Subject: Re: [PATCH 5/5] net/cpsw: redo rx skb allocation in rx path

From: Mugunthan V N <[email-masked]>
Date: Thu, 18 Apr 2013 17:20:56 +0530

On 4/18/2013 3:22 AM, Sebastian Andrzej Siewior wrote:
> In case that we run into OOM during the allocation of the new rx-skb we
> don't get one and we have one skb less than we used to have. If this
> continues to happen then we end up with no rx-skbs at all.
> This patch changes the following:
> - if we fail to allocate the new skb, then we treat the currently
>    completed skb as the new one and so drop the currently received data.
> - instead of testing multiple times if the device is gone we rely one
>    the status field which is set to -ENOSYS in case the channel is going
>    down and incomplete requests are purged.
>    cpdma_chan_stop() removes most of the packages with -ENOSYS. The
>    currently active packet which is removed has the "tear down" bit set.
>    So if that bit is set, we send ENOSYS as well otherwise we pass the
>    status bits which are required to figure out which of the two possible
>    just finished.
>
> Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
> ---
>   drivers/net/ethernet/ti/cpsw.c          |   33 ++++++++++++-------------------
>   drivers/net/ethernet/ti/davinci_cpdma.c |    7 ++++++-
>   2 files changed, 19 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/net/ethernet/ti/cpsw.c b/drivers/net/ethernet/ti/cpsw.c
> index 559b020..f684e9b 100644
> --- a/drivers/net/ethernet/ti/cpsw.c
> +++ b/drivers/net/ethernet/ti/cpsw.c
> @@ -469,43 +469,36 @@ void cpsw_tx_handler(void *token, int len, int status)
>   void cpsw_rx_handler(void *token, int len, int status)
>   {
>   	struct sk_buff		*skb = token;
> +	struct sk_buff		*new_skb;
>   	struct net_device	*ndev = skb->dev;
>   	struct cpsw_priv	*priv = netdev_priv(ndev);
>   	int			ret = 0;
>   
>   	cpsw_dual_emac_src_port_detect(status, priv, ndev, skb);
>   
> -	/* free and bail if we are shutting down */
> -	if (unlikely(!netif_running(ndev)) ||
> -			unlikely(!netif_carrier_ok(ndev))) {
> +	if (unlikely(status < 0)) {
> +		/* the interface is going down, skbs are purged */
>   		dev_kfree_skb_any(skb);
>   		return;
>   	}
> -	if (likely(status >= 0)) {
> +
> +	new_skb = netdev_alloc_skb_ip_align(ndev, priv->rx_packet_max);
> +	if (new_skb) {
>   		skb_put(skb, len);
>   		cpts_rx_timestamp(priv->cpts, skb);
>   		skb->protocol = eth_type_trans(skb, ndev);
>   		netif_receive_skb(skb);
>   		priv->stats.rx_bytes += len;
>   		priv->stats.rx_packets++;
> -		skb = NULL;
> -	}
> -
> -	if (unlikely(!netif_running(ndev))) {
> -		if (skb)
> -			dev_kfree_skb_any(skb);
> -		return;
> +	} else {
> +		priv->stats.rx_dropped++;
> +		new_skb = skb;
Why you want to drop a successfully received packet as you memory alloc 
failed?
Let the stack get it processed and there after you can continue with one 
less
rx skb
>   	}
>   
> -	if (likely(!skb)) {
> -		skb = netdev_alloc_skb_ip_align(ndev, priv->rx_packet_max);
> -		if (WARN_ON(!skb))
> -			return;
> -
> -		ret = cpdma_chan_submit(priv->rxch, skb, skb->data,
> -					skb_tailroom(skb), 0);
> -	}
> -	WARN_ON(ret < 0);
> +	ret = cpdma_chan_submit(priv->rxch, new_skb, new_skb->data,
> +			skb_tailroom(new_skb), 0);
> +	if (WARN_ON(ret < 0))
> +		dev_kfree_skb_any(new_skb);
>   }
>   
>   static irqreturn_t cpsw_interrupt(int irq, void *dev_id)
> diff --git a/drivers/net/ethernet/ti/davinci_cpdma.c b/drivers/net/ethernet/ti/davinci_cpdma.c
> index 3cc20e7..6b0a89f 100644
> --- a/drivers/net/ethernet/ti/davinci_cpdma.c
> +++ b/drivers/net/ethernet/ti/davinci_cpdma.c
> @@ -776,6 +776,7 @@ static int __cpdma_chan_process(struct cpdma_chan *chan)
>   	struct cpdma_ctlr		*ctlr = chan->ctlr;
>   	struct cpdma_desc __iomem	*desc;
>   	int				status, outlen;
> +	int				cb_status = 0;
>   	struct cpdma_desc_pool		*pool = ctlr->pool;
>   	dma_addr_t			desc_dma;
>   	unsigned long			flags;
> @@ -811,8 +812,12 @@ static int __cpdma_chan_process(struct cpdma_chan *chan)
>   	}
>   
>   	spin_unlock_irqrestore(&chan->lock, flags);
> +	if (unlikely(status & CPDMA_DESC_TD_COMPLETE))
> +		cb_status = -ENOSYS;
> +	else
> +		cb_status = status;
>   
> -	__cpdma_chan_free(chan, desc, outlen, status);
> +	__cpdma_chan_free(chan, desc, outlen, cb_status);
>   	return status;
>   
>   unlock_ret:

Regards
Mugunthan V N