[https://nvbugs/6104831][fix] Detach pruned trie children

[chienchunhung]

Summary by CodeRabbit

• Bug Fixes

  • Fixed a critical assertion error in batch manager operations that could cause crashes during memory block removal and reallocation sequences.

• Tests

  • Added comprehensive unit tests covering batch manager edge cases to prevent assertion failure regression.

Summary

Fixes the KV-cache-block trie invariant violation from NVBugs 6104831 by detaching a removed child node's parent back-pointer before erasing it from the parent's child map.

This prevents later clearValue() / freeBlockAndAllDescendants() cascade pruning from walking back to a parent that no longer owns the child and firing cascade prune: parent did not find this node as a child.

Related PR

Depends on #13571, which adds the reproducer tests.

Test Coverage

Updated the four NVBugs 6104831 RadixBlockTreeTest reproducers from EXPECT_THROW to EXPECT_NO_THROW, so they now verify the fixed behavior for:

• orphaned block detach
• orphaned subtree eviction via freeBlockAndAllDescendants
• storeBlocks-style block re-keying
• prefix-overlapping insert / evict / reuse stress loop

Also verified the full radixBlockTreeTest suite remains green.

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📥 Commits

Reviewing files that changed from the base of the PR and between c30d9c7 and d301166.

📒 Files selected for processing (2)

• cpp/include/tensorrt_llm/batch_manager/templatedTrie.h
• cpp/tests/unit_tests/batch_manager/radixBlockTreeTest.cpp

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📝 Walkthrough

Walkthrough

This PR adds a bidirectional edge cleanup in the Node::clearNode method to properly detach child nodes from their parent by resetting back-pointers, and introduces four comprehensive unit tests to validate the fix prevents cascade-prune assertion failures during block reattachment operations.

Changes

Cohort / File(s)	Summary
Bidirectional edge cleanup and regression tests cpp/include/tensorrt_llm/batch_manager/templatedTrie.h, cpp/tests/unit_tests/batch_manager/radixBlockTreeTest.cpp	Added bidirectional edge update in Node::clearNode to reset child node back-pointers before removal, and introduced four new unit tests covering orphaned block detachment, cascade-prune scenarios, block re-keying sequences, and stress testing for overlapping prefix operations.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The PR title clearly identifies the fix: detaching pruned trie children to prevent cascade-prune assertion errors.
Description check	✅ Passed	The PR description includes all required sections: summary of the fix, related PR dependency, comprehensive test coverage details, and completed PR checklist.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[chienchunhung]

/bot run --disable-fail-fast

[tensorrt-cicd]

PR_Github #46515 [ run ] triggered by Bot. Commit: d301166 Link to invocation

[tensorrt-cicd]

PR_Github #46515 [ run ] completed with state SUCCESS. Commit: d301166
/LLM/main/L0_MergeRequest_PR pipeline #36574 completed with status: 'FAILURE'

CI Report

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