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

[Sean Paul]

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 

Reviewed-by: Sean Paul 

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

[Oleksandr Andrushchenko]

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 
Reviewed-by: Oleksandr Andrushchenko 
> ---
>   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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[Intel-gfx] [PATCH 1/6] drm: Fix drm_release() and device unplug

[Noralf Trønnes]

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 
---
 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

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