netdev - Re: [PATCH RFC] net: decrease the length of backlog queue immediately after it's detached from sk

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Message-ID: <56FB6642.4040002@huawei.com>
Date:	Wed, 30 Mar 2016 13:38:11 +0800
From:	Yang Yingliang <yangyingliang@...wei.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	<netdev@...r.kernel.org>, <davem@...emloft.net>
Subject: Re: [PATCH RFC] net: decrease the length of backlog queue immediately
 after it's detached from sk



On 2016/3/30 13:25, Eric Dumazet wrote:
> On Wed, 2016-03-30 at 13:16 +0800, Yang Yingliang wrote:
>> When task A hold the sk owned in tcp_sendmsg, if lots of packets
>> arrive and the packets will be added to backlog queue. The packets
>> will be handled in release_sock called from tcp_sendmsg. When the
>> sk_backlog is removed from sk, the length will not decrease until
>> all the packets in backlog queue are handled. This may leads to the
>> new packets be dropped because the lenth is too big. So set the
>> lenth to 0 immediately after it's detached from sk.
>>
>> Signed-off-by: Yang Yingliang <yangyingliang@...wei.com>
>> ---
>>   net/core/sock.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/net/core/sock.c b/net/core/sock.c
>> index 47fc8bb..108be05 100644
>> --- a/net/core/sock.c
>> +++ b/net/core/sock.c
>> @@ -1933,6 +1933,7 @@ static void __release_sock(struct sock *sk)
>>
>>   	do {
>>   		sk->sk_backlog.head = sk->sk_backlog.tail = NULL;
>> +		sk->sk_backlog.len = 0;
>>   		bh_unlock_sock(sk);
>>
>>   		do {
>
> Certainly not.
>
> Have you really missed the comment ?
>
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=8eae939f1400326b06d0c9afe53d2a484a326871

My kernel is 4.1 LTS, it seems don't have this patch. I will try this 
patch later.

Thanks
Yang
>
>
> I do not believe the case you describe can happen, unless a misbehaving
> driver cooks fat skb (with skb->truesize being far more bigger than
> skb->len)
>
>
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>