[https://nvbugs/6104831][test] Add reproducers for KV-cache-block cascade prune assertion#13571
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Add unit tests that isolate the KV-cache-block trie invariant violation behind the cascade-prune assertion seen in NVBugs 6104831. Signed-off-by: Chien-Chun Hung <2679986+chienchunhung@users.noreply.github.com>
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…rmanent wedge Document the multi-signature disaggregated-serving wedge surfaced by the rc11 deployment. The report covers the 1P1D reproducer harness, the six labelled failure signatures (sender-side broken-promise after ready, trie cascade-prune assertion, decode-side bad optional access, gen-side checkGenTransferStatus blocking on at_least_num=1, receiver-side queued cancel broken-promise, and the suspected control-path send stall), their mapping to chained test/fix PR pairs (NVIDIA#13571/NVIDIA#13572 for sig NVIDIA#2, NVIDIA#13639/NVIDIA#13640 for sig #1), the in-flight fixes for sig NVIDIA#4 and sig NVIDIA#5, and the relationship to the unrelated companion fixes NVIDIA#12718 and NVIDIA#13119 which are not in rc11. Includes an investigation timeline that explains why each signature surfaced only after the previous one was fixed, and a test-coverage analysis of why the existing unit and integration tests did not catch any of these bugs. Signed-off-by: Chien-Chun Hung <2679986+chienchunhung@users.noreply.github.com> Made-with: Cursor
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@coderabbitai summary
Summary
Manifest a bug by introducing 4 new unit tests under
RadixBlockTreeTest. These tests deterministically reproduce thetemplatedTrie.h:249 cascade prune: parent did not find this node as a childassertion observed on the Dynamo 1P1D disagg deployment hang documented in NVBugs 6104831. Tests pass on rc7+ through currentmain— i.e., they pass because the assertion fires, i.e., errors thrown. Once the underlying fix lands, they must be flipped fromEXPECT_THROWtoEXPECT_NO_THROWto serve as the regression net.Root cause (high level)
KVCacheBlock::removeNextBlockcallsmLookupNode->clearNode(blockKey)to erase a child entry from the parent'smNextNodesmap but does not reset the orphaned child'smPrevNodeweak back-pointer. Any subsequent operation that empties the orphaned node and lets cascade-prune run (attachToLookupNode'sclearValue,detachFromLookupNode, orfreeBlockAndAllDescendants) walks back viamPrevNodeto a parent map that no longer contains the entry and fires the assertion. The lone production caller of this pattern is the re-keying block atWindowBlockManager::storeBlocks(kvCacheManager.cpp:2289-2297). The structural defect was introduced byf931f4e9e2(UnifiedBlockTree refactor, in rc7); rc11 is just when a real workload first hit the trigger sequence.Tests added (all
RadixBlockTreeTest::Regression_NVBugs6104831_*)DetachOrphanedBlockFiresAssertion— minimal direct repro: orphan viaremoveNextBlock, thendetachFromLookupNode. Isolates the trie-invariant violation.FreeBlockAndAllDescendantsOnOrphanedSubtree— same root cause via the literal bug-report stack trace (addSequence → … → freeBlockAndAllDescendants).StoreBlocksRekeyTriggersAssertion— mirrorskvCacheManager.cpp:2289-2297verbatim:prev->removeNextBlock(oldKey); setBlockKey(newKey); searchRoot->addNextBlock(newKey, block).StressPrefixOverlappingInsertEvictReuseLoop— workload mirror with shared system prefix + per-request suffixes + periodicfreeBlockAndAllDescendants. Asserts the bug fires under workload-like operation order.PR Checklist
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