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Add recursion guard to the c-api #8796

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

Add recursion guard to the c-api #8796

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6bdf40f
Add recursion guard to the c-api
bschoenmaeckers Sep 23, 2026
5eb882c
Do not change with_recursion as this has side effects
bschoenmaeckers Oct 1, 2026
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Do not change with_recursion as this has side effects
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@bschoenmaeckers
bschoenmaeckers committed Oct 1, 2026
commit 5eb882cddee62d0fdc44923742a56712f135a1da
34 changes: 24 additions & 10 deletions crates/vm/src/vm/mod.rs
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Expand Up @@ -2586,15 +2586,7 @@ impl VirtualMachine {
}

/// Enter a native-recursion section equivalent to `Py_EnterRecursiveCall`.
///
/// This bounds native recursion that pushes no Python frame, against the
/// native stack. That is a separate budget from the frame limit
/// `sys.setrecursionlimit()` sets, so nesting counted here does not come
/// out of what Python code has left to call with.
pub fn enter_recursive_call(&self, _where: &str) -> PyResult<()> {
// `check_c_stack_overflow()` answers no unconditionally where the stack
// pointer cannot be read, which would leave this guard with nothing to
// stop. A count of the nesting stands in for the measurement there.
#[cfg(any(miri, target_env = "musl"))]
let counted_too_deep =
self.native_recursion_depth.get() >= Self::NATIVE_RECURSION_LIMIT_UNMEASURED;
Expand Down Expand Up @@ -2623,11 +2615,33 @@ impl VirtualMachine {
/// Used to run the body of a (possibly) recursive function. It will raise a
/// RecursionError if recursive functions are nested far too many times,
/// preventing a stack overflow.
/// `Py_EnterRecursiveCall`: bounds native recursion that pushes no Python
/// frame, against the native stack. That is a separate budget from the
/// frame limit `sys.setrecursionlimit()` sets, so nesting counted here does
/// not come out of what Python code has left to call with.
pub fn with_recursion<R, F: FnOnce() -> PyResult<R>>(&self, _where: &str, f: F) -> PyResult<R> {
self.enter_recursive_call(_where)?;
// `check_c_stack_overflow()` answers no unconditionally where the stack
// pointer cannot be read, which would leave this guard with nothing to
// stop. A count of the nesting stands in for the measurement there.
#[cfg(any(miri, target_env = "musl"))]
let counted_too_deep =
self.native_recursion_depth.get() >= Self::NATIVE_RECURSION_LIMIT_UNMEASURED;
#[cfg(not(any(miri, target_env = "musl")))]
let counted_too_deep = false;

if counted_too_deep || self.check_c_stack_overflow() {
return Err(
self.new_recursion_error(format!("maximum recursion depth exceeded {_where}"))
);
}

#[cfg(any(miri, target_env = "musl"))]
let _native_depth_guard = scopeguard::guard((), |()| self.leave_recursive_call());
let _native_depth_guard = {
self.native_recursion_depth.update(|d| d + 1);
scopeguard::guard((), |()| {
self.native_recursion_depth.update(|d| d.saturating_sub(1))
})
};

f()
}
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