Re: [PATCH iwl-net v2 1/2] e1000e: fix Rx skb DMA map error sentinel

["Ruinskiy, Dima" <dima.ruinskiy@intel.com>]

On 13/09/2026 20:15, Matt Vollrath wrote:
> Upon encountering a DMA_MAPPING_ERROR during skb allocation and mapping,
> the driver would leave DMA_MAPPING_ERROR in the buffer_info->dma field.
> This would lead several buffer_info->dma == 0 conditions down unwanted
> paths:
> 
> * In e1000_alloc_jumbo_rx_buffers(), it would not re-attempt the failed
>    mapping and instead write DMA_MAPPING_ERROR to the h/w descriptor on
>    the next allocation call. On cleaning or teardown it would attempt to
>    dma_unmap_page() DMA_MAPPING_ERROR. This case would only be
>    reachable at MTU > 1518 and page size > 16K.
> * In e1000_clean_rx_ring(), it would attempt to dma_unmap_page/single()
>    DMA_MAPPING_ERROR (unless cleaned by the jumbo path first). This case
>    would be reachable at any combination of MTU and page size.
> 
> Use buffer_info->dma = 0 as the sentinel for "DMA is not mapped." Set it
> immediately upon detecting the failure.
> 
> The map error value was 0 on some platforms (including most common x86)
> until error values were unified to DMA_MAPPING_ERROR in v4.20/v5.0.
> Since then the error handling in this driver has been incorrect on all
> platforms.
> 
> Signed-off-by: Matt Vollrath <tactii@gmail.com>
> Suggested-by: Jakub Kicinski <kuba@kernel.org>
> Fixes: bc7f75fa9788 ("[E1000E]: New pci-express e1000 driver (currently for ICH9 devices only)")
> Cc: stable@vger.kernel.org
> ---
> v2:
> * Add history blurb to description.
> ---
>   drivers/net/ethernet/intel/e1000e/netdev.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/e1000e/netdev.c b/drivers/net/ethernet/intel/e1000e/netdev.c
> index 844f31ab37ad..26f45ee8c7e7 100644
> --- a/drivers/net/ethernet/intel/e1000e/netdev.c
> +++ b/drivers/net/ethernet/intel/e1000e/netdev.c
> @@ -691,6 +691,7 @@ static void e1000_alloc_rx_buffers(struct e1000_ring *rx_ring,
>   						  adapter->rx_buffer_len,
>   						  DMA_FROM_DEVICE);
>   		if (dma_mapping_error(&pdev->dev, buffer_info->dma)) {
> +			buffer_info->dma = 0;
>   			dev_err(&pdev->dev, "Rx DMA map failed\n");
>   			adapter->rx_dma_failed++;
>   			break;
> @@ -791,6 +792,7 @@ static void e1000_alloc_rx_buffers_ps(struct e1000_ring *rx_ring,
>   						  adapter->rx_ps_bsize0,
>   						  DMA_FROM_DEVICE);
>   		if (dma_mapping_error(&pdev->dev, buffer_info->dma)) {
> +			buffer_info->dma = 0;
>   			dev_err(&pdev->dev, "Rx DMA map failed\n");
>   			adapter->rx_dma_failed++;
>   			/* cleanup skb */
> @@ -877,6 +879,7 @@ static void e1000_alloc_jumbo_rx_buffers(struct e1000_ring *rx_ring,
>   							PAGE_SIZE,
>   							DMA_FROM_DEVICE);
>   			if (dma_mapping_error(&pdev->dev, buffer_info->dma)) {
> +				buffer_info->dma = 0;
>   				adapter->alloc_rx_buff_failed++;
>   				break;
>   			}
> 
> base-commit: 78445023439506ebd83b86d40b1e428a3b309d4a
Reviewed-by: Dima Ruinskiy <dima.ruinskiy@intel.com>