Hi Nadav,
On Tuesday, 7 August 2018 03:58:05 EEST Nadav Amit wrote:
> at 4:58 PM, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote:
> > 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@xxxxxxxxxxxxxxxx>
> >> Cc: Mauro Carvalho Chehab <mchehab@xxxxxxxxxx>
> >> Cc: linux-media@xxxxxxxxxxxxxxx
> >> Cc: linux-kernel@xxxxxxxxxxxxxxx
> >>
> >> Signed-off-by: Nadav Amit <namit@xxxxxxxxxx>
> >> ---
> >> 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…
You're right, it isn't. I'll include this patch in my next pull request for
v4.20.
--
Regards,
Laurent Pinchart
