Re: [PATCH net] net: axienet: free outstanding TX buffers in axienet_dma_bd_release()

[Jacob Keller <jacob.e.keller@intel.com>]

On 9/27/2026 1:10 AM, Sagi Maimon wrote:
> axienet_dma_bd_release() walks the RX ring to unmap and free every
> receive buffer before releasing it, but frees the TX descriptor ring
> with dma_free_coherent() alone.  Any descriptor that
> axienet_free_tx_chain() had not yet reclaimed still holds its skb and
> its streaming DMA mapping, and both are lost.
> 
> axienet_stop() disables TX NAPI and stops the DMA engine before calling
> it, so nothing reclaims those descriptors afterwards.  Bringing the
> interface down while frames are in flight therefore leaks up to
> lp->tx_bd_num skbs and mappings each time.
> 
> Walk the TX ring the way axienet_dma_err_handler() already does: unmap
> every descriptor whose cntrl is still set - axienet_free_tx_chain()
> clears it on reclaim - and free any skb still attached.  The DMA engine
> has been stopped by then, so the hardware no longer references the
> buffers.  On the axienet_dma_bd_init() error path the TX ring has just
> been allocated zeroed, so the walk does nothing.
> 
> This was reported by the Sashiko AI review bot.
> 
> Tested on an AXI Ethernet MAC behind a PCIe endpoint: traffic passes,
> and after each of ten down/up cycles and five module reloads, all made
> with traffic running and each running axienet_dma_bd_release(), traffic
> resumes and nothing is logged.  The leak itself was not measured.
> 
> Fixes: 8a3b7a252dca ("drivers/net/ethernet/xilinx: added Xilinx AXI Ethernet driver")
> Assisted-by: LLM sparse
> Signed-off-by: Sagi Maimon <maimon.sagi@gmail.com>
> ---
> 
> Notes:
>     Found by the Sashiko review of v2 of "net: axienet: bound TX completion
>     cleanup by the NAPI budget":
>     https://lore.kernel.org/netdev/20260917115657.20697-1-maimon.sagi@gmail.com/
>     It is independent of that patch and applies on its own.
> 

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>

>  .../net/ethernet/xilinx/xilinx_axienet_main.c  | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> index 1722b7038f34..02bcb89d1bbe 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> @@ -187,6 +187,24 @@ static void axienet_dma_bd_release(struct net_device *ndev)
>  	struct axienet_local *lp = netdev_priv(ndev);
>  
>  	/* If we end up here, tx_bd_v must have been DMA allocated. */
> +	for (i = 0; i < lp->tx_bd_num; i++) {
> +		struct axidma_bd *cur_p = &lp->tx_bd_v[i];
> +
> +		/* axienet_free_tx_chain() clears cntrl when it reclaims a
> +		 * descriptor, so a non-zero value means the mapping is live.
> +		 */
> +		if (cur_p->cntrl) {
> +			dma_addr_t addr = desc_get_phys_addr(lp, cur_p);
> +
> +			dma_unmap_single(lp->dev, addr,
> +					 (cur_p->cntrl &
> +					  XAXIDMA_BD_CTRL_LENGTH_MASK),
> +					 DMA_TO_DEVICE);
> +		}
> +		if (cur_p->skb)
> +			dev_kfree_skb(cur_p->skb);
> +	}
> +
>  	dma_free_coherent(lp->dev,
>  			  sizeof(*lp->tx_bd_v) * lp->tx_bd_num,
>  			  lp->tx_bd_v,
> 
> base-commit: a7bfaba4823e3c165bb2004c74eff7c096672bc7