Subject: Re: [PATCH 2/3] sh_eth: Fix skb alloc size and alignment adjust rule.

From: Sergei Shtylyov <[email-masked]>
Date: Fri, 14 Nov 2014 01:48:39 +0300

On 11/13/2014 10:05 AM, Yoshihiro Kaneko wrote:

> From: Mitsuhiro Kimura <[email-masked]>

> In the current driver, allocation size of skb does not care the alignment
> adjust after allocation.
> And also, in the current implementation, buffer alignment method by
> sh_eth_set_receive_align function has a bug that this function displace
> buffer start address forcedly when the alignment is corrected.
> In the result, tail of the skb will exceed allocated area and kernel panic
> will be occurred.

    Oh, have never seen panic but Geert has reported WARNINGs from the DMA 
debug code...

> This patch fix this issue.

> Signed-off-by: Mitsuhiro Kimura <[email-masked]>
> Signed-off-by: Yoshihiro Kaneko <[email-masked]>
> ---
>   drivers/net/ethernet/renesas/sh_eth.c | 35 ++++++++++++++---------------------
>   drivers/net/ethernet/renesas/sh_eth.h |  2 ++
>   2 files changed, 16 insertions(+), 21 deletions(-)

> diff --git a/drivers/net/ethernet/renesas/sh_eth.c b/drivers/net/ethernet/renesas/sh_eth.c
> index 49e963e..0e4a407 100644
> --- a/drivers/net/ethernet/renesas/sh_eth.c
> +++ b/drivers/net/ethernet/renesas/sh_eth.c
> @@ -917,21 +917,12 @@ static int sh_eth_reset(struct net_device *ndev)
>   	return ret;
>   }
>
> -#if defined(CONFIG_CPU_SH4) || defined(CONFIG_ARCH_SHMOBILE)
>   static void sh_eth_set_receive_align(struct sk_buff *skb)
>   {
> -	int reserve;
> -
> -	reserve = SH4_SKB_RX_ALIGN - ((u32)skb->data & (SH4_SKB_RX_ALIGN - 1));
> +	u32 reserve = (u32)skb->data & (SH_ETH_RX_ALIGN - 1);

    Please keep an empty line after declaration, as it was before this patch.

>   	if (reserve)
> -		skb_reserve(skb, reserve);
> -}
> -#else
> -static void sh_eth_set_receive_align(struct sk_buff *skb)
> -{
> -	skb_reserve(skb, SH2_SH3_SKB_RX_ALIGN);
> +		skb_reserve(skb, SH_ETH_RX_ALIGN - reserve);
>   }
> -#endif
>
>
>   /* CPU <-> EDMAC endian convert */
> @@ -1119,6 +1110,7 @@ static void sh_eth_ring_format(struct net_device *ndev)
>   	struct sh_eth_txdesc *txdesc = NULL;
>   	int rx_ringsize = sizeof(*rxdesc) * mdp->num_rx_ring;
>   	int tx_ringsize = sizeof(*txdesc) * mdp->num_tx_ring;
> +	int skbuff_size = mdp->rx_buf_sz + SH_ETH_RX_ALIGN - 1;
>
>   	mdp->cur_rx = 0;
>   	mdp->cur_tx = 0;
> @@ -1131,21 +1123,21 @@ static void sh_eth_ring_format(struct net_device *ndev)
>   	for (i = 0; i < mdp->num_rx_ring; i++) {
>   		/* skb */
>   		mdp->rx_skbuff[i] = NULL;
> -		skb = netdev_alloc_skb(ndev, mdp->rx_buf_sz);
> +		skb = netdev_alloc_skb(ndev, skbuff_size);
>   		mdp->rx_skbuff[i] = skb;
>   		if (skb == NULL)
>   			break;
> -		dma_map_single(&ndev->dev, skb->data, mdp->rx_buf_sz,
> -			       DMA_FROM_DEVICE);
>   		sh_eth_set_receive_align(skb);
>
>   		/* RX descriptor */
>   		rxdesc = &mdp->rx_ring[i];
> +		/* The size of the buffer is 16 byte boundary. */

    Is *on* 16 byte boundary, you mean?

> +		rxdesc->buffer_length = ALIGN(mdp->rx_buf_sz, 16);
> +		dma_map_single(&ndev->dev, skb->data, rxdesc->buffer_length,
> +			       DMA_FROM_DEVICE);
>   		rxdesc->addr = virt_to_phys(skb->data);
>   		rxdesc->status = cpu_to_edmac(mdp, RD_RACT | RD_RFP);
>
> -		/* The size of the buffer is 16 byte boundary. */

    Ah, you're just copying an existent comment... well, seems a good time to 
fix it then. :-)

[...]
> @@ -1448,8 +1441,8 @@ static int sh_eth_rx(struct net_device *ndev, u32 intr_status, int *quota)
>   			if (mdp->cd->rpadir)
>   				skb_reserve(skb, NET_IP_ALIGN);
>   			dma_sync_single_for_cpu(&ndev->dev, rxdesc->addr,
> -						mdp->rx_buf_sz,
> -						DMA_FROM_DEVICE);
> +					ALIGN(mdp->rx_buf_sz, 16),
> +					DMA_FROM_DEVICE);

    Please keep the original alignment of the continuation lines.

>   			skb_put(skb, pkt_len);
>   			skb->protocol = eth_type_trans(skb, ndev);
>   			netif_receive_skb(skb);
> @@ -1468,13 +1461,13 @@ static int sh_eth_rx(struct net_device *ndev, u32 intr_status, int *quota)
>   		rxdesc->buffer_length = ALIGN(mdp->rx_buf_sz, 16);
>
>   		if (mdp->rx_skbuff[entry] == NULL) {
> -			skb = netdev_alloc_skb(ndev, mdp->rx_buf_sz);
> +			skb = netdev_alloc_skb(ndev, skbuff_size);
>   			mdp->rx_skbuff[entry] = skb;
>   			if (skb == NULL)
>   				break;	/* Better luck next round. */
> -			dma_map_single(&ndev->dev, skb->data, mdp->rx_buf_sz,
> -				       DMA_FROM_DEVICE);
>   			sh_eth_set_receive_align(skb);
> +			dma_map_single(&ndev->dev, skb->data,
> +				       rxdesc->buffer_length, DMA_FROM_DEVICE);
>
>   			skb_checksum_none_assert(skb);
>   			rxdesc->addr = virt_to_phys(skb->data);
> diff --git a/drivers/net/ethernet/renesas/sh_eth.h b/drivers/net/ethernet/renesas/sh_eth.h
> index b37c427..d138ebe 100644
> --- a/drivers/net/ethernet/renesas/sh_eth.h
> +++ b/drivers/net/ethernet/renesas/sh_eth.h
> @@ -163,8 +163,10 @@ enum {
>   /* Driver's parameters */
>   #if defined(CONFIG_CPU_SH4) || defined(CONFIG_ARCH_SHMOBILE)
>   #define SH4_SKB_RX_ALIGN	32
> +#define SH_ETH_RX_ALIGN		(SH4_SKB_RX_ALIGN)

    () not needed.

>   #else
>   #define SH2_SH3_SKB_RX_ALIGN	2
> +#define SH_ETH_RX_ALIGN		(SH2_SH3_SKB_RX_ALIGN)

    Likewise.
    And I don't think we still need {SH2_SH3|SH4}_SKB_RX_ALIGN after this patch.

[...]

WBR, Sergei