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

From: Gabriel C <nix.or.die@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: christian.brauner@canonical.com,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	Ellie Reeves <ellierevves@gmail.com>,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Seth Forshee <seth.forshee@canonical.com>
Subject: Re: [BREAKAGE] Since 4.18, kernel sets SB_I_NODEV implicitly on userns mounts, breaking systemd-nspawn
Date: Sun, 23 Dec 2018 00:32:41 +0100	[thread overview]
Message-ID: <CAEJqkgjF7HBcvD=2QHTTipjv1kmpWwRATp1VLnu8KDe6cGMvhg@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wg-6jYZ=bJWdyBR=n8QOfwHTZZdzSUUPgFW+NGCV-pe2g@mail.gmail.com>

Am So., 23. Dez. 2018 um 00:02 Uhr schrieb Linus Torvalds
<torvalds@linux-foundation.org>:
>
> On Sat, Dec 22, 2018 at 2:49 PM Christian Brauner
> <christian.brauner@canonical.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