After commit bcdde7e2 (sysfs: make __sysfs_remove_dir() recursive)
I'm seeing traces analogous to the one below in Thunderbolt testing:

WARNING: CPU: 3 PID: 76 at /scratch/rafael/work/linux-pm/fs/sysfs/group.c:214 sysfs_remove_group+0x59/0xe0()
 sysfs group ffffffff81c6c500 not found for kobject '0000:08'
 Modules linked in: ...
 CPU: 3 PID: 76 Comm: kworker/u16:7 Not tainted 3.13.0-rc1+ #76
 Hardware name: Acer Aspire S5-391/Venus    , BIOS V1.02 05/29/2012
 Workqueue: kacpi_hotplug acpi_hotplug_work_fn
  0000000000000009 ffff8801644b9ac8 ffffffff816b23bf 0000000000000007
  ffff8801644b9b18 ffff8801644b9b08 ffffffff81046607 ffff88016925b800
  0000000000000000 ffffffff81c6c500 ffff88016924f928 ffff88016924f800
 Call Trace:
  [<ffffffff816b23bf>] dump_stack+0x4e/0x71
  [<ffffffff81046607>] warn_slowpath_common+0x87/0xb0
  [<ffffffff810466d1>] warn_slowpath_fmt+0x41/0x50
  [<ffffffff811e42ef>] ? sysfs_get_dirent_ns+0x6f/0x80
  [<ffffffff811e5389>] sysfs_remove_group+0x59/0xe0
  [<ffffffff8149f00b>] dpm_sysfs_remove+0x3b/0x50
  [<ffffffff81495818>] device_del+0x58/0x1c0
  [<ffffffff814959c8>] device_unregister+0x48/0x60
  [<ffffffff813254fe>] pci_remove_bus+0x6e/0x80
  [<ffffffff81325548>] pci_remove_bus_device+0x38/0x110
  [<ffffffff8132555d>] pci_remove_bus_device+0x4d/0x110
  [<ffffffff81325639>] pci_stop_and_remove_bus_device+0x19/0x20
  [<ffffffff813418d0>] disable_slot+0x20/0xe0
  [<ffffffff81341a38>] acpiphp_check_bridge+0xa8/0xd0
  [<ffffffff813427ad>] hotplug_event+0x17d/0x220
  [<ffffffff81342880>] hotplug_event_work+0x30/0x70
  [<ffffffff8136d665>] acpi_hotplug_work_fn+0x18/0x24
  [<ffffffff81061331>] process_one_work+0x261/0x450
  [<ffffffff81061a7e>] worker_thread+0x21e/0x370
  [<ffffffff81061860>] ? rescuer_thread+0x300/0x300
  [<ffffffff81068342>] kthread+0xd2/0xe0
  [<ffffffff81068270>] ? flush_kthread_worker+0x70/0x70
  [<ffffffff816c19bc>] ret_from_fork+0x7c/0xb0
  [<ffffffff81068270>] ? flush_kthread_worker+0x70/0x70

(Mika Westerberg sees them too in his tests).

Some investigation documented in kernel bug #65281 led me to the
conclusion that the source of the problem is the device_del() in
pci_stop_dev() as it now causes the sysfs directory of the device to be
removed recursively along with all of its subdirectories.  That includes
the sysfs directory of the device's subordinate bus (dev->subordinate) and
its "power" group.

Consequently, when pci_remove_bus() is called for dev->subordinate in
pci_remove_bus_device(), it calls device_unregister(&bus->dev), but at this
point the sysfs directory of bus->dev doesn't exist any more and its
"power" group doesn't exist either.  Thus, when dpm_sysfs_remove() called
from device_del() tries to remove that group, it triggers the above
warning.

That indicates a logical mistake in the design of
pci_stop_and_remove_bus_device(), which causes bus device objects to be
left behind their parents (bridge device objects) and can be fixed by
moving the device_del() from pci_stop_dev() into pci_destroy_dev(), so
pci_remove_bus() can be called for the device's subordinate bus before the
device itself is unregistered from the hierarchy.  Still, the driver, if
any, should be detached from the device in pci_stop_dev(), so use
device_release_driver() directly from there.

References: https://bugzilla.kernel.org/show_bug.cgi?id=65281#c6Reported-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>