mptcp: cleanup writer wake-up

After commit 5cf92bba ("mptcp: re-enable sndbuf autotune"), the
MPTCP_NOSPACE bit is redundant: it is always set and cleared together with
SOCK_NOSPACE.

Let's drop the first and always relay on the latter, dropping a bunch
of useless code.
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Mat Martineau <martineau@kernel.org>
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/protocol.c

@@ -1692,15 +1692,6 @@ static void __mptcp_subflow_push_pending(struct sock *sk, struct sock *ssk, bool
 	}
 }
 
-static void mptcp_set_nospace(struct sock *sk)
-{
-	/* enable autotune */
-	set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
-
-	/* will be cleared on avail space */
-	set_bit(MPTCP_NOSPACE, &mptcp_sk(sk)->flags);
-}
-
 static int mptcp_disconnect(struct sock *sk, int flags);
 
 static int mptcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
@@ -1874,7 +1865,7 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 		continue;
 
 wait_for_memory:
-		mptcp_set_nospace(sk);
+		set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
 		__mptcp_push_pending(sk, msg->msg_flags);
 		ret = sk_stream_wait_memory(sk, &timeo);
 		if (ret)
@@ -3945,8 +3936,8 @@ static __poll_t mptcp_check_writeable(struct mptcp_sock *msk)
 	if (sk_stream_is_writeable(sk))
 		return EPOLLOUT | EPOLLWRNORM;
 
-	mptcp_set_nospace(sk);
-	smp_mb__after_atomic(); /* msk->flags is changed by write_space cb */
+	set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
+	smp_mb__after_atomic(); /* NOSPACE is changed by mptcp_write_space() */
 	if (sk_stream_is_writeable(sk))
 		return EPOLLOUT | EPOLLWRNORM;
 

net/mptcp/protocol.h

@@ -113,10 +113,9 @@
 #define MPTCP_RST_TRANSIENT	BIT(0)
 
 /* MPTCP socket atomic flags */
-#define MPTCP_NOSPACE		1
-#define MPTCP_WORK_RTX		2
-#define MPTCP_FALLBACK_DONE	4
-#define MPTCP_WORK_CLOSE_SUBFLOW 5
+#define MPTCP_WORK_RTX		1
+#define MPTCP_FALLBACK_DONE	2
+#define MPTCP_WORK_CLOSE_SUBFLOW 3
 
 /* MPTCP socket release cb flags */
 #define MPTCP_PUSH_PENDING	1
@@ -810,12 +809,9 @@ static inline bool mptcp_data_fin_enabled(const struct mptcp_sock *msk)
 
 static inline void mptcp_write_space(struct sock *sk)
 {
-	if (sk_stream_is_writeable(sk)) {
-		/* pairs with memory barrier in mptcp_poll */
-		smp_mb();
-		if (test_and_clear_bit(MPTCP_NOSPACE, &mptcp_sk(sk)->flags))
-			sk_stream_write_space(sk);
-	}
+	/* pairs with memory barrier in mptcp_poll */
+	smp_mb();
+	sk_stream_write_space(sk);
 }
 
 static inline void __mptcp_sync_sndbuf(struct sock *sk)