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 syncing 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.

Fixes: dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale")
Signed-off-by: Paolo Abeni <[email protected]>
Co-developed-by: Matthieu Baerts <[email protected]>
Signed-off-by: Matthieu Baerts <[email protected]>
Reviewed-by: Eric Dumazet <[email protected]>
Acked-by: Soheil Hassas Yeganeh <[email protected]>
Link: https://lore.kernel.org/r/20230720-upstream-net-next-20230720-mptcp-fix-rcv-buffer-auto-tuning-v1-1-175ef12b8380@tessares.net
Signed-off-by: Jakub Kicinski <[email protected]>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index d17cb8ab4c48c95dcc1250b31c0f050caed5e67a..6ebf54992ffeebc8dd83226ed764d0a2716ce9c1 100644 (file)
--- 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 22323b1fa18427069e9c2443fd53f70fb0f2d26d..68da265399704b96aaf9895600e201f3caf8e2e7 100644 (file)
--- 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);
        WRITE_ONCE(msk->subflow, ssock);
        subflow = mptcp_subflow_ctx(ssock->sk);
@@ -1881,6 +1882,7 @@ 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 = U8_MAX;
        u32 time, advmss = 1;
        u64 rtt_us, mstamp;
 
@@ -1911,9 +1913,11 @@ 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;
 
@@ -1922,8 +1926,8 @@ 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;
 
@@ -1932,18 +1936,13 @@ 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 37fbe22e2433d551d45e1ad148e8603bad5b5733..795f422e8597eeac1d4f40fcd0f52e246e020d9c 100644 (file)
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -321,6 +321,7 @@ struct mptcp_sock {
                u64     time;   /* start time of measurement window */
                u64     rtt_us; /* last maximum rtt of subflows */
        } rcvq_space;
+       u8              scaling_ratio;
 
        u32             subflow_id;
        u32             setsockopt_seq;
@@ -351,9 +352,14 @@ 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 9ee3b7abbaf6dd2340c1d2142e834e898a7fcfa8..ad7080fabb2ff3ac1bd4eb3071f522b32ed91e8f 100644 (file)
--- 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)