In drm_is_current_master_locked, accessing drm_file.master should be
protected by either drm_file.master_lookup_lock or
drm_device.master_mutex. This was previously awkward to assert with
lockdep.
Following patch ("locking/lockdep: Provide lockdep_assert{,_once}()
helpers"), this assertion is now convenient. So we add in the
assertion and explain this lock design in the kerneldoc.
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
Acked-by: Boqun Feng <boqun.feng@xxxxxxxxx>
Acked-by: Waiman Long <longman@xxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
drivers/gpu/drm/drm_auth.c | 6 +++---
include/drm/drm_file.h | 4 ++++
2 files changed, 7 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c
index 9c24b8cc8e36..6f4d7ff23c80 100644
--- a/drivers/gpu/drm/drm_auth.c
+++ b/drivers/gpu/drm/drm_auth.c
@@ -63,9 +63,9 @@
static bool drm_is_current_master_locked(struct drm_file *fpriv)
{
- /* Either drm_device.master_mutex or drm_file.master_lookup_lock
- * should be held here.
- */
+ lockdep_assert_once(lockdep_is_held(&fpriv->master_lookup_lock) ||
+ lockdep_is_held(&fpriv->minor->dev->master_mutex));
+
return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
}
diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h
index 726cfe0ff5f5..a3acb7ac3550 100644
--- a/include/drm/drm_file.h
+++ b/include/drm/drm_file.h
@@ -233,6 +233,10 @@ struct drm_file {
* this only matches &drm_device.master if the master is the currently
* active one.
*
+ * To update @master, both &drm_device.master_mutex and
+ * @master_lookup_lock need to be held, therefore holding either of
+ * them is safe and enough for the read side.
+ *
* When dereferencing this pointer, either hold struct
* &drm_device.master_mutex for the duration of the pointer's use, or
* use drm_file_get_master() if struct &drm_device.master_mutex is not
--
2.25.1
