netdev - Re: [PATCH net-next] net: init sk

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Message-ID: <CALOAHbDajHPN9Z3TTWFBwpd1H16RVRRYYiUMrUELE3JxeZo+qw@mail.gmail.com>
Date:   Tue, 24 Apr 2018 19:47:31 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        netdev@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] net: init sk_cookie for inet socket

On Tue, Apr 24, 2018 at 7:41 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
>
> On 04/23/2018 09:39 PM, Yafang Shao wrote:
>> On Tue, Apr 24, 2018 at 12:09 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>>>
>>>
>>> On 04/23/2018 08:58 AM, David Miller wrote:
>>>> From: Yafang Shao <laoar.shao@...il.com>
>>>> Date: Sun, 22 Apr 2018 21:50:04 +0800
>>>>
>>>>> With sk_cookie we can identify a socket, that is very helpful for
>>>>> traceing and statistic, i.e. tcp tracepiont and ebpf.
>>>>> So we'd better init it by default for inet socket.
>>>>> When using it, we just need call atomic64_read(&sk->sk_cookie).
>>>>>
>>>>> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
>>>>
>>>> Applied, thank you.
>>>>
>>>
>>> This is adding yet another atomic_inc on a global cache line.
>>>
>>
>> That's a trade-off.
>>
>>> Most applications do not need the cookie being ever set.
>>>
>>> The existing mechanism was fine. Set it on demand.
>>
>> There are some drawback in the existing mechanism.
>> - we have to set the net->cookie_gen and then sk->sk_cookie when we
>> want to get the sk_cookie, that's a little expensive as well.
>
> Same cost.
>
>>   After that change, sock_gen_cookie() could be replaced by
>> atomic64_read(&sk->sk_cookie) in most places.
>
> Same cost than the helper.
>
>>
>> - If the application want to get the sk_cookie, it must set it first.
>>    What if the application don't have the permision to write?
>>    Furthermore, maybe it is a security concern ?
>
>
> Maybe ? Please elaborate.
>
> Your patch destroys SYNFLOOD behavior.
>
> I have spent months of work solving the SYNFLOOD behavior, your patch crushes it.
>

Could you pls. explain the issue to me ?

> I am not that happy.
>
> Please revert this patch.
>

OK. I will revert it.

> Thank you.