From: Jakub Kicinski <kuba@kernel.org>
To: Xie He <xie.he.0141@gmail.com>
Cc: Julian Wiedmann <jwi@linux.ibm.com>,
"David S. Miller" <davem@davemloft.net>,
Linux X25 <linux-x25@vger.kernel.org>,
Linux Kernel Network Developers <netdev@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Martin Schiller <ms@dev.tdt.de>
Subject: Re: [PATCH net] net: lapb: Copy the skb before sending a packet
Date: Tue, 2 Feb 2021 08:41:40 -0800 [thread overview]
Message-ID: <20210202084140.642a9cc1@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com> (raw)
In-Reply-To: <CAJht_ENcz1A+C8=tJ_wP8kQby4OuyWirJC+c+-ngg5D54dpHNg@mail.gmail.com>
On Mon, 1 Feb 2021 22:25:17 -0800 Xie He wrote:
> On Mon, Feb 1, 2021 at 8:42 PM Jakub Kicinski <kuba@kernel.org> wrote:
> >
> > On Mon, 1 Feb 2021 08:14:31 -0800 Xie He wrote:
> > > On Mon, Feb 1, 2021 at 6:10 AM Julian Wiedmann <jwi@linux.ibm.com> wrote:
> [...]
> > >
> > > 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.
>
> The modification happens after skb_clone. If we call skb_cow_head
> after skb_clone (before the modification), then skb_cow_head would
> always see that the skb is a clone and would always copy it. Therefore
> skb_clone + skb_cow_head is equivalent to skb_copy.
You're right. I thought cow_head is a little more clever.
next prev parent reply other threads:[~2021-02-02 16:44 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-01 5:57 [PATCH net] net: lapb: Copy the skb before sending a packet Xie He
2021-02-01 10:05 ` Martin Schiller
2021-02-01 10:49 ` Xie He
2021-02-01 12:47 ` Martin Schiller
2021-02-01 14:10 ` Julian Wiedmann
2021-02-01 16:14 ` Xie He
2021-02-02 4:42 ` Jakub Kicinski
2021-02-02 6:25 ` Xie He
2021-02-02 16:41 ` Jakub Kicinski [this message]
2021-02-02 9:04 ` David Laight
2021-02-02 16:50 ` patchwork-bot+netdevbpf
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