Hi,
Thanks for all the helpful feedback on the previous version.
Taking all the suggestions together, this series now converts drm_device.master_mutex into master_rwsem, and also attempts to remove drm_file.master_lookup_lock. There might still be lock inversions lurking, so the output from Intel-gfx CI should be interesting to see.
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: Replace master_lookup_lock with master_rwsem by untangling remaining lock hierarchy inversions
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
Desmond Cheong Zhi Xi (5): 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: remove drm_file.master_lookup_lock
drivers/gpu/drm/drm_auth.c | 54 ++++++++++++------------ drivers/gpu/drm/drm_debugfs.c | 4 +- drivers/gpu/drm/drm_drv.c | 3 +- drivers/gpu/drm/drm_file.c | 7 ++-- drivers/gpu/drm/drm_internal.h | 1 + drivers/gpu/drm/drm_ioctl.c | 48 ++++++++++++--------- drivers/gpu/drm/drm_lease.c | 69 ++++++++++++++----------------- drivers/gpu/drm/drm_mode_object.c | 14 +++++-- include/drm/drm_auth.h | 6 +-- include/drm/drm_device.h | 15 +++++-- include/drm/drm_file.h | 17 +++----- include/drm/drm_lease.h | 2 +- 12 files changed, 125 insertions(+), 115 deletions(-)