netdev - [PATCH net] Revert "net: correct sk_acceptq_is

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Date:   Wed, 31 Mar 2021 09:35:12 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Eric Dumazet <eric.dumazet@...il.com>,
        iuyacan <yacanliu@....com>
Subject: [PATCH net] Revert "net: correct sk_acceptq_is_full()"

From: Eric Dumazet <edumazet@...gle.com>

This reverts commit f211ac154577ec9ccf07c15f18a6abf0d9bdb4ab.

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

History:

64a146513f8f12ba204b7bf5cb7e9505594ead42 [NET]: Revert incorrect accept queue backlog changes.
8488df894d05d6fa41c2bd298c335f944bb0e401 [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: f211ac154577 ("net: correct sk_acceptq_is_full()")
Cc: iuyacan <yacanliu@....com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 include/net/sock.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/net/sock.h b/include/net/sock.h
index 3e3a5da2ce5aedbcfaca1880eb7c2e239c86b5ae..8487f58da36d21335f690edd2194986c3d4fed23 100644
--- a/include/net/sock.h
+++ b/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);
 }
 
 /*
-- 
2.31.0.291.g576ba9dcdaf-goog