diff mbox series

[v2,1/3] drm: use the lookup lock in drm_is_current_master

Message ID 20210724111824.59266-2-desmondcheongzx@gmail.com (mailing list archive)
State New, archived
Headers show
Series drm, drm/vmwgfx: fixes and updates related to drm_master | expand

Commit Message

Desmond Cheong Zhi Xi July 24, 2021, 11:18 a.m. UTC 
Inside drm_is_current_master, using the outer drm_device.master_mutex
to protect reads of drm_file.master makes the function prone to creating
lock hierarchy inversions. Instead, we can use the
drm_file.master_lookup_lock that sits at the bottom of the lock
hierarchy.

Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
---
 drivers/gpu/drm/drm_auth.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

Comments

Daniel Vetter July 27, 2021, 1:04 p.m. UTC | #1 
On Sat, Jul 24, 2021 at 07:18:22PM +0800, Desmond Cheong Zhi Xi wrote:
> Inside drm_is_current_master, using the outer drm_device.master_mutex
> to protect reads of drm_file.master makes the function prone to creating
> lock hierarchy inversions. Instead, we can use the
> drm_file.master_lookup_lock that sits at the bottom of the lock
> hierarchy.
> 
> Reported-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
> Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Applied to drm-misc-next, thanks for your patch.
-Daniel

> ---
>  drivers/gpu/drm/drm_auth.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
> index f00354bec3fb..9c24b8cc8e36 100644
> --- a/drivers/gpu/drm/drm_auth.c
> +++ b/drivers/gpu/drm/drm_auth.c
> @@ -63,8 +63,9 @@
>  
>  static bool drm_is_current_master_locked(struct drm_file *fpriv)
>  {
> -	lockdep_assert_held_once(&fpriv->minor->dev->master_mutex);
> -
> +	/* Either drm_device.master_mutex or drm_file.master_lookup_lock
> +	 * should be held here.
> +	 */
>  	return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
>  }
>  
> @@ -82,9 +83,9 @@ bool drm_is_current_master(struct drm_file *fpriv)
>  {
>  	bool ret;
>  
> -	mutex_lock(&fpriv->minor->dev->master_mutex);
> +	spin_lock(&fpriv->master_lookup_lock);
>  	ret = drm_is_current_master_locked(fpriv);
> -	mutex_unlock(&fpriv->minor->dev->master_mutex);
> +	spin_unlock(&fpriv->master_lookup_lock);
>  
>  	return ret;
>  }
> -- 
> 2.25.1
>
diff mbox series

Patch

diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index f00354bec3fb..9c24b8cc8e36 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -63,8 +63,9 @@ 
 
 static bool drm_is_current_master_locked(struct drm_file *fpriv)
 {
-	lockdep_assert_held_once(&fpriv->minor->dev->master_mutex);
-
+	/* Either drm_device.master_mutex or drm_file.master_lookup_lock
+	 * should be held here.
+	 */
 	return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
 }
 
@@ -82,9 +83,9 @@  bool drm_is_current_master(struct drm_file *fpriv)
 {
 	bool ret;
 
-	mutex_lock(&fpriv->minor->dev->master_mutex);
+	spin_lock(&fpriv->master_lookup_lock);
 	ret = drm_is_current_master_locked(fpriv);
-	mutex_unlock(&fpriv->minor->dev->master_mutex);
+	spin_unlock(&fpriv->master_lookup_lock);
 
 	return ret;
 }