netdev - RE: [PATCH v2] net: mv643xx_eth: Fix highmem support in non-TSO egress path

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Date:	Thu, 22 Jan 2015 12:40:25 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Ezequiel Garcia' <ezequiel.garcia@...e-electrons.com>,
	David Miller <davem@...emloft.net>,
	Russell King <linux@....linux.org.uk>
CC:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"B38611@...escale.com" <B38611@...escale.com>,
	"fabio.estevam@...escale.com" <fabio.estevam@...escale.com>
Subject: RE: [PATCH v2] net: mv643xx_eth: Fix highmem support in non-TSO
 egress path

From: Ezequiel Garcia
> Commit 69ad0dd7af22b61d9e0e68e56b6290121618b0fb
> Author: Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
> Date:   Mon May 19 13:59:59 2014 -0300
> 
>     net: mv643xx_eth: Use dma_map_single() to map the skb fragments
> 
> caused a nasty regression by removing the support for highmem skb
> fragments. By using page_address() to get the address of a fragment's
> page, we are assuming a lowmem page. However, such assumption is incorrect,
> as fragments can be in highmem pages, resulting in very nasty issues.
> 
> This commit fixes this by using the skb_frag_dma_map() helper,
> which takes care of mapping the skb fragment properly. Additionally,
> the type of mapping is now tracked, so it can be unmapped using
> dma_unmap_page or dma_unmap_single when appropriate.
> 
> Fixes: 69ad0dd7af22 ("net: mv643xx_eth: Use dma_map_single() to map the skb fragments")
> Reported-by: Russell King <rmk+kernel@....linux.org.uk>
> Signed-off-by: Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
...
> @@ -2048,6 +2068,11 @@ static int txq_init(struct mv643xx_eth_private *mp, int index)
>  					nexti * sizeof(struct tx_desc);
>  	}
> 
> +	txq->tx_desc_mapping = kcalloc(txq->tx_ring_size, sizeof(char),
> +				       GFP_KERNEL);
> +	if (!txq->tx_desc_mapping)
> +		return -ENOMEM;
> +
>  	/* Allocate DMA buffers for TSO MAC/IP/TCP headers */
>  	txq->tso_hdrs = dma_alloc_coherent(mp->dev->dev.parent,
>  					   txq->tx_ring_size * TSO_HEADER_SIZE,

I'm guessing there is an error path for dma_alloc_coherent() failing.
You've not modified it to free tx_desc_mapping.

	David

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