diff mbox series

[v7,1/3] media: uvcvideo: Refactor the status irq API

Message ID 20240926-guenter-mini-v7-1-690441953d4a@chromium.org
State Accepted
Commit 44f703386021e90cc33346f0ed3beb0274cedd68
Headers show
Series uvcvideo: Attempt N to land UVC race conditions fixes | expand

Commit Message

Ricardo Ribalda Sept. 26, 2024, 5:49 a.m. UTC 
There are two different use-cases of uvc_status():

- adding/removing a user when the camera is open/closed
- stopping/starting when the camera is suspended/resumed

Make the API reflect these two use-cases and move all the refcounting
and locking logic to the uvc_status.c file.

No functional change is expected from this patch.

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
---
 drivers/media/usb/uvc/uvc_driver.c | 13 ++--------
 drivers/media/usb/uvc/uvc_status.c | 53 ++++++++++++++++++++++++++++++++++++--
 drivers/media/usb/uvc/uvc_v4l2.c   | 22 +++++-----------
 drivers/media/usb/uvc/uvcvideo.h   | 10 ++++---
 4 files changed, 65 insertions(+), 33 deletions(-)

Comments

Laurent Pinchart Sept. 26, 2024, 2:39 p.m. UTC | #1 
Hi Ricardo,

Thank you for the patch.

On Thu, Sep 26, 2024 at 05:49:57AM +0000, Ricardo Ribalda wrote:
> There are two different use-cases of uvc_status():
> 
> - adding/removing a user when the camera is open/closed
> - stopping/starting when the camera is suspended/resumed
> 
> Make the API reflect these two use-cases and move all the refcounting
> and locking logic to the uvc_status.c file.
> 
> No functional change is expected from this patch.
> 
> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
>  drivers/media/usb/uvc/uvc_driver.c | 13 ++--------
>  drivers/media/usb/uvc/uvc_status.c | 53 ++++++++++++++++++++++++++++++++++++--
>  drivers/media/usb/uvc/uvc_v4l2.c   | 22 +++++-----------
>  drivers/media/usb/uvc/uvcvideo.h   | 10 ++++---
>  4 files changed, 65 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index f0febdc08c2d..31e8942f1ef8 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -2116,7 +2116,6 @@ static int uvc_probe(struct usb_interface *intf,
>  	INIT_LIST_HEAD(&dev->streams);
>  	kref_init(&dev->ref);
>  	atomic_set(&dev->nmappings, 0);
> -	mutex_init(&dev->lock);
>  
>  	dev->udev = usb_get_dev(udev);
>  	dev->intf = usb_get_intf(intf);
> @@ -2288,10 +2287,7 @@ static int uvc_suspend(struct usb_interface *intf, pm_message_t message)
>  	/* Controls are cached on the fly so they don't need to be saved. */
>  	if (intf->cur_altsetting->desc.bInterfaceSubClass ==
>  	    UVC_SC_VIDEOCONTROL) {
> -		mutex_lock(&dev->lock);
> -		if (dev->users)
> -			uvc_status_stop(dev);
> -		mutex_unlock(&dev->lock);
> +		uvc_status_suspend(dev);
>  		return 0;
>  	}
>  
> @@ -2322,12 +2318,7 @@ static int __uvc_resume(struct usb_interface *intf, int reset)
>  				return ret;
>  		}
>  
> -		mutex_lock(&dev->lock);
> -		if (dev->users)
> -			ret = uvc_status_start(dev, GFP_NOIO);
> -		mutex_unlock(&dev->lock);
> -
> -		return ret;
> +		return uvc_status_resume(dev);
>  	}
>  
>  	list_for_each_entry(stream, &dev->streams, list) {
> diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
> index a78a88c710e2..e438ae5af2e8 100644
> --- a/drivers/media/usb/uvc/uvc_status.c
> +++ b/drivers/media/usb/uvc/uvc_status.c
> @@ -257,6 +257,8 @@ int uvc_status_init(struct uvc_device *dev)
>  	unsigned int pipe;
>  	int interval;
>  
> +	mutex_init(&dev->status_lock);
> +
>  	if (ep == NULL)
>  		return 0;
>  
> @@ -302,18 +304,22 @@ void uvc_status_cleanup(struct uvc_device *dev)
>  	kfree(dev->status);
>  }
>  
> -int uvc_status_start(struct uvc_device *dev, gfp_t flags)
> +static int uvc_status_start(struct uvc_device *dev, gfp_t flags)
>  {
> +	lockdep_assert_held(&dev->status_lock);
> +
>  	if (dev->int_urb == NULL)
>  		return 0;
>  
>  	return usb_submit_urb(dev->int_urb, flags);
>  }
>  
> -void uvc_status_stop(struct uvc_device *dev)
> +static void uvc_status_stop(struct uvc_device *dev)
>  {
>  	struct uvc_ctrl_work *w = &dev->async_ctrl;
>  
> +	lockdep_assert_held(&dev->status_lock);
> +
>  	/*
>  	 * Prevent the asynchronous control handler from requeing the URB. The
>  	 * barrier is needed so the flush_status change is visible to other
> @@ -350,3 +356,46 @@ void uvc_status_stop(struct uvc_device *dev)
>  	 */
>  	smp_store_release(&dev->flush_status, false);
>  }
> +
> +int uvc_status_resume(struct uvc_device *dev)
> +{
> +	guard(mutex)(&dev->status_lock);
> +
> +	if (dev->status_users)
> +		return  uvc_status_start(dev, GFP_NOIO);

