nvme-pci: fix race condition between reset and nvme_dev_disable()

nvme_dev_disable() modifies the dev->online_queues field, therefore
nvme_pci_update_nr_queues() should avoid racing against it, otherwise
we could end up passing invalid values to blk_mq_update_nr_hw_queues().

 WARNING: CPU: 39 PID: 61303 at drivers/pci/msi/api.c:347
          pci_irq_get_affinity+0x187/0x210
 Workqueue: nvme-reset-wq nvme_reset_work [nvme]
 RIP: 0010:pci_irq_get_affinity+0x187/0x210
 Call Trace:
  <TASK>
  ? blk_mq_pci_map_queues+0x87/0x3c0
  ? pci_irq_get_affinity+0x187/0x210
  blk_mq_pci_map_queues+0x87/0x3c0
  nvme_pci_map_queues+0x189/0x460 [nvme]
  blk_mq_update_nr_hw_queues+0x2a/0x40
  nvme_reset_work+0x1be/0x2a0 [nvme]

Fix the bug by locking the shutdown_lock mutex before using
dev->online_queues. Give up if nvme_dev_disable() is running or if
it has been executed already.

Fixes: 949928c1 ("NVMe: Fix possible queue use after freed")
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Maurizio Lombardi <mlombard@redhat.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/host/pci.c

@@ -2506,17 +2506,29 @@ static unsigned int nvme_pci_nr_maps(struct nvme_dev *dev)
 	return 1;
 }
 
-static void nvme_pci_update_nr_queues(struct nvme_dev *dev)
+static bool 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;
+		return true;
+	}
+
+	/* Give up if we are racing with nvme_dev_disable() */
+	if (!mutex_trylock(&dev->shutdown_lock))
+		return false;
+
+	/* Check if nvme_dev_disable() has been executed already */
+	if (!dev->online_queues) {
+		mutex_unlock(&dev->shutdown_lock);
+		return false;
 	}
 
 	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);
+	mutex_unlock(&dev->shutdown_lock);
+	return true;
 }
 
 static int nvme_pci_enable(struct nvme_dev *dev)
@@ -2797,7 +2809,8 @@ static void nvme_reset_work(struct work_struct *work)
 		nvme_dbbuf_set(dev);
 		nvme_unquiesce_io_queues(&dev->ctrl);
 		nvme_wait_freeze(&dev->ctrl);
-		nvme_pci_update_nr_queues(dev);
+		if (!nvme_pci_update_nr_queues(dev))
+			goto out;
 		nvme_unfreeze(&dev->ctrl);
 	} else {
 		dev_warn(dev->ctrl.device, "IO queues lost\n");