Re: [PATCH 1/6] drm: Fix drm_release() and device unplug

[Sean Paul <sean-p7yTbzM4H96eqtR555YLDQ@public.gmane.org>]

On Sun, Feb 03, 2019 at 04:41:55PM +0100, Noralf Trønnes wrote:
> If userspace has open fd(s) when drm_dev_unplug() is run, it will result
> in drm_dev_unregister() being called twice. First in drm_dev_unplug() and
> then later in drm_release() through the call to drm_put_dev().
> 
> Since userspace already holds a ref on drm_device through the drm_minor,
> it's not necessary to add extra ref counting based on no open file
> handles. Instead just drm_dev_put() unconditionally in drm_dev_unplug().
> 
> We now has this:
> - Userpace holds a ref on drm_device as long as there's open fd(s)
> - The driver holds a ref on drm_device as long as it's bound to the
>   struct device
> 
> When both sides are done with drm_device, it is released.
> 
> Signed-off-by: Noralf Trønnes <noralf@tronnes.org>

Reviewed-by: Sean Paul <sean@poorly.run>

> ---
>  drivers/gpu/drm/drm_drv.c  | 6 +-----
>  drivers/gpu/drm/drm_file.c | 6 ++----
>  2 files changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 381581b01d48..05bbc2b622fc 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -376,11 +376,7 @@ void drm_dev_unplug(struct drm_device *dev)
>  	synchronize_srcu(&drm_unplug_srcu);
>  
>  	drm_dev_unregister(dev);
> -
> -	mutex_lock(&drm_global_mutex);
> -	if (dev->open_count == 0)
> -		drm_dev_put(dev);
> -	mutex_unlock(&drm_global_mutex);
> +	drm_dev_put(dev);
>  }
>  EXPORT_SYMBOL(drm_dev_unplug);
>  
> diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c
> index 46f48f245eb5..3f20f598cd7c 100644
> --- a/drivers/gpu/drm/drm_file.c
> +++ b/drivers/gpu/drm/drm_file.c
> @@ -479,11 +479,9 @@ int drm_release(struct inode *inode, struct file *filp)
>  
>  	drm_file_free(file_priv);
>  
> -	if (!--dev->open_count) {
> +	if (!--dev->open_count)
>  		drm_lastclose(dev);
> -		if (drm_dev_is_unplugged(dev))
> -			drm_put_dev(dev);
> -	}
> +
>  	mutex_unlock(&drm_global_mutex);
>  
>  	drm_minor_release(minor);
> -- 
> 2.20.1
> 

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