[PATCH v2] drm: Do not call drm_dev_unregister twice on drm_unplug_dev

[Daniel Vetter]

On Sun, May 28, 2017 at 07:16:55PM +0200, Hans de Goede wrote:
> Since commit a39be606f99d ("drm: Do a full device unregister when
> unplugging") drm_unplug_dev has been calling drm_dev_unregister followed
> by a drm_put_dev when open_count reaches 0. This drm_put_dev calls
> drm_dev_unregister again. Since drm_dev_unregister is not protected
> against being called multiple times this leads to havoc.
> 
> This commit fixes this by calling drm_dev_unref instead of drm_put_dev.
> 
> Fixes: a39be606f99d ("drm: Do a full device unregister when unplugging")
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Marco Diego Aurélio Mesquita <marcodiegomesquita at gmail.com>
> Reported-by: Marco Diego Aurélio Mesquita <marcodiegomesquita at gmail.com>
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> ---
> Note I don't have any USB display devices at hand for testing atm so
> this patch has only been compile tested.
> ---
> Changes in v2:
> -Remove unnecessary mutex changes

Offending patch is in 4.8 ... do we need cc: stable? Does this need a
bugreport link?
-Daniel

> ---
>  drivers/gpu/drm/drm_drv.c  | 6 +++---
>  drivers/gpu/drm/drm_file.c | 2 +-
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index b5c6bb46a425..30b5382bf877 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -364,9 +364,9 @@ void drm_unplug_dev(struct drm_device *dev)
>  
>  	drm_device_set_unplugged(dev);
>  
> -	if (dev->open_count == 0) {
> -		drm_put_dev(dev);
> -	}
> +	if (dev->open_count == 0)
> +		drm_dev_unref(dev);
> +
>  	mutex_unlock(&drm_global_mutex);
>  }
>  EXPORT_SYMBOL(drm_unplug_dev);
> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> index 3783b659cd38..edba71c8ccc3 100644
> --- a/drivers/gpu/drm/drm_file.c
> +++ b/drivers/gpu/drm/drm_file.c
> @@ -424,7 +424,7 @@ int drm_release(struct inode *inode, struct file *filp)
>  	if (!--dev->open_count) {
>  		drm_lastclose(dev);
>  		if (drm_device_is_unplugged(dev))
> -			drm_put_dev(dev);
> +			drm_dev_unref(dev);
>  	}
>  	mutex_unlock(&drm_global_mutex);
>  
> -- 
> 2.13.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch