{"record":{"id":"62cb8e0e8f9f0d24","repo":"huggingface/candle","slug":"seqlens-k-has-to-be-contiguous-62cb8e","errorCode":null,"errorMessage":"seqlens_k has to be contiguous","messagePattern":"seqlens_k has to be contiguous","errorType":"validation","errorClass":null,"httpStatus":null,"severity":"error","filePath":"candle-flash-attn/src/lib.rs","lineNumber":498,"sourceCode":"\n        let (seqlens_q, seqlens_q_layout) = self.seqlens_q.storage_and_layout();\n        let seqlens_q = match &*seqlens_q {\n            candle::Storage::Cuda(c) => c.as_cuda_slice::<u32>()?, // Should be i32!\n            _ => candle::bail!(\"seqlens_q must be a cuda tensor\"),\n        };\n        let seqlens_q = match seqlens_q_layout.contiguous_offsets() {\n            Some((o1, o2)) => seqlens_q.slice(o1..o2),\n            None => candle::bail!(\"seqlens_q has to be contiguous\"),\n        };\n\n        let (seqlens_k, seqlens_k_layout) = self.seqlens_k.storage_and_layout();\n        let seqlens_k = match &*seqlens_k {\n            candle::Storage::Cuda(c) => c.as_cuda_slice::<u32>()?, // Should be i32!\n            _ => candle::bail!(\"seqlens_k must be a cuda tensor\"),\n        };\n        let seqlens_k = match seqlens_k_layout.contiguous_offsets() {\n            Some((o1, o2)) => seqlens_k.slice(o1..o2),\n            None => candle::bail!(\"seqlens_k has to be contiguous\"),\n        };\n\n        let block_table = if let Some(block_table) = self.block_table.as_ref() {\n            let (block_table_storage, block_table_layout) = block_table.storage_and_layout();\n            match &*block_table_storage {\n                candle::Storage::Cuda(_) => {}\n                _ => candle::bail!(\"block_table must be a cuda tensor\"),\n            }\n            let block_table_stride = block_table_layout.shape().dims2()?.1;\n            if block_table_layout.stride().last().copied() != Some(1) {\n                candle::bail!(\"block_table last dimension must be contiguous\")\n            }\n            Some((\n                block_table_storage,\n                block_table_layout.start_offset(),\n                block_table_stride,\n            ))\n        } else {","sourceCodeStart":480,"sourceCodeEnd":516,"githubUrl":"https://github.com/huggingface/candle/blob/d5fee525bfde3273eb7c9b75fd2bc4937be867ca/candle-flash-attn/src/lib.rs#L480-L516","documentation":"Raised in candle-flash-attn/src/lib.rs when the `seqlens_k` tensor's layout has no contiguous offsets, i.e. the tensor is not contiguous in memory (e.g. sliced or strided). The kernel reads it as a flat device slice, so call `.contiguous()` on it before invoking flash-attn.","triggerScenarios":"Passing a seqlens_k view created by narrow/slice/strided indexing without making it contiguous.","commonSituations":"Slicing cu_seqlens_k out of a larger pinned metadata buffer, transposing or reshaping metadata tensors before the attention call.","solutions":["Call .contiguous() on seqlens_k before the call","Store seqlens as a standalone flat contiguous tensor rather than a view","Rebuild the tensor with Tensor::from_vec when in doubt"],"exampleFix":"// before\nlet seqlens_k = big_buf.i((.., 0))?; // possibly non-contiguous\n// after\nlet seqlens_k = big_buf.i((.., 0))?.contiguous()?;","handlingStrategy":"validation","validationCode":"fn ensure_contiguous_k(t: &Tensor) -> candle::Result<Tensor> {\n    if t.is_contiguous() { Ok(t.clone()) } else { t.contiguous() }\n}\nlet seqlens_k = ensure_contiguous_k(&seqlens_k)?;","typeGuard":"fn contiguous_cuda_u32_k(t: &Tensor) -> bool {\n    t.is_contiguous() && t.device().is_cuda() && t.dtype() == candle::DType::U32\n}","tryCatchPattern":"match flash_attn_varlen(&q, &k, &v, &seqlens_q, &seqlens_k.contiguous()?, scale, max_q, max_k, None, None, None) {\n    Err(e) if e.to_string().contains(\"has to be contiguous\") => { /* rebuild seqlens_k */ }\n    r => r?,\n}","preventionTips":["Apply .contiguous() after any indexing/view of seqlens","Store metadata as flat contiguous 1D tensors","Unit-test layouts with t.is_contiguous() assertions"],"tags":["cuda","flash-attention","contiguity","varlen"],"backgroundTag":"tensor-not-contiguous","analyzedSha":"d5fee525bfde3273eb7c9b75fd2bc4937be867ca","analyzedAt":"2026-09-02T00:15:47.023Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-09T06:17:21.866Z"}