linux-kernel - Re: [PATCH 12/16] [media] lmedm04: get rid of on-stack dma buffers

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Date:	Tue, 15 Mar 2011 20:54:43 +0000
From:	Malcolm Priestley <tvboxspy@...il.com>
To:	Florian Mickler <florian@...kler.org>
Cc:	mchehab@...radead.org, oliver@...kum.org, jwjstone@...tmail.fm,
	linux-kernel@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...hat.com>,
	linux-media@...r.kernel.org
Subject: Re: [PATCH 12/16] [media] lmedm04: get rid of on-stack dma buffers

The patch failed for the following reason.

On Tue, 2011-03-15 at 09:43 +0100, Florian Mickler wrote:
> usb_control_msg initiates (and waits for completion of) a dma transfer using
> the supplied buffer. That buffer thus has to be seperately allocated on
> the heap.
> 
> In lib/dma_debug.c the function check_for_stack even warns about it:
> 	WARNING: at lib/dma-debug.c:866 check_for_stack
> 
> Note: This change is tested to compile only, as I don't have the hardware.
> 
> Signed-off-by: Florian Mickler <florian@...kler.org>
> ---
>  drivers/media/dvb/dvb-usb/lmedm04.c |   16 +++++++++++++---
>  1 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/dvb/dvb-usb/lmedm04.c b/drivers/media/dvb/dvb-usb/lmedm04.c
> index 0a3e88f..bec5439 100644
> --- a/drivers/media/dvb/dvb-usb/lmedm04.c
> +++ b/drivers/media/dvb/dvb-usb/lmedm04.c
> @@ -314,12 +314,17 @@ static int lme2510_int_read(struct dvb_usb_adapter *adap)
>  static int lme2510_return_status(struct usb_device *dev)
>  {
>  	int ret = 0;
> -	u8 data[10] = {0};
> +	u8 *data;
> +
> +	data = kzalloc(10, GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
>  
>  	ret |= usb_control_msg(dev, usb_rcvctrlpipe(dev, 0),
>  			0x06, 0x80, 0x0302, 0x00, data, 0x0006, 200);
>  	info("Firmware Status: %x (%x)", ret , data[2]);
>  
> +	kfree(data);
>  	return (ret < 0) ? -ENODEV : data[2];

data has been killed off when we need the buffer contents.
changing to the following fixed.

	ret = (ret < 0) ? -ENODEV : data[2];

	kfree(data);

	return ret;


> @@ -603,7 +608,7 @@ static int lme2510_download_firmware(struct usb_device *dev,
>  					const struct firmware *fw)
>  {
>  	int ret = 0;
> -	u8 data[512] = {0};
> +	u8 *data;
>  	u16 j, wlen, len_in, start, end;
>  	u8 packet_size, dlen, i;
>  	u8 *fw_data;
> @@ -611,6 +616,11 @@ static int lme2510_download_firmware(struct usb_device *dev,
>  	packet_size = 0x31;
>  	len_in = 1;
>  
> +	data = kzalloc(512, GFP_KERNEL);
> +	if (!data) {
> +		info("FRM Could not start Firmware Download (Buffer allocation failed)");

Longer than 80 characters, 

> +		return -ENOMEM;
> +	}
>  
>  	info("FRM Starting Firmware Download");
>  
> @@ -654,7 +664,7 @@ static int lme2510_download_firmware(struct usb_device *dev,
>  	else
>  		info("FRM Firmware Download Completed - Resetting Device");
>  
> -
> +	kfree(data);
>  	return (ret < 0) ? -ENODEV : 0;
>  }
>  

Otherwise the patch as corrected has been put on test. No initial
problems have been encountered.

Regards 

Malcolm



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