nvme_reset_work is a little fragile as it needs to handle both resetting
a live controller and initializing one during probe.  Split out the initial
probe and open code it in nvme_probe and leave nvme_reset_work to just do
the live controller reset.

This fixes a recently introduced bug where nvme_dev_disable causes a NULL
pointer dereferences in blk_mq_quiesce_tagset because the tagset pointer
is not set when the reset state is entered directly from the new state.
The separate probe code can skip the reset state and probe directly and
fixes this.

To make sure the system isn't single threaded on enabling nvme
controllers, set the PROBE_PREFER_ASYNCHRONOUS flag in the device_driver
structure so that the driver core probes in parallel.

Fixes: 98d81f0df70c ("nvme: use blk_mq_[un]quiesce_tagset")
Reported-by: Gerd Bayer <gbayer@linux.ibm.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
---
  drivers/nvme/host/pci.c | 139 ++++++++++++++++++++++++----------------
  1 file changed, 83 insertions(+), 56 deletions(-)

diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
index 1b3c96a4b7c90..1c8c70767cb8a 100644
--- a/drivers/nvme/host/pci.c
+++ b/drivers/nvme/host/pci.c

@@ -2821,15 +2821,7 @@ static void nvme_reset_work(struct work_struct *work)
  	result = nvme_pci_enable(dev);
  	if (result)
  		goto out_unlock;
-
-	if (!dev->ctrl.admin_q) {
-		result = nvme_pci_alloc_admin_tag_set(dev);
-		if (result)
-			goto out_unlock;
-	} else {
-		nvme_start_admin_queue(&dev->ctrl);
-	}
-
+	nvme_start_admin_queue(&dev->ctrl);
  	mutex_unlock(&dev->shutdown_lock);
  
  	/*

@@ -2854,9 +2846,6 @@ static void nvme_reset_work(struct work_struct *work)
  		 */
  		memset(dev->dbbuf_dbs, 0, nvme_dbbuf_size(dev));
  		memset(dev->dbbuf_eis, 0, nvme_dbbuf_size(dev));
-	} else {
-		if (dev->ctrl.oacs & NVME_CTRL_OACS_DBBUF_SUPP)
-			nvme_dbbuf_dma_alloc(dev);
  	}
  
  	if (dev->ctrl.hmpre) {

@@ -2869,37 +2858,23 @@ static void nvme_reset_work(struct work_struct *work)
  	if (result)
  		goto out;
  
-	if (dev->ctrl.tagset) {
-		/*
-		 * This is a controller reset and we already have a tagset.
-		 * Freeze and update the number of I/O queues as thos might have
-		 * changed.  If there are no I/O queues left after this reset,
-		 * keep the controller around but remove all namespaces.
-		 */
-		if (dev->online_queues > 1) {
-			nvme_start_queues(&dev->ctrl);
-			nvme_wait_freeze(&dev->ctrl);
-			nvme_pci_update_nr_queues(dev);
-			nvme_dbbuf_set(dev);
-			nvme_unfreeze(&dev->ctrl);
-		} else {
-			dev_warn(dev->ctrl.device, "IO queues lost\n");
-			nvme_mark_namespaces_dead(&dev->ctrl);
-			nvme_start_queues(&dev->ctrl);
-			nvme_remove_namespaces(&dev->ctrl);
-			nvme_free_tagset(dev);
-		}
+	/*
+	 * Freeze and update the number of I/O queues as thos might have
+	 * changed.  If there are no I/O queues left after this reset, keep the
+	 * controller around but remove all namespaces.
+	 */
+	if (dev->online_queues > 1) {
+		nvme_start_queues(&dev->ctrl);
+		nvme_wait_freeze(&dev->ctrl);
+		nvme_pci_update_nr_queues(dev);
+		nvme_dbbuf_set(dev);
+		nvme_unfreeze(&dev->ctrl);
  	} else {
-		/*
-		 * First probe.  Still allow the controller to show up even if
-		 * there are no namespaces.
-		 */
-		if (dev->online_queues > 1) {
-			nvme_pci_alloc_tag_set(dev);
-			nvme_dbbuf_set(dev);
-		} else {
-			dev_warn(dev->ctrl.device, "IO queues not created\n");
-		}
+		dev_warn(dev->ctrl.device, "IO queues lost\n");
+		nvme_mark_namespaces_dead(&dev->ctrl);
+		nvme_start_queues(&dev->ctrl);
+		nvme_remove_namespaces(&dev->ctrl);
+		nvme_free_tagset(dev);