Namespace removal deadlock in case of namespace detach command

[Keith Busch]

On Mon, Apr 18, 2016 at 12:00:51PM +0000, Sunad Bhandary S wrote:
> On receipt of a namespace attribute changed AER, we acquire the namespace mutex lock before proceeding to scan and validate the namespace list.
> In case of namespace detach/delete command, nvme_ns_remove function deadlocks trying to acquire the already held lock.

You're right, thanks for the catch. Do you have a fix, or should we
propose one?