netdev - [PATCH net-next] tcp: ensure prior synack rtx behavior with small backlogs

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Message-ID: <1444168198.9555.19.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Tue, 06 Oct 2015 14:49:58 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev <netdev@...r.kernel.org>
Subject: [PATCH net-next] tcp: ensure prior synack rtx behavior with small
 backlogs

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

Some applications use a listen() backlog of 1.

Prior kernels were silently enforcing a qlen_log of 4, so that we were
sending up to /proc/sys/net/ipv4/tcp_synack_retries SYNACK messages.

Fixes: ef547f2ac16b ("tcp: remove max_qlen_log")
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/ipv4/inet_connection_sock.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv4/inet_connection_sock.c b/net/ipv4/inet_connection_sock.c
index 89eedfbd4ad5..514b9e910bd4 100644
--- a/net/ipv4/inet_connection_sock.c
+++ b/net/ipv4/inet_connection_sock.c
@@ -579,7 +579,7 @@ static void reqsk_timer_handler(unsigned long data)
 	 * ones are about to clog our table.
 	 */
 	qlen = reqsk_queue_len(queue);
-	if ((qlen << 1) > sk_listener->sk_max_ack_backlog) {
+	if ((qlen << 1) > max(8U, sk_listener->sk_max_ack_backlog)) {
 		int young = reqsk_queue_len_young(queue) << 1;
 
 		while (thresh > 2) {


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