On Wed, 2012-11-21 at 16:39 -0800, Greg Kroah-Hartman wrote:

3.0-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Huang Ying <redacted>

commit 90b5c1d7c45eeb622302680ff96ed30c1a2b6f0e upstream.

If a PCI device and its parents are put into D3cold, unbinding the
device will trigger deadlock as follow:

- driver_unbind
  - device_release_driver
    - device_lock(dev)				<--- previous lock here
    - __device_release_driver
      - pm_runtime_get_sync
        ...
          - rpm_resume(dev)
            - rpm_resume(dev->parent)
              ...
                - pci_pm_runtime_resume
                  ...
                  - pci_set_power_state
                    - __pci_start_power_transition
                      - pci_wakeup_bus(dev->parent->subordinate)
                        - pci_walk_bus
                          - device_lock(dev)	<--- deadlock here


If we do not do device_lock in pci_walk_bus, we can avoid deadlock.
Device_lock in pci_walk_bus is introduced in commit:
d71374dafbba7ec3f67371d3b7e9f6310a588808, corresponding email thread
is: https://lkml.org/lkml/2006/5/26/38.  The patch author Zhang Yanmin
said device_lock is added to pci_walk_bus because:

  Some error handling functions call pci_walk_bus. For example, PCIe
  aer. Here we lock the device, so the driver wouldn't detach from the
  device, as the cb might call driver's callback function.

So I fixed the deadlock as follows:

- remove device_lock from pci_walk_bus
- add device_lock into callback if callback will call driver's callback

I checked pci_walk_bus users one by one, and found only PCIe aer needs
device lock.

[...]

What about eeh_report_error() in
arch/powerpc/platforms/pseries/eeh_driver.c?

Also, is the deadlock even possible before this change in Linux 3.6?

commit 448bd857d48e69b33ef323739dc6d8ca20d4cda7
Author: Huang Ying [off-list ref]
Date:   Sat Jun 23 10:23:51 2012 +0800

    PCI/PM: add PCIe runtime D3cold support

Ben.

-- 
Ben Hutchings
Never attribute to conspiracy what can adequately be explained by stupidity.