{"record":{"id":"32ef25ca632fd395","repo":"sgl-project/sglang","slug":"kv-canary-lut-len-must-be-non-negative-got-lut","errorCode":null,"errorMessage":"kv-canary: lut_len must be non-negative, got {lut_len}","messagePattern":"kv-canary: lut_len must be non-negative, got (.+?)","errorType":"validation","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"python/sglang/kernels/ops/kv_canary/plan/offsets_kernel.py","lineNumber":173,"sourceCode":"        )\n    if write_offsets_len <= 0:\n        raise ValueError(\n            f\"kv-canary: write_offsets_len must be positive, got {write_offsets_len}\"\n        )\n    if write_req_capacity < 0:\n        raise ValueError(\n            f\"kv-canary: write_req_capacity must be non-negative, got {write_req_capacity}\"\n        )\n    if verify_capacity < 0:\n        raise ValueError(\n            f\"kv-canary: verify_capacity must be non-negative, got {verify_capacity}\"\n        )\n    if req_to_token_stride0 <= 0:\n        raise ValueError(\n            f\"kv-canary: req_to_token_stride0 must be positive, got {req_to_token_stride0}\"\n        )\n    if lut_len < 0:\n        raise ValueError(f\"kv-canary: lut_len must be non-negative, got {lut_len}\")\n    if not isinstance(has_swa_lut, bool):\n        raise ValueError(\n            f\"kv-canary: has_swa_lut must be bool, got {type(has_swa_lut).__name__}\"\n        )\n    if has_swa_lut and lut_len <= 0:\n        raise ValueError(\"kv-canary: lut_len must be positive when has_swa_lut is True\")\n    if not has_swa_lut and lut_len != 0:\n        raise ValueError(\"kv-canary: lut_len must be 0 when has_swa_lut is False\")\n\n    _require_len(req_pool_indices, \"req_pool_indices\", bs)\n    _require_len(prefix_lens, \"prefix_lens\", bs)\n    _require_len(extend_seq_lens, \"extend_seq_lens\", bs)\n    _require_2d(req_to_token, \"req_to_token\")\n    _require_min_len(lut_tensor, \"lut_tensor\", max(lut_len, 1))\n    _require_min_len(\n        out_verify_offsets_scratch,\n        \"out_verify_offsets_scratch\",\n        _PLAN_BS_BLOCK_SIZE + 1,","sourceCodeStart":155,"sourceCodeEnd":191,"githubUrl":"https://github.com/sgl-project/sglang/blob/0132848349585cfe6aae51c4941cbae872505f8a/python/sglang/kernels/ops/kv_canary/plan/offsets_kernel.py#L155-L191","documentation":"lut_len reports the length of the full-to-SWA LUT passed to the offsets kernel and must be non-negative; negative lengths indicate a shape extraction bug in the caller.","triggerScenarios":"Calling launch_plan_offsets_kernel with lut_len < 0 (usually derived from int(lut.shape[0]) of a malformed tensor or an arithmetic underflow).","commonSituations":"LUT length computed as (a - b) that underflows; passing -1 as a 'no LUT' sentinel instead of 0 with has_swa_lut=False.","solutions":["Use the prepare helper that derives (lut, lut_len, has_swa_lut) from the tensor or None, guaranteeing non-negative lut_len","Pass lut_len=0 with has_swa_lut=False when there is no LUT"],"exampleFix":"// before\nlaunch_plan_offsets_kernel(..., lut_len=-1, has_swa_lut=False)\n// after\nlaunch_plan_offsets_kernel(..., lut_len=0, has_swa_lut=False)","handlingStrategy":"validation","validationCode":"lut_len = max(0, int(lut_len))\nassert (lut_len > 0) == has_swa_lut or lut_len == 0","typeGuard":null,"tryCatchPattern":null,"preventionTips":["Derive lut_len from the tensor shape, never from arithmetic"],"tags":["kv-canary","lut","argument-validation"],"backgroundTag":"invalid-argument-value","analyzedSha":"0132848349585cfe6aae51c4941cbae872505f8a","analyzedAt":"2026-08-28T05:10:05.995Z","schemaVersion":2},"datasetVersion":"2026-08-28T06:17:29.519Z"}