Currently sk_rethink_txhash() re-rolls the socket's txhash on RTO, PLB, and spurious-retransmission events, but the cached route is reused and the new hash is not propagated into the ECMP path selection logic. Two changes are needed to make rehash select a different local ECMP path:
1. Add __sk_dst_reset() alongside sk_rethink_txhash() in tcp_write_timeout(), tcp_rcv_spurious_retrans(), and tcp_plb_check_rehash() so the cached dst is invalidated and the next transmit triggers a fresh route lookup. 2. Set fl6->mp_hash from sk_txhash (or tcp_rsk(req)->txhash for SYN/ACK retransmits and syncookies) in tcp_v6_connect(), inet6_sk_rebuild_header(), inet6_csk_route_req(), inet6_csk_route_socket(), and cookie_v6_check() so fib6_select_path() picks a path based on the new hash. The expression uses (txhash >> 1) ?: 1 to guarantee a non-zero mp_hash, since fib6_select_path() treats zero as unset and falls back to rt6_multipath_hash(). This is conditioned on fib_multipath_hash_policy == 0 (L3) because policies 1-3 compute a deterministic hash from the flow keys (e.g., symmetric 5-tuple for policy 1) which must not be overridden by a random txhash. It is necessary to update mp_hash explicitly because the default ECMP hash derives from fl6->flowlabel via np->flow_label, which is not updated from sk_txhash (REPFLOW is off by default). ip6_make_flowlabel() cannot help either, as it runs after the route lookup. sk_set_txhash() is moved before ip6_dst_lookup_flow() in tcp_v6_connect() so the initial ECMP path is selected by the same txhash that subsequent route rebuilds will use. This avoids unintended path changes when the cached dst is naturally invalidated (e.g., by PMTU discovery or route changes). The dst reset is guarded by sk->sk_family == AF_INET6 since IPv4 ECMP does not currently use sk_txhash for path selection. For IPv4-mapped IPv6 sockets this produces a redundant dst reset on a cold path (RTO/PLB); the subsequent IPv4 route lookup returns the same result. tcp_rsk(req)->txhash initialization is moved before route_req() in tcp_conn_request() so that inet6_csk_route_req() reads a valid hash on the initial SYN/ACK. Signed-off-by: Neil Spring <[email protected]> --- net/ipv4/tcp_input.c | 6 ++++-- net/ipv4/tcp_plb.c | 7 ++++++- net/ipv4/tcp_timer.c | 4 ++++ net/ipv6/af_inet6.c | 3 +++ net/ipv6/inet6_connection_sock.c | 6 ++++++ net/ipv6/syncookies.c | 3 +++ net/ipv6/tcp_ipv6.c | 13 +++++++++++-- 7 files changed, 37 insertions(+), 5 deletions(-) diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 7995a89bafc9..8f602a665b71 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -5020,8 +5020,10 @@ static void tcp_rcv_spurious_retrans(struct sock *sk, skb->protocol == htons(ETH_P_IPV6) && (tcp_sk(sk)->inet_conn.icsk_ack.lrcv_flowlabel != ntohl(ip6_flowlabel(ipv6_hdr(skb)))) && - sk_rethink_txhash(sk)) + sk_rethink_txhash(sk)) { NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPDUPLICATEDATAREHASH); + __sk_dst_reset(sk); + } /* Save last flowlabel after a spurious retrans. */ tcp_save_lrcv_flowlabel(sk, skb); @@ -7636,6 +7638,7 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops, tcp_rsk(req)->af_specific = af_ops; tcp_rsk(req)->ts_off = 0; tcp_rsk(req)->req_usec_ts = false; + tcp_rsk(req)->txhash = net_tx_rndhash(); #if IS_ENABLED(CONFIG_MPTCP) tcp_rsk(req)->is_mptcp = 0; #endif @@ -7717,7 +7720,6 @@ int tcp_conn_request(struct request_sock_ops *rsk_ops, } #endif tcp_rsk(req)->snt_isn = isn; - tcp_rsk(req)->txhash = net_tx_rndhash(); tcp_rsk(req)->syn_tos = TCP_SKB_CB(skb)->ip_dsfield; tcp_openreq_init_rwin(req, sk, dst); sk_rx_queue_set(req_to_sk(req), skb); diff --git a/net/ipv4/tcp_plb.c b/net/ipv4/tcp_plb.c index c11a0cd3f8fe..accdd83dfc3d 100644 --- a/net/ipv4/tcp_plb.c +++ b/net/ipv4/tcp_plb.c @@ -78,7 +78,12 @@ void tcp_plb_check_rehash(struct sock *sk, struct tcp_plb_state *plb) if (plb->pause_until) return; - sk_rethink_txhash(sk); + if (sk_rethink_txhash(sk)) { +#if