Segmentation fault in async recursion

[dullbananas]

To reproduce:

use std::future::Future;

#[inline(never)]
async fn recurse(n: usize) {
    let x = [77u8; 70000];
    if n != 0 {
        std::future::poll_fn(move |cx| {
            stacker::maybe_grow(140 * 1024, 8 * 1024, move || {
                Box::pin(recurse(n - 1)).as_mut().poll(cx)
            })
        })
        .await;
    }
    #[allow(dropping_copy_types)]
    drop(x);
}

#[test]
fn foof() {
    futures_lite::future::block_on(recurse(10000))
}

Error message:

process didn't exit successfully: `/home/dullbananas/Dropbox/stacker/target/debug/deps/segfault-6753b3a3d075b2b5 foof --exact --show-output` (signal: 11, SIGSEGV: invalid memory reference)

cargo 1.86.0 (adf9b6ad1 2025-02-28)

Linux 6.14.5-300.t2.fc42.x86_64

[nstilt1]

I don't know exactly what is wrong with your code, but the stack size is 8 KiB. You have a variable using up 70 KB.

I set the red zone to 55 KiB and the stack size to 140 KiB, and it runs. But to be honest, I'm kind of a noob when it comes to async code and async recursive functions, especially when you combine it with running on portable stacks. This is not something they teach in school, but from the docs, it seems like the red zone should be a little more than 70 KB for extra safety and the stack size to be at least one or two times 70 KB.