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

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Date:	Tue, 29 Mar 2016 22:25:20 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Yang Yingliang <yangyingliang@...wei.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 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


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)