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:

quoted

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.