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Message-ID: <20250724120840.GL11202@pendragon.ideasonboard.com>
Date: Thu, 24 Jul 2025 15:08:40 +0300
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Ricardo Ribalda <ribalda@...omium.org>
Cc: Hans de Goede <hansg@...nel.org>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: uvcvideo: Drop stream->mutex
Hi Ricardo,
Thank you for the patch.
On Thu, Jul 17, 2025 at 07:56:45AM +0000, Ricardo Ribalda wrote:
> Since commit c93d73c9c2cf ("media: uvcvideo: Use vb2 ioctl and fop
> helpers"), the IOCTLs are serialized. Due to this there is no more need
> to protect ctrl, cur_format or cur_frame from concurrent access.
>
> Drop stream->mutex after thanking it for years of good service.
>
> Use this opportunity to do fix some CodeStyle.
Is that about the following change only:
- if (format == NULL || frame == NULL) {
+ if (!format || !frame)
or is there something else I missed ?
>
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
> ---
> drivers/media/usb/uvc/uvc_driver.c | 4 ----
> drivers/media/usb/uvc/uvc_metadata.c | 8 ++------
> drivers/media/usb/uvc/uvc_v4l2.c | 39 ++++++++----------------------------
> drivers/media/usb/uvc/uvcvideo.h | 6 ------
> 4 files changed, 10 insertions(+), 47 deletions(-)
>
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index 775bede0d93d9b3e5391914aa395326d3de6a3b1..3039e6a533b82dd917050d416c9ced8756d69170 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -183,8 +183,6 @@ static void uvc_stream_delete(struct uvc_streaming *stream)
> if (stream->async_wq)
> destroy_workqueue(stream->async_wq);
>
> - mutex_destroy(&stream->mutex);
> -
> usb_put_intf(stream->intf);
>
> kfree(stream->formats);
> @@ -201,8 +199,6 @@ static struct uvc_streaming *uvc_stream_new(struct uvc_device *dev,
> if (stream == NULL)
> return NULL;
>
> - mutex_init(&stream->mutex);
> -
> stream->dev = dev;
> stream->intf = usb_get_intf(intf);
> stream->intfnum = intf->cur_altsetting->desc.bInterfaceNumber;
> diff --git a/drivers/media/usb/uvc/uvc_metadata.c b/drivers/media/usb/uvc/uvc_metadata.c
> index 229e08ff323eed9129d835b24ea2e8085bb713b8..d1d4fade634bd3f8b12bbaa75388db42aecc25ea 100644
> --- a/drivers/media/usb/uvc/uvc_metadata.c
> +++ b/drivers/media/usb/uvc/uvc_metadata.c
> @@ -100,14 +100,10 @@ static int uvc_meta_v4l2_set_format(struct file *file, void *fh,
> * Metadata buffers would still be perfectly parseable, but it's more
> * consistent and cleaner to disallow that.
> */
> - mutex_lock(&stream->mutex);
> -
> if (vb2_is_busy(&stream->meta.queue.queue))
> - ret = -EBUSY;
> - else
> - stream->meta.format = fmt->dataformat;
> + return -EBUSY;
>
> - mutex_unlock(&stream->mutex);
> + stream->meta.format = fmt->dataformat;
>
> return ret;
return 0;
> }
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index 160f9cf6e6dbdbf39e3eff56a5d5ea1d977fbe22..d7be4d59f0c73b983aa01321f4acc8f8bf6e83ef 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -329,14 +329,12 @@ static int uvc_v4l2_try_format(struct uvc_streaming *stream,
> * developers test their webcams with the Linux driver as well as with
> * the Windows driver).
