nvme-pci: allocate tagset on reset if necessary

If a drive is unable to create IO queues on the initial probe, a
subsequent reset will need to allocate the tagset if IO queue creation
is successful. Without this, blk_mq_update_nr_hw_queues will crash on a
bad pointer due to the invalid tagset.

Fixes: eac3ef2 ("nvme-pci: split the initial probe from the rest path")
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/host/pci.c

@@ -2508,6 +2508,12 @@ static unsigned int nvme_pci_nr_maps(struct nvme_dev *dev)
 
 static void nvme_pci_update_nr_queues(struct nvme_dev *dev)
 {
+	if (!dev->ctrl.tagset) {
+		nvme_alloc_io_tag_set(&dev->ctrl, &dev->tagset, &nvme_mq_ops,
+				nvme_pci_nr_maps(dev), sizeof(struct nvme_iod));
+		return;
+	}
+
 	blk_mq_update_nr_hw_queues(&dev->tagset, dev->online_queues - 1);
 	/* free previously allocated queues that are no longer usable */
 	nvme_free_queues(dev, dev->online_queues);