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

[Steven Rostedt]

On Fri, 15 Nov 2019 13:48:23 +0000
Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:

> > 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.

I don't know about debugfs, but at least tracefs (which cut and pasted
from debugfs) does not allow that. At least in theory it doesn't allow
that (and if it does, it's a bug in the locking at the higher levels).

And perhaps debugfs shouldn't allow that either. As it is only suppose
to be a light weight way to interact with the kernel, hence the name
"debugfs".

Yu, do you have a test case for the "infinite loop" case?

-- Steve