Re: [PATCH 4.4 02/15] [media] siano: make it work again with CONFIG_VMAP_STACK

[Eddie Chapman <eddie@ehuk.net>]

On 21/02/17 13:01, Greg Kroah-Hartman wrote:
> 4.4-stable review patch.  If anyone has any objections, please let me know.
>
> ------------------
>
> From: Mauro Carvalho Chehab <mchehab@s-opensource.com>
>
> commit f9c85ee67164b37f9296eab3b754e543e4e96a1c upstream.
>
> Reported as a Kaffeine bug:
> 	https://bugs.kde.org/show_bug.cgi?id=375811
>
> The USB control messages require DMA to work. We cannot pass
> a stack-allocated buffer, as it is not warranted that the
> stack would be into a DMA enabled area.
>
> On Kernel 4.9, the default is to not accept DMA on stack anymore
> on x86 architecture. On other architectures, this has been a
> requirement since Kernel 2.2. So, after this patch, this driver
> should likely work fine on all archs.
>
> Tested with USB ID 2040:5510: Hauppauge Windham
>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>
> ---
>  drivers/media/usb/siano/smsusb.c |   18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
>
> --- a/drivers/media/usb/siano/smsusb.c
> +++ b/drivers/media/usb/siano/smsusb.c
> @@ -200,22 +200,30 @@ static int smsusb_start_streaming(struct
>  static int smsusb_sendrequest(void *context, void *buffer, size_t size)
>  {
>  	struct smsusb_device_t *dev = (struct smsusb_device_t *) context;
> -	struct sms_msg_hdr *phdr = (struct sms_msg_hdr *) buffer;
> -	int dummy;
> +	struct sms_msg_hdr *phdr;
> +	int dummy, ret;
>
>  	if (dev->state != SMSUSB_ACTIVE) {
>  		pr_debug("Device not active yet\n");
>  		return -ENOENT;
>  	}
>
> +	phdr = kmalloc(size, GFP_KERNEL);
> +	if (!phdr)
> +		return -ENOMEM;
> +	memcpy(phdr, buffer, size);
> +
>  	pr_debug("sending %s(%d) size: %d\n",
>  		  smscore_translate_msg(phdr->msg_type), phdr->msg_type,
>  		  phdr->msg_length);
>
>  	smsendian_handle_tx_message((struct sms_msg_data *) phdr);
> -	smsendian_handle_message_header((struct sms_msg_hdr *)buffer);
> -	return usb_bulk_msg(dev->udev, usb_sndbulkpipe(dev->udev, 2),
> -			    buffer, size, &dummy, 1000);
> +	smsendian_handle_message_header((struct sms_msg_hdr *)phdr);
> +	ret = usb_bulk_msg(dev->udev, usb_sndbulkpipe(dev->udev, 2),
> +			    phdr, size, &dummy, 1000);
> +
> +	kfree(phdr);
> +	return ret;
>  }
>
>  static char *smsusb1_fw_lkup[] = {

Hello Greg,

According to the bug report linked to in the commit message this is only 
needed in 4.9 and higher.

Eddie