Fix fsdp2_aware_weight_update masking setup errors with UnboundLocalError - #2295
Fix fsdp2_aware_weight_update masking setup errors with UnboundLocalError#2295harshal-96 wants to merge 2 commits into
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…rror fsdp2_aware_weight_update assigns root_module, fsdp_param_group and fsdp_param_mapping only after unshard() succeeds inside the try block, but the finally block referenced them unconditionally. When setup fails (typically a CUDA OOM in unshard() while exporting a large MoE model), the finally block raised UnboundLocalError, which replaces the original exception and hides the real failure. Initialize fsdp_param_mapping as a sentinel before the try and skip the finally-block update when setup never completed, so the original error propagates unchanged. Adds a CPU regression test that simulates a setup failure and asserts the original error type surfaces, plus a passthrough sanity test for non-FSDP roots. Fixes NVIDIA#1859 Signed-off-by: harshal-96 <harshal.dhandrut@gmail.com>
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Included review availability: Your plan provides up to 12 included reviews per hour; 10 remain after this review. 📝 WalkthroughWalkthroughThe FSDP2-aware weight update context manager now preserves setup exceptions instead of replacing them with cleanup-related ChangesFSDP2 error handling
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: ⚪ Minimal · up to This localized fix preserves the original setup error instead of replacing it with an UnboundLocalError, with regression coverage for the affected paths; no actionable merge-blocking risk remains after normal checks and review. Suggested reviewers: 🚥 Pre-merge checks | ✅ 5 | ❌ 1❌ Failed checks (1 warning)
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Full details: Linked Issues checkExplanation The changes satisfy issue Full details: Security Anti-PatternsExplanation PASS. The PR fix changes only
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In `@tests/unit/torch/quantization/test_utils.py`:
- Line 81: Update the test around _get_enclosing_fsdp_module so module discovery
succeeds, then make root_module.unshard() raise and invoke
create_fsdp_param_mapping(). Assert that the original exception propagates to
the caller, ensuring the test exercises the intended unshard() failure path.
- Around line 69-73: Move the imports for mock, FSDPModule, core_utils, and
fsdp2_aware_weight_update from test/function scope to the module-level import
section in test_utils.py, so failures occur during collection; retain any local
import only with a brief comment explaining a required circular-import or
optional-dependency reason.
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modelopt/torch/quantization/utils/core_utils.pytests/unit/torch/quantization/test_utils.py
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- Parametrize the regression test over both setup-failure points: module discovery and the reported scenario where discovery succeeds and unshard() itself raises (verified to reproduce the masking before the fix and pass after). - Move test imports to module scope per test guidelines. Signed-off-by: harshal-96 <harshal.dhandrut@gmail.com>
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What does this PR do?
Type of change: Bug fix
Overview: Fixes #1859.
fsdp2_aware_weight_updateassignsroot_module,fsdp_param_groupandfsdp_param_mappingonly afterunshard()succeeds inside thetryblock, but thefinallyblock referenced them unconditionally. When setup fails — typically a CUDA OOM raised byunshard()while exporting a large MoE model — thefinallyblock raisedUnboundLocalError, which (per Python semantics) replaces the original exception and hides the real failure from the user.This PR initializes
fsdp_param_mappingas aNonesentinel before thetryand skips the finally-block update when setup never completed, so the original error propagates unchanged. When setup did complete, behavior is identical to before.Testing
test_fsdp2_aware_weight_update_preserves_setup_error: simulates a setup failure and asserts the originalRuntimeErrorsurfaces. Fails before this change (the error is replaced by a finally-block error), passes after.test_fsdp2_aware_weight_update_non_fsdp_body_error_passthrough: non-FSDP roots keep transparent error propagation.tests/unit/torch/quantization/test_utils.py: 24 passed.Before your PR is "Ready for review"
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