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Fix out-of-bound access in cudf::detail::label_segments #11497

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merged 3 commits into from
Aug 9, 2022
Merged

Fix out-of-bound access in cudf::detail::label_segments #11497

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8e262e1
Fix out-of-bound access
ttnghia Aug 9, 2022
afdefba
Add `static_cast` for the number of labels
ttnghia Aug 9, 2022
0489a3f
Use dependent type for `static_cast`
ttnghia Aug 9, 2022
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33 changes: 19 additions & 14 deletions cpp/include/cudf/detail/labeling/label_segments.cuh
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Original file line number Diff line number Diff line change
Expand Up @@ -67,10 +67,12 @@ void label_segments(InputIterator offsets_begin,
OutputIterator label_end,
rmm::cuda_stream_view stream)
{
auto const num_labels = thrust::distance(label_begin, label_end);

// If the output array is empty, that means we have all empty segments.
// In such cases, we must terminate immediately. Otherwise, the `for_each` loop below may try to
// access memory of the output array, resulting in "illegal memory access" error.
if (thrust::distance(label_begin, label_end) == 0) { return; }
if (num_labels == 0) { return; }

// When the output array is not empty, always fill it with `0` value first.
using OutputType = typename thrust::iterator_value<OutputIterator>::type;
Expand All @@ -83,19 +85,22 @@ void label_segments(InputIterator offsets_begin,
// very large segment.
if (thrust::distance(offsets_begin, offsets_end) <= 2) { return; }

thrust::for_each(rmm::exec_policy(stream),
offsets_begin + 1, // exclude the first offset value
offsets_end - 1, // exclude the last offset value
[offsets = offsets_begin, output = label_begin] __device__(auto const idx) {
// Zero-normalized offsets.
auto const dst_idx = idx - (*offsets);

// Scatter value `1` to the index at (idx - offsets[0]).
// In case we have repeated offsets (i.e., we have empty segments), this
// `atomicAdd` call will make sure the label values corresponding to these
// empty segments will be skipped in the output.
atomicAdd(&output[dst_idx], OutputType{1});
});
thrust::for_each(
rmm::exec_policy(stream),
offsets_begin + 1, // exclude the first offset value
offsets_end - 1, // exclude the last offset value
[num_labels, offsets = offsets_begin, output = label_begin] __device__(auto const idx) {
// Zero-normalized offsets.
auto const dst_idx = idx - (*offsets);
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// Scatter value `1` to the index at (idx - offsets[0]).
// Note that we need to check for out of bound, since the offset values may be invalid due to
// empty segments at the end.
// In case we have repeated offsets (i.e., we have empty segments), this `atomicAdd` call will
// make sure the label values corresponding to these empty segments will be skipped in the
// output.
if (dst_idx < num_labels) { atomicAdd(&output[dst_idx], OutputType{1}); }
});
thrust::inclusive_scan(rmm::exec_policy(stream), label_begin, label_end, label_begin);
}

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