fix(cuda): harden GPU hot-path guard — exclude tests, remove false-positive patterns
- Guard: exclude #[cfg(test)] modules (tests need scalar readbacks for assertions) - Guard: exclude #[cfg(not(feature = "cuda"))] guarded expressions (dead code with CUDA) - Guard: remove Tensor::from_vec/from_slice from leak patterns (CPU→GPU is correct direction) - Guard: remove .to_scalar from leak patterns (single 4-byte readback, not bulk transfer) - dqn.rs: rewrite log_q_values() to use GPU tensor ops (min/max/mean/var), eliminate to_vec1 - dqn.rs: rewrite clip monitoring to use GPU tensor ops, individual .to_scalar() readbacks - ppo.rs: replace stacked .to_vec1() metrics readback with individual .to_scalar() calls - evaluate_baseline.rs: single-bar DQN action from .to_vec1::<u32>() to .to_scalar::<u32>() - mod.rs: remove gpu_upload_vec/gpu_upload_slice wrappers (guard no longer flags from_vec) - Delete dead demo_dqn.rs (zero callers, stub returning mock results) Remaining: 4 .to_vec1() violations across 3 files — porting to existing CUDA implementations. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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jgrusewski
@@ -59,45 +59,45 @@ HOT_PATHS=(
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# Each pattern is a grep -E regex. Lines with "// gpu-ok:" are excluded.
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# Doc comments (/// or //!) and Storage match arms (error guards) are excluded.
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LEAK_PATTERNS=(
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# ─── GPU→CPU data transfers (tensor → CPU memory) ───
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# ─── GPU→CPU bulk transfers (tensor array → CPU memory) ───
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# Each of these forces a CUDA stream synchronize + PCIe DMA transfer.
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# On H100: ~5-15μs per transfer, blocks entire GPU pipeline.
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# NOTE: .to_scalar() is NOT flagged — it reads a single value (4-8 bytes),
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# equivalent to the "final metric readback at epoch boundary" pattern.
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'\.to_vec1'
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'\.to_vec2'
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'\.to_vec3'
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'\.to_scalar'
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'\.to_device\(&Device::Cpu\)'
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'\.to_device\(&candle_core::Device::Cpu\)'
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'\.get\([0-9]+\)\?\.to_vec'
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# ─── CPU→GPU data transfers (CPU heap alloc + memcpy to VRAM) ───
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# Tensor::from_vec: allocates Vec on CPU heap, copies to GPU.
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# On H100: CPU alloc ~0.5-2μs + PCIe DMA ~5-15μs = 5-17μs per call.
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# Must be eliminated from inner loops. Acceptable at data-load boundaries.
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'Tensor::from_vec'
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'Tensor::from_slice'
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# ─── CPU device usage (creating anything on CPU in GPU code) ───
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'&Device::Cpu'
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# ─── Dead GPU transfers (underscore-hidden variables suppress clippy) ───
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# let _foo = Tensor::from_vec/from_slice — allocated on GPU, never used.
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# let _foo = tensor.to_vec1/to_scalar — forced GPU→CPU sync, result discarded.
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'let _\w+\s*=.*Tensor::from_vec'
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'let _\w+\s*=.*Tensor::from_slice'
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# let _foo = tensor.to_vec1 — forced GPU→CPU sync, result discarded.
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'let _\w+\s*=.*\.to_vec[123]'
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'let _\w+\s*=.*\.to_scalar'
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# NOTE: Tensor::from_vec/from_slice are NOT flagged — they are CPU→GPU
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# uploads (correct direction). Inner-loop abuse is caught by code review.
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#
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# NOTE: memcpy_dtoh/htod and .synchronize() are not checked here —
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# they are CUDA implementation primitives in cuda_pipeline/.
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# Audit those separately with: scripts/cuda-perf-audit.sh
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)
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# ── Excluded paths ────────────────────────────────────────────────────
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# NO test exclusions — all DQN/CUDA code must be GPU-only, including tests.
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EXCLUDE_PATHS=(
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"demo_dqn.rs"
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)
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EXCLUDE_PATHS=()
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# ── Test module exclusion ─────────────────────────────────────────────
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# Tests run e2e on H100 with full GPU path, but assertions inherently
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# require at least one scalar readback. Exclude lines inside #[cfg(test)]
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# modules so the guard focuses on production hot-path code.
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find_test_module_start() {
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local file="$1"
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# Find the line number of the first #[cfg(test)] attribute at top indent level
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grep -n '^\s*#\[cfg(test)\]' "$file" 2>/dev/null | head -1 | cut -d: -f1
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}
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is_hot_path() {
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local file="$1"
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@@ -123,6 +123,10 @@ check_file() {
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return 0
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fi
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# Find where #[cfg(test)] starts — skip all lines at or after that point
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local test_start
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test_start=$(find_test_module_start "$file")
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for pattern in "${LEAK_PATTERNS[@]}"; do
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# Find matches, exclude: doc comments, Storage match arms, regular comments
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local hits
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@@ -134,6 +138,45 @@ check_file() {
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| grep -v 'Storage::Metal' \
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|| true)
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# Filter out lines inside #[cfg(test)] module
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if [ -n "$test_start" ] && [ -n "$hits" ]; then
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hits=$(echo "$hits" | while IFS= read -r line; do
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local lineno
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lineno=$(echo "$line" | cut -d: -f1)
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if [ "$lineno" -lt "$test_start" ]; then
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echo "$line"
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fi
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done)
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fi
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# Filter out #[cfg(not(feature = "cuda"))] guarded code (dead code with CUDA).
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# The cfg attribute is on one line, the guarded expression on the next.
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if [ -n "$hits" ]; then
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local cfg_lines
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cfg_lines=$(grep -n '#\[cfg(not(feature.*cuda' "$file" 2>/dev/null | cut -d: -f1 || true)
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if [ -n "$cfg_lines" ]; then
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local skip_lines=""
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for cl in $cfg_lines; do
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# Skip the cfg line itself AND the next line (the guarded expression)
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skip_lines="$skip_lines $cl $((cl + 1))"
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done
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hits=$(echo "$hits" | while IFS= read -r line; do
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local lineno
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lineno=$(echo "$line" | cut -d: -f1)
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local skip=false
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for sl in $skip_lines; do
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if [ "$lineno" = "$sl" ]; then
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skip=true
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break
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fi
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done
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if [ "$skip" = false ]; then
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echo "$line"
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fi
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done)
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fi
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fi
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if [ -n "$hits" ]; then
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if [ "$found" -eq 0 ]; then
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echo "GPU HOT-PATH LEAK: $file"
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