[1/2] e1000: Fix DMA mapping error handling on TX

There were a few issues in the DMA mapping error handling in e1000_tx_map
which I found via fault injection.

If we fail to map the first descriptor count will end up as -1 but the
check of (count >= 0) will still be true since count is unsigned. Instead
of changing count to be signed, just simplify the logic.

Secondly, when we wrap the tx ring we rely on i to go negative, but it
was unsigned.

Signed-off-by: Anton Blanchard <anton@samba.org>
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On Thu, Jan 21, 2010 at 03:42, Anton Blanchard <anton@samba.org> wrote:
>
> There were a few issues in the DMA mapping error handling in e1000_tx_map
> which I found via fault injection.
>
> If we fail to map the first descriptor count will end up as -1 but the
> check of (count >= 0) will still be true since count is unsigned. Instead
> of changing count to be signed, just simplify the logic.
>
> Secondly, when we wrap the tx ring we rely on i to go negative, but it
> was unsigned.
>
> Signed-off-by: Anton Blanchard <anton@samba.org>
> ---
>
> Index: linux.trees.git/drivers/net/e1000/e1000_main.c
> ===================================================================
> --- linux.trees.git.orig/drivers/net/e1000/e1000_main.c 2010-01-21 11:10:00.000000000 +1100
> +++ linux.trees.git/drivers/net/e1000/e1000_main.c      2010-01-21 11:12:52.000000000 +1100
> @@ -2693,8 +2693,9 @@ static int e1000_tx_map(struct e1000_ada
>        struct pci_dev *pdev = adapter->pdev;
>        struct e1000_buffer *buffer_info;
>        unsigned int len = skb_headlen(skb);
> -       unsigned int offset = 0, size, count = 0, i;
> +       unsigned int offset = 0, size, count = 0;
>        unsigned int f;
> +       int i;
>
>        i = tx_ring->next_to_use;
>
> @@ -2802,10 +2803,8 @@ static int e1000_tx_map(struct e1000_ada
>  dma_error:
>        dev_err(&pdev->dev, "TX DMA map failed\n");
>        buffer_info->dma = 0;
> -       count--;
>
> -       while (count >= 0) {
> -               count--;
> +       while (count--) {
>                i--;
>                if (i < 0)
>                        i += tx_ring->count;

This patch does not apply to the current e1000 driver in net-2.6, much
of this patch has already been corrected (applied) by Roel Kluin
recent patch.