Cheng Committed by Jakub Kicinski
Browse files

tcp: fix TCP socket rehash stats mis-accounting 



The previous commit 32efcc06 ("tcp: export count for rehash attempts")
would mis-account rehashing SNMP and socket stats:

  a. During handshake of an active open, only counts the first
     SYN timeout

  b. After handshake of passive and active open, stop updating
     after (roughly) TCP_RETRIES1 recurring RTOs

  c. After the socket aborts, over count timeout_rehash by 1

This patch fixes this by checking the rehash result from sk_rethink_txhash.

Fixes: 32efcc06 ("tcp: export count for rehash attempts")
Signed-off-by: default avatarYuchung Cheng <ycheng@google.com>
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Link: https://lore.kernel.org/r/20210119192619.1848270-1-ycheng@google.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 8e4052c3

include/net/sock.h

+12 −5
Original line number Diff line number Diff line
@@ -1921,10 +1921,13 @@ static inline void sk_set_txhash(struct sock *sk) 
	sk->sk_txhash = net_tx_rndhash();

}



static inline void sk_rethink_txhash(struct sock *sk)

static inline bool sk_rethink_txhash(struct sock *sk)

{

	if (sk->sk_txhash)

	if (sk->sk_txhash) {

		sk_set_txhash(sk);

		return true;

	}

	return false;

}



static inline struct dst_entry *
@@ -1947,12 +1950,10 @@ sk_dst_get(struct sock *sk) 
	return dst;

}



static inline void dst_negative_advice(struct sock *sk)

static inline void __dst_negative_advice(struct sock *sk)

{

	struct dst_entry *ndst, *dst = __sk_dst_get(sk);



	sk_rethink_txhash(sk);



	if (dst && dst->ops->negative_advice) {

		ndst = dst->ops->negative_advice(dst);
@@ -1964,6 +1965,12 @@ static inline void dst_negative_advice(struct sock *sk) 
	}

}



static inline void dst_negative_advice(struct sock *sk)

{

	sk_rethink_txhash(sk);

	__dst_negative_advice(sk);

}



static inline void

__sk_dst_set(struct sock *sk, struct dst_entry *dst)

{

net/ipv4/tcp_input.c

+2 −3
Original line number Diff line number Diff line
@@ -4397,11 +4397,10 @@ static void tcp_rcv_spurious_retrans(struct sock *sk, const struct sk_buff *skb) 
	 * The receiver remembers and reflects via DSACKs. Leverage the

	 * DSACK state and change the txhash to re-route speculatively.

	 */

	if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq) {

		sk_rethink_txhash(sk);

	if (TCP_SKB_CB(skb)->seq == tcp_sk(sk)->duplicate_sack[0].start_seq &&

	    sk_rethink_txhash(sk))

		NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH);

}

}



static void tcp_send_dupack(struct sock *sk, const struct sk_buff *skb)

{

net/ipv4/tcp_timer.c

+8 −14
Original line number Diff line number Diff line
@@ -219,14 +219,8 @@ static int tcp_write_timeout(struct sock *sk) 
	int retry_until;



	if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV)) {

		if (icsk->icsk_retransmits) {

			dst_negative_advice(sk);

		} else {

			sk_rethink_txhash(sk);

			tp->timeout_rehash++;

			__NET_INC_STATS(sock_net(sk),

					LINUX_MIB_TCPTIMEOUTREHASH);

		}

		if (icsk->icsk_retransmits)

			__dst_negative_advice(sk);

		retry_until = icsk->icsk_syn_retries ? : net->ipv4.sysctl_tcp_syn_retries;

		expired = icsk->icsk_retransmits >= retry_until;

	} else {
@@ -234,12 +228,7 @@ static int tcp_write_timeout(struct sock *sk) 
			/* Black hole detection */

			tcp_mtu_probing(icsk, sk);



			dst_negative_advice(sk);

		} else {

			sk_rethink_txhash(sk);

			tp->timeout_rehash++;

			__NET_INC_STATS(sock_net(sk),

					LINUX_MIB_TCPTIMEOUTREHASH);

			__dst_negative_advice(sk);

		}



		retry_until = net->ipv4.sysctl_tcp_retries2;
@@ -270,6 +259,11 @@ static int tcp_write_timeout(struct sock *sk) 
		return 1;

	}



	if (sk_rethink_txhash(sk)) {

		tp->timeout_rehash++;

		__NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTREHASH);

	}



	return 0;

}