nvme-pci: remove nvmeq->tags

There is no real need to have a pointer to the tagset in
struct nvme_queue, as we only need it in a single place, and that place
can derive the used tagset from the device and qid trivially.  This
fixes a problem with stale pointer exposure when tagsets are reset,
and also shrinks the nvme_queue structure.  It also matches what most
other transports have done since day 1.
Reported-by: Edmund Nadolski <edmund.nadolski@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/host/pci.c

@@ -167,7 +167,6 @@ struct nvme_queue {
 	 /* only used for poll queues: */
 	spinlock_t cq_poll_lock ____cacheline_aligned_in_smp;
 	volatile struct nvme_completion *cqes;
-	struct blk_mq_tags **tags;
 	dma_addr_t sq_dma_addr;
 	dma_addr_t cq_dma_addr;
 	u32 __iomem *q_db;
@@ -376,29 +375,17 @@ static int nvme_admin_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
 
 	WARN_ON(hctx_idx != 0);
 	WARN_ON(dev->admin_tagset.tags[0] != hctx->tags);
-	WARN_ON(nvmeq->tags);
 
 	hctx->driver_data = nvmeq;
-	nvmeq->tags = &dev->admin_tagset.tags[0];
 	return 0;
 }
 
-static void nvme_admin_exit_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
-{
-	struct nvme_queue *nvmeq = hctx->driver_data;
-
-	nvmeq->tags = NULL;
-}
-
 static int nvme_init_hctx(struct blk_mq_hw_ctx *hctx, void *data,
 			  unsigned int hctx_idx)
 {
 	struct nvme_dev *dev = data;
 	struct nvme_queue *nvmeq = &dev->queues[hctx_idx + 1];
 
-	if (!nvmeq->tags)
-		nvmeq->tags = &dev->tagset.tags[hctx_idx];
-
 	WARN_ON(dev->tagset.tags[hctx_idx] != hctx->tags);
 	hctx->driver_data = nvmeq;
 	return 0;
@@ -948,6 +935,13 @@ static inline void nvme_ring_cq_doorbell(struct nvme_queue *nvmeq)
 		writel(head, nvmeq->q_db + nvmeq->dev->db_stride);
 }
 
+static inline struct blk_mq_tags *nvme_queue_tagset(struct nvme_queue *nvmeq)
+{
+	if (!nvmeq->qid)
+		return nvmeq->dev->admin_tagset.tags[0];
+	return nvmeq->dev->tagset.tags[nvmeq->qid - 1];
+}
+
 static inline void nvme_handle_cqe(struct nvme_queue *nvmeq, u16 idx)
 {
 	volatile struct nvme_completion *cqe = &nvmeq->cqes[idx];
@@ -972,7 +966,7 @@ static inline void nvme_handle_cqe(struct nvme_queue *nvmeq, u16 idx)
 		return;
 	}
 
-	req = blk_mq_tag_to_rq(*nvmeq->tags, cqe->command_id);
+	req = blk_mq_tag_to_rq(nvme_queue_tagset(nvmeq), cqe->command_id);
 	trace_nvme_sq(req, cqe->sq_head, nvmeq->sq_tail);
 	nvme_end_request(req, cqe->status, cqe->result);
 }
@@ -1572,7 +1566,6 @@ static const struct blk_mq_ops nvme_mq_admin_ops = {
 	.queue_rq	= nvme_queue_rq,
 	.complete	= nvme_pci_complete_rq,
 	.init_hctx	= nvme_admin_init_hctx,
-	.exit_hctx      = nvme_admin_exit_hctx,
 	.init_request	= nvme_init_request,
 	.timeout	= nvme_timeout,
 };