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Date:   Wed, 22 Nov 2023 15:32:24 +0200
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Ricardo Ribalda <ribalda@chromium.org>
Cc:     Mauro Carvalho Chehab <mchehab@kernel.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Tomasz Figa <tfiga@chromium.org>,
        Alan Stern <stern@rowland.harvard.edu>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        Sean Paul <seanpaul@chromium.org>,
        Sakari Ailus <sakari.ailus@linux.intel.com>
Subject: Re: [PATCH v5 2/3] media: uvcvideo: Always use uvc_status_stop()
Message-ID: <20231122133224.GD3909@pendragon.ideasonboard.com>
References: <20231122-guenter-mini-v5-0-15d8cd8ed74f@chromium.org>
 <20231122-guenter-mini-v5-2-15d8cd8ed74f@chromium.org>
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In-Reply-To: <20231122-guenter-mini-v5-2-15d8cd8ed74f@chromium.org>
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Hi Ricardo,

Thank you for the patch.

On Wed, Nov 22, 2023 at 11:45:48AM +0000, Ricardo Ribalda wrote:
> The only thread safe way to stop the status handler is with uvc_status.

The commit message should explain why.

> Let's remove all the code paths partially stopping uvc_status.

And should explain what the implications are.

> Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
> ---
>  drivers/media/usb/uvc/uvc_ctrl.c   | 4 ----
>  drivers/media/usb/uvc/uvc_driver.c | 2 +-
>  drivers/media/usb/uvc/uvc_status.c | 8 ++++----
>  drivers/media/usb/uvc/uvc_v4l2.c   | 2 +-
>  drivers/media/usb/uvc/uvcvideo.h   | 2 +-
>  5 files changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/media/usb/uvc/uvc_ctrl.c b/drivers/media/usb/uvc/uvc_ctrl.c
> index e59a463c2761..8e22a07e3e7b 100644
> --- a/drivers/media/usb/uvc/uvc_ctrl.c
> +++ b/drivers/media/usb/uvc/uvc_ctrl.c
> @@ -2765,10 +2765,6 @@ void uvc_ctrl_cleanup_device(struct uvc_device *dev)
>  	struct uvc_entity *entity;
>  	unsigned int i;
>  
> -	/* Can be uninitialized if we are aborting on probe error. */
> -	if (dev->async_ctrl.work.func)
> -		cancel_work_sync(&dev->async_ctrl.work);
> -
>  	/* Free controls and control mappings for all entities. */
>  	list_for_each_entry(entity, &dev->entities, list) {
>  		for (i = 0; i < entity->ncontrols; ++i) {
> diff --git a/drivers/media/usb/uvc/uvc_driver.c b/drivers/media/usb/uvc/uvc_driver.c
> index ded2cb6ce14f..d5dbf2644272 100644
> --- a/drivers/media/usb/uvc/uvc_driver.c
> +++ b/drivers/media/usb/uvc/uvc_driver.c
> @@ -2282,7 +2282,7 @@ static int uvc_suspend(struct usb_interface *intf, pm_message_t message)
>  	    UVC_SC_VIDEOCONTROL) {
>  		mutex_lock(&dev->lock);
>  		if (dev->users)
> -			uvc_status_stop(dev);
> +			uvc_status_stop(dev, true);
>  		mutex_unlock(&dev->lock);
>  		return 0;
>  	}
> diff --git a/drivers/media/usb/uvc/uvc_status.c b/drivers/media/usb/uvc/uvc_status.c
> index a78a88c710e2..9c5da1244999 100644
> --- a/drivers/media/usb/uvc/uvc_status.c
> +++ b/drivers/media/usb/uvc/uvc_status.c
> @@ -292,7 +292,7 @@ int uvc_status_init(struct uvc_device *dev)
>  
>  void uvc_status_unregister(struct uvc_device *dev)
>  {
> -	usb_kill_urb(dev->int_urb);
> +	uvc_status_stop(dev, false);
>  	uvc_input_unregister(dev);
>  }
>  
> @@ -310,7 +310,7 @@ int uvc_status_start(struct uvc_device *dev, gfp_t flags)
>  	return usb_submit_urb(dev->int_urb, flags);
>  }
>  
> -void uvc_status_stop(struct uvc_device *dev)
> +void uvc_status_stop(struct uvc_device *dev, bool run_async_work)
>  {
>  	struct uvc_ctrl_work *w = &dev->async_ctrl;
>  
> @@ -326,7 +326,7 @@ void uvc_status_stop(struct uvc_device *dev)
>  	 * Cancel any pending asynchronous work. If any status event was queued,
>  	 * process it synchronously.
>  	 */
> -	if (cancel_work_sync(&w->work))
> +	if (cancel_work_sync(&w->work) && run_async_work)
>  		uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
>  
>  	/* Kill the urb. */
> @@ -338,7 +338,7 @@ void uvc_status_stop(struct uvc_device *dev)
>  	 * cancelled before returning or it could then race with a future
>  	 * uvc_status_start() call.
>  	 */
> -	if (cancel_work_sync(&w->work))
> +	if (cancel_work_sync(&w->work) && run_async_work)
>  		uvc_ctrl_status_event(w->chain, w->ctrl, w->data);
>  
>  	/*
> diff --git a/drivers/media/usb/uvc/uvc_v4l2.c b/drivers/media/usb/uvc/uvc_v4l2.c
> index f4988f03640a..f90206263ff4 100644
> --- a/drivers/media/usb/uvc/uvc_v4l2.c
> +++ b/drivers/media/usb/uvc/uvc_v4l2.c
> @@ -672,7 +672,7 @@ static int uvc_v4l2_release(struct file *file)
>  
>  	mutex_lock(&stream->dev->lock);
>  	if (--stream->dev->users == 0)
> -		uvc_status_stop(stream->dev);
> +		uvc_status_stop(stream->dev, false);
>  	mutex_unlock(&stream->dev->lock);
>  
>  	usb_autopm_put_interface(stream->dev->intf);
> diff --git a/drivers/media/usb/uvc/uvcvideo.h b/drivers/media/usb/uvc/uvcvideo.h
> index 6fb0a78b1b00..ba8f8c1f2c83 100644
> --- a/drivers/media/usb/uvc/uvcvideo.h
> +++ b/drivers/media/usb/uvc/uvcvideo.h
> @@ -745,7 +745,7 @@ 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);
> +void uvc_status_stop(struct uvc_device *dev, bool run_async_work);
>  
>  /* Controls */
>  extern const struct uvc_control_mapping uvc_ctrl_power_line_mapping_limited;
> 

-- 
Regards,

Laurent Pinchart