linux-kernel - Re: [PATCH v9] drm: Unplug drm device when unregistering it

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Date:   Wed, 12 Apr 2017 11:03:21 -0400
From:   Sean Paul <seanpaul@...omium.org>
To:     Jeffy Chen <jeffy.chen@...k-chips.com>
Cc:     linux-kernel@...r.kernel.org, briannorris@...omium.org,
        dianders@...omium.org, tfiga@...omium.org, seanpaul@...omium.org,
        zyw@...k-chips.com, marcheu@...omium.org, mark.yao@...k-chips.com,
        hshi@...omium.org, Daniel Vetter <daniel.vetter@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        dri-devel@...ts.freedesktop.org,
        Chris Wilson <chris@...is-wilson.co.uk>,
        David Airlie <airlied@...ux.ie>, Tom Gundersen <teg@...m.no>,
        Dave Airlie <airlied@...hat.com>
Subject: Re: [PATCH v9] drm: Unplug drm device when unregistering it

On Wed, Apr 12, 2017 at 04:56:21PM +0800, Jeffy Chen wrote:
> After unbinding drm, the user space may still owns the drm dev fd, and
> may still be able to call drm ioctl.
> 
> We're using an unplugged state to prevent something like that, so let's
> reuse it here.
> 
> Also drop drm_unplug_dev, because it would be unused after other changes.
> 
> Signed-off-by: Jeffy Chen <jeffy.chen@...k-chips.com>
> 
> Changes in v9:
> Move drm_device_set_plug_state into drm_drv.c .
> 
> Changes in v8:
> Fix hang when unregistering drm dev with open_count 0.
> 
> Changes in v7:
> Add drm_device_set_plug_state helper.
> 
> Changes in v6:
> Reuse unplug status.
> 
> Changes in v5:
> Fix wrong git account.
> 
> Changes in v2:
> Fix some commit messages.
> 

Hi Jeffy,
A couple bookkeeping notes:

- Please end the commit message with your Signed-off-by tag
- No need to send cover letters for one patch. All info should be in the commit
  message. Include superfluous information (such as tested on 4.4 kernel) after
  ---

> ---
>  drivers/gpu/drm/drm_drv.c     | 26 ++++++++++----------------
>  drivers/gpu/drm/udl/udl_drv.c |  2 +-
>  include/drm/drmP.h            |  6 ------
>  include/drm/drm_drv.h         |  1 -
>  4 files changed, 11 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index b5c6bb4..e1da4d1 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -355,22 +355,6 @@ void drm_put_dev(struct drm_device *dev)
>  }
>  EXPORT_SYMBOL(drm_put_dev);
>  
> -void drm_unplug_dev(struct drm_device *dev)
> -{
> -	/* for a USB device */
> -	drm_dev_unregister(dev);
> -
> -	mutex_lock(&drm_global_mutex);
> -
> -	drm_device_set_unplugged(dev);
> -
> -	if (dev->open_count == 0) {
> -		drm_put_dev(dev);
> -	}
> -	mutex_unlock(&drm_global_mutex);
> -}
> -EXPORT_SYMBOL(drm_unplug_dev);
> -
>  /*
>   * DRM internal mount
>   * We want to be able to allocate our own "struct address_space" to control
> @@ -733,6 +717,13 @@ static void remove_compat_control_link(struct drm_device *dev)
>  	kfree(name);
>  }
>  
> +static inline void drm_device_set_plug_state(struct drm_device *dev,
> +					     bool plugged)
> +{
> +	smp_wmb();
> +	atomic_set(&dev->unplugged, !plugged);
> +}
> +
>  /**
>   * drm_dev_register - Register DRM device
>   * @dev: Device to register
> @@ -787,6 +778,8 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags)
>  	if (drm_core_check_feature(dev, DRIVER_MODESET))
>  		drm_modeset_register_all(dev);
>  
> +	drm_device_set_plug_state(dev, true);
> +
>  	ret = 0;
>  
>  	DRM_INFO("Initialized %s %d.%d.%d %s for %s on minor %d\n",
> @@ -826,6 +819,7 @@ void drm_dev_unregister(struct drm_device *dev)
>  	drm_lastclose(dev);
>  
>  	dev->registered = false;
> +	drm_device_set_plug_state(dev, false);
>  
>  	if (drm_core_check_feature(dev, DRIVER_MODESET))
>  		drm_modeset_unregister_all(dev);
> diff --git a/drivers/gpu/drm/udl/udl_drv.c b/drivers/gpu/drm/udl/udl_drv.c
> index cd8b017..5dbd916 100644
> --- a/drivers/gpu/drm/udl/udl_drv.c
> +++ b/drivers/gpu/drm/udl/udl_drv.c
> @@ -108,7 +108,7 @@ static void udl_usb_disconnect(struct usb_interface *interface)
>  	drm_kms_helper_poll_disable(dev);
>  	udl_fbdev_unplug(dev);
>  	udl_drop_usb(dev);
> -	drm_unplug_dev(dev);
> +	drm_dev_unregister(dev);

I think you need drm_dev_unref here as well.

Sean

>  }
>  
>  /*
> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
> index 3bfafcd..980a204 100644
> --- a/include/drm/drmP.h
> +++ b/include/drm/drmP.h
> @@ -488,12 +488,6 @@ static __inline__ int drm_core_check_feature(struct drm_device *dev,
>  	return ((dev->driver->driver_features & feature) ? 1 : 0);
>  }
>  
> -static inline void drm_device_set_unplugged(struct drm_device *dev)
> -{
> -	smp_wmb();
> -	atomic_set(&dev->unplugged, 1);
> -}
> -
>  static inline int drm_device_is_unplugged(struct drm_device *dev)
>  {
>  	int ret = atomic_read(&dev->unplugged);
> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> index 0fefc3f..eb63078 100644
> --- a/include/drm/drm_drv.h
> +++ b/include/drm/drm_drv.h
> @@ -544,7 +544,6 @@ void drm_dev_unregister(struct drm_device *dev);
>  void drm_dev_ref(struct drm_device *dev);
>  void drm_dev_unref(struct drm_device *dev);
>  void drm_put_dev(struct drm_device *dev);
> -void drm_unplug_dev(struct drm_device *dev);
>  
>  int drm_dev_set_unique(struct drm_device *dev, const char *name);
>  
> -- 
> 2.1.4
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS