Re: [PATCH 1/3] dcache: add a new enum type for 'dentry_d_lock_class'

[Al Viro <viro@zeniv.linux.org.uk>]

On Fri, Nov 15, 2019 at 08:38:13AM -0500, Steven Rostedt wrote:
> On Fri, 15 Nov 2019 13:16:25 +0000
> Al Viro <viro@zeniv.linux.org.uk> wrote:
> 
> > I want to understand the overall situation.  No argument, list_empty()
> > in there is BS, for many reasons.  But I wonder if trying to keep the
> > current structure of the iterator _and_ the use of simple_rmdir()/simple_unlink()
> > is the right approach.
> 
> My guess is that debugfs was written to be as simple as possible.
> Nothing too complex. And in doing so, may have issues as you are
> pointing out. Just a way to allow communications between user space and
> kernel space (as tracefs started out).
> 
> BTW, what do you mean by "can debugfs_remove_recursive() rely upon the
> lack of attempts to create new entries inside the subtree it's trying
> to kill?"

Is it possible for something to call e.g. debugfs_create_dir() (or any
similar primitive) with parent inside the subtree that has been
passed to debugfs_remove_recursive() call that is still in progress?

If debugfs needs to cope with that, debugfs_remove_recursive() needs
considerably heavier locking, to start with.