mptcp: Wake up MPTCP worker when DATA_FIN found on a TCP FIN packet

jira LE-1907
Rebuild_History Non-Buildable kernel-4.18.0-294.el8
commit-author Mat Martineau <[email protected]>
commit ef59b19

When receiving a DATA_FIN MPTCP option on a TCP FIN packet, the DATA_FIN
information would be stored but the MPTCP worker did not get
scheduled. In turn, the MPTCP socket state would remain in
TCP_ESTABLISHED and no blocked operations would be awakened.

TCP FIN packets are seen by the MPTCP socket when moving skbs out of the
subflow receive queues, so schedule the MPTCP worker when a skb with
DATA_FIN but no data payload is moved from a subflow queue. Other cases
(DATA_FIN on a bare TCP ACK or on a packet with data payload) are
already handled.

Closes: multipath-tcp/mptcp_net-next#84
Fixes: 43b54c6 ("mptcp: Use full MPTCP-level disconnect state machine")
	Acked-by: Paolo Abeni <[email protected]>
	Signed-off-by: Mat Martineau <[email protected]>
	Signed-off-by: Matthieu Baerts <[email protected]>
	Signed-off-by: David S. Miller <[email protected]>
(cherry picked from commit ef59b19)
	Signed-off-by: Jonathan Maple <[email protected]>

net/mptcp/subflow.c

@@ -696,7 +696,7 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
 
 	if (mpext->data_fin == 1) {
 		if (data_len == 1) {
-			mptcp_update_rcv_data_fin(msk, mpext->data_seq);
+			bool updated = mptcp_update_rcv_data_fin(msk, mpext->data_seq);
 			pr_debug("DATA_FIN with no payload seq=%llu", mpext->data_seq);
 			if (subflow->map_valid) {
 				/* A DATA_FIN might arrive in a DSS
@@ -707,6 +707,9 @@ static enum mapping_status get_mapping_status(struct sock *ssk,
 				skb_ext_del(skb, SKB_EXT_MPTCP);
 				return MAPPING_OK;
 			} else {
+				if (updated && schedule_work(&msk->work))
+					sock_hold((struct sock *)msk);
+
 				return MAPPING_DATA_FIN;
 			}
 		} else {