fatal runtime error: assertion failed: output.write(&bytes).is_ok() about rust HOT 6 OPEN

On a machine with Ubuntu and nix I had around with Linux 5.15.0-101-generic, this works. On my two systems with new NixOS and Linux 6.9.2 it fails.

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Ah, a relatively small diff, then! Should be easy to find the offending commit. torvalds/linux@f610c35...c8eef17

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I have verified that downgrading to linux kernel 6.8.11 makes the problem go away.

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Nix builds are kind of reproducible, so that's very unexpected

Nix does not take kernel version into account in its reproducibility guarantees.

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Yes, everything else is locked in place (kind of). That's why I immediately suspected the kernel might be a problem.

So to sum up: something about very recent linux kernel version is breaking some assumptions in Rust standard code w.r.t forking/execing, which leads to this internal panic. It's hard for me to tell is it a kernel regression, or Rust's stdlib assumptions were incorrect, or maybe I'm missing something else entirely.

I am happening to witness it because I'm running as recent kernel version as NixOS can provide trying to avoid some bcachefs bugs. With time the problem might become more widespread.

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🤔 , dozens of rebuild + reboot cycles... . I'll see if I can find a time to do it. No promises. :D

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