Re: [RFC] Don't propagate automount

[Ian Kent <raven@themaw.net>]

On Fri, 2019-09-27 at 15:41 +0800, Ian Kent wrote:
> 
> > > I initially thought this was the result of a "fix" in the mount
> > > propagation code but it occurred to me that propagation is meant
> > > to occur between mount trees not within them so this might be a
> > > bug.
> > > 
> > > I probably should have worked out exactly what upstream kernel
> > > this started happening in and then done a bisect and tried to
> > > work out if the change was doing what it was supposed to.
> > > 
> > > Anyway, I'll need to do that now for us to discuss this sensibly.
> > > 
> > > > > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > > > > 
> > > > > diff --git a/fs/pnode.c b/fs/pnode.c
> > > > > index 49f6d7ff2139..b960805d7954 100644
> > > > > --- a/fs/pnode.c
> > > > > +++ b/fs/pnode.c
> > > > > @@ -292,6 +292,9 @@ int propagate_mnt(struct mount *dest_mnt,
> > > > > struct
> > > > > mountpoint *dest_mp,
> > > > >  	struct mount *m, *n;
> > > > >  	int ret = 0;
> > > > >  
> > > > > +	if (source_mnt->mnt_mountpoint->d_flags &
> > > > > DCACHE_NEED_AUTOMOUNT)
> > > > > +		return 0;
> > > > > +
> > > > 
> > > > Possible problem with this is it will probably prevent mount
> > > > propagation in both directions which will break stuff.
> > > > 
> > > > I had originally assumed the problem was mount propagation
> > > > back to the parent mount but now I'm not sure that this is
> > > > actually what is meant to happen.

Goldwyn,

TBH I'm already a bit over this particularly since it's a
solved problem from my POV.

I've gone back as far as Fedora 20 and 3.11.10-301.fc20 also
behaves like this.

Unless someone says this behaviour is not the way kernel
mount propagation should behave I'm not going to spend
more time on it.

The ability to use either "slave" or "private" autofs pseudo
mount options in master map mount entries that are susceptible
to this mount propagation behaviour was included in autofs-5.1.5
and the patches used are present on kernel.org if you need to
back port them to an earlier release.

https://mirrors.edge.kernel.org/pub/linux/daemons/autofs/v5/patches-5.1.5/autofs-5.1.4-set-bind-mount-as-propagation-slave.patch

https://mirrors.edge.kernel.org/pub/linux/daemons/autofs/v5/patches-5.1.5/autofs-5.1.4-add-master-map-pseudo-options-for-mount-propagation.patch

It shouldn't be too difficult to back port them but they might
have other patch dependencies. I will help with that if you
need it.

Ian