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Fix illegal memory access through off-by-one error in num_splits_dynamic_ptr init #1747

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Fix illegal memory access through off-by-one error in num_splits_dynamic_ptr init #1747

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5 changes: 4 additions & 1 deletion hopper/flash_api.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -972,7 +972,10 @@ mha_fwd(at::Tensor q, // (b, s_q, h, d) or (total_q, h, d) if there is cu_seql
tile_count_semaphore.zero_(); // If varlen we'll manually do the zero-ing
}
params.tile_count_semaphore = scheduler_needs_semaphore ? tile_count_semaphore.data_ptr<int>() : nullptr;
params.num_splits_dynamic_ptr = use_dynamic_split ? tile_count_semaphore.data_ptr<int>() + 1 : nullptr;

params.num_splits_dynamic_ptr = use_dynamic_split ?
tile_count_semaphore.data_ptr<int>() + int(scheduler_needs_semaphore)
: nullptr;
}

if (q_v_.has_value()) {
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