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Drop replaced exception and traceback fields outside locks #9600

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Merged
youknowone merged 2 commits into from
Nov 4, 2026
Merged

Drop replaced exception and traceback fields outside locks #9600

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e073997
Drop replaced exception fields outside locks
youknowdot Nov 3, 2026
1eaab8c
Drop replaced traceback links outside the lock
youknowdot Nov 3, 2026
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5 changes: 4 additions & 1 deletion crates/vm/src/builtins/traceback.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -92,7 +92,10 @@ impl Py<PyTraceback> {
}
}
}
*zelf.next.lock() = value;
// Dropping the old chain can finalize a frame whose locals reenter
// this traceback. Publish the replacement before releasing the lock.
let old = core::mem::replace(&mut *zelf.next.lock(), value);
drop(old);
Ok(())
}
}
Expand Down
28 changes: 20 additions & 8 deletions crates/vm/src/exceptions.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -743,18 +743,30 @@ impl PyBaseException {
}

impl PyBaseException {
// Replaced references may run Python finalizers. Release their locks
// before dropping the old values so those finalizers can reenter safely.
pub fn set_traceback(&self, traceback: Option<PyTracebackRef>) {
*self.traceback.write() = traceback;
let old = core::mem::replace(&mut *self.traceback.write(), traceback);
drop(old);
}

pub fn set_cause(&self, cause: Option<PyRef<Self>>) {
let mut c = self.cause.write();
self.set_suppress_context(true);
*c = cause;
let old = {
let mut current = self.cause.write();
self.set_suppress_context(true);
core::mem::replace(&mut *current, cause)
};
drop(old);
}

pub fn set_context(&self, context: Option<PyRef<Self>>) {
*self.context.write() = context;
let old = core::mem::replace(&mut *self.context.write(), context);
drop(old);
}

fn set_args_tuple(&self, args: PyTupleRef) {
let old = core::mem::replace(&mut *self.args.write(), args);
drop(old);
}

pub(super) fn __suppress_context__(&self) -> bool {
Expand Down Expand Up @@ -873,7 +885,7 @@ impl Py<PyBaseException> {
};
let args: ArgIterable = value.try_into_value(vm)?;
let args = args.iter(vm)?.collect::<PyResult<Vec<_>>>()?;
*self.args.write() = PyTuple::new_ref(args, &vm.ctx);
self.set_args_tuple(PyTuple::new_ref(args, &vm.ctx));
Ok(())
}

Expand Down Expand Up @@ -958,7 +970,7 @@ impl Py<PyBaseException> {
impl PyRef<PyBaseException> {
#[pymethod]
fn with_traceback(self, tb: Option<PyTracebackRef>) -> Self {
*self.traceback.write() = tb;
self.set_traceback(tb);
self
}
}
Expand All @@ -984,7 +996,7 @@ impl Initializer for PyBaseException {
type Args = FuncArgs;

fn init(zelf: &Py<Self>, args: Self::Args, vm: &VirtualMachine) -> PyResult<()> {
*zelf.args.write() = PyTuple::new_ref(args.args, &vm.ctx);
zelf.set_args_tuple(PyTuple::new_ref(args.args, &vm.ctx));
Ok(())
}
}
Expand Down
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