Issue with AWUPF when using multiple controllers in a subsystem

[Christoph Hellwig]

On Thu, Apr 10, 2025 at 10:07:22AM +0100, Keith Busch wrote:
> You'll get different results depending on the non-deterministic order we
> enumerate. Can't we just change the stacked limit to the smallest
> observed value as we go?

That means discovering a new controller could lower the limit while
a file system is using it.  Not a good idea.  That's why I suggested
only supporting the namespace variant ASAP until we actually grow
users relying on it.