On Mon, Aug 02, 2021 at 06:59:57PM +0800, Desmond Cheong Zhi Xi wrote:

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@gmail.com Acked-by: Boqun Feng boqun.feng@gmail.com Acked-by: Waiman Long longman@redhat.com Acked-by: Peter Zijlstra (Intel) peterz@infradead.org

Both patches pushed to drm-misc-next, thanks. -Daniel

---

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