lkml.org 
[lkml]   [2018]   [Aug]   [6]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] usb: fix uvc_alloc_entity() allocation alignment
Date
at 4:58 PM, Laurent Pinchart <laurent.pinchart@ideasonboard.com> wrote:

> Hi Nadav,
>
> Thank you for the patch.
>
> On Monday, 4 June 2018 16:47:13 EEST Nadav Amit wrote:
>> The use of ALIGN() in uvc_alloc_entity() is incorrect, since the size of
>> (entity->pads) is not a power of two. As a stop-gap, until a better
>> solution is adapted, use roundup() instead.
>>
>> Found by a static assertion. Compile-tested only.
>>
>> Fixes: 4ffc2d89f38a ("uvcvideo: Register subdevices for each entity")
>>
>> Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>> Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
>> Cc: linux-media@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>>
>> Signed-off-by: Nadav Amit <namit@vmware.com>
>> ---
>> drivers/media/usb/uvc/uvc_driver.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/media/usb/uvc/uvc_driver.c
>> b/drivers/media/usb/uvc/uvc_driver.c index 2469b49b2b30..6b989d41c034
>> 100644
>> --- a/drivers/media/usb/uvc/uvc_driver.c
>> +++ b/drivers/media/usb/uvc/uvc_driver.c
>> @@ -909,7 +909,7 @@ static struct uvc_entity *uvc_alloc_entity(u16 type, u8
>> id, unsigned int size;
>> unsigned int i;
>>
>> - extra_size = ALIGN(extra_size, sizeof(*entity->pads));
>> + extra_size = roundup(extra_size, sizeof(*entity->pads));
>> num_inputs = (type & UVC_TERM_OUTPUT) ? num_pads : num_pads - 1;
>> size = sizeof(*entity) + extra_size + sizeof(*entity->pads) * num_pads
>> + num_inputs;
>
> The purpose of this alignment is to make sure that entity->pads will be
> properly aligned. In theory the size of uvc_entity should be taken into
> account too, but the structure contains pointers, so its size should already
> be properly aligned. This patch thus looks good to me. What made you say it's
> a stop-gap measure ?

Thanks. It’s been a while. Anyhow, I don’t know how “hot” this code is, but
roundup uses a div operations, so if it is “hot” you may want a different
way to align with lower overhead.

I presume it is not…

Regards,
Nadav
\
 
 \ /
  Last update: 2018-08-07 02:59    [W:0.067 / U:0.396 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site