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

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Message-ID: <54C0FAA0.9040002@free-electrons.com>
Date:	Thu, 22 Jan 2015 10:26:56 -0300
From:	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>
To:	David Laight <David.Laight@...LAB.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

On 01/22/2015 09:40 AM, David Laight wrote:
> 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.
> 

Yeah, you guess right.
-- 
Ezequiel García, Free Electrons
Embedded Linux, Kernel and Android Engineering
http://free-electrons.com
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