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

[Marco Diego Aurélio Mesquita]

On Mon, May 29, 2017 at 5:25 PM, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> 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);
>

I have no experience writing drivers. So, feel free to disregard my
suggestion if it does not makes sense. I'm trying to update a driver
for a USB device and Hans is helping me with it. I had some problems
when plugging and unplugging the device and ended finding Jeffy's
patch. I made the same changes to the driver I was working on and it
behaved a bit better. When I told Hans about it, he found the problem
with the calls in drm_release.

I'm not sure what is the best way to fix/improve the situation but,
wouldn't it be a good idea to guard dangerous calls like unregister or
unplug so that there are no side effects if they are called more times
then they should? I mean, if a driver does so, it is already broken,
but I think that keeping the kernel safe is a better choice, no?