netdev - [PATCH] tcp/dccp: allow a connection when sk_max_ack

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Message-Id: <20250102171426.915276-1-dzq.aishenghu0@gmail.com>
Date: Thu,  2 Jan 2025 17:14:26 +0000
From: Zhongqiu Duan <dzq.aishenghu0@...il.com>
To: netdev@...r.kernel.org
Cc: davem@...emloft.net,
	edumazet@...gle.com,
	kerneljasonxing@...il.com,
	kuba@...nel.org,
	pabeni@...hat.com,
	kuniyu@...zon.com
Subject: [PATCH] tcp/dccp: allow a connection when sk_max_ack_backlog is zero

If the backlog of listen() is set to zero, sk_acceptq_is_full() allows
one connection to be made, but inet_csk_reqsk_queue_is_full() does not.
When the net.ipv4.tcp_syncookies is zero, inet_csk_reqsk_queue_is_full()
will cause an immediate drop before the sk_acceptq_is_full() check in
tcp_conn_request(), resulting in no connection can be made.

This patch tries to keep consistent with 64a146513f8f ("[NET]: Revert
incorrect accept queue backlog changes.").

Link: https://lore.kernel.org/netdev/20250102080258.53858-1-kuniyu@amazon.com/
Fixes: ef547f2ac16b ("tcp: remove max_qlen_log")
Signed-off-by: Zhongqiu Duan <dzq.aishenghu0@...il.com>
---
 include/net/inet_connection_sock.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/net/inet_connection_sock.h b/include/net/inet_connection_sock.h
index 3c82fad904d4..c7f42844c79a 100644
--- a/include/net/inet_connection_sock.h
+++ b/include/net/inet_connection_sock.h
@@ -282,7 +282,7 @@ static inline int inet_csk_reqsk_queue_len(const struct sock *sk)
 
 static inline int inet_csk_reqsk_queue_is_full(const struct sock *sk)
 {
-	return inet_csk_reqsk_queue_len(sk) >= READ_ONCE(sk->sk_max_ack_backlog);
+	return inet_csk_reqsk_queue_len(sk) > READ_ONCE(sk->sk_max_ack_backlog);
 }
 
 bool inet_csk_reqsk_queue_drop(struct sock *sk, struct request_sock *req);
-- 
2.34.1