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Fix _at_fork_reinit to write INIT directly instead of calling unlock() #7312

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Merged
youknowone merged 2 commits into from
Mar 3, 2026
Merged

Fix _at_fork_reinit to write INIT directly instead of calling unlock() #7312

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f00fcd2
Fix _at_fork_reinit to write INIT directly instead of calling unlock()
youknowone Mar 2, 2026
2893430
Add import lock (IMP_LOCK) reinit after fork
youknowone Mar 2, 2026
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Fix _at_fork_reinit to write INIT directly instead of calling unlock() 
unlock() goes through unlock_slow() which accesses parking_lot's
global hash table to unpark waiters. After fork(), this hash table
contains stale entries from dead parent threads, making unlock_slow()
unsafe. Writing INIT directly bypasses parking_lot internals entirely.
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@youknowone
youknowone committed Mar 2, 2026
commit f00fcd2f13172e420a5997e113e3176efc47dbc4
20 changes: 6 additions & 14 deletions crates/vm/src/stdlib/thread.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -152,15 +152,9 @@ pub(crate) mod _thread {

#[pymethod]
fn _at_fork_reinit(&self, _vm: &VirtualMachine) -> PyResult<()> {
if self.mu.is_locked() {
unsafe {
self.mu.unlock();
};
}
// Casting to AtomicCell is as unsafe as CPython code.
// Using AtomicCell will prevent compiler optimizer move it to somewhere later unsafe place.
// It will be not under the cell anymore after init call.

// Reset the mutex to unlocked by directly writing the INIT value.
// Do NOT call unlock() here — after fork(), unlock_slow() would
// try to unpark stale waiters from dead parent threads.
let new_mut = RawMutex::INIT;
unsafe {
let old_mutex: &AtomicCell<RawMutex> = core::mem::transmute(&self.mu);
Expand Down Expand Up @@ -252,11 +246,9 @@ pub(crate) mod _thread {

#[pymethod]
fn _at_fork_reinit(&self, _vm: &VirtualMachine) -> PyResult<()> {
if self.mu.is_locked() {
unsafe {
self.mu.unlock();
};
}
// Reset the reentrant mutex to unlocked by directly writing INIT.
// Do NOT call unlock() — after fork(), the slow path would try
// to unpark stale waiters from dead parent threads.
self.count.store(0, core::sync::atomic::Ordering::Relaxed);
let new_mut = RawRMutex::INIT;
unsafe {
Expand Down