When closing the msk->first socket in __mptcp_close_ssk(), if there's
another subflow available, it's better to avoid resetting it, just shut
down it.

This patch adds a new helper __mptcp_subflow_disconnect(), and reuse
flag MPTCP_CF_FASTCLOSE in this case. When MPTCP_CF_FASTCLOSE isn't set,
we invoke tcp_shutdown() instead of tcp_disconnect().

Co-developed-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
---
 net/mptcp/protocol.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 30e0c29ae0a4..1a54d55f8bb2 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -2366,6 +2366,26 @@ bool __mptcp_retransmit_pending_data(struct sock *sk)
 #define MPTCP_CF_PUSH		BIT(1)
 #define MPTCP_CF_FASTCLOSE	BIT(2)
 
+/* be sure to send a reset only if the caller asked for it, also
+ * clean completely the subflow status when the subflow reaches
+ * TCP_CLOSE state
+ */
+static void __mptcp_subflow_disconnect(struct sock *ssk,
+				       struct mptcp_subflow_context *subflow,
+				       unsigned int flags)
+{
+	if (((1 << ssk->sk_state) & (TCPF_CLOSE | TCPF_LISTEN)) ||
+	    (flags & MPTCP_CF_FASTCLOSE)) {
+		/* The MPTCP code never wait on the subflow sockets, TCP-level
+		 * disconnect should never fail
+		 */
+		WARN_ON_ONCE(tcp_disconnect(ssk, 0));
+		mptcp_subflow_ctx_reset(subflow);
+	} else {
+		tcp_shutdown(ssk, SEND_SHUTDOWN);
+	}
+}
+
 /* subflow sockets can be either outgoing (connect) or incoming
  * (accept).
  *
@@ -2403,7 +2423,7 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 	lock_sock_nested(ssk, SINGLE_DEPTH_NESTING);
 
 	if ((flags & MPTCP_CF_FASTCLOSE) && !__mptcp_check_fallback(msk)) {
-		/* be sure to force the tcp_disconnect() path,
+		/* be sure to force the tcp_close path
 		 * to generate the egress reset
 		 */
 		ssk->sk_lingertime = 0;
@@ -2413,11 +2433,7 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 
 	need_push = (flags & MPTCP_CF_PUSH) && __mptcp_retransmit_pending_data(sk);
 	if (!dispose_it) {
-		/* The MPTCP code never wait on the subflow sockets, TCP-level
-		 * disconnect should never fail
-		 */
-		WARN_ON_ONCE(tcp_disconnect(ssk, 0));
-		mptcp_subflow_ctx_reset(subflow);
+		__mptcp_subflow_disconnect(ssk, subflow, flags);
 		release_sock(ssk);
 
 		goto out;
-- 
2.35.3