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Date:   Sun, 12 May 2019 04:39:01 +0200
From:   Andrew Lunn <>
To:     Vladimir Oltean <>
Subject: Re: [PATCH net 2/3] net: dsa: Remove dangerous DSA_SKB_CLONE() macro

On Sat, May 11, 2019 at 11:14:46PM +0300, Vladimir Oltean wrote:
> This does not cause any bug now because it has no users, but its body
> contains two pointer definitions within a code block:
> 		struct sk_buff *clone = _clone;	\
> 		struct sk_buff *skb = _skb;	\
> When calling the macro as DSA_SKB_CLONE(clone, skb), these variables
> would obscure the arguments that the macro was called with, and the
> initializers would be a no-op instead of doing their job (undefined
> behavior, by the way, but GCC nicely puts NULL pointers instead).
> So simply remove this broken macro and leave users to simply call
> "DSA_SKB_CB(skb)->clone = clone" by hand when needed.
> There is one functional difference when doing what I just suggested
> above: the control block won't be transferred from the original skb into
> the clone. Since there's no foreseen need for the control block in the
> clone ATM, this is ok.
> Fixes: b68b0dd0fb2d ("net: dsa: Keep private info in the skb->cb")
> Signed-off-by: Vladimir Oltean <>

If it has no users, it should not of been merged.

Reviewed-by: Andrew Lunn <>


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