[PATCH net 1/1] net: fec: update dirty_tx even if no skb

[Fugang Duan]

From: Troy Kisky <troy.kisky at boundarydevices.com> Sent: Friday, April 22, 2016 10:01 AM
> To: netdev at vger.kernel.org; davem at davemloft.net; Fugang Duan
> <fugang.duan at nxp.com>; lznuaa at gmail.com
> Cc: Fabio Estevam <fabio.estevam at nxp.com>; l.stach at pengutronix.de;
> andrew at lunn.ch; tremyfr at gmail.com; gerg at uclinux.org; linux-arm-
> kernel at lists.infradead.org; johannes at sipsolutions.net;
> stillcompiling at gmail.com; sergei.shtylyov at cogentembedded.com;
> arnd at arndb.de; holgerschurig at gmail.com; Troy Kisky
> <troy.kisky at boundarydevices.com>
> Subject: [PATCH net 1/1] net: fec: update dirty_tx even if no skb
> 
> If dirty_tx isn't updated, then dma_unmap_single will be called twice.
> 
> This fixes a
> [   58.420980] ------------[ cut here ]------------
> [   58.425667] WARNING: CPU: 0 PID: 377 at /home/schurig/d/mkarm/linux-
> 4.5/lib/dma-debug.c:1096 check_unmap+0x9d0/0xab8()
> [   58.436405] fec 2188000.ethernet: DMA-API: device driver tries to free DMA
> memory it has not allocated [device address=0x0000000000000000] [size=66
> bytes]
> 
> encountered by Holger
> 
> Signed-off-by: Troy Kisky <troy.kisky at boundarydevices.com>
> Tested-by: <holgerschurig at gmail.com>
> ---
>  drivers/net/ethernet/freescale/fec_main.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/fec_main.c
> b/drivers/net/ethernet/freescale/fec_main.c
> index 08243c2..b71654c 100644
> --- a/drivers/net/ethernet/freescale/fec_main.c
> +++ b/drivers/net/ethernet/freescale/fec_main.c
> @@ -1197,10 +1197,8 @@ fec_enet_tx_queue(struct net_device *ndev, u16
> queue_id)
>  					 fec16_to_cpu(bdp->cbd_datlen),
>  					 DMA_TO_DEVICE);
>  		bdp->cbd_bufaddr = cpu_to_fec32(0);
> -		if (!skb) {
> -			bdp = fec_enet_get_nextdesc(bdp, &txq->bd);
> -			continue;
> -		}
> +		if (!skb)
> +			goto skb_done;
> 
>  		/* Check for errors. */
>  		if (status & (BD_ENET_TX_HB | BD_ENET_TX_LC | @@ -1239,7
> +1237,7 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
> 
>  		/* Free the sk buffer associated with this last transmit */
>  		dev_kfree_skb_any(skb);
> -
> +skb_done:
>  		/* Make sure the update to bdp and tx_skbuff are performed
>  		 * before dirty_tx
>  		 */
> --
> 2.5.0

The patch is fine for me.
Can you review below patch that also fix the issue. It can take much effort due to less rmb() and READ_ONCE() operation that is very sensitive for duplex Gbps test for i.MX6SX/i.MX7d SOC. (i.MX6SX can reach at 1.4Gbps, i.MX7D can reach at 1.8Gbps.)

--- a/drivers/net/ethernet/freescale/fec_main.c
+++ b/drivers/net/ethernet/freescale/fec_main.c
@@ -1160,12 +1160,13 @@ static void
 fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
 {
        struct  fec_enet_private *fep;
-       struct bufdesc *bdp;
+       struct bufdesc *bdp, *bdp_t;
        unsigned short status;
        struct  sk_buff *skb;
        struct fec_enet_priv_tx_q *txq;
        struct netdev_queue *nq;
        int     index = 0;
+       int     i, bdnum;
        int     entries_free;

        fep = netdev_priv(ndev);
@@ -1187,20 +1188,28 @@ fec_enet_tx_queue(struct net_device *ndev, u16 queue_id)
                if (status & BD_ENET_TX_READY)
                        break;

-               index = fec_enet_get_bd_index(bdp, &txq->bd);
-
+               bdp_t = bdp;
+               bdnum = 1;
+               index = fec_enet_get_bd_index(txq->tx_bd_base, bdp_t, fep);
                skb = txq->tx_skbuff[index];
-               txq->tx_skbuff[index] = NULL;
-               if (!IS_TSO_HEADER(txq, fec32_to_cpu(bdp->cbd_bufaddr)))
-                       dma_unmap_single(&fep->pdev->dev,
-                                        fec32_to_cpu(bdp->cbd_bufaddr),
-                                        fec16_to_cpu(bdp->cbd_datlen),
-                                        DMA_TO_DEVICE);
-               bdp->cbd_bufaddr = cpu_to_fec32(0);
-               if (!skb) {
-                       bdp = fec_enet_get_nextdesc(bdp, &txq->bd);
-                       continue;
+               while (!skb) {
+                       bdp_t = fec_enet_get_nextdesc(bdp_t, &txq->bd);
+                       index = fec_enet_get_bd_index(txq->tx_bd_base, bdp_t, fep);
+                       skb = txq->tx_skbuff[index];
+                       bdnum++;
+               }
+               status = fec16_to_cpu(READ_ONCE(bdp->cbd_sc));
+               if (status & BD_ENET_TX_READY)
+                       break;
+
+               for (i = 0; i < bdnum; i++) {
+                       if (!IS_TSO_HEADER(txq, bdp->cbd_bufaddr))
+                               dma_unmap_single(&fep->pdev->dev, bdp->cbd_bufaddr,
+                                                bdp->cbd_datlen, DMA_TO_DEVICE);
+                       bdp->cbd_bufaddr = 0;
+                       if (i < bdnum - 1)
+                               bdp = fec_enet_get_nextdesc(bdp, &txq->bd);
                }
+               txq->tx_skbuff[index] = NULL;


Regards,
Andy