Re: [PATCH v11] drm: Unplug drm device when unregistering it (v8)

[Sean Paul]

On Thu, Apr 13, 2017 at 03:32:44PM +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.
> 
> Verified on rk3399 chromebook kevin(with cros 4.4 kernel), no more crashes
> when unbinding drm with ui service still running.
> 
> v2: Fix some commit messages.
> v3: Reuse unplug status.
> v4: Add drm_device_set_plug_state helper.
> v5: Fix hang when unregistering drm dev with open_count 0.
> v6: Move drm_device_set_plug_state into drm_drv.
> v7: Add missing drm_dev_unref in udl_drv.
> v8: Fix compiler errors after enable udl.
> 
> Signed-off-by: Jeffy Chen <jeffy.chen@xxxxxxxxxxxxxx>
> 
> ---

Hi Jeffy,
Given the trouble we've had with this patch already, coupled with the fact that
unbinding while userspace is active is a contrived/pathological case, I don't
think it's worth picking this patch upstream.

If it's really causing issues downstream, you can add my Reviewed-by for a CHROMIUM
patch, but I'd rather not carry patches in the CrOS repo if we don't need to.

Sean

> 
>  drivers/gpu/drm/drm_drv.c     | 26 ++++++++++----------------
>  drivers/gpu/drm/udl/udl_drv.c |  3 ++-
>  include/drm/drmP.h            |  6 ------
>  include/drm/drm_drv.h         |  1 -
>  4 files changed, 12 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..fc73e24 100644
> --- a/drivers/gpu/drm/udl/udl_drv.c
> +++ b/drivers/gpu/drm/udl/udl_drv.c
> @@ -108,7 +108,8 @@ 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);
> +	drm_dev_unref(dev);
>  }
>  
>  /*
> 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