[PATCH net-next 13/13] mptcp: send explicit ack on delayed ack_seq incr

[Paolo Abeni]

When the worker moves some bytes from the OoO queue into
the receive queue, the msk->ask_seq is updated, the MPTCP-level
ack carrying that value needs to wait the next ingress packet,
possibly slowing down or hanging the peer

Signed-off-by: Paolo Abeni <pab...@redhat.com>
---
 net/mptcp/protocol.c | 36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 05daed57ae4a..bb9a0bc7ee33 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -405,13 +405,27 @@ static void mptcp_set_timeout(const struct sock *sk, 
const struct sock *ssk)
        mptcp_sk(sk)->timer_ival = tout > 0 ? tout : TCP_RTO_MIN;
 }
 
-static void mptcp_check_data_fin(struct sock *sk)
+static void mptcp_send_ack(struct mptcp_sock *msk)
+{
+       struct mptcp_subflow_context *subflow;
+
+       mptcp_for_each_subflow(msk, subflow) {
+               struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
+
+               lock_sock(ssk);
+               tcp_send_ack(ssk);
+               release_sock(ssk);
+       }
+}
+
+static bool mptcp_check_data_fin(struct sock *sk)
 {
        struct mptcp_sock *msk = mptcp_sk(sk);
        u64 rcv_data_fin_seq;
+       bool ret = false;
 
        if (__mptcp_check_fallback(msk) || !msk->first)
-               return;
+               return ret;
 
        /* Need to ack a DATA_FIN received from a peer while this side
         * of the connection is in ESTABLISHED, FIN_WAIT1, or FIN_WAIT2.
@@ -427,8 +441,6 @@ static void mptcp_check_data_fin(struct sock *sk)
         */
 
        if (mptcp_pending_data_fin(sk, &rcv_data_fin_seq)) {
-               struct mptcp_subflow_context *subflow;
-
                WRITE_ONCE(msk->ack_seq, msk->ack_seq + 1);
                WRITE_ONCE(msk->rcv_data_fin, 0);
 
@@ -452,17 +464,11 @@ static void mptcp_check_data_fin(struct sock *sk)
                        break;
                }
 
+               ret = true;
                mptcp_set_timeout(sk, NULL);
-               mptcp_for_each_subflow(msk, subflow) {
-                       struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
-
-                       lock_sock(ssk);
-                       tcp_send_ack(ssk);
-                       release_sock(ssk);
-               }
-
+               mptcp_send_ack(msk);
                if (sock_flag(sk, SOCK_DEAD))
-                       return;
+                       return ret;
 
                sk->sk_state_change(sk);
                if (sk->sk_shutdown == SHUTDOWN_MASK ||
@@ -471,6 +477,7 @@ static void mptcp_check_data_fin(struct sock *sk)
                else
                        sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_IN);
        }
+       return ret;
 }
 
 static bool __mptcp_move_skbs_from_subflow(struct mptcp_sock *msk,
@@ -1542,7 +1549,8 @@ static bool __mptcp_move_skbs(struct mptcp_sock *msk)
        } while (!done);
 
        if (mptcp_ofo_queue(msk) || moved > 0) {
-               mptcp_check_data_fin((struct sock *)msk);
+               if (!mptcp_check_data_fin((struct sock *)msk))
+                       mptcp_send_ack(msk);
                return true;
        }
        return false;
-- 
2.26.2