linux-kernel - Re: [BREAKAGE] Since 4.18, kernel sets SB_I_NODEV implicitly on userns mounts, breaking systemd-nspawn

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Date:   Sun, 23 Dec 2018 00:32:41 +0100
From:   Gabriel C <nix.or.die@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     christian.brauner@...onical.com,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Ellie Reeves <ellierevves@...il.com>,
        Linux List Kernel Mailing <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Seth Forshee <seth.forshee@...onical.com>
Subject: Re: [BREAKAGE] Since 4.18, kernel sets SB_I_NODEV implicitly on
 userns mounts, breaking systemd-nspawn

Am So., 23. Dez. 2018 um 00:02 Uhr schrieb Linus Torvalds
<torvalds@...ux-foundation.org>:
>
> On Sat, Dec 22, 2018 at 2:49 PM Christian Brauner
> <christian.brauner@...onical.com> wrote:
> >
> > To be fair, no one apart from me was pointing out that it actually
> > breaks people including systemd folks
> > even though I was bringing it up with them. I even tried to fix all of
> > userspace after this got NACKED
>
> Seriously, the "we don't break user space" is the #1 rule in the
> kernel, and people should _know_ it's the #1 rule.
>
> If somebody ignores that rule, it needs to be escalated to me.
> Immediately. Because I need to know.
>

I do that usually but I didn't saw Christian's revert the time and I
never hit that issue.
Just saw that now because the unusual  [BREAKAGE] prefix.

> I need to know so that I can override the bogus NAK, and so that we
> can fix the breakage ASAP. The absolute last thing we need is some
> other user space then starting to rely on the new behavior, which just
> compounds the problem and makes it a *much* bigger problem.
>

Yes and you are right ..
https://github.com/lxc/lxc/pull/2438

I've added an comment there about 4.20.0.

BR,

Gabriel