Fix bus error or segfault from roi_align with large batchsize#9441
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zy1git wants to merge 3 commits intopytorch:mainfrom
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Fix bus error or segfault from roi_align with large batchsize#9441zy1git wants to merge 3 commits intopytorch:mainfrom
zy1git wants to merge 3 commits intopytorch:mainfrom
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🔗 Helpful Links🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/vision/9441
Note: Links to docs will display an error until the docs builds have been completed. ✅ No FailuresAs of commit d9ab5ce with merge base 6f131f1 ( This comment was automatically generated by Dr. CI and updates every 15 minutes. |
NicolasHug
reviewed
Mar 16, 2026
| output_bytes = n_rois * channels * pooled_h * pooled_w * 4 # float32 | ||
| if output_bytes > 9 * 1024**3: | ||
| pytest.skip("Test requires ~9 GB of memory") | ||
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all these values are statically defined. This if block is either always True or always False.
NicolasHug
reviewed
Mar 16, 2026
| x = torch.rand(num_imgs, channels, height, width, dtype=torch.float32, device=device) | ||
| rois = torch.zeros(n_rois, 5, dtype=torch.float32, device=device) | ||
| except RuntimeError: | ||
| pytest.skip("Not enough memory to allocate test tensors") |
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Please verify tests aren't not being skipped on the CI. If they pass, remove the try/except, if they don't, we'll have to consider other strategies to test this.
NicolasHug
reviewed
Mar 16, 2026
| template <typename T> | ||
| void roi_align_backward_kernel_impl( | ||
| int nthreads, | ||
| int64_t nthreads, |
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Can you explain why nthreads needs to be int64_t? It should never need to be that large?
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Summary
Bug: roi_align in torchvision crashes with a bus error/segfault on CPU or returns silently wrong (all-zero) results on CUDA when the total number of output elements exceeds
INT_MAX(~2.1 billion). This is caused by 32-bit int overflow in index arithmetic within the C++ and CUDA kernels.Root Cause: The kernels use int for composite index calculations like n × channels × pooled_width × pooled_height and pointer offsets like (roi_batch_ind × channels + c) × height × width. When these products exceed 2,147,483,647, the int wraps to a negative value, causing out-of-bounds memory access.
Example: FasterRCNN with batch_size=172 generates ~172,000 ROIs. The output index reaches 171,999 × 256 × 7 × 7 = 2,157,555,456 > INT_MAX, which matches the reporter's observed threshold exactly.
Fix: Promoted int to int64_t for all index, offset, and stride variables in the relevant files.
Test Plan
New overflow regression test
pytest test/test_ops.py::TestRoIAlign::test_roi_align_large_index -vExisting tests — verify no regressions
pytest test/test_ops.py::TestRoIAlign -vFixes #8206