Fix stuck systemctl poweroff could block terminate

[chemwolf6922]

Summary of the Pull Request

The systemctl poweroff call is async after the operation is enqueued per https://man7.org/linux/man-pages/man1/systemctl.1.html. However, in some rare cases it could block. And that will block the wsl --terminate call. For example: #40433 (comment)
This PR moves the calling logic to a separate thread, so the fallback timeout is always started in the systemd path.

PR Checklist

• Closes: Link to issue #xxx
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

No new tests are added as the original failure could not be easily reproduced.

[Copilot]

Pull request overview

This PR adjusts the Linux-side instance termination path in systemd mode so that a potentially-blocking systemctl poweroff invocation cannot prevent the termination timeout/fallback (reboot(RB_POWER_OFF)) from being reached.

Changes:

• Run systemctl poweroff on a detached thread to avoid blocking wsl --terminate when systemctl hangs.
• Always start the existing BootInitTimeout-based fallback timer on the main path and force reboot(RB_POWER_OFF) on timeout.

[benhillis]

Instead of a local std::thread(...).detach(), use the existing UtilCreateChildProcess helper. This will simplify the code.

    if (Config.BootInit && !Config.BootStartWriteSocket)
    {
        THROW_LAST_ERROR_IF(UtilSetSignalHandlers(g_SavedSignalActions, false) < 0);

        //
        // systemctl poweroff is normally async but can block in rare cases. Run it in a
        // child process so a stuck invocation can't prevent the fallback timeout below.
        //
        UtilCreateChildProcess("poweroff", []() {
            if (UtilExecCommandLine("systemctl poweroff", nullptr) < 0)
            {
                LOG_ERROR("systemctl poweroff failed, calling reboot(RB_POWER_OFF)");
                reboot(RB_POWER_OFF);
            }
        });

        std::this_thread::sleep_for(std::chrono::milliseconds(Config.BootInitTimeout));
        LOG_ERROR("systemctl poweroff did not terminate the instance in {} ms, calling reboot(RB_POWER_OFF)", Config.BootInitTimeout);
    }

[chemwolf6922]

Do we need a new process for this?

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 1 comment.