nvme: special case AEN requests

AEN requests are different from other requests in that they don't time out
or can easily be cancelled.  Because of that we should not use the blk-mq
infrastructure but just special case them in the completion path.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

drivers/nvme/host/pci.c

@@ -49,6 +49,13 @@
 #define SQ_SIZE(depth)		(depth * sizeof(struct nvme_command))
 #define CQ_SIZE(depth)		(depth * sizeof(struct nvme_completion))
 		
+/*
+ * We handle AEN commands ourselves and don't even let the
+ * block layer know about them.
+ */
+#define NVME_NR_AEN_COMMANDS	1
+#define NVME_AQ_BLKMQ_DEPTH	(NVME_AQ_DEPTH - NVME_NR_AEN_COMMANDS)
+
 unsigned char admin_timeout = 60;
 module_param(admin_timeout, byte, 0644);
 MODULE_PARM_DESC(admin_timeout, "timeout in seconds for admin commands");
@@ -355,23 +362,23 @@ static void *cancel_cmd_info(struct nvme_cmd_info *cmd, nvme_completion_fn *fn)
 	return ctx;
 }
 
-static void async_req_completion(struct nvme_queue *nvmeq, void *ctx,
+static void nvme_complete_async_event(struct nvme_dev *dev,
 		struct nvme_completion *cqe)
 {
-	u32 result = le32_to_cpup(&cqe->result);
-	u16 status = le16_to_cpup(&cqe->status) >> 1;
+	u16 status = le16_to_cpu(cqe->status) >> 1;
+	u32 result = le32_to_cpu(cqe->result);
 
 	if (status == NVME_SC_SUCCESS || status == NVME_SC_ABORT_REQ)
-		++nvmeq->dev->ctrl.event_limit;
+		++dev->ctrl.event_limit;
 	if (status != NVME_SC_SUCCESS)
 		return;
 
 	switch (result & 0xff07) {
 	case NVME_AER_NOTICE_NS_CHANGED:
-		dev_info(nvmeq->q_dmadev, "rescanning\n");
-		queue_work(nvme_workq, &nvmeq->dev->scan_work);
+		dev_info(dev->dev, "rescanning\n");
+		queue_work(nvme_workq, &dev->scan_work);
 	default:
-		dev_warn(nvmeq->q_dmadev, "async event result %08x\n", result);
+		dev_warn(dev->dev, "async event result %08x\n", result);
 	}
 }
 
@@ -404,7 +411,7 @@ static void *nvme_finish_cmd(struct nvme_queue *nvmeq, int tag,
 }
 
 /**
- * nvme_submit_cmd() - Copy a command into a queue and ring the doorbell
+ * __nvme_submit_cmd() - Copy a command into a queue and ring the doorbell
  * @nvmeq: The queue to use
  * @cmd: The command to send
  *
@@ -853,15 +860,31 @@ static void __nvme_process_cq(struct nvme_queue *nvmeq, unsigned int *tag)
 		void *ctx;
 		nvme_completion_fn fn;
 		struct nvme_completion cqe = nvmeq->cqes[head];
-		if ((le16_to_cpu(cqe.status) & 1) != phase)
+		u16 status = le16_to_cpu(cqe.status);
+
+		if ((status & 1) != phase)
 			break;
 		nvmeq->sq_head = le16_to_cpu(cqe.sq_head);
 		if (++head == nvmeq->q_depth) {
 			head = 0;
 			phase = !phase;
 		}
+
 		if (tag && *tag == cqe.command_id)
 			*tag = -1;
+
+		/*
+		 * AEN requests are special as they don't time out and can
+		 * survive any kind of queue freeze and often don't respond to
+		 * aborts.  We don't even bother to allocate a struct request
+		 * for them but rather special case them here.
+		 */
+		if (unlikely(nvmeq->qid == 0 &&
+				cqe.command_id >= NVME_AQ_BLKMQ_DEPTH)) {
+			nvme_complete_async_event(nvmeq->dev, &cqe);
+			continue;
+		}
+
 		ctx = nvme_finish_cmd(nvmeq, cqe.command_id, &fn);
 		fn(nvmeq, ctx, &cqe);
 	}
@@ -926,29 +949,15 @@ static int nvme_poll(struct blk_mq_hw_ctx *hctx, unsigned int tag)
 	return 0;
 }
 
-static int nvme_submit_async_admin_req(struct nvme_dev *dev)
+static void nvme_submit_async_event(struct nvme_dev *dev)
 {
-	struct nvme_queue *nvmeq = dev->queues[0];
 	struct nvme_command c;
-	struct nvme_cmd_info *cmd_info;
-	struct request *req;
-
-	req = blk_mq_alloc_request(dev->ctrl.admin_q, WRITE,
-			BLK_MQ_REQ_NOWAIT | BLK_MQ_REQ_RESERVED);
-	if (IS_ERR(req))
-		return PTR_ERR(req);
-
-	req->cmd_flags |= REQ_NO_TIMEOUT;
-	cmd_info = blk_mq_rq_to_pdu(req);
-	nvme_set_info(cmd_info, NULL, async_req_completion);
 
 	memset(&c, 0, sizeof(c));
 	c.common.opcode = nvme_admin_async_event;
-	c.common.command_id = req->tag;
+	c.common.command_id = NVME_AQ_BLKMQ_DEPTH + --dev->ctrl.event_limit;
 
-	blk_mq_free_request(req);
-	__nvme_submit_cmd(nvmeq, &c);
-	return 0;
+	__nvme_submit_cmd(dev->queues[0], &c);
 }
 
 static void async_cmd_info_endio(struct request *req, int error)
@@ -1387,8 +1396,7 @@ static int nvme_alloc_admin_tags(struct nvme_dev *dev)
 	if (!dev->ctrl.admin_q) {
 		dev->admin_tagset.ops = &nvme_mq_admin_ops;
 		dev->admin_tagset.nr_hw_queues = 1;
-		dev->admin_tagset.queue_depth = NVME_AQ_DEPTH;
-		dev->admin_tagset.reserved_tags = 1;
+		dev->admin_tagset.queue_depth = NVME_AQ_BLKMQ_DEPTH;
 		dev->admin_tagset.timeout = ADMIN_TIMEOUT;
 		dev->admin_tagset.numa_node = dev_to_node(dev->dev);
 		dev->admin_tagset.cmd_size = nvme_cmd_size(dev);
@@ -1496,11 +1504,8 @@ static int nvme_kthread(void *data)
 				spin_lock_irq(&nvmeq->q_lock);
 				nvme_process_cq(nvmeq);
 
-				while (i == 0 && dev->ctrl.event_limit > 0) {
-					if (nvme_submit_async_admin_req(dev))
-						break;
-					dev->ctrl.event_limit--;
-				}
+				while (i == 0 && dev->ctrl.event_limit > 0)
+					nvme_submit_async_event(dev);
 				spin_unlock_irq(&nvmeq->q_lock);
 			}
 		}
@@ -2151,7 +2156,7 @@ static void nvme_reset_work(struct work_struct *work)
 	if (result)
 		goto free_tags;
 
-	dev->ctrl.event_limit = 1;
+	dev->ctrl.event_limit = NVME_NR_AEN_COMMANDS;
 
 	result = nvme_dev_list_add(dev);
 	if (result)