mptcp: better msk receive window updates

Move mptcp_cleanup_rbuf() related checks inside the mentioned
helper and extend them to mirror TCP checks more closely.

Additionally drop the 'rmem_pending' hack, since commit 87952603
("mptcp: protect the rx path with the msk socket spinlock") we
can use instead 'rmem_released'.

Fixes: ea4ca586 ("mptcp: refine MPTCP-level ack scheduling")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/mptcp/options.c

@@ -498,8 +498,8 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
 {
 	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
 	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	u64 snd_data_fin_enable, ack_seq;
 	unsigned int dss_size = 0;
-	u64 snd_data_fin_enable;
 	struct mptcp_ext *mpext;
 	unsigned int ack_size;
 	bool ret = false;
@@ -531,13 +531,14 @@ static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
 		return ret;
 	}
 
+	ack_seq = READ_ONCE(msk->ack_seq);
 	if (READ_ONCE(msk->use_64bit_ack)) {
 		ack_size = TCPOLEN_MPTCP_DSS_ACK64;
-		opts->ext_copy.data_ack = READ_ONCE(msk->ack_seq);
+		opts->ext_copy.data_ack = ack_seq;
 		opts->ext_copy.ack64 = 1;
 	} else {
 		ack_size = TCPOLEN_MPTCP_DSS_ACK32;
-		opts->ext_copy.data_ack32 = (uint32_t)READ_ONCE(msk->ack_seq);
+		opts->ext_copy.data_ack32 = (uint32_t)ack_seq;
 		opts->ext_copy.ack64 = 0;
 	}
 	opts->ext_copy.use_ack = 1;

net/mptcp/protocol.c

@@ -457,7 +457,18 @@ static bool mptcp_subflow_cleanup_rbuf(struct sock *ssk)
 static void mptcp_cleanup_rbuf(struct mptcp_sock *msk)
 {
 	struct sock *ack_hint = READ_ONCE(msk->ack_hint);
+	int old_space = READ_ONCE(msk->old_wspace);
 	struct mptcp_subflow_context *subflow;
+	struct sock *sk = (struct sock *)msk;
+	bool cleanup;
+
+	/* this is a simple superset of what tcp_cleanup_rbuf() implements
+	 * so that we don't have to acquire the ssk socket lock most of the time
+	 * to do actually nothing
+	 */
+	cleanup = __mptcp_space(sk) - old_space >= max(0, old_space);
+	if (!cleanup)
+		return;
 
 	/* if the hinted ssk is still active, try to use it */
 	if (likely(ack_hint)) {
@@ -1865,7 +1876,7 @@ static void __mptcp_splice_receive_queue(struct sock *sk)
 	skb_queue_splice_tail_init(&sk->sk_receive_queue, &msk->receive_queue);
 }
 
-static bool __mptcp_move_skbs(struct mptcp_sock *msk, unsigned int rcv)
+static bool __mptcp_move_skbs(struct mptcp_sock *msk)
 {
 	struct sock *sk = (struct sock *)msk;
 	unsigned int moved = 0;
@@ -1885,13 +1896,10 @@ static bool __mptcp_move_skbs(struct mptcp_sock *msk, unsigned int rcv)
 
 		slowpath = lock_sock_fast(ssk);
 		mptcp_data_lock(sk);
+		__mptcp_update_rmem(sk);
 		done = __mptcp_move_skbs_from_subflow(msk, ssk, &moved);
 		mptcp_data_unlock(sk);
-		if (moved && rcv) {
-			WRITE_ONCE(msk->rmem_pending, min(rcv, moved));
-			tcp_cleanup_rbuf(ssk, 1);
-			WRITE_ONCE(msk->rmem_pending, 0);
-		}
+		tcp_cleanup_rbuf(ssk, moved);
 		unlock_sock_fast(ssk, slowpath);
 	} while (!done);
 
@@ -1904,6 +1912,7 @@ static bool __mptcp_move_skbs(struct mptcp_sock *msk, unsigned int rcv)
 		ret |= __mptcp_ofo_queue(msk);
 		__mptcp_splice_receive_queue(sk);
 		mptcp_data_unlock(sk);
+		mptcp_cleanup_rbuf(msk);
 	}
 	if (ret)
 		mptcp_check_data_fin((struct sock *)msk);
@@ -1933,7 +1942,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 	target = sock_rcvlowat(sk, flags & MSG_WAITALL, len);
 
 	while (copied < len) {
-		int bytes_read, old_space;
+		int bytes_read;
 
 		bytes_read = __mptcp_recvmsg_mskq(msk, msg, len - copied);
 		if (unlikely(bytes_read < 0)) {
@@ -1944,14 +1953,11 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 
 		copied += bytes_read;
 
-		if (skb_queue_empty(&msk->receive_queue) &&
-		    __mptcp_move_skbs(msk, len - copied))
-			continue;
-
 		/* be sure to advertise window change */
-		old_space = READ_ONCE(msk->old_wspace);
-		if ((tcp_space(sk) - old_space) >= old_space)
-			mptcp_cleanup_rbuf(msk);
+		mptcp_cleanup_rbuf(msk);
+
+		if (skb_queue_empty(&msk->receive_queue) && __mptcp_move_skbs(msk))
+			continue;
 
 		/* only the master socket status is relevant here. The exit
 		 * conditions mirror closely tcp_recvmsg()
@@ -1979,7 +1985,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 				/* race breaker: the shutdown could be after the
 				 * previous receive queue check
 				 */
-				if (__mptcp_move_skbs(msk, len - copied))
+				if (__mptcp_move_skbs(msk))
 					continue;
 				break;
 			}
@@ -2012,7 +2018,7 @@ static int mptcp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len,
 		/* .. race-breaker: ssk might have gotten new data
 		 * after last __mptcp_move_skbs() returned false.
 		 */
-		if (unlikely(__mptcp_move_skbs(msk, 0)))
+		if (unlikely(__mptcp_move_skbs(msk)))
 			set_bit(MPTCP_DATA_READY, &msk->flags);
 	} else if (unlikely(!test_bit(MPTCP_DATA_READY, &msk->flags))) {
 		/* data to read but mptcp_wait_data() cleared DATA_READY */

net/mptcp/protocol.h

@@ -234,7 +234,6 @@ struct mptcp_sock {
 	u64		wnd_end;
 	unsigned long	timer_ival;
 	u32		token;
-	int		rmem_pending;
 	int		rmem_released;
 	unsigned long	flags;
 	bool		can_ack;
@@ -293,7 +292,7 @@ static inline struct mptcp_sock *mptcp_sk(const struct sock *sk)
 
 static inline int __mptcp_space(const struct sock *sk)
 {
-	return tcp_space(sk) + READ_ONCE(mptcp_sk(sk)->rmem_pending);
+	return tcp_space(sk) + READ_ONCE(mptcp_sk(sk)->rmem_released);
 }
 
 static inline struct mptcp_data_frag *mptcp_send_head(const struct sock *sk)