Running maturin develop can trigger SIGSEV in running process

[cswinter]

Bug Description

I ran maturin develop while a PyO3/maturin package was being used by another Python process, and the Python process died with
terminated by signal SIGSEGV (Address boundary error).

Your Python version (python -V)

Python 3.8.10

Your pip version (pip -V)

pip 21.3.1

What bindings you're using

pyo3

Does cargo build work?

• Yes, it works

If on windows, have you checked that you aren't accidentally using unix path (those with the forward slash /)?

• Yes

Steps to Reproduce

1. Install a Rust/Python package with maturin develop
2. Start a Python process that imports and calls into the Rust library
3. Run maturin develop again while Python process is still running
4. Segfault

[cswinter]

This could still be a coincidence, but the timing was very suspicious and the program was running fine before many times and doesn't use any unsafe code.

[davidhewitt]

This sounds completely expected, although it may be worth pointing out in the docs.

As far as I'm aware, in Linux it's completely expected that if you replace a shared library while a process has loaded part of it into memory, then when the process needs to load more of the shared library you're almost certain to get crashes like this.

[davidhewitt]

Oh, actually it might be possible for us to change something? https://stackoverflow.com/questions/3855004/overwriting-library-file-causes-segmentation-fault

[messense]

@cswinter Can you try to remove the existing so file first here:

maturin/src/module_writer.rs

Line 630 in 133b3f9

let target = rust_module.join(&so_filename);