In the Linux kernel, the following vulnerability has been resolved: driver core: Avoid warning when removing a device while its supplier is unbinding During driver removal, the following warning can appear: WARNING: CPU: 1 PID: 139 …

Overview

In the Linux kernel, the following vulnerability has been resolved:

driver core: Avoid warning when removing a device while its supplier is unbinding

During driver removal, the following warning can appear: WARNING: CPU: 1 PID: 139 at drivers/base/core.c:1497 __device_links_no_driver+0xcc/0xfc ... Call trace: __device_links_no_driver+0xcc/0xfc (P) device_links_driver_cleanup+0xa8/0xf0 device_release_driver_internal+0x208/0x23c device_links_unbind_consumers+0xe0/0x108 device_release_driver_internal+0xec/0x23c device_links_unbind_consumers+0xe0/0x108 device_release_driver_internal+0xec/0x23c device_links_unbind_consumers+0xe0/0x108 device_release_driver_internal+0xec/0x23c driver_detach+0xa0/0x12c bus_remove_driver+0x6c/0xbc driver_unregister+0x30/0x60 pci_unregister_driver+0x20/0x9c lan966x_pci_driver_exit+0x18/0xa90 [lan966x_pci]

This warning is triggered when a consumer is removed because the links status of its supplier is not DL_DEV_DRIVER_BOUND and the link flag DL_FLAG_SYNC_STATE_ONLY is not set.

The topology in terms of consumers/suppliers used was the following (consumer ---> supplier):

  i2c -----------> OIC ----> PCI device
   |                ^
   |                |
   +---> pinctrl ---+

When the PCI device is removed, the OIC (interrupt controller) has to be removed. In order to remove the OIC, pinctrl and i2c need to be removed and to remove pinctrl, i2c need to be removed. The removal order is:

1. i2c
2. pinctrl
3. OIC
4. PCI device

In details, the removal sequence is the following (with 0000:01:00.0 the PCI device): driver_detach: call device_release_driver_internal(0000:01:00.0)... device_links_busy(0000:01:00.0): links->status = DL_DEV_UNBINDING device_links_unbind_consumers(0000:01:00.0): 0000:01:00.0--oic link->status = DL_STATE_SUPPLIER_UNBIND call device_release_driver_internal(oic)... device_links_busy(oic): links->status = DL_DEV_UNBINDING device_links_unbind_consumers(oic): oic--pinctrl link->status = DL_STATE_SUPPLIER_UNBIND call device_release_driver_internal(pinctrl)... device_links_busy(pinctrl): links->status = DL_DEV_UNBINDING device_links_unbind_consumers(pinctrl): pinctrl--i2c link->status = DL_STATE_SUPPLIER_UNBIND call device_release_driver_internal(i2c)... device_links_busy(i2c): links->status = DL_DEV_UNBINDING __device_links_no_driver(i2c)... pinctrl--i2c link->status is DL_STATE_SUPPLIER_UNBIND oic--i2c link->status is DL_STATE_ACTIVE oic--i2c link->supplier->links.status is DL_DEV_UNBINDING

The warning is triggered by the i2c removal because the OIC (supplier) links status is not DL_DEV_DRIVER_BOUND. Its links status is indeed set to DL_DEV_UNBINDING.

It is perfectly legit to have the links status set to DL_DEV_UNBINDING in that case. Indeed we had started to unbind the OIC which triggered the consumer unbinding and didn't finish yet when the i2c is unbound.

Avoid the warning when the supplier links status is set to DL_DEV_UNBINDING and thus support this removal sequence without any warnings.

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.