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

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Date:   Tue, 23 May 2017 14:26:53 +0200
From:   Roman Kapl <roman.kapl@...go.com>
To:     David Miller <davem@...emloft.net>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH] net: set default value for somaxconn

On 05/22/2017 08:18 PM, David Miller wrote:
> From: Roman Kapl <roman.kapl@...go.com>
> Date: Mon, 22 May 2017 14:22:41 +0200
>
>> 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>
> I see the problem, but this changes behavior.
>
> Existing code will set somaxconn to the default value for every namespace
> that is created.
>
> But with you changes, any modification made to init_net's value will
> get inherited by any namespace created as a child thereafterwards.
Hmm, I can not find where somaxconn is inherited. But I see this needs 
to be per-net.
>
> You really need to make this happen via pernet_operations, or even
> inside of setup_net().
I will create new pernet_operations in net_namespace.c, move the 
somaxconn initialization there and send a new patch.

Thanks for comments, Roman Kapl