[SRU][R][PATCH 0/1] Dock ethernet stops working after Thunderbolt dock unplug on Dell systems

[AceLan Kao]

From: "Chia-Lin Kao (AceLan)" <acelan.kao at canonical.com>

BugLink: https://bugs.launchpad.net/bugs/2162704

[Impact]
On Dell systems (CID: 202512-38252) the ethernet port on a Thunderbolt dock
stops working after the dock is unplugged and plugged back in, or after a
reboot with the dock attached. It does not happen every time.

The USB port code never detaches the Type-C connector when the component is
unbound, so the Type-C port keeps a pointer to a USB device that is already
freed. UCSI then walks that stale pointer when the PD partner disconnects.
This leaves the Thunderbolt tunnel in a bad state, and the dock's igc NIC
fails to come up:

[ 12.992293] igc 0000:2e:00.0 eth0: PCIe link lost, device now detached
[ 12.992986] igc: Failed to read reg 0x0!
[ 12.993077] WARNING: CPU: 9 PID: 129 at drivers/net/ethernet/intel/igc/igc_main.c:7005 igc_rd32+0xa4/0xc0 [igc]
[ 12.993344] igc_disable_pcie_master+0x16/0xa0 [igc]
[ 12.993361] igc_reset_hw_base+0x14/0x170 [igc]
[ 12.993376] igc_reset+0x63/0x110 [igc]
[ 12.993387] igc_io_slot_reset+0x9e/0xd0 [igc]
[ 12.993397] report_slot_reset+0x5d/0xc0
[ 12.993430] pcie_do_recovery+0x209/0x400
[ 12.993439] aer_isr_one_error_type+0x235/0x430
[ 12.993453] aer_isr+0x4e/0x80
[ 12.993461] irq_thread+0xf4/0x1f0

The stale pointer also shows up as a second sysfs link removal:

kernfs: can not remove 'typec', no directory
WARNING: CPU: 6 PID: 55 at fs/kernfs/dir.c:1706 kernfs_remove_by_name_ns+0xe9/0xf0
Workqueue: events ucsi_handle_connector_change [typec_ucsi]
Call Trace:
 sysfs_remove_link+0x19/0x50
 typec_unregister_partner+0x6e/0x120 [typec]
 ucsi_unregister_partner+0x107/0x150 [typec_ucsi]
 ucsi_handle_connector_change+0x3ec/0x490 [typec_ucsi]

With worse timing the same stale pointer is used after the memory is freed,
which is a use-after-free instead of a warning.

[Fix]
Call typec_deattach() in connector_unbind() before clearing
port_dev->connector, so unbind mirrors what connector_bind() does. This
clears port->usb2_dev/usb3_dev while the connector is still valid, so UCSI
no longer sees a freed USB device.

Upstream commit, merged in v7.2-rc5:
e0b291fe1179 usb: core: port: Deattach Type-C connector on component unbind

Link:
https://lore.kernel.org/lkml/20260611071201.1235545-1-acelan.kao@canonical.com/

[Test Plan]
Attach a Thunderbolt dock with an ethernet port to the system.

1. Unplug and replug the dock 20 times, checking dmesg after each replug:
   $ sudo dmesg -w | grep -E "igc|typec|kernfs"

2. Or reboot 20 times with the dock attached and check dmesg after boot:
   $ sudo dmesg | grep -E "PCIe link lost|Failed to read reg|can not remove 'typec'"

Also check the dock ethernet actually works after each cycle:
   $ ip link show
   $ ping -c 3 <gateway>

Without patch: "PCIe link lost, device now detached", "igc: Failed to read
reg 0x0!" and the igc_rd32 WARNING show up in dmesg, and the dock ethernet
interface does not come up.

With patch: no such messages in dmesg, and the dock ethernet interface comes
up every time.

[Where problems could occur]
Could break USB Type-C connector handling in drivers/usb/core/port.c and the
typec class.

If typec_deattach() is called on a port that was never attached, or the child
device is already gone, the Type-C partner sysfs links could be removed too
early. That would show up as a missing typec symlink under the USB port, or
as "can not remove" warnings from kernfs on dock unplug. Devices that only
use the Type-C connector class for USB enumeration, such as USB4/Thunderbolt
docks and USB-C monitors, are the ones that would notice.

The change is two lines and only runs on the unbind path, so normal
enumeration is not affected.

Chia-Lin Kao (AceLan) (1):
  usb: core: port: Deattach Type-C connector on component unbind

 drivers/usb/core/port.c | 2 ++
 1 file changed, 2 insertions(+)

-- 
2.53.0