mptcp: send explicit ack on delayed ack_seq incr

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 <pabeni@redhat.com>

net/mptcp/protocol.c

@@ -395,13 +395,27 @@ 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.
@@ -417,8 +431,6 @@ 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);
 
@@ -442,17 +454,11 @@ 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 ||
@@ -461,6 +467,7 @@ 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,
@@ -1532,7 +1539,8 @@ 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;