Double space afer return. I'll fix when applying.

> +
> +	return 0;
> +}
> +
> +void uvc_status_suspend(struct uvc_device *dev)
> +{
> +	guard(mutex)(&dev->status_lock);
> +
> +	if (dev->status_users)
> +		uvc_status_stop(dev);
> +}
> +
> +int uvc_status_get(struct uvc_device *dev)
> +{
> +	int ret = 0;
> +
> +	guard(mutex)(&dev->status_lock);
> +
> +	if (!dev->status_users)
> +		ret = uvc_status_start(dev, GFP_KERNEL);
> +	if (!ret)
> +		dev->status_users++;

Thanks for the scoped guard, we can write

	if (!dev->status_users) {
		int ret = uvc_status_start(dev, GFP_KERNEL);
		if (ret)
			return ret;
	}

	dev->status_users++;

	return 0;

which I think is nicer to read. If that's fine with you I'll do this
locally, not need to a new version.

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> +
> +	return ret;
> +}
> +
> +void uvc_status_put(struct uvc_device *dev)
> +{
> +	guard(mutex)(&dev->status_lock);
> +
> +	if (dev->status_users == 1)
> +		uvc_status_stop(dev);
> +	WARN_ON(!dev->status_users);
> +	if (dev->status_users)
> +		dev->status_users--;
> +}
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index f4988f03640a..97c5407f6603 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -628,20 +628,13 @@ static int uvc_v4l2_open(struct file *file)
>  		return -ENOMEM;
>  	}
>  
> -	mutex_lock(&stream->dev->lock);
> -	if (stream->dev->users == 0) {
> -		ret = uvc_status_start(stream->dev, GFP_KERNEL);
> -		if (ret < 0) {
> -			mutex_unlock(&stream->dev->lock);
> -			usb_autopm_put_interface(stream->dev->intf);
> -			kfree(handle);
> -			return ret;
> -		}
> +	ret = uvc_status_get(stream->dev);
> +	if (ret) {
> +		usb_autopm_put_interface(stream->dev->intf);
> +		kfree(handle);
> +		return ret;
>  	}
>  
> -	stream->dev->users++;
> -	mutex_unlock(&stream->dev->lock);
> -
>  	v4l2_fh_init(&handle->vfh, &stream->vdev);
>  	v4l2_fh_add(&handle->vfh);
>  	handle->chain = stream->chain;
> @@ -670,10 +663,7 @@ static int uvc_v4l2_release(struct file *file)
>  	kfree(handle);
>  	file->private_data = NULL;
>  
> -	mutex_lock(&stream->dev->lock);
> -	if (--stream->dev->users == 0)
> -		uvc_status_stop(stream->dev);
> -	mutex_unlock(&stream->dev->lock);
> +	uvc_status_put(stream->dev);
>  
>  	usb_autopm_put_interface(stream->dev->intf);
>  	return 0;
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index b7d24a853ce4..07f9921d83f2 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -563,8 +563,6 @@ struct uvc_device {
>  
>  	const struct uvc_device_info *info;
>  
> -	struct mutex lock;		/* Protects users */
> -	unsigned int users;
>  	atomic_t nmappings;
>  
>  	/* Video control interface */
> @@ -586,6 +584,8 @@ struct uvc_device {
>  	struct usb_host_endpoint *int_ep;
>  	struct urb *int_urb;
>  	struct uvc_status *status;
> +	struct mutex status_lock; /* Protects status_users */
> +	unsigned int status_users;
>  	bool flush_status;
>  
>  	struct input_dev *input;
> @@ -752,8 +752,10 @@ int uvc_register_video_device(struct uvc_device *dev,
>  int uvc_status_init(struct uvc_device *dev);
>  void uvc_status_unregister(struct uvc_device *dev);
>  void uvc_status_cleanup(struct uvc_device *dev);
> -int uvc_status_start(struct uvc_device *dev, gfp_t flags);
> -void uvc_status_stop(struct uvc_device *dev);
> +int uvc_status_resume(struct uvc_device *dev);
> +void uvc_status_suspend(struct uvc_device *dev);
> +int uvc_status_get(struct uvc_device *dev);
> +void uvc_status_put(struct uvc_device *dev);
>  
>  /* Controls */
>  extern const struct v4l2_subscribed_event_ops uvc_ctrl_sub_ev_ops;
Ricardo Ribalda Sept. 27, 2024, 6:09 a.m. UTC | #2 
Hi Laurent

