[PATCH] ixgbe: fix MDIO bus leak when rejecting SFP module

[Richard Patel <ripatel@wii.dev>]

Plugging in an unsupported SFP module caused ixgbe NICs to get
wedged permanently.

ixgbe unregisters the netdev when rejecting an SFP transceiver as
unsupported.

  ixgbe 0000:3b:00.0: failed to initialize because an unsupported SFP+ module type was detected.
  ixgbe 0000:3b:00.0: Reload the driver after installing a supported module.
  ixgbe 0000:3b:00.0: removed PHC on enp59s0

This code path failed to unregister an MDIO bus owned by that
netdev, so when unregister_netdev() tries to tear it down
(via device_del() -> devres_release_all() -> mdiobus_free()),
it trips over the leaked registration.

  ixgbe-mdio-0000:3b:00.0: not in UNREGISTERED state
  WARNING: drivers/net/phy/mdio_bus_provider.c:711 at mdiobus_free+0x3d/0x50, CPU#21: kworker/u128:0/12

This prevents ixgbe from reloading, even after PCIe remove/rescan:

  sysfs: cannot create duplicate filename '/class/mdio_bus/ixgbe-mdio-0000:3b:00.0'

Call mdiobus_unregister() before unregistering the netdev,
like ixgbe_service_task() does after a firmware error.

Fixes: 8fa10ef01260 ("ixgbe: register a mdiobus")
Signed-off-by: Richard Patel <ripatel@wii.dev>
---
 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index f91856498eb2..fca57749218b 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -8470,6 +8470,10 @@ static void ixgbe_sfp_detection_subtask(struct ixgbe_adapter *adapter)
 			  "SFP+ module type was detected.\n");
 		e_dev_err("Reload the driver after installing a "
 			  "supported module.\n");
+		if (adapter->mii_bus) {
+			mdiobus_unregister(adapter->mii_bus);
+			adapter->mii_bus = NULL;
+		}
 		unregister_netdev(adapter->netdev);
 	}
 }
-- 
2.52.0