Date: Tue, 1 Dec 2015 15:58:53 -0600
From: "Serge E. Hallyn" <serge.hallyn@ubuntu.com>
To: Tejun Heo <tj@kernel.org>
Cc: "Serge E. Hallyn" <serge.hallyn@ubuntu.com>, serge@hallyn.com,
        linux-kernel@vger.kernel.org, adityakali@google.com,
        linux-api@vger.kernel.org, containers@lists.linux-foundation.org,
        cgroups@vger.kernel.org, lxc-devel@lists.linuxcontainers.org,
        akpm@linux-foundation.org, ebiederm@xmission.com
Subject: Re: [PATCH 7/8] cgroup: mount cgroupns-root when inside non-init
 cgroupns
Message-ID: <20151201215853.GA9153@mail.hallyn.com>
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 <20151127051745.GA24521@mail.hallyn.com>
 <20151130150938.GF3535@mtj.duckdns.org>
 <20151201040704.GA31067@mail.hallyn.com>
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On Tue, Dec 01, 2015 at 11:46:49AM -0500, Tejun Heo wrote:
> Hey, Serge.
> 
> On Mon, Nov 30, 2015 at 10:07:04PM -0600, Serge E. Hallyn wrote:
> > So actually the way the code is now, the first mount cannot
> > be done from a non-init user namespace; and kernfs_obtain_root()
> > is only called from non-init user namespace.  So can we assume
> > that the root dentry will be instantiated?  (or can it get
> > evicted?)
> > 
> > If we can assume that then most of that fn can go away.
> 
> The v2 hierarchy is always mounted and non-init ns shouldn't be able
> to create new v1 hierarchies, so the root dentry should always be
> there.

I mispoke before though - it's not the hierarchy's root dentry,
but rather a dentry for a descendent cgroup which will become the
root dentry for the new superblock.  We do know that there must be
a css_set with a cgroup.  I'm still trying to track down whether
that cgrou's inode's dentry can ever be flushed.  I would think
not but am not sure.
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