[PATCH mptcp-next v2 04/21] mptcp: establish subflows from either end of connection

From: Kishen Maloor <kishen.maloor@intel.com>
To: kishen.maloor@intel.com, mptcp@lists.linux.dev
Subject: [PATCH mptcp-next v2 04/21] mptcp: establish subflows from either end of connection
Date: Wed, 12 Jan 2022 17:15:06 -0500	[thread overview]
Message-ID: <20220112221523.1829397-5-kishen.maloor@intel.com> (raw)
In-Reply-To: <20220112221523.1829397-1-kishen.maloor@intel.com>

This change updates internal logic to permit subflows to be
established from either the client or server ends of MPTCP
connections. This symmetry and added flexibility may be
harnessed by PM implementations running on either end in
creating new subflows.

The essence of this change lies in not relying on the
"server_side" flag (which continues to be available if needed).

v2: check for 3rd ACK retransmission only on passive side
of the MPJ handshake

Signed-off-by: Kishen Maloor <kishen.maloor@intel.com>
---
 net/mptcp/options.c  | 2 +-
 net/mptcp/protocol.c | 5 +----
 net/mptcp/protocol.h | 2 --
 3 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index cceba8c7806d..89808816db06 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -921,7 +921,7 @@ static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
 		if (TCP_SKB_CB(skb)->seq == subflow->ssn_offset + 1 &&
 		    TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq &&
 		    subflow->mp_join && (mp_opt->suboptions & OPTIONS_MPTCP_MPJ) &&
-		    READ_ONCE(msk->pm.server_side))
+		    !subflow->request_join)
 			tcp_send_ack(ssk);
 		goto fully_established;
 	}
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 4012f844eec1..408a05bff633 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3248,15 +3248,12 @@ bool mptcp_finish_join(struct sock *ssk)
 		return false;
 	}
 
-	if (!msk->pm.server_side)
+	if (!list_empty(&subflow->node))
 		goto out;
 
 	if (!mptcp_pm_allow_new_subflow(msk))
 		goto err_prohibited;
 
-	if (WARN_ON_ONCE(!list_empty(&subflow->node)))
-		goto err_prohibited;
-
 	/* active connections are already on conn_list.
 	 * If we can't acquire msk socket lock here, let the release callback
 	 * handle it
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index e2a67d3469f6..c50247673c7e 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -908,10 +908,8 @@ static inline bool mptcp_check_infinite_map(struct sk_buff *skb)
 static inline bool subflow_simultaneous_connect(struct sock *sk)
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
-	struct sock *parent = subflow->conn;
 
 	return sk->sk_state == TCP_ESTABLISHED &&
-	       !mptcp_sk(parent)->pm.server_side &&
 	       !subflow->conn_finished;
 }
 
-- 
2.31.1

