mptcp: use delegate action to schedule 3rd ack retrans

Scheduling a delack in mptcp_established_options_mp() is
not a good idea: such function is called by tcp_send_ack() and
the pending delayed ack will be cleared shortly after by the
tcp_event_ack_sent() call in __tcp_transmit_skb().

Instead use the mptcp delegated action infrastructure to
schedule the delayed ack after the current bh processing completes.

Additionally moves the schedule_3rdack_retransmission() helper
into protocol.c to avoid making it visible in a different compilation
unit.

Fixes: ec3edaa7ca6ce02f ("mptcp: Add handling of outgoing MP_JOIN requests")
Reviewed-by: Mat Martineau <mathew.j.martineau>@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 42 insertions, 9 deletions

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index b7e32e316738..c82a76d2d0bf 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -1596,7 +1596,8 @@ static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk)
 			if (!xmit_ssk)
 				goto out;
 			if (xmit_ssk != ssk) {
-				mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk));
+				mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk),
+						       MPTCP_DELEGATE_SEND);
 				goto out;
 			}
 
@@ -2943,7 +2944,7 @@ void __mptcp_check_push(struct sock *sk, struct sock *ssk)
 		if (xmit_ssk == ssk)
 			__mptcp_subflow_push_pending(sk, ssk);
 		else if (xmit_ssk)
-			mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk));
+			mptcp_subflow_delegate(mptcp_subflow_ctx(xmit_ssk), MPTCP_DELEGATE_SEND);
 	} else {
 		set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags);
 	}
@@ -2993,18 +2994,50 @@ static void mptcp_release_cb(struct sock *sk)
 	__mptcp_update_rmem(sk);
 }
 
+/* MP_JOIN client subflow must wait for 4th ack before sending any data:
+ * TCP can't schedule delack timer before the subflow is fully established.
+ * MPTCP uses the delack timer to do 3rd ack retransmissions
+ */
+static void schedule_3rdack_retransmission(struct sock *ssk)
+{
+	struct inet_connection_sock *icsk = inet_csk(ssk);
+	struct tcp_sock *tp = tcp_sk(ssk);
+	unsigned long timeout;
+
+	if (mptcp_subflow_ctx(ssk)->fully_established)
+		return;
+
+	/* reschedule with a timeout above RTT, as we must look only for drop */
+	if (tp->srtt_us)
+		timeout = usecs_to_jiffies(tp->srtt_us >> (3 - 1));
+	else
+		timeout = TCP_TIMEOUT_INIT;
+	timeout += jiffies;
+
+	WARN_ON_ONCE(icsk->icsk_ack.pending & ICSK_ACK_TIMER);
+	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
+	icsk->icsk_ack.timeout = timeout;
+	sk_reset_timer(ssk, &icsk->icsk_delack_timer, timeout);
+}
+
 void mptcp_subflow_process_delegated(struct sock *ssk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(ssk);
 	struct sock *sk = subflow->conn;
 
-	mptcp_data_lock(sk);
-	if (!sock_owned_by_user(sk))
-		__mptcp_subflow_push_pending(sk, ssk);
-	else
-		set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags);
-	mptcp_data_unlock(sk);
-	mptcp_subflow_delegated_done(subflow);
+	if (test_bit(MPTCP_DELEGATE_SEND, &subflow->delegated_status)) {
+		mptcp_data_lock(sk);
+		if (!sock_owned_by_user(sk))
+			__mptcp_subflow_push_pending(sk, ssk);
+		else
+			set_bit(MPTCP_PUSH_PENDING, &mptcp_sk(sk)->flags);
+		mptcp_data_unlock(sk);
+		mptcp_subflow_delegated_done(subflow, MPTCP_DELEGATE_SEND);
+	}
+	if (test_bit(MPTCP_DELEGATE_ACK, &subflow->delegated_status)) {
+		schedule_3rdack_retransmission(ssk);
+		mptcp_subflow_delegated_done(subflow, MPTCP_DELEGATE_ACK);
+	}
 }
 
 static int mptcp_hash(struct sock *sk)