mptcp: fix accounting on rmem

Linked to previous commit: "mptcp: fix tcp-mem accounting"

rmem accounting is always done on the meta but tcp_mem (sk_rmem_schedule
call) is done on the individual subflows.

Properly split between meta and subflow in tcp_try_rmem_schedule.

Fixes: c50cf08 ("Fix: mptcp_try_rmem_schedule removed")
Signed-off-by: Nathan Atta <nathan.atta@tessares.net>
Signed-off-by: Tim Froidcoeur <tim.froidcoeur@tessares.net>
Acked-by: Christoph Paasch <cpaasch@apple.com>
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
(cherry picked from commit 0bdffb3)
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>
(cherry picked from commit 7424545)
Signed-off-by: Matthieu Baerts <matthieu.baerts@tessares.net>

net/ipv4/tcp_input.c

@@ -4533,17 +4533,16 @@ static int tcp_prune_queue(struct sock *sk);
 static int tcp_try_rmem_schedule(struct sock *sk, struct sk_buff *skb,
 				 unsigned int size)
 {
-	if (mptcp(tcp_sk(sk)))
-		sk = mptcp_meta_sk(sk);
+	struct sock *meta_sk = mptcp(tcp_sk(sk)) ? mptcp_meta_sk(sk) : sk;
 
-	if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
+	if (atomic_read(&meta_sk->sk_rmem_alloc) > meta_sk->sk_rcvbuf ||
 	    !sk_rmem_schedule(sk, skb, size)) {
 
-		if (tcp_prune_queue(sk) < 0)
+		if (tcp_prune_queue(meta_sk) < 0)
 			return -1;
 
 		while (!sk_rmem_schedule(sk, skb, size)) {
-			if (!tcp_prune_ofo_queue(sk))
+			if (!tcp_prune_ofo_queue(meta_sk))
 				return -1;
 		}
 	}