[PATCH v4] nvmet: synchronize sqhd update

[Christoph Hellwig]

On Wed, Oct 18, 2017 at 02:33:59PM -0700, James Smart wrote:
> In testing target io in read write mix, we did indeed get into cases
> where sqhd didn't update properly and slowly missed enough updates to
> shutdown the queue.
> 
> Protect the updating sqhd by using cmpxchg
> 
> Signed-off-by: James Smart <james.smart at broadcom.com>

Applied to nvme-4.14 with a small changelog fixup.