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Date: Fri, 20 Oct 2023 18:43:48 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Andrew Lunn <andrew@lunn.ch>
Cc: Daniel Borkmann <daniel@iogearbox.net>, bpf@vger.kernel.org,
 netdev@vger.kernel.org, martin.lau@linux.dev, razor@blackwall.org,
 ast@kernel.org, andrii@kernel.org, john.fastabend@gmail.com,
 sdf@google.com, toke@kernel.org
Subject: Re: [PATCH bpf-next v2 1/7] netkit, bpf: Add bpf programmable net
 device
Message-ID: <20231020184348.528aa62c@kernel.org>
In-Reply-To: <33467f55-4bbf-4078-af21-d91c6aab82ee@lunn.ch>
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	<33467f55-4bbf-4078-af21-d91c6aab82ee@lunn.ch>
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On Sat, 21 Oct 2023 00:18:53 +0200 Andrew Lunn wrote:
> > +	err = rtnl_configure_link(peer, ifmp, 0, NULL);
> > +	if (err < 0)
> > +		goto err_configure_peer;  
> 
> Seeing code after calling register_netdevice() often means bugs. The
> interface is live, and in use before the function even returns. The
> kernel can try to get an IP address, mount an NFS root etc. This might
> be safe, because you have two linked interfaces here, and the other
> one is not yet registered. Maybe some comment about this would be
> good, or can the rtnl_configure_link() be done earlier?

These are in the newlink callback, rtnl is held throughout.
Which is not to say that corresponding code in veth wasn't 
a source of many bugs :S