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

[Chris Wilson]

On Fri, Apr 14, 2017 at 11:15:04AM -0400, Sean Paul wrote:
> 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.

Would a

Fixes: a39be606f99d ("drm: Do a full device unregister when unplugging")
Reported-by: Marco Diego Aurélio Mesquita <marcodiegomesquita@xxxxxxxxx>
Cc: Hans de Goede <hdegoede@xxxxxxxxxx>

convince us to look into this patch again?
-Chris

> > 
> >  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);

-- 
Chris Wilson, Intel Open Source Technology Centre