[PATCH] virtio_net: Fix probe failed when modprobe virtio_net

[Li Zetao]

When doing the following test steps, an error was found:
  step 1: modprobe virtio_net succeeded
    # modprobe virtio_net        <-- OK

  step 2: fault injection in register_netdevice()
    # modprobe -r virtio_net     <-- OK
    # ...
      FAULT_INJECTION: forcing a failure.
      name failslab, interval 1, probability 0, space 0, times 0
      CPU: 0 PID: 3521 Comm: modprobe
      Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
      Call Trace:
       <TASK>
       ...
       should_failslab+0xa/0x20
       ...
       dev_set_name+0xc0/0x100
       netdev_register_kobject+0xc2/0x340
       register_netdevice+0xbb9/0x1320
       virtnet_probe+0x1d72/0x2658 [virtio_net]
       ...
       </TASK>
      virtio_net: probe of virtio0 failed with error -22

  step 3: modprobe virtio_net failed
    # modprobe virtio_net        <-- failed
      virtio_net: probe of virtio0 failed with error -2

The root cause of the problem is that the queues are not
disable on the error handling path when register_netdevice()
fails in virtnet_probe(), resulting in an error "-ENOENT"
returned in the next modprobe call in setup_vq().

virtio_pci_modern_device uses virtqueues to send or
receive message, and "queue_enable" records whether the
queues are available. In vp_modern_find_vqs(), all queues
will be selected and activated, but once queues are enabled
there is no way to go back except reset.

Fix it by reset virtio device on error handling path.

Fixes: 1fcf0512c9c8 ("virtio_pci: modern driver")
Signed-off-by: Li Zetao <lizetao1@xxxxxxxxxx>
---
 drivers/net/virtio_net.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7106932c6f88..86e52454b5b5 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -3949,12 +3949,11 @@ static int virtnet_probe(struct virtio_device *vdev)
 	return 0;
 
 free_unregister_netdev:
-	virtio_reset_device(vdev);
-
 	unregister_netdev(dev);
 free_failover:
 	net_failover_destroy(vi->failover);
 free_vqs:
+	virtio_reset_device(vdev);
 	cancel_delayed_work_sync(&vi->refill);
 	free_receive_page_frags(vi);
 	virtnet_del_vqs(vi);
-- 
2.25.1