linux-kernel - Re: [RFC] Add critical process prctl

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Message-ID: <CALCETrU2Wycgdfo8vLZQUnx1J9ro=6ddSkP37BhsfBkKL1mbMA@mail.gmail.com>
Date:   Tue, 10 Sep 2019 09:56:53 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Daniel Colascione <dancol@...gle.com>
Cc:     Tim Murray <timmurray@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [RFC] Add critical process prctl

On Wed, Sep 4, 2019 at 5:53 PM Daniel Colascione <dancol@...gle.com> wrote:
>
> A task with CAP_SYS_ADMIN can mark itself PR_SET_TASK_CRITICAL,
> meaning that if the task ever exits, the kernel panics. This facility
> is intended for use by low-level core system processes that cannot
> gracefully restart without a reboot. This prctl allows these processes
> to ensure that the system restarts when they die regardless of whether
> the rest of userspace is operational.

The kind of panic produced by init crashing is awful -- logs don't get
written, etc.  I'm wondering if you would be better off with a new
watchdog-like device that, when closed, kills the system in a
configurable way (e.g. after a certain amount of time, while still
logging something and having a decent chance of getting the logs
written out.)  This could plausibly even be an extension to the
existing /dev/watchdog API.

--Andy