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.vet...@ffwll.ch>
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheon...@gmail.com>
Reviewed-by: Daniel Vetter <daniel.vet...@ffwll.ch>
---
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
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