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5e6b21bce9
Root cause analysis showed that the previous workaround was fixing the
symptom in the wrong layer.
Problem:
kernel BUG at drivers/dma-buf/dma-resv.c:319!
BUG_ON(fobj->num_fences >= fobj->max_fences)
Workqueue: events amdgpu_userq_restore_worker
- amdgpu_evf_mgr_attach_fence() had been temporarily taught to reserve/add
fence bookkeeping internally as a workaround.
- This hid the real contract violation and made reservation policy implicit
inside a helper.
Review clarification:
- The helper-side dma_resv_add_fence-related workaround was only an intended
proposal sent for review discussion, not the final direction.
- Final fix keeps fence-slot reservation explicit in callers and leaves the
helper free of policy decisions.
Findings from investigation:
- drm_exec_prepare_obj() both locks and reserves fence slots.
- drm_exec_lock_obj() only locks and does not reserve slots.
- Existing attach_fence callers in the GEM/userq restore flows already reserve
TTM_NUM_MOVE_FENCES + 1 before adding the bookkeeping eviction fence.
- The WPTR mapping path in mes_userq_create_wptr_mapping() used
drm_exec_lock_obj() and then called amdgpu_evf_mgr_attach_fence(), so this
specific path could add a fence without pre-reserved space.
Fix:
- Switch the WPTR mapping path to drm_exec_prepare_obj(...,
TTM_NUM_MOVE_FENCES + 1), restoring the caller-side reservation contract.
- Remove the helper-side reservation workaround from
amdgpu_evf_mgr_attach_fence().
Why this is the right layer:
- Reservation policy stays explicit at call sites that define how many fences
may be added in that execution context.
- The helper only performs validate + add_fence when called with a properly
prepared reservation object, matching the existing drm_exec model.
Fixes:
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