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

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On 2/3/19 5:41 PM, 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:
s/has/have ?
> - 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@xxxxxxxxxxx>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> ---
>   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);
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