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GeezerVison is showing github.com — Fix thread-safety in GC, type cache, and instruction cache by youknowone · Pull Request #7355 · RustPython/RustPython

Fix thread-safety in GC, type cache, and instruction cache #7355

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Merged
youknowone merged 6 commits into RustPython:main from youknowone:gc-use-after-free
Mar 5, 2026

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Merged

Fix thread-safety in GC, type cache, and instruction cache #7355

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70169e8
Fix thread-safety in GC, type cache, and instruction cache
youknowone Mar 5, 2026
b0ad917
Fix RLock _acquire_restore tuple handling and unxfail threading test
youknowone Mar 5, 2026
de01099
Align type cache seqlock writer protocol with CPython
youknowone Mar 5, 2026
8683977
RLock: use single parking_lot level, track recursion manually
youknowone Mar 5, 2026
3e31d22
Add try_to_owned_from_ptr to avoid &PyObject on stale ptrs
youknowone Mar 5, 2026
b3de227
Fix CI: spelling typo and xfail flaky test_thread_safety
youknowone Mar 5, 2026
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4 changes: 2 additions & 2 deletions 4 Lib/test/_test_multiprocessing.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4815,9 +4815,9 @@ def test_finalize(self):
result = [obj for obj in iter(conn.recv, 'STOP')]
self.assertEqual(result, ['a', 'b', 'd10', 'd03', 'd02', 'd01', 'e'])

# TODO: RUSTPYTHON - gc.get_threshold() and gc.set_threshold() not implemented
@unittest.expectedFailure
@support.requires_resource('cpu')
# TODO: RUSTPYTHON; dict iteration races with concurrent GC mutations
@unittest.expectedFailure
def test_thread_safety(self):
# bpo-24484: _run_finalizers() should be thread-safe
def cb():
Expand Down
4 changes: 0 additions & 4 deletions 4 Lib/test/test_threading.py
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Expand Up @@ -2141,10 +2141,6 @@ def __init__(self, a, *, b) -> None:
CustomRLock(1, b=2)
self.assertEqual(warnings_log, [])

@unittest.expectedFailure # TODO: RUSTPYTHON
def test_release_save_unacquired(self):
return super().test_release_save_unacquired()

@unittest.skip('TODO: RUSTPYTHON; flaky test')
def test_different_thread(self):
return super().test_different_thread()
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2 changes: 1 addition & 1 deletion 2 crates/common/src/refcount.rs
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Expand Up @@ -123,7 +123,7 @@ impl RefCount {
pub fn safe_inc(&self) -> bool {
let mut old = State::from_raw(self.state.load(Ordering::Relaxed));
loop {
if old.destructed() {
if old.destructed() || old.strong() == 0 {
return false;
}
if (old.strong() as usize) >= STRONG {
Expand Down
50 changes: 35 additions & 15 deletions 50 crates/compiler-core/src/bytecode.rs
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Expand Up @@ -12,7 +12,7 @@ use core::{
cell::UnsafeCell,
hash, mem,
ops::Deref,
sync::atomic::{AtomicU8, AtomicU16, Ordering},
sync::atomic::{AtomicU8, AtomicU16, AtomicUsize, Ordering},
};
use itertools::Itertools;
use malachite_bigint::BigInt;
Expand Down Expand Up @@ -411,6 +411,10 @@ impl TryFrom<&[u8]> for CodeUnit {
pub struct CodeUnits {
units: UnsafeCell<Box<[CodeUnit]>>,
adaptive_counters: Box<[AtomicU16]>,
/// Pointer-sized cache entries for descriptor pointers.
/// Single atomic load/store prevents torn reads when multiple threads
/// specialize the same instruction concurrently.
pointer_cache: Box<[AtomicUsize]>,
}

// SAFETY: All cache operations use atomic read/write instructions.
Expand All @@ -432,9 +436,15 @@ impl Clone for CodeUnits {
.iter()
.map(|c| AtomicU16::new(c.load(Ordering::Relaxed)))
.collect();
let pointer_cache = self
.pointer_cache
.iter()
.map(|c| AtomicUsize::new(c.load(Ordering::Relaxed)))
.collect();
Self {
units: UnsafeCell::new(units),
adaptive_counters,
pointer_cache,
}
}
}
Expand Down Expand Up @@ -472,13 +482,19 @@ impl<const N: usize> From<[CodeUnit; N]> for CodeUnits {
impl From<Vec<CodeUnit>> for CodeUnits {
fn from(value: Vec<CodeUnit>) -> Self {
let units = value.into_boxed_slice();
let adaptive_counters = (0..units.len())
let len = units.len();
let adaptive_counters = (0..len)
.map(|_| AtomicU16::new(0))
.collect::<Vec<_>>()
.into_boxed_slice();
let pointer_cache = (0..len)
.map(|_| AtomicUsize::new(0))
.collect::<Vec<_>>()
.into_boxed_slice();
Self {
units: UnsafeCell::new(units),
adaptive_counters,
pointer_cache,
}
}
}
Expand Down Expand Up @@ -600,25 +616,29 @@ impl CodeUnits {
lo | (hi << 16)
}

/// Write a u64 value across four consecutive CACHE code units starting at `index`.
/// Store a pointer-sized value atomically in the pointer cache at `index`.
///
/// Uses a single `AtomicUsize` store to prevent torn writes when
/// multiple threads specialize the same instruction concurrently.
///
/// # Safety
/// Same requirements as `write_cache_u16`.
pub unsafe fn write_cache_u64(&self, index: usize, value: u64) {
unsafe {
self.write_cache_u32(index, value as u32);
self.write_cache_u32(index + 2, (value >> 32) as u32);
}
/// - `index` must be in bounds.
/// - `value` must be `0` or a valid `*const PyObject` encoded as `usize`.
/// - Callers must follow the cache invalidation/upgrade protocol:
/// invalidate the version guard before writing and publish the new
/// version after writing.
pub unsafe fn write_cache_ptr(&self, index: usize, value: usize) {
self.pointer_cache[index].store(value, Ordering::Relaxed);
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}

/// Read a u64 value from four consecutive CACHE code units starting at `index`.
/// Load a pointer-sized value atomically from the pointer cache at `index`.
///
/// Uses a single `AtomicUsize` load to prevent torn reads.
///
/// # Panics
/// Panics if `index + 3` is out of bounds.
pub fn read_cache_u64(&self, index: usize) -> u64 {
let lo = self.read_cache_u32(index) as u64;
let hi = self.read_cache_u32(index + 2) as u64;
lo | (hi << 32)
/// Panics if `index` is out of bounds.
pub fn read_cache_ptr(&self, index: usize) -> usize {
self.pointer_cache[index].load(Ordering::Relaxed)
}

/// Read adaptive counter bits for instruction at `index`.
Expand Down
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