netdev - Re: [PATCH] pch_gbe: don't come up if we can't allocate buffers

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Date:	Thu, 25 Oct 2012 10:40:58 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Veaceslav Falico <vfalico@...hat.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net,
	richardcochran@...il.com, tshimizu818@...il.com,
	andy.cress@...kontron.com, erwan.velu@...iacaerospace.com
Subject: Re: [PATCH] pch_gbe: don't come up if we can't allocate buffers

On Thu, 2012-10-25 at 09:10 +0200, Veaceslav Falico wrote:
> Currently, even if pch_gbe_alloc_tx/rx_buffers (even partially) fail, we
> bring the interface up. It mihgt confuse the user (if he requested specific
> amount of buffers) and can lead to different bugs.
> 
> Add error handling to these functions and clean after them in case of
> failure. It also resolves a possible NULL pointer dereference in
> pch_gbe_alloc_tx_buffers(), in case of netdev_alloc_skb() failure. It's ok
> to (paritally) fail for pch_gbe_alloc_rx_buffers() in some situation, so
> don't clean inside and rather handle skb freeing outside of the function.
> 
> This patch also adds tx_alloc_buff_failed ethtool counter.

This should not be needed :

> -static void pch_gbe_alloc_tx_buffers(struct pch_gbe_adapter *adapter,
> +static int pch_gbe_alloc_tx_buffers(struct pch_gbe_adapter *adapter,
>  					struct pch_gbe_tx_ring *tx_ring)
>  {
>  	struct pch_gbe_buffer *buffer_info;
> @@ -1506,6 +1521,7 @@ static void pch_gbe_alloc_tx_buffers(struct pch_gbe_adapter *adapter,
>  	unsigned int i;
>  	unsigned int bufsz;
>  	struct pch_gbe_tx_desc *tx_desc;
> +	int err;
>  
>  	bufsz =
>  	    adapter->hw.mac.max_frame_size + PCH_GBE_DMA_ALIGN + NET_IP_ALIGN;
> @@ -1513,12 +1529,26 @@ static void pch_gbe_alloc_tx_buffers(struct pch_gbe_adapter *adapter,
>  	for (i = 0; i < tx_ring->count; i++) {
>  		buffer_info = &tx_ring->buffer_info[i];
>  		skb = netdev_alloc_skb(adapter->netdev, bufsz);
> +		if (unlikely(!skb)) {
> +			adapter->stats.tx_alloc_buff_failed++;
> +			err = -ENOMEM;
> +			goto freeall;
> +		}

Hmmm

These skbs should be allocated using GFP_KERNEL, to lower risk of OOM,
using a mere alloc_skb(bufsz, GFP_KERNEL)

Only skbs for rx 'need' netdev_alloc_skb() to add a NET_SKB_PAD
headroom.

	skb = alloc_skb(bufsz, GFP_KERNEL);
	if (!skb)
		goto fail;
	skb_reserve(skb, NET_IP_ALIGN);

And BTW, we dont really need skbs here, only a bounce buffer so that we
can copy frames on it... (kmalloc() instead of alloc_skb())

>  		skb_reserve(skb, PCH_GBE_DMA_ALIGN);

PCH_GBE_DMA_ALIGN is zero ...

>  		buffer_info->skb = skb;
>  		tx_desc = PCH_GBE_TX_DESC(*tx_ring, i);
>  		tx_desc->gbec_status = (DSC_INIT16);
>  	}
> -	return;
> +	return 0;
> +
> +freeall:
> +	for (i--; i >= 0; i--) {
> +		dev_kfree_skb_any(buffer_info->skb);
> +		buffer_info->skb = NULL;
> +		tx_desc = PCH_GBE_TX_DESC(*tx_ring, i);
> +		tx_desc->gbec_status = 0;
> +	}
> +	return err;
>  }
>  


Also I would call pch_gbe_alloc_tx_buffers() _after_
pch_gbe_alloc_rx_buffers() (Since rx allocations probably are using
GFP_ATOMIC allocations)



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