NVMe: Memory barrier before queue_count is incremented

Protects against reordering and/or preempting which would allow the
kthread to access the queue descriptor before it is set up

Signed-off-by: Jon Derrick <jonathan.derrick@intel.com>
Acked-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c
index 9682e29b4171..cae7cac6cc43 100644
--- a/drivers/block/nvme-core.c
+++ b/drivers/block/nvme-core.c
@@ -1453,9 +1453,12 @@ 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: