netdev - Re: [PATCH net] net: lapb: Copy the skb before sending a packet

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Date:   Mon, 1 Feb 2021 20:42:24 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Xie He <xie.he.0141@...il.com>
Cc:     Julian Wiedmann <jwi@...ux.ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Linux X25 <linux-x25@...r.kernel.org>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Martin Schiller <ms@....tdt.de>
Subject: Re: [PATCH net] net: lapb: Copy the skb before sending a packet

On Mon, 1 Feb 2021 08:14:31 -0800 Xie He wrote:
> On Mon, Feb 1, 2021 at 6:10 AM Julian Wiedmann <jwi@...ux.ibm.com> wrote:
> > This sounds a bit like you want skb_cow_head() ... ?  
> 
> Calling "skb_cow_head" before we call "skb_clone" would indeed solve
> the problem of writes to our clones affecting clones in other parts of
> the system. But since we are still writing to the skb after
> "skb_clone", it'd still be better to replace "skb_clone" with
> "skb_copy" to avoid interference between our own clones.

Why call skb_cow_head() before skb_clone()? skb_cow_head should be
called before the data in skb head is modified. I'm assuming you're only
modifying "front" of the frame, right? skb_cow_head() should do nicely
in that case.