IS_ENABLED(CONFIG_IPV6) + if (sk->sk_family == AF_INET6) + __sk_dst_reset(sk); +#endif + } plb->consec_cong_rounds = 0; WRITE_ONCE(tcp_sk(sk)->plb_rehash, tcp_sk(sk)->plb_rehash + 1); NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPPLBREHASH); diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index 322db13333c7..24c1c19eda6e 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -300,6 +300,10 @@ static int tcp_write_timeout(struct sock *sk) if (sk_rethink_txhash(sk)) { WRITE_ONCE(tp->timeout_rehash, tp->timeout_rehash + 1); __NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPTIMEOUTREHASH); +#if IS_ENABLED(CONFIG_IPV6) + if (sk->sk_family == AF_INET6) + __sk_dst_reset(sk); +#endif } return 0; diff --git a/net/ipv6/af_inet6.c b/net/ipv6/af_inet6.c index 0a88b376141d..8e8f94b1f2a4 100644 --- a/net/ipv6/af_inet6.c +++ b/net/ipv6/af_inet6.c @@ -823,6 +823,9 @@ int inet6_sk_rebuild_header(struct sock *sk) fl6->flowi6_uid = sk_uid(sk); security_sk_classify_flow(sk, flowi6_to_flowi_common(fl6)); + if (ip6_multipath_hash_policy(sock_net(sk)) == 0) + fl6->mp_hash = (sk->sk_txhash >> 1) ?: 1; + rcu_read_lock(); final_p = fl6_update_dst(fl6, rcu_dereference(np->opt), &np->final); rcu_read_unlock(); diff --git a/net/ipv6/inet6_connection_sock.c b/net/ipv6/inet6_connection_sock.c index 37534e116899..4e10299ba0bd 100644 --- a/net/ipv6/inet6_connection_sock.c +++ b/net/ipv6/inet6_connection_sock.c @@ -48,6 +48,9 @@ struct dst_entry *inet6_csk_route_req(const struct sock *sk, fl6->flowi6_uid = sk_uid(sk); security_req_classify_flow(req, flowi6_to_flowi_common(fl6)); + if (ip6_multipath_hash_policy(sock_net(sk)) == 0) + fl6->mp_hash = (tcp_rsk(req)->txhash >> 1) ?: 1; + if (!dst) { dst = ip6_dst_lookup_flow(sock_net(sk), sk, fl6, final_p); if (IS_ERR(dst)) @@ -70,6 +73,9 @@ struct dst_entry *inet6_csk_route_socket(struct sock *sk, fl6->saddr = np->saddr; fl6->flowlabel = np->flow_label; IP6_ECN_flow_xmit(sk, fl6->flowlabel); + + if (ip6_multipath_hash_policy(sock_net(sk)) == 0) + fl6->mp_hash = (sk->sk_txhash >> 1) ?: 1; fl6->flowi6_oif = sk->sk_bound_dev_if; fl6->flowi6_mark = sk->sk_mark; fl6->fl6_sport = inet->inet_sport; diff --git a/net/ipv6/syncookies.c b/net/ipv6/syncookies.c index 4f6f0d751d6c..f43f10bd2822 100644 --- a/net/ipv6/syncookies.c +++ b/net/ipv6/syncookies.c @@ -245,6 +245,9 @@ struct sock *cookie_v6_check(struct sock *sk, struct sk_buff *skb) fl6.flowi6_uid = sk_uid(sk); security_req_classify_flow(req, flowi6_to_flowi_common(&fl6)); + if (ip6_multipath_hash_policy(net) == 0) + fl6.mp_hash = (tcp_rsk(req)->txhash >> 1) ?: 1; + dst = ip6_dst_lookup_flow(net, sk, &fl6, final_p); if (IS_ERR(dst)) { SKB_DR_SET(reason, IP_OUTNOROUTES); diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c index 2c3f7a739709..231eed3d4f7b 100644 --- a/net/ipv6/tcp_ipv6.c +++ b/net/ipv6/tcp_ipv6.c @@ -258,6 +258,8 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr_unsized *uaddr, if (!ipv6_addr_any(&sk->sk_v6_rcv_saddr)) saddr = &sk->sk_v6_rcv_saddr; + sk_set_txhash(sk); + fl6->flowi6_proto = IPPROTO_TCP; fl6->daddr = sk->sk_v6_daddr; fl6->saddr = saddr ? *saddr : np->saddr; @@ -275,6 +277,15 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr_unsized *uaddr, security_sk_classify_flow(sk, flowi6_to_flowi_common(fl6)); + /* Non-zero mp_hash bypasses rt6_multipath_hash() in + * fib6_select_path(), letting txhash control ECMP path + * selection so that sk_rethink_txhash() rehashes onto a + * different path. Policies 1-3 derive a deterministic + * hash from the flow keys and must not be overridden. + */ + if (ip6_multipath_hash_policy(net) == 0) + fl6->mp_hash = (sk->sk_txhash >> 1) ?: 1; + dst = ip6_dst_lookup_flow(net, sk, fl6, final_p); if (IS_ERR(dst)) { err = PTR_ERR(dst); @@ -313,8 +324,6 @@ static int tcp_v6_connect(struct sock *sk, struct sockaddr_unsized *uaddr, if (err) goto late_failure; - sk_set_txhash(sk); - if (likely(!tp->repair)) { union tcp_seq_and_ts_off st; -- 2.53.0-Meta
