[PATCH v5 0/6] drm: update locking for modesetting

Desmond Cheong Zhi Xi desmondcheongzx at gmail.com
Mon Aug 23 17:14:31 UTC 2021


I updated the series to untangle more lock inversions caught by the
Intel-gfx CI, but again there might be more that I missed.

This series now converts drm_device.master_mutex into master_rwsem, and
also removes drm_file.master_lookup_lock.

Overall, this series makes the following changes:

- Patch 1: Fix a potential null ptr dereference in drm_master_release

- Patch 2: Convert master_mutex into rwsem (avoids creating a new lock)

- Patch 3: Update global mutex locking in the ioctl handler (avoids
deadlock when grabbing read lock on master_rwsem in drm_ioctl_kernel)

- Patch 4: Plug races with drm modesetting rights

- Patch 5: Untagle remaining lock hierarchy inversions between
modeset_mutex and master_rwsem

- Patch 6: Replace master_lookup_lock with master_rwsem

v4 -> v5:
- Avoid calling drm_file_get_master while holding on to the modeset
mutex, caught by the Intel-gfx CI (split previous patch 5 into the new
patch 5 & 6)

v3 -> v4 (suggested by Daniel Vetter):
- Drop a patch that added an unnecessary master_lookup_lock in
drm_master_release (previously patch 2)
- Drop a patch that addressed a non-existent race in
drm_is_current_master_locked (previously patch 3)
- Remove fixes for non-existent null ptr dereferences (previous patch 4)
- Protect drm_master.magic_map,unique{_len} with master_rwsem instead of
master_lookup_lock (dropped previous patch 5)
- Drop the patch that moved master_lookup_lock into struct drm_device
(previously patch 1)
- Drop a patch to export task_work_add (previously patch 8)
- Revert the check for the global mutex in the ioctl handler to use
drm_core_check_feature instead of drm_dev_needs_global_mutex
- Push down master_rwsem locking for selected ioctls to avoid lock
hierarchy inversions, and to allow us to hold write locks on
master_rwsem instead of flushing readers
- Remove master_lookup_lock by replacing it with master_rwsem

v2 -> v3:
- Unexport drm_master_flush, as suggested by Daniel Vetter.
- Merge master_mutex and master_rwsem, as suggested by Daniel Vetter.
- Export task_work_add, reported by kernel test robot.
- Make master_flush static, reported by kernel test robot.
- Move master_lookup_lock into struct drm_device.
- Add a missing lock on master_lookup_lock in drm_master_release.
- Fix a potential race in drm_is_current_master_locked.
- Fix potential null ptr dereferences in drm_{auth, ioctl}.
- Protect magic_map,unique{_len} with  master_lookup_lock.
- Convert master_mutex into a rwsem.
- Update global mutex locking in the ioctl handler.

v1 -> v2 (suggested by Daniel Vetter):
- Address an additional race when drm_open runs.
- Switch from SRCU to rwsem to synchronise readers and writers.
- Implement drm_master_flush with task_work so that flushes can be
queued to run before returning to userspace without creating a new
DRM_MASTER_FLUSH ioctl flag.

Best wishes,

Desmond Cheong Zhi Xi (6):
  drm: fix null ptr dereference in drm_master_release
  drm: convert drm_device.master_mutex into a rwsem
  drm: lock drm_global_mutex earlier in the ioctl handler
  drm: avoid races with modesetting rights
  drm: avoid circular locks with modeset_mutex and master_rwsem
  drm: remove drm_file.master_lookup_lock

 drivers/gpu/drm/drm_atomic_uapi.c |  4 +-
 drivers/gpu/drm/drm_auth.c        | 57 +++++++++++----------
 drivers/gpu/drm/drm_debugfs.c     |  4 +-
 drivers/gpu/drm/drm_drv.c         |  3 +-
 drivers/gpu/drm/drm_encoder.c     |  7 ++-
 drivers/gpu/drm/drm_file.c        |  7 ++-
 drivers/gpu/drm/drm_framebuffer.c |  2 +-
 drivers/gpu/drm/drm_internal.h    |  1 +
 drivers/gpu/drm/drm_ioctl.c       | 48 +++++++++++-------
 drivers/gpu/drm/drm_lease.c       | 83 ++++++++++++++-----------------
 drivers/gpu/drm/drm_mode_object.c | 16 ++++--
 drivers/gpu/drm/drm_plane.c       | 17 +++++--
 drivers/gpu/drm/drm_property.c    |  6 +--
 include/drm/drm_auth.h            |  6 +--
 include/drm/drm_device.h          | 15 ++++--
 include/drm/drm_file.h            | 17 ++-----
 include/drm/drm_lease.h           |  4 +-
 17 files changed, 165 insertions(+), 132 deletions(-)


More information about the Linux-kernel-mentees mailing list