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

Submitted by Noralf Trønnes on Feb. 3, 2019, 3:41 p.m.

Details

Message ID 20190203154200.61479-2-noralf@tronnes.org
State New
Series "drm/drv: Remove drm_dev_unplug()"
Headers show

Commit Message

Noralf Trønnes Feb. 3, 2019, 3:41 p.m.
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>
---
 drivers/gpu/drm/drm_drv.c  | 6 +-----
 drivers/gpu/drm/drm_file.c | 6 ++----
 2 files changed, 3 insertions(+), 9 deletions(-)

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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);

Comments

Oleksandr Andrushchenko Feb. 4, 2019, 10:17 a.m.
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@tronnes.org>

Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>

> ---

>   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);
Sean Paul Feb. 7, 2019, 9 p.m.
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
>