RE: [PATCH iwl-net v2] ixgbe: fix MDIO bus lifetime

-----Original Message-----
From: Richard Patel <redacted>
Sent: Sunday, September 6, 2026 4:33 AM
To: intel-wired-lan@lists.osuosl.org
Cc: Nguyen, Anthony L <anthony.l.nguyen@intel.com>; Kitszel,
Przemyslaw [off-list ref]; Andrew Lunn
[off-list ref]; Steve Douthit [off-list ref];
netdev@vger.kernel.org; linux-kernel@vger.kernel.org; Richard Patel
[off-list ref]
Subject: [PATCH iwl-net v2] ixgbe: fix MDIO bus lifetime

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'

Switch to devm_mdiobus_register(), drop custom unregister calls.
This is safe because the bus is already devm-allocated, so unregister
always happens before free.

Assisted-by: LLM
Fixes: 8fa10ef01260 ("ixgbe: register a mdiobus")
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Richard Patel <redacted>
---
v1 -> v2: use devm_mdiobus_register() instead of another
          mdiobus_unregister() call
v1: https://lore.kernel.org/netdev/20260826042945.2344686-1-
ripatel@wii.dev/

 drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 9 ++-------
drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c  | 2 +-
 2 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index f91856498eb2..96f60269fca6 100644

--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -8471,6 +8471,7 @@ static void ixgbe_sfp_detection_subtask(struct

ixgbe_adapter *adapter)
 		e_dev_err("Reload the driver after installing a "
 			  "supported module.\n");
 		unregister_netdev(adapter->netdev);
+		adapter->mii_bus = NULL;
 	}
 }

@@ -8693,11 +8694,8 @@ static void ixgbe_service_task(struct

work_struct *work)
 	}
 	if (ixgbe_check_fw_error(adapter)) {
 		if (!test_bit(__IXGBE_DOWN, &adapter->state)) {
-			if (adapter->mii_bus) {
-				mdiobus_unregister(adapter->mii_bus);
-				adapter->mii_bus = NULL;
-			}
 			unregister_netdev(adapter->netdev);
+			adapter->mii_bus = NULL;
 		}
 		ixgbe_service_event_complete(adapter);
 		return;

@@ -12104,9 +12102,6 @@ static void ixgbe_remove(struct pci_dev *pdev)
 	if (adapter->hw.mac.type == ixgbe_mac_e610)
 		ixgbe_disable_link_status_events(adapter);

-	if (adapter->mii_bus)
-		mdiobus_unregister(adapter->mii_bus);
-
 #ifdef CONFIG_IXGBE_DCA
 	if (adapter->flags & IXGBE_FLAG_DCA_ENABLED) {
 		adapter->flags &= ~IXGBE_FLAG_DCA_ENABLED; diff --git

a/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c
b/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c
index ab733e73927d..74631cb2ddbc 100644

--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_phy.c

@@ -1086,7 +1086,7 @@ int ixgbe_mii_bus_init(struct ixgbe_hw *hw)
 	hw->phy.mdio.mode_support = MDIO_SUPPORTS_C45 |

MDIO_SUPPORTS_C22;

 	adapter->mii_bus = bus;
-	return mdiobus_register(bus);
+	return devm_mdiobus_register(dev, bus);
 }

 /**
--
2.52.0