netdev - [PATCH] net: set default value for somaxconn

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Message-Id: <20170522122241.28389-1-roman.kapl@sysgo.com>
Date:   Mon, 22 May 2017 14:22:41 +0200
From:   Roman Kapl <roman.kapl@...go.com>
To:     davem@...emloft.net, netdev@...r.kernel.org
Cc:     Roman Kapl <roman.kapl@...go.com>
Subject: [PATCH] net: set default value for somaxconn

The default value for somaxconn is set in sysctl_core_net_init(), but this
function is not called when kernel is configured without CONFIG_SYSCTL.

This results in the kernel not being able to accept TCP connections,
because the backlog has zero size. Usually, the user ends up with:
"TCP: request_sock_TCP: Possible SYN flooding on port 7. Dropping request.  Check SNMP counters."

Before ef547f2ac16 (tcp: remove max_qlen_log), the effects were less
severe, because the backlog was always at least eight slots long.

Signed-off-by: Roman Kapl <roman.kapl@...go.com>
---
 net/core/net_namespace.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
index 1934efd..4f3bbff 100644
--- a/net/core/net_namespace.c
+++ b/net/core/net_namespace.c
@@ -37,6 +37,9 @@ EXPORT_SYMBOL_GPL(net_namespace_list);
 struct net init_net = {
 	.count		= ATOMIC_INIT(1),
 	.dev_base_head	= LIST_HEAD_INIT(init_net.dev_base_head),
+	.core = {
+		.sysctl_somaxconn = SOMAXCONN,
+	},
 };
 EXPORT_SYMBOL(init_net);

-- 
2.10.1