netdev - Re: [PATCH] amd-xgbe: set skb to NULL after freeing it

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Date:   Thu, 29 Nov 2018 15:37:56 +0800
From:   PanBian <bianpan2016@....com>
To:     David Miller <davem@...emloft.net>
Cc:     thomas.lendacky@....com, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] amd-xgbe: set skb to NULL after freeing it

On Wed, Nov 28, 2018 at 10:49:31AM -0800, David Miller wrote:
> From: Pan Bian <bianpan2016@....com>
> Date: Wed, 28 Nov 2018 16:09:45 +0800
> 
> If either of these two cases are executed, it means that it must be
> the case that:
> 
> 	!last || context_next
> 
> is FALSE, therefore the conditional in the tail code of this function:
> 
> 	/* Check if we need to save state before leaving */
> 	if (received && (!last || context_next)) {
> 		rdata = XGBE_GET_DESC_DATA(ring, ring->cur);
> 		rdata->state_saved = 1;
> 		rdata->state.skb = skb;
> 		rdata->state.len = len;
> 		rdata->state.error = error;
> 	}
> 
> will not trigger, and therefore we will not record the free'd SKB.
> 
> And if we iterate the loop again, it is guaranteed that 'skb' will
> be set to a new packet or NULL.
> 
> So there is no problem here.

Got it. Sorry for my misunderstanding. Thank you and Tom for the 
detailed explanations.

Pan