[PATCH v2] nvmet: add missing locks around nvmet_ns_revalidate

[Christoph Hellwig]

On Thu, Mar 10, 2022 at 02:25:11AM +0100, Niels Dossche wrote:
> nvmet_ns_changed states via lockdep that the ns->subsys->lock must be
> held. The only caller of nvmet_ns_changed which does not acquire that
> lock is nvmet_ns_revalidate.

So acquire it in nvmet_ns_revalidate only when we actually call
nvmet_ns_changed.  Otherwise we take a subsystem-wide lock for every
Identify Namespace all.