Commit 28be2405 authored by Desmond Cheong Zhi Xi's avatar Desmond Cheong Zhi Xi Committed by Simona Vetter
Browse files

drm: use the lookup lock in drm_is_current_master 



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: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: default avatarDesmond Cheong Zhi Xi <desmondcheongzx@gmail.com>
Reviewed-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210724111824.59266-2-desmondcheongzx@gmail.com
parent c29758cd

drivers/gpu/drm/drm_auth.c

+5 −4
Original line number Diff line number Diff line
@@ -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;

}