From bf9cb14c74a8fea37adb3556d0c08c301828372e Mon Sep 17 00:00:00 2001 From: Paolo Abeni Date: Thu, 20 Jul 2023 09:03:32 +0200 Subject: [PATCH] mptcp: fix rcv buffer auto-tuning. The MPTCP code uses the assumption that the tcp_win_from_space() helper does not use any TCP-specific field, and thus works correctly operating on an MPTCP socket. The commit dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale") broke such assumption, and as a consequence most MPTCP connections stall on zero-window event due to auto-tuning changing the rcv buffer size quite randomly. Address the issue synching again the MPTCP auto-tuning code with the TCP one. To achieve that, factor out the windows size logic in socket independent helpers, and reuse them in mptcp_rcv_space_adjust(). The MPTCP level scaling_ratio is selected as the minimum one from the all the subflows, as a worst-case estimate. Co-developed-by: Matthieu Baerts Signed-off-by: Matthieu Baerts Signed-off-by: Paolo Abeni --- include/net/tcp.h | 20 +++++++++++++++----- net/mptcp/protocol.c | 14 +++++++------- net/mptcp/protocol.h | 8 +++++++- net/mptcp/subflow.c | 2 +- 4 files changed, 30 insertions(+), 14 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index c5fb9007992002..794642fbd72413 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1430,22 +1430,32 @@ void tcp_select_initial_window(const struct sock *sk, int __space, __u32 *window_clamp, int wscale_ok, __u8 *rcv_wscale, __u32 init_rcv_wnd); -static inline int tcp_win_from_space(const struct sock *sk, int space) +static inline int __tcp_win_from_space(u8 scaling_ratio, int space) { - s64 scaled_space = (s64)space * tcp_sk(sk)->scaling_ratio; + s64 scaled_space = (s64)space * scaling_ratio; return scaled_space >> TCP_RMEM_TO_WIN_SCALE; } -/* inverse of tcp_win_from_space() */ -static inline int tcp_space_from_win(const struct sock *sk, int win) +static inline int tcp_win_from_space(const struct sock *sk, int space) +{ + return __tcp_win_from_space(tcp_sk(sk)->scaling_ratio, space); +} + +/* inverse of __tcp_win_from_space() */ +static inline int __tcp_space_from_win(u8 scaling_ratio, int win) { u64 val = (u64)win << TCP_RMEM_TO_WIN_SCALE; - do_div(val, tcp_sk(sk)->scaling_ratio); + do_div(val, scaling_ratio); return val; } +static inline int tcp_space_from_win(const struct sock *sk, int win) +{ + return __tcp_space_from_win(tcp_sk(sk)->scaling_ratio, win); +} + static inline void tcp_scaling_ratio_init(struct sock *sk) { /* Assume a conservative default of 1200 bytes of payload per 4K page. diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index 9f00a0288a0abd..3ab67e0dfda97d 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -90,6 +90,7 @@ static int __mptcp_socket_create(struct mptcp_sock *msk) if (err) return err; + msk->scaling_ratio = tcp_sk(ssock->sk)->scaling_ratio; WRITE_ONCE(msk->first, ssock->sk); subflow = mptcp_subflow_ctx(ssock->sk); list_add(&subflow->node, &msk->conn_list); @@ -1906,6 +1907,7 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied) { struct mptcp_subflow_context *subflow; struct sock *sk = (struct sock *)msk; + u8 scaling_ratio = 255; u32 time, advmss = 1; u64 rtt_us, mstamp; @@ -1936,9 +1938,11 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied) rtt_us = max(sf_rtt_us, rtt_us); advmss = max(sf_advmss, advmss); + scaling_ratio = min(tp->scaling_ratio, scaling_ratio); } msk->rcvq_space.rtt_us = rtt_us; + msk->scaling_ratio = scaling_ratio; if (time < (rtt_us >> 3) || rtt_us == 0) return; @@ -1947,8 +1951,8 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied) if (READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_moderate_rcvbuf) && !(sk->sk_userlocks & SOCK_RCVBUF_LOCK)) { - int rcvmem, rcvbuf; u64 rcvwin, grow; + int rcvbuf; rcvwin = ((u64)msk->rcvq_space.copied << 1) + 16 * advmss; @@ -1957,18 +1961,14 @@ static void mptcp_rcv_space_adjust(struct mptcp_sock *msk, int copied) do_div(grow, msk->rcvq_space.space); rcvwin += (grow << 1); - rcvmem = SKB_TRUESIZE(advmss + MAX_TCP_HEADER); - while (tcp_win_from_space(sk, rcvmem) < advmss) - rcvmem += 128; - do_div(rcvwin, advmss); - rcvbuf = min_t(u64, rcvwin * rcvmem, + rcvbuf = min_t(u64, __tcp_space_from_win(scaling_ratio, rcvwin), READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_rmem[2])); if (rcvbuf > sk->sk_rcvbuf) { u32 window_clamp; - window_clamp = tcp_win_from_space(sk, rcvbuf); + window_clamp = __tcp_win_from_space(scaling_ratio, rcvbuf); WRITE_ONCE(sk->sk_rcvbuf, rcvbuf); /* Make subflows follow along. If we do not do this, we diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index 1b4457c44fe894..86cd4d9e8432d7 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -293,6 +293,7 @@ struct mptcp_sock { bool csum_enabled; bool allow_infinite_fallback; u8 mpc_endpoint_id; + u8 scaling_ratio; u8 recvmsg_inq:1, cork:1, nodelay:1, @@ -349,9 +350,14 @@ static inline int __mptcp_rmem(const struct sock *sk) return atomic_read(&sk->sk_rmem_alloc) - READ_ONCE(mptcp_sk(sk)->rmem_released); } +static inline int mptcp_win_from_space(const struct sock *sk, int space) +{ + return __tcp_win_from_space(mptcp_sk(sk)->scaling_ratio, space); +} + static inline int __mptcp_space(const struct sock *sk) { - return tcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf) - __mptcp_rmem(sk)); + return mptcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf) - __mptcp_rmem(sk)); } static inline struct mptcp_data_frag *mptcp_send_head(const struct sock *sk) diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index 9ee3b7abbaf6dd..ad7080fabb2ff3 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -1359,7 +1359,7 @@ void mptcp_space(const struct sock *ssk, int *space, int *full_space) const struct sock *sk = subflow->conn; *space = __mptcp_space(sk); - *full_space = tcp_full_space(sk); + *full_space = mptcp_win_from_space(sk, READ_ONCE(sk->sk_rcvbuf)); } void __mptcp_error_report(struct sock *sk)