> */
> - mutex_lock(&stream->mutex);
> if (stream->dev->quirks & UVC_QUIRK_PROBE_EXTRAFIELDS)
> probe->dwMaxVideoFrameSize =
> stream->ctrl.dwMaxVideoFrameSize;
>
> /* Probe the device. */
> ret = uvc_probe_video(stream, probe);
> - mutex_unlock(&stream->mutex);
> if (ret < 0)
> return ret;
>
> @@ -395,19 +393,15 @@ static int uvc_ioctl_g_fmt(struct file *file, void *fh,
> struct uvc_streaming *stream = handle->stream;
> const struct uvc_format *format;
> const struct uvc_frame *frame;
> - int ret = 0;
>
> if (fmt->type != stream->type)
> return -EINVAL;
>
> - mutex_lock(&stream->mutex);
> format = stream->cur_format;
> frame = stream->cur_frame;
>
> - if (format == NULL || frame == NULL) {
> - ret = -EINVAL;
> - goto done;
> - }
> + if (!format || !frame)
> + return -EINVAL;
>
> fmt->fmt.pix.pixelformat = format->fcc;
> fmt->fmt.pix.width = frame->wWidth;
> @@ -419,9 +413,7 @@ static int uvc_ioctl_g_fmt(struct file *file, void *fh,
> fmt->fmt.pix.xfer_func = format->xfer_func;
> fmt->fmt.pix.ycbcr_enc = format->ycbcr_enc;
>
> -done:
> - mutex_unlock(&stream->mutex);
> - return ret;
> + return 0;
> }
>
> static int uvc_ioctl_s_fmt(struct file *file, void *fh,
> @@ -441,19 +433,14 @@ static int uvc_ioctl_s_fmt(struct file *file, void *fh,
> if (ret < 0)
> return ret;
>
> - mutex_lock(&stream->mutex);
> - if (vb2_is_busy(&stream->queue.queue)) {
> - ret = -EBUSY;
> - goto done;
> - }
> + if (vb2_is_busy(&stream->queue.queue))
> + return -EBUSY;
>
> stream->ctrl = probe;
> stream->cur_format = format;
> stream->cur_frame = frame;
>
> -done:
> - mutex_unlock(&stream->mutex);
> - return ret;
> + return 0;
> }
>
> static int uvc_ioctl_g_parm(struct file *file, void *fh,
> @@ -466,9 +453,7 @@ static int uvc_ioctl_g_parm(struct file *file, void *fh,
> if (parm->type != stream->type)
> return -EINVAL;
>
> - mutex_lock(&stream->mutex);
> numerator = stream->ctrl.dwFrameInterval;
> - mutex_unlock(&stream->mutex);
>
You can drop the blank line here.
> denominator = 10000000;
> v4l2_simplify_fraction(&numerator, &denominator, 8, 333);
> @@ -519,12 +504,9 @@ static int uvc_ioctl_s_parm(struct file *file, void *fh,
> uvc_dbg(stream->dev, FORMAT, "Setting frame interval to %u/%u (%u)\n",
> timeperframe.numerator, timeperframe.denominator, interval);
>
> - mutex_lock(&stream->mutex);
>
Double blank line.
> - if (uvc_queue_streaming(&stream->queue)) {
> - mutex_unlock(&stream->mutex);
> + if (uvc_queue_streaming(&stream->queue))
> return -EBUSY;
> - }
>
> format = stream->cur_format;
> frame = stream->cur_frame;
> @@ -556,14 +538,11 @@ static int uvc_ioctl_s_parm(struct file *file, void *fh,
>
> /* Probe the device with the new settings. */
> ret = uvc_probe_video(stream, &probe);
> - if (ret < 0) {
> - mutex_unlock(&stream->mutex);
> + if (ret < 0)
> return ret;
> - }
>
> stream->ctrl = probe;
> stream->cur_frame = frame;
> - mutex_unlock(&stream->mutex);
>
> /* Return the actual frame period. */
> timeperframe.numerator = probe.dwFrameInterval;
> @@ -941,10 +920,8 @@ static int uvc_ioctl_g_selection(struct file *file, void *fh,
>
> sel->r.left = 0;
> sel->r.top = 0;
> - mutex_lock(&stream->mutex);
> sel->r.width = stream->cur_frame->wWidth;
> sel->r.height = stream->cur_frame->wHeight;
> - mutex_unlock(&stream->mutex);
>
> return 0;
> }
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index 757254fc4fe930ae61c9d0425f04d4cd074a617e..86765b9d7935f0888476249c3fb826cd7f36b35c 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -469,12 +469,6 @@ struct uvc_streaming {
> const struct uvc_format *cur_format;
> const struct uvc_frame *cur_frame;
>
> - /*
> - * Protect access to ctrl, cur_format, cur_frame and hardware video
> - * probe control.
> - */
> - struct mutex mutex;
> -
Could you please instead keep this mutex and drop uvc_video_queue.mutex
? The rationale is that the same lock is now used to protect the queue
operations and to serialize the ioctls. It's therefore a higher-level
lock, which should be stored in the higher-level object, not in the
queue.
You can then also drop the lock assignment in uvc_queue.c that reads
queue->queue.lock = &queue->mutex;
as videobuf2 and the V4L2 core will use the video device lock when no
queue lock is set. The comment at the top of uvc_queue.c may need to be
updated.
> /* Buffers queue. */
> unsigned int frozen : 1;
> struct uvc_video_queue queue;
>
> ---
> base-commit: d968e50b5c26642754492dea23cbd3592bde62d8
> change-id: 20250716-uvc-onelocksless-b66658e01f89
--
Regards,
Laurent Pinchart
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