On Fri, May 23, 2025 at 07:32:38AM +0100, Al Viro wrote: > On Thu, May 15, 2025 at 01:25:27PM +0200, Christian Brauner wrote: > > > Al, I want to kill this again and restore the pre v6.15 behavior. > > Allowing mount propagation for detached trees was a crazy > > idea on my part. It's a pain and it regresses userspace. If composefs is > > broken by this then systemd will absolutely get broken by my change as > > well. > > > > Something like this will allow to restore the status-quo: > > > -#define IS_MNT_NEW(m) (!(m)->mnt_ns) > > +#define IS_MNT_NEW(m) (!(m)->mnt_ns || is_anon_ns((m)->mnt_ns)) > > FWIW, I'm not sure that ever had been quite correct, no matter how you > call the macro. I'm not up to building a counterexample right now, > will do in the morning... The point is that we can't do mount propagation with detached trees without regressing userspace. And we didn't do it before. I don't specifically care how we block this but it needs to go out again. Otherwise we release a kernel with the new semantics that regress userspace.