On Thu, 26 Sept 2024 at 16:39, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
>
> Hi Ricardo,
>
> Thank you for the patch.
>
> On Thu, Sep 26, 2024 at 05:49:57AM +0000, Ricardo Ribalda wrote:
> > There are two different use-cases of uvc_status():
> >
> > - adding/removing a user when the camera is open/closed
> > - stopping/starting when the camera is suspended/resumed
> >
> > Make the API reflect these two use-cases and move all the refcounting
> > and locking logic to the uvc_status.c file.
> >
> > No functional change is expected from this patch.
> >
> > Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> > Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> > ---
> >  drivers/media/usb/uvc/uvc_driver.c | 13 ++--------
> >  drivers/media/usb/uvc/uvc_status.c | 53 ++++++++++++++++++++++++++++++++++++--
> >  drivers/media/usb/uvc/uvc_v4l2.c   | 22 +++++-----------
> >  drivers/media/usb/uvc/uvcvideo.h   | 10 ++++---
> >  4 files changed, 65 insertions(+), 33 deletions(-)
> >
> > diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> > index f0febdc08c2d..31e8942f1ef8 100644
> > --- a/drivers/media/usb/uvc/uvc_driver.c
> > +++ b/drivers/media/usb/uvc/uvc_driver.c
> > @@ -2116,7 +2116,6 @@ static int uvc_probe(struct usb_interface *intf,
> >       INIT_LIST_HEAD(&dev->streams);
> >       kref_init(&dev->ref);
> >       atomic_set(&dev->nmappings, 0);
> > -     mutex_init(&dev->lock);
> >
> >       dev->udev = usb_get_dev(udev);
> >       dev->intf = usb_get_intf(intf);
> > @@ -2288,10 +2287,7 @@ static int uvc_suspend(struct usb_interface *intf, pm_message_t message)
> >       /* Controls are cached on the fly so they don't need to be saved. */
> >       if (intf->cur_altsetting->desc.bInterfaceSubClass ==
> >           UVC_SC_VIDEOCONTROL) {
> > -             mutex_lock(&dev->lock);
> > -             if (dev->users)
> > -                     uvc_status_stop(dev);
> > -             mutex_unlock(&dev->lock);
> > +             uvc_status_suspend(dev);
> >               return 0;
> >       }
> >
> > @@ -2322,12 +2318,7 @@ static int __uvc_resume(struct usb_interface *intf, int reset)
> >                               return ret;
> >               }
> >
> > -             mutex_lock(&dev->lock);
> > -             if (dev->users)
> > -                     ret = uvc_status_start(dev, GFP_NOIO);
> > -             mutex_unlock(&dev->lock);
> > -
> > -             return ret;
> > +             return uvc_status_resume(dev);
> >       }
> >
> >       list_for_each_entry(stream, &dev->streams, list) {
> > diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
> > index a78a88c710e2..e438ae5af2e8 100644
> > --- a/drivers/media/usb/uvc/uvc_status.c
> > +++ b/drivers/media/usb/uvc/uvc_status.c
> > @@ -257,6 +257,8 @@ int uvc_status_init(struct uvc_device *dev)
> >       unsigned int pipe;
> >       int interval;
> >
> > +     mutex_init(&dev->status_lock);
> > +
> >       if (ep == NULL)
> >               return 0;
> >
> > @@ -302,18 +304,22 @@ void uvc_status_cleanup(struct uvc_device *dev)
> >       kfree(dev->status);
> >  }
> >
> > -int uvc_status_start(struct uvc_device *dev, gfp_t flags)
> > +static int uvc_status_start(struct uvc_device *dev, gfp_t flags)
> >  {
> > +     lockdep_assert_held(&dev->status_lock);
> > +
> >       if (dev->int_urb == NULL)
> >               return 0;
> >
> >       return usb_submit_urb(dev->int_urb, flags);
> >  }
> >
> > -void uvc_status_stop(struct uvc_device *dev)
> > +static void uvc_status_stop(struct uvc_device *dev)
> >  {
> >       struct uvc_ctrl_work *w = &dev->async_ctrl;
> >
> > +     lockdep_assert_held(&dev->status_lock);
> > +
> >       /*
> >        * Prevent the asynchronous control handler from requeing the URB. The
> >        * barrier is needed so the flush_status change is visible to other
> > @@ -350,3 +356,46 @@ void uvc_status_stop(struct uvc_device *dev)
> >        */
> >       smp_store_release(&dev->flush_status, false);
> >  }
> > +
> > +int uvc_status_resume(struct uvc_device *dev)
> > +{
> > +     guard(mutex)(&dev->status_lock);
> > +
> > +     if (dev->status_users)
> > +             return  uvc_status_start(dev, GFP_NOIO);
>
> Double space afer return. I'll fix when applying.
>
> > +
> > +     return 0;
> > +}
> > +
> > +void uvc_status_suspend(struct uvc_device *dev)
> > +{
> > +     guard(mutex)(&dev->status_lock);
> > +
> > +     if (dev->status_users)
> > +             uvc_status_stop(dev);
> > +}
> > +
> > +int uvc_status_get(struct uvc_device *dev)
> > +{
> > +     int ret = 0;
> > +
> > +     guard(mutex)(&dev->status_lock);
> > +
> > +     if (!dev->status_users)
> > +             ret = uvc_status_start(dev, GFP_KERNEL);
> > +     if (!ret)
> > +             dev->status_users++;
>
> Thanks for the scoped guard, we can write
>
>         if (!dev->status_users) {
>                 int ret = uvc_status_start(dev, GFP_KERNEL);
>                 if (ret)
>                         return ret;
>         }
>
>         dev->status_users++;
>
>         return 0;
>
> which I think is nicer to read. If that's fine with you I'll do this
> locally, not need to a new version.

