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SubjectRe: [PATCH] amd-xgbe: set skb to NULL after freeing it
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From: Pan Bian <bianpan2016@163.com>
Date: Wed, 28 Nov 2018 16:09:45 +0800

> @@ -2754,6 +2754,7 @@ static int xgbe_rx_poll(struct xgbe_channel *channel, int budget)
> netif_err(pdata, rx_err, netdev,
> "error in received packet\n");
> dev_kfree_skb(skb);
> + skb = NULL;
> goto next_packet;
> }
>
> @@ -2806,6 +2807,7 @@ static int xgbe_rx_poll(struct xgbe_channel *channel, int budget)
> netif_err(pdata, rx_err, netdev,
> "packet length exceeds configured MTU\n");
> dev_kfree_skb(skb);
> + skb = NULL;
> goto next_packet;
> }
>
> --
> 2.7.4

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.

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