[PATCH 5/5] NVMe: IO queue deletion re-write

[hch@infradead.org (Christoph Hellwig)]

> Aww, I really liked the re-queuing! :) It encapsulates deleting a
> queue-pair as a single, two-step operation.

I think it can still be nicely encapsulated when using the
workqueue.  And I think that's essential as requeuing for
a different command breaks all kinds of assumptions.

> There's a failure scenario that complicates work item handling. It has
> the same flaw kthread workers had if work is queued deeper than available
> tags, and then the controller stops responding. It's a mess to clean
> that up and synchronize when everything times out. Issuing everything
> from the main thread and irq callback is painless in comparison.

True, that's not getting simpler.

> But I didn't like having to store the "struct command" in the nvme_queue
> either, so I'm happy to consider alternatives if I've missed seeing an
> elegant solution.

Just curious:  why do we even both with the async queue shutdown.  At
least the controllers I have access to complete queue deletions very
quickly.