[PATCH] NVMe: Memory barrier before queue_count is incremented

[keith.busch@intel.com (Keith Busch)]

On Wed, 27 May 2015, Jon Derrick wrote:
> Protects against reordering and/or preempting which would allow the
> kthread to access the queue descriptor before it is set up

Looks good to me.

Acked-by: Keith Busch <keith.busch at intel.com>

> Signed-off-by: Jon Derrick <jonathan.derrick at intel.com>
> ---
> drivers/block/nvme-core.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c
> index c42bc53..2b0c817 100644
> --- a/drivers/block/nvme-core.c
> +++ b/drivers/block/nvme-core.c
> @@ -1463,9 +1463,12 @@ static struct nvme_queue *nvme_alloc_queue(struct nvme_dev *dev, int qid,
> 	nvmeq->q_db = &dev->dbs[qid * 2 * dev->db_stride];
> 	nvmeq->q_depth = depth;
> 	nvmeq->qid = qid;
> -	dev->queue_count++;
> 	dev->queues[qid] = nvmeq;
>
> +	/* make sure queue descriptor is set before queue count, for kthread */
> +	mb();
> +	dev->queue_count++;
> +
> 	return nvmeq;
>
>  free_cqdma:
> -- 
> 2.1.4
>
>