The existing mptcp_subflow_send_ack() function handles subflow locking,
but it's also sometimes necessary to force an ack from a caller that
already holds the subflow socket lock. This is required for the
following commit.

Fixes: 340fa6667a69 ("mptcp: Only send extra TCP acks in eligible socket states")
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
---
 net/mptcp/protocol.c | 9 +++++++--
 net/mptcp/protocol.h | 1 +
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 3efbae948707..b96a80c8e22a 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -506,13 +506,18 @@ static inline bool tcp_can_send_ack(const struct sock *ssk)
 	       (TCPF_SYN_SENT | TCPF_SYN_RECV | TCPF_TIME_WAIT | TCPF_CLOSE | TCPF_LISTEN));
 }
 
+void __mptcp_subflow_send_ack(struct sock *ssk)
+{
+	if (tcp_can_send_ack(ssk))
+		tcp_send_ack(ssk);
+}
+
 void mptcp_subflow_send_ack(struct sock *ssk)
 {
 	bool slow;
 
 	slow = lock_sock_fast(ssk);
-	if (tcp_can_send_ack(ssk))
-		tcp_send_ack(ssk);
+	__mptcp_subflow_send_ack(ssk);
 	unlock_sock_fast(ssk, slow);
 }
 
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index c14d70c036d0..033c995772dc 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -607,6 +607,7 @@ void __init mptcp_subflow_init(void);
 void mptcp_subflow_shutdown(struct sock *sk, struct sock *ssk, int how);
 void mptcp_close_ssk(struct sock *sk, struct sock *ssk,
 		     struct mptcp_subflow_context *subflow);
+void __mptcp_subflow_send_ack(struct sock *ssk);
 void mptcp_subflow_send_ack(struct sock *ssk);
 void mptcp_subflow_reset(struct sock *ssk);
 void mptcp_subflow_queue_clean(struct sock *ssk);
-- 
2.37.0