Thanks! indeed it looks nicer :)
>
> Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
>
> > +
> > +     return ret;
> > +}
> > +
> > +void uvc_status_put(struct uvc_device *dev)
> > +{
> > +     guard(mutex)(&dev->status_lock);
> > +
> > +     if (dev->status_users == 1)
> > +             uvc_status_stop(dev);
> > +     WARN_ON(!dev->status_users);
> > +     if (dev->status_users)
> > +             dev->status_users--;
> > +}
> > diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> > index f4988f03640a..97c5407f6603 100644
> > --- a/drivers/media/usb/uvc/uvc_v4l2.c
> > +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> > @@ -628,20 +628,13 @@ static int uvc_v4l2_open(struct file *file)
> >               return -ENOMEM;
> >       }
> >
> > -     mutex_lock(&stream->dev->lock);
> > -     if (stream->dev->users == 0) {
> > -             ret = uvc_status_start(stream->dev, GFP_KERNEL);
> > -             if (ret < 0) {
> > -                     mutex_unlock(&stream->dev->lock);
> > -                     usb_autopm_put_interface(stream->dev->intf);
> > -                     kfree(handle);
> > -                     return ret;
> > -             }
> > +     ret = uvc_status_get(stream->dev);
> > +     if (ret) {
> > +             usb_autopm_put_interface(stream->dev->intf);
> > +             kfree(handle);
> > +             return ret;
> >       }
> >
> > -     stream->dev->users++;
> > -     mutex_unlock(&stream->dev->lock);
> > -
> >       v4l2_fh_init(&handle->vfh, &stream->vdev);
> >       v4l2_fh_add(&handle->vfh);
> >       handle->chain = stream->chain;
> > @@ -670,10 +663,7 @@ static int uvc_v4l2_release(struct file *file)
> >       kfree(handle);
> >       file->private_data = NULL;
> >
> > -     mutex_lock(&stream->dev->lock);
> > -     if (--stream->dev->users == 0)
> > -             uvc_status_stop(stream->dev);
> > -     mutex_unlock(&stream->dev->lock);
> > +     uvc_status_put(stream->dev);
> >
> >       usb_autopm_put_interface(stream->dev->intf);
> >       return 0;
> > diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> > index b7d24a853ce4..07f9921d83f2 100644
> > --- a/drivers/media/usb/uvc/uvcvideo.h
> > +++ b/drivers/media/usb/uvc/uvcvideo.h
> > @@ -563,8 +563,6 @@ struct uvc_device {
> >
> >       const struct uvc_device_info *info;
> >
> > -     struct mutex lock;              /* Protects users */
> > -     unsigned int users;
> >       atomic_t nmappings;
> >
> >       /* Video control interface */
> > @@ -586,6 +584,8 @@ struct uvc_device {
> >       struct usb_host_endpoint *int_ep;
> >       struct urb *int_urb;
> >       struct uvc_status *status;
> > +     struct mutex status_lock; /* Protects status_users */
> > +     unsigned int status_users;
> >       bool flush_status;
> >
> >       struct input_dev *input;
> > @@ -752,8 +752,10 @@ int uvc_register_video_device(struct uvc_device *dev,
> >  int uvc_status_init(struct uvc_device *dev);
> >  void uvc_status_unregister(struct uvc_device *dev);
> >  void uvc_status_cleanup(struct uvc_device *dev);
> > -int uvc_status_start(struct uvc_device *dev, gfp_t flags);
> > -void uvc_status_stop(struct uvc_device *dev);
> > +int uvc_status_resume(struct uvc_device *dev);
> > +void uvc_status_suspend(struct uvc_device *dev);
> > +int uvc_status_get(struct uvc_device *dev);
> > +void uvc_status_put(struct uvc_device *dev);
> >
> >  /* Controls */
> >  extern const struct v4l2_subscribed_event_ops uvc_ctrl_sub_ev_ops;
>
> --
> Regards,
>
> Laurent Pinchart
diff mbox series

