[v7,0/7] drm: update locking for modesetting

Message

Desmond Cheong Zhi Xi Aug. 25, 2021, 2:21 p.m. UTC

Sorry for the noise. Sending out a new version because the Intel-gfx CI
caught that __drm_mode_object_find has to be exported for loadable
modules like the Intel and VMware DRM drivers.

Hi,

Updated the series again to avoid recursive locking caught by the
Intel-gfx CI. Patch 5 touches a number of files, including the Intel and
VMware drivers, but most changes are simply switching a function call to
the appropriate locked/unlocked version.

Overall, this series fixes races with modesetting rights, converts
drm_device.master_mutex into master_rwsem, and removes
drm_file.master_lookup_lock.

- 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: Modify drm_mode_object_find to fix potential recursive
locking of master_rwsem and lock inversions between modeset_mutex and
master_rwsem

- Patch 6: Remove remaining potential lock inversions between
modeset_mutex and master_rwsem

- Patch 7: Replace master_lookup_lock with master_rwsem

v6 -> v7:
- Export __drm_mode_object_find for loadable modules, caught by the
Intel-gfx CI (patch 5)

v5 -> v6:
- Fix recursive locking on master_rwsem, caught by the Intel-gfx CI
(patch 5 & 6)

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

v3 -> v4 (suggested by Daniel Vetter):
- Drop a patch that added an unnecessary master_lookup_lock in
drm_master_release
- Drop a patch that addressed a non-existent race in
drm_is_current_master_locked
- Remove fixes for non-existent null ptr dereferences
- Protect drm_master.magic_map,unique{_len} with master_rwsem instead of
master_lookup_lock
- Drop the patch that moved master_lookup_lock into struct drm_device
- Drop a patch to export task_work_add
- 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

Desmond Cheong Zhi Xi (7):
  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 in drm_mode_object_find
  drm: avoid circular locks with modeset_mutex and master_rwsem
  drm: remove drm_file.master_lookup_lock

 drivers/gpu/drm/drm_atomic_uapi.c            |  7 +-
 drivers/gpu/drm/drm_auth.c                   | 57 ++++++------
 drivers/gpu/drm/drm_color_mgmt.c             |  2 +-
 drivers/gpu/drm/drm_crtc.c                   |  5 +-
 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                  | 94 ++++++++++----------
 drivers/gpu/drm/drm_mode_object.c            | 28 +++++-
 drivers/gpu/drm/drm_plane.c                  | 22 +++--
 drivers/gpu/drm/drm_property.c               |  6 +-
 drivers/gpu/drm/i915/display/intel_overlay.c |  2 +-
 drivers/gpu/drm/i915/display/intel_sprite.c  |  2 +-
 drivers/gpu/drm/vmwgfx/vmwgfx_kms.c          |  2 +-
 include/drm/drm_auth.h                       |  6 +-
 include/drm/drm_connector.h                  | 23 +++++
 include/drm/drm_crtc.h                       | 22 +++++
 include/drm/drm_device.h                     | 15 +++-
 include/drm/drm_file.h                       | 17 ++--
 include/drm/drm_lease.h                      |  2 +
 include/drm/drm_mode_object.h                |  3 +
 include/drm/drm_plane.h                      | 20 +++++
 26 files changed, 264 insertions(+), 143 deletions(-)