Re: 6.7.0-rc1 + hacks deadlock bug, wifi netdev delete + cat of debugfs file.

[Benjamin Berg <benjamin@sipsolutions.net>]

On Wed, 2023-11-08 at 17:07 +0100, Johannes Berg wrote:
> >  From the backtrace in the removal logic, it seems that something waits
> > for a debugfs file to be closed.
> 
> Yes, debugfs remove waits for it to no longer have active users, but
> that cannot succeed because the users are blocked on acquiring the
> mutex.
> 
> > Maybe the logic attempting to get the
> > mutex in debugfs can check if file is waiting to be deleted,
> > combined with a try-mutex-lock logic, and bail out that way?
> 
> I don't know if there's a way to check that, but I'm also not sure how
> you'd even implement that?

Is it likely that we have lock contention for debugfs operations?

If it is relatively unlikely, then maybe just doing a mutex_trylock()
and immediately failing the operation with -EAGAIN could be a solution?
Obviously userspace would need some retry logic, but that is simple and
it could solve the delete problem.

Benjamin