netdev - Re: [PATCH net-next] skbuff: update sk truesize in pskb_expand

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Message-Id: <20111015.000235.314539622449271332.davem@davemloft.net>
Date:	Sat, 15 Oct 2011 00:02:35 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	roy.qing.li@...il.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] skbuff: update sk truesize in pskb_expand_head

From: RongQing Li <roy.qing.li@...il.com>
Date: Sat, 15 Oct 2011 11:52:22 +0800

> About incorrectly impact on socket, I am consider it, but I still no
> idea about it.

Sockets attach themselves to packets, and assign a destructor.

This destructor atomically decrements the receive or send buffer
space used, and amount decremented is skb->truesize.

Therefore if you change skb->truesize on such an SKB, the wrong
amount will be decremented when the destructor is called.

This is a very fundamental aspec of SKB handling, perhaps you should
familiarize yourself with SKBs a little bit more before modifying code
which manages them.
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