Patch

diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
index f0febdc08c2d..31e8942f1ef8 100644
--- a/drivers/media/usb/uvc/uvc_driver.c
+++ b/drivers/media/usb/uvc/uvc_driver.c
@@ -2116,7 +2116,6 @@  static int uvc_probe(struct usb_interface *intf,
 	INIT_LIST_HEAD(&dev->streams);
 	kref_init(&dev->ref);
 	atomic_set(&dev->nmappings, 0);
-	mutex_init(&dev->lock);
 
 	dev->udev = usb_get_dev(udev);
 	dev->intf = usb_get_intf(intf);
@@ -2288,10 +2287,7 @@  static int uvc_suspend(struct usb_interface *intf, pm_message_t message)
 	/* Controls are cached on the fly so they don't need to be saved. */
 	if (intf->cur_altsetting->desc.bInterfaceSubClass ==
 	    UVC_SC_VIDEOCONTROL) {
-		mutex_lock(&dev->lock);
-		if (dev->users)
-			uvc_status_stop(dev);
-		mutex_unlock(&dev->lock);
+		uvc_status_suspend(dev);
 		return 0;
 	}
 
@@ -2322,12 +2318,7 @@  static int __uvc_resume(struct usb_interface *intf, int reset)
 				return ret;
 		}
 
-		mutex_lock(&dev->lock);
-		if (dev->users)
-			ret = uvc_status_start(dev, GFP_NOIO);
-		mutex_unlock(&dev->lock);
-
-		return ret;
+		return uvc_status_resume(dev);
 	}
 
 	list_for_each_entry(stream, &dev->streams, list) {
diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
index a78a88c710e2..e438ae5af2e8 100644
--- a/drivers/media/usb/uvc/uvc_status.c
+++ b/drivers/media/usb/uvc/uvc_status.c
@@ -257,6 +257,8 @@  int uvc_status_init(struct uvc_device *dev)
 	unsigned int pipe;
 	int interval;
 
+	mutex_init(&dev->status_lock);
+
 	if (ep == NULL)
 		return 0;
 
@@ -302,18 +304,22 @@  void uvc_status_cleanup(struct uvc_device *dev)
 	kfree(dev->status);
 }
 
-int uvc_status_start(struct uvc_device *dev, gfp_t flags)
+static int uvc_status_start(struct uvc_device *dev, gfp_t flags)
 {
+	lockdep_assert_held(&dev->status_lock);
+
 	if (dev->int_urb == NULL)
 		return 0;
 
 	return usb_submit_urb(dev->int_urb, flags);
 }
 
-void uvc_status_stop(struct uvc_device *dev)
+static void uvc_status_stop(struct uvc_device *dev)
 {
 	struct uvc_ctrl_work *w = &dev->async_ctrl;
 
