NVMe: add ->exit_hctx() hook

If we do teardown and setup of the queue and block related parts
of the driver, then we should clear nvmeq->hctx once we kill the
hardware queue.

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

drivers/block/nvme-core.c

@@ -171,6 +171,13 @@ static int nvme_admin_init_request(void *data, struct request *req,
 	return 0;
 }
 
+static void nvme_exit_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
+{
+	struct nvme_queue *nvmeq = hctx->driver_data;
+
+	nvmeq->hctx = NULL;
+}
+
 static int nvme_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
 			  unsigned int hctx_idx)
 {
@@ -1335,6 +1342,7 @@ static struct blk_mq_ops nvme_mq_admin_ops = {
 	.queue_rq	= nvme_admin_queue_rq,
 	.map_queue	= blk_mq_map_queue,
 	.init_hctx	= nvme_admin_init_hctx,
+	.exit_hctx	= nvme_exit_hctx,
 	.init_request	= nvme_admin_init_request,
 	.timeout	= nvme_timeout,
 };
@@ -1343,6 +1351,7 @@ static struct blk_mq_ops nvme_mq_ops = {
 	.queue_rq	= nvme_queue_rq,
 	.map_queue	= blk_mq_map_queue,
 	.init_hctx	= nvme_init_hctx,
+	.exit_hctx	= nvme_exit_hctx,
 	.init_request	= nvme_init_request,
 	.timeout	= nvme_timeout,
 };