[Bugfix] Fix integer overflow in libtorch_stable/activation_kernels.cu pointer arithmetic#44026
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…u pointer arithmetic After vllm-project#42663 migrated activation_kernels.cu into csrc/libtorch_stable/, the int32 overflow at blockIdx.x * d / blockIdx.x * 2 * d carried over unchanged. blockIdx.x is unsigned int and d is int, so the product is evaluated in 32-bit and overflows once it exceeds INT_MAX (about 2.15 billion), corrupting the pointer and silently reading/writing the wrong memory. Affected sites in csrc/libtorch_stable/activation_kernels.cu: - act_and_mul_kernel lines 82, 84 - act_and_mul_kernel_with_param lines 320, 322 - activation_kernel lines 529, 530 Pattern adopted: `const int64_t token_idx = blockIdx.x;` near the top of each affected kernel, then substitute in the buggy multiplications. Matches the existing `swigluoai_and_mul_kernel` pattern in the same file, which already does the int64_t promotion. A one-line comment at the first site documents the rationale; the subsequent sites use the same pattern without restating it. Closes vllm-project#42860 Signed-off-by: Dhruvil <dhruvilparikh79@gmail.com>
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What does this PR do?
act_and_mul_kernel,act_and_mul_kernel_with_param, andactivation_kernelincsrc/libtorch_stable/activation_kernels.cucompute pointer offsets viablockIdx.x * d(or* 2 * d) whereblockIdx.xisunsigned intanddisint, so the product is evaluated in 32-bit and overflows once it exceeds INT_MAX. For large hidden sizes this corrupts the pointer arithmetic and reads/writes the wrong memory.Lift
const int64_t token_idx = blockIdx.x;near the top of each affected kernel and substitute into the buggy multiplications. Matches the existingswigluoai_and_mul_kernelpattern in the same file. One-line comment at the first site; subsequent sites use the same pattern without restating.Replaces #42861 (against the pre-migration
csrc/activation_kernels.cu) which was opened before #42663 moved the kernels intocsrc/libtorch_stable/. Substantive fix is unchanged. Diff lands at the new path with @mgoin's "one line at most" comment-trim ask pre-applied.Closes #42860
Test Plan
Duplicate-work check
gh pr list --repo vllm-project/vllm --state open --search "libtorch_stable activation_kernels"returns nothing else for #42860. Pre-migration sibling #42861 is being closed in favor of this PR.AI Assistance Disclosure
Drafted with Claude assistance. I am the human contributor accountable for this PR; I read every changed line and verified the int64_t promotion matches the existing
swigluoai_and_mul_kernelprecedent in the same file.