mptcp:fm: recreate subflows after an error

If a subflow is closed because of an error, it will be recreated if
create_on_err parameter is set.

For that, we need to store the previously recorded error (sk->sk_err)
and look at it when closing the subflow.

Note that here, we limit the retry on ETIMEDOUT error, like it was done
before. Otherwise, we might end up looping on subflow-creations, if we
are sending a SYN+MP_JOIN that results in a TCP-RST (ECONNREFUSED).

Fixes: 133537d (mptcp: Recreate subflows after a timeout)
Signed-off-by: Matthieu Baerts <[email protected]>
Signed-off-by: Christoph Paasch <[email protected]>

include/net/mptcp.h

@@ -185,6 +185,7 @@ struct mptcp_tcp_sock {
 	u8	path_index;
 	u8	loc_id;
 	u8	rem_id;
+	u8	sk_err;
 
 #define MPTCP_SCHED_SIZE 16
 	u8	mptcp_sched[MPTCP_SCHED_SIZE] __aligned(8);

net/mptcp/mptcp_ctrl.c

@@ -620,6 +620,9 @@ static void mptcp_sock_def_error_report(struct sock *sk)
 		}
 	}
 
+	/* record this info that can be used by PM after the sf close */
+	tp->mptcp->sk_err = sk->sk_err;
+
 	if (mpcb->infinite_mapping_rcv || mpcb->infinite_mapping_snd ||
 	    mpcb->send_infinite_mapping) {
 		struct sock *meta_sk = mptcp_meta_sk(sk);

net/mptcp/mptcp_fullmesh.c

@@ -1686,12 +1686,16 @@ static void full_mesh_delete_subflow(struct sock *sk)
 {
 	struct fullmesh_priv *fmp = fullmesh_get_priv(tcp_sk(sk)->mpcb);
 	struct mptcp_fm_ns *fm_ns = fm_get_ns(sock_net(sk));
+	struct sock *meta_sk = mptcp_meta_sk(sk);
 	struct mptcp_loc_addr *mptcp_local;
 	int index, i;
 
 	if (!create_on_err)
 		return;
 
+	if (!mptcp_can_new_subflow(meta_sk))
+		return;
+
 	rcu_read_lock_bh();
 	mptcp_local = rcu_dereference_bh(fm_ns->local);
 
@@ -1741,6 +1745,10 @@ static void full_mesh_delete_subflow(struct sock *sk)
 
 out:
 	rcu_read_unlock_bh();
+
+	/* re-schedule the creation of failed subflows */
+	if (tcp_sk(sk)->mptcp->sk_err == ETIMEDOUT || sk->sk_err == ETIMEDOUT)
+		full_mesh_create_subflows(meta_sk);
 }
 
 /* Output /proc/net/mptcp_fullmesh */