Struct uvc_frame and interval (u32*) are packaged together on
streaming->formats on a single contiguous allocation.
Right now they allocated right after uvc_format, without taking into
consideration their required alignment.
This is working fine because both structures have a field with a
pointer, but it will stop working when the sizeof() of any of those
structs is not a multiple of the sizeof(void*).
Enforce that alignment during the allocation.
Signed-off-by: Ricardo Ribalda <[email protected]>
---
This is better than 3 allocations, and do not have any performance
penalty.
I have tried this patch printing the size and the address of the
pointers in the old and the new mode, and it looks the same.
[ 2.235223] drivers/media/usb/uvc/uvc_driver.c:694 uvc_parse_streaming 432
[ 2.235249] drivers/media/usb/uvc/uvc_driver.c:704 uvc_parse_streaming 432
[ 2.235256] drivers/media/usb/uvc/uvc_driver.c:714 uvc_parse_streaming 00000000d32087cc 00000000d3803788
[ 2.235265] drivers/media/usb/uvc/uvc_driver.c:720 uvc_parse_streaming 00000000d32087cc 00000000d3803788
---
Changes in v2: Thanks Laurent.
- Enforce alignment during allocation instead of using __aligned()
macros.
- Link to v1: https://lore.kernel.org/r/[email protected]
---
drivers/media/usb/uvc/uvc_driver.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)
diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index 7aefa76a42b31..7d9844ba3b205 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -663,16 +663,26 @@ static int uvc_parse_streaming(struct uvc_device *dev,
goto error;
}
- size = nformats * sizeof(*format) + nframes * sizeof(*frame)
- + nintervals * sizeof(*interval);
+ /*
+ * Allocate memory for the formats, the frames and the intervals,
+ * plus any required padding to guarantee that everything has the
+ * correct alignment.
+ */
+ size = nformats * sizeof(*format);
+ size = ALIGN(size, __alignof__(*frame)) + nframes * sizeof(*frame);
+ size = ALIGN(size, __alignof__(*interval))
+ + nintervals * sizeof(*interval);
+
format = kzalloc(size, GFP_KERNEL);
- if (format == NULL) {
+ if (!format) {
ret = -ENOMEM;
goto error;
}
- frame = (struct uvc_frame *)&format[nformats];
- interval = (u32 *)&frame[nframes];
+ frame = (void *)format + nformats * sizeof(*format);
+ frame = PTR_ALIGN(frame, __alignof__(*frame));
+ interval = (void *)frame + nframes * sizeof(*frame);
+ interval = PTR_ALIGN(interval, __alignof__(*interval));
streaming->format = format;
streaming->nformats = nformats;
---
base-commit: 58390c8ce1bddb6c623f62e7ed36383e7fa5c02f
change-id: 20230501-uvc-align-6ff202b68dab
Best regards,
--
Ricardo Ribalda <[email protected]>
Hi Ricardo,
Thank you for the patch.
On Thu, Apr 04, 2024 at 05:56:18PM +0000, Ricardo Ribalda wrote:
> Struct uvc_frame and interval (u32*) are packaged together on
> streaming->formats on a single contiguous allocation.
>
> Right now they allocated right after uvc_format, without taking into
s/they/they are/
> consideration their required alignment.
>
> This is working fine because both structures have a field with a
> pointer, but it will stop working when the sizeof() of any of those
> structs is not a multiple of the sizeof(void*).
>
> Enforce that alignment during the allocation.
>
> Signed-off-by: Ricardo Ribalda <[email protected]>
> ---
> This is better than 3 allocations, and do not have any performance
> penalty.
>
> I have tried this patch printing the size and the address of the
> pointers in the old and the new mode, and it looks the same.
>
> [ 2.235223] drivers/media/usb/uvc/uvc_driver.c:694 uvc_parse_streaming 432
> [ 2.235249] drivers/media/usb/uvc/uvc_driver.c:704 uvc_parse_streaming 432
> [ 2.235256] drivers/media/usb/uvc/uvc_driver.c:714 uvc_parse_streaming 00000000d32087cc 00000000d3803788
> [ 2.235265] drivers/media/usb/uvc/uvc_driver.c:720 uvc_parse_streaming 00000000d32087cc 00000000d3803788
> ---
> Changes in v2: Thanks Laurent.
> - Enforce alignment during allocation instead of using __aligned()
> macros.
> - Link to v1: https://lore.kernel.org/r/[email protected]
> ---
> drivers/media/usb/uvc/uvc_driver.c | 20 +++++++++++++++-----
> 1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index 7aefa76a42b31..7d9844ba3b205 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -663,16 +663,26 @@ static int uvc_parse_streaming(struct uvc_device *dev,
> goto error;
> }
>
> - size = nformats * sizeof(*format) + nframes * sizeof(*frame)
> - + nintervals * sizeof(*interval);
> + /*
> + * Allocate memory for the formats, the frames and the intervals,
> + * plus any required padding to guarantee that everything has the
> + * correct alignment.
> + */
> + size = nformats * sizeof(*format);
> + size = ALIGN(size, __alignof__(*frame)) + nframes * sizeof(*frame);
> + size = ALIGN(size, __alignof__(*interval))
> + + nintervals * sizeof(*interval);
You have two extra spaces here. I'll fix when applying.
Reviewed-by: Laurent Pinchart <[email protected]>
> +
> format = kzalloc(size, GFP_KERNEL);
> - if (format == NULL) {
> + if (!format) {
> ret = -ENOMEM;
> goto error;
> }
>
> - frame = (struct uvc_frame *)&format[nformats];
> - interval = (u32 *)&frame[nframes];
> + frame = (void *)format + nformats * sizeof(*format);
> + frame = PTR_ALIGN(frame, __alignof__(*frame));
> + interval = (void *)frame + nframes * sizeof(*frame);
> + interval = PTR_ALIGN(interval, __alignof__(*interval));
>
> streaming->format = format;
> streaming->nformats = nformats;
>
> ---
> base-commit: 58390c8ce1bddb6c623f62e7ed36383e7fa5c02f
> change-id: 20230501-uvc-align-6ff202b68dab
--
Regards,
Laurent Pinchart