+	lockdep_assert_held(&dev->status_lock);
+
 	/*
 	 * Prevent the asynchronous control handler from requeing the URB. The
 	 * barrier is needed so the flush_status change is visible to other
@@ -350,3 +356,46 @@  void uvc_status_stop(struct uvc_device *dev)
 	 */
 	smp_store_release(&dev->flush_status, false);
 }
+
+int uvc_status_resume(struct uvc_device *dev)
+{
+	guard(mutex)(&dev->status_lock);
+
+	if (dev->status_users)
+		return  uvc_status_start(dev, GFP_NOIO);
+
+	return 0;
+}
+
+void uvc_status_suspend(struct uvc_device *dev)
+{
+	guard(mutex)(&dev->status_lock);
+
+	if (dev->status_users)
+		uvc_status_stop(dev);
+}
+
+int uvc_status_get(struct uvc_device *dev)
+{
+	int ret = 0;
+
+	guard(mutex)(&dev->status_lock);
+
+	if (!dev->status_users)
+		ret = uvc_status_start(dev, GFP_KERNEL);
+	if (!ret)
+		dev->status_users++;
+
+	return ret;
+}
+
+void uvc_status_put(struct uvc_device *dev)
+{
+	guard(mutex)(&dev->status_lock);
+
+	if (dev->status_users == 1)
+		uvc_status_stop(dev);
+	WARN_ON(!dev->status_users);
+	if (dev->status_users)
+		dev->status_users--;
+}
diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
index f4988f03640a..97c5407f6603 100644
--- a/drivers/media/usb/uvc/uvc_v4l2.c
+++ b/drivers/media/usb/uvc/uvc_v4l2.c
@@ -628,20 +628,13 @@  static int uvc_v4l2_open(struct file *file)
 		return -ENOMEM;
 	}
 
-	mutex_lock(&stream->dev->lock);
-	if (stream->dev->users == 0) {
-		ret = uvc_status_start(stream->dev, GFP_KERNEL);
-		if (ret < 0) {
-			mutex_unlock(&stream->dev->lock);
-			usb_autopm_put_interface(stream->dev->intf);
-			kfree(handle);
-			return ret;
-		}
+	ret = uvc_status_get(stream->dev);
+	if (ret) {
+		usb_autopm_put_interface(stream->dev->intf);
+		kfree(handle);
+		return ret;
 	}
 
-	stream->dev->users++;
-	mutex_unlock(&stream->dev->lock);
-
 	v4l2_fh_init(&handle->vfh, &stream->vdev);
 	v4l2_fh_add(&handle->vfh);
 	handle->chain = stream->chain;
@@ -670,10 +663,7 @@  static int uvc_v4l2_release(struct file *file)
 	kfree(handle);
 	file->private_data = NULL;
 
-	mutex_lock(&stream->dev->lock);
-	if (--stream->dev->users == 0)
-		uvc_status_stop(stream->dev);
-	mutex_unlock(&stream->dev->lock);
+	uvc_status_put(stream->dev);
 
 	usb_autopm_put_interface(stream->dev->intf);
 	return 0;
diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
index b7d24a853ce4..07f9921d83f2 100644
--- a/drivers/media/usb/uvc/uvcvideo.h
+++ b/drivers/media/usb/uvc/uvcvideo.h
@@ -563,8 +563,6 @@  struct uvc_device {
 
 	const struct uvc_device_info *info;
 
-	struct mutex lock;		/* Protects users */
-	unsigned int users;
 	atomic_t nmappings;
 
 	/* Video control interface */
@@ -586,6 +584,8 @@  struct uvc_device {
 	struct usb_host_endpoint *int_ep;
 	struct urb *int_urb;
 	struct uvc_status *status;
+	struct mutex status_lock; /* Protects status_users */
+	unsigned int status_users;
 	bool flush_status;
 
 	struct input_dev *input;
@@ -752,8 +752,10 @@  int uvc_register_video_device(struct uvc_device *dev,
 int uvc_status_init(struct uvc_device *dev);
 void uvc_status_unregister(struct uvc_device *dev);
 void uvc_status_cleanup(struct uvc_device *dev);
-int uvc_status_start(struct uvc_device *dev, gfp_t flags);
-void uvc_status_stop(struct uvc_device *dev);
+int uvc_status_resume(struct uvc_device *dev);
+void uvc_status_suspend(struct uvc_device *dev);
+int uvc_status_get(struct uvc_device *dev);
+void uvc_status_put(struct uvc_device *dev);
 
 /* Controls */
 extern const struct v4l2_subscribed_event_ops uvc_ctrl_sub_ev_ops;