Revert "net: correct sk_acceptq_is_full()"

This reverts commit f211ac1.

We had similar attempt in the past, and we reverted it.

History:

64a1465 [NET]: Revert incorrect accept queue backlog changes.
8488df8 [NET]: Fix bugs in "Whether sock accept queue is full" checking

I am adding a fat comment so that future attempts will
be much harder.

Fixes: f211ac1 ("net: correct sk_acceptq_is_full()")
Cc: iuyacan <[email protected]>
Signed-off-by: Eric Dumazet <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: Eric Dumazet

include/net/sock.h

@@ -934,9 +934,13 @@ static inline void sk_acceptq_added(struct sock *sk)
 	WRITE_ONCE(sk->sk_ack_backlog, sk->sk_ack_backlog + 1);
 }
 
+/* Note: If you think the test should be:
+ *	return READ_ONCE(sk->sk_ack_backlog) >= READ_ONCE(sk->sk_max_ack_backlog);
+ * Then please take a look at commit 64a146513f8f ("[NET]: Revert incorrect accept queue backlog changes.")
+ */
 static inline bool sk_acceptq_is_full(const struct sock *sk)
 {
-	return READ_ONCE(sk->sk_ack_backlog) >= READ_ONCE(sk->sk_max_ack_backlog);
+	return READ_ONCE(sk->sk_ack_backlog) > READ_ONCE(sk->sk_max_ack_backlog);
 }
 
 /*