[BUG] Parquet reader can use an uninitialized required BINARY length under a null ancestor - #23755
[BUG] Parquet reader can use an uninitialized required BINARY length under a null ancestor#23755abigalekim wants to merge 4 commits into
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WalkthroughThe Parquet decoder preserves ancestor validity fallback for required, non-repeated leaves without a leaf validity map. It applies the selected ancestor validity offset while zero-filling the leaf output buffer. ChangesParquet null-position filling
Estimated code review effort: 2 (Simple) | ~10 minutes Merge Risk: 🟡 Moderate · up to When a required binary field has a null ancestor, validity handling can use unrelated bitmap bits and produce incorrect decoded values. The change is not merge-ready until this correctness risk is fixed or explicitly accepted. Suggested reviewers: 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
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In `@cpp/src/io/parquet/page_decode.cuh`:
- Line 1505: Preserve the ancestor validity-map start offset before level
decoding mutates ni.valid_map_offset, and use that saved value in the fallback
around the validity-map helper instead of the mutable final offset. Keep
leaf_ni’s existing offset behavior unchanged.
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cpp/src/io/parquet/page_decode.cuh
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| // A required Parquet leaf can be absent because one of its ancestors is optional. Since with RMM, | ||
| // the reader reader can leave the validity map associated w/the ancestor unwritten, this code | ||
| // zero-fills the gap rows by borrowing the nearest ancestor's validity bitmap instead. | ||
| auto const& ni = [&]() -> PageNestingDecodeInfo const& { |
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Great find. unfortunately more needs to be fixed: zero_fill_null_positions_shared() won't even be called from most of the call-sites in this scenario because it's using the wrong valid_map and computing the wrong num_values (e.g. the call in page_data.cu). Perhaps this logic needs to be factored out into a utility function so it can be used at those locations as well.
| auto const& ni = s->nesting.nesting_info[leaf_level_index]; | ||
| auto const& leaf_ni = s->nesting.nesting_info[leaf_level_index]; | ||
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| // A required Parquet leaf can be absent because one of its ancestors is optional. Since with RMM, |
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This is not related to RMM.
| // A required Parquet leaf can be absent because one of its ancestors is optional. Since with RMM, | ||
| // the reader reader can leave the validity map associated w/the ancestor unwritten, this code | ||
| // zero-fills the gap rows by borrowing the nearest ancestor's validity bitmap instead. |
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| // A required Parquet leaf can be absent because one of its ancestors is optional. Since with RMM, | |
| // the reader reader can leave the validity map associated w/the ancestor unwritten, this code | |
| // zero-fills the gap rows by borrowing the nearest ancestor's validity bitmap instead. | |
| // A required Parquet leaf can be absent because one of its ancestors is optional. In such cases, | |
| // zero-fill the gap rows by borrowing the nearest ancestor's validity bitmap instead. |
| return true; | ||
| } | ||
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| /** |
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Please add a test for this. A pytest is also fine if you would like to use a small existing parquet file (add to cudf/python/cudf/cudf/tests/data/parquet) instead of generating one everytime.
| if ((ni.valid_map == nullptr) || (num_values == 0)) { return; } | ||
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| auto const data_out = ni.data_out; | ||
| if (&ni != &leaf_ni) { valid_map_offset = ni.valid_map_offset; } |
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| if (&ni != &leaf_ni) { valid_map_offset = ni.valid_map_offset; } |
Each caller can pass the offset it already knows. In decode_fixed.cu:1193, take init_valid_map_offset from the helper suggested by Paul above. In page_data.cu and the delta kernels the ancestor's valid_map_offset is advanced while decoding (page_decode.cuh:872), so reading it here gives the end of the written range rather than the start.
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Please update the PR description to briefly say what it does (to achieve what and how) in a small paragraph (2-3 lines or so) instead of simply linking the original issue. |
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This won't cover all cases. For Handing the pointer to both isn't safe either: the masks are memset to all-valid before decode (reader_impl_preprocess.cu:1114-1118) and the owner writes them from a different block/stream, so a sibling can read all-ones and skip the fill. It would also need a separate ownership flag, since null-count accumulation uses that same nullptr sentinel (reader_impl.cpp:488-492). Fixing this one will be trickier ... we could use the definition levels at this point? Not sure if this should be done here or a separate PR. FYI @mhaseeb123 |
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Description
Fixes #23655.
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