PCI: pciehp: Use per-slot workqueues to avoid deadlock
authorYijing Wang <wangyijing@huawei.com>
Fri, 11 Jan 2013 02:15:54 +0000 (10:15 +0800)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Mon, 28 Jan 2013 04:49:01 +0000 (20:49 -0800)
commit4400d958826604db944e3a86d922e02f689b74d7
treed03c7223364bf5b40124d3ae655c2cbf169f5f93
parent48310adbde5b3448b85d6d6d404cc7ee16339ae5
PCI: pciehp: Use per-slot workqueues to avoid deadlock

commit c2be6f93b383c873a4f9d521afa49b1b67d06085 upstream.

When we have a hotplug-capable PCIe port with a second hotplug-capable
PCIe port below it, removing the device below the upstream port causes
a deadlock.

The deadlock happens because we use the pciehp_wq workqueue to run
pciehp_power_thread(), which uses pciehp_disable_slot() to remove devices
below the upstream port.  When we remove the downstream PCIe port, we call
pciehp_remove(), the pciehp driver's .remove() method.  That calls
flush_workqueue(pciehp_wq), which deadlocks because the
pciehp_power_thread() work item is still running.

This patch avoids the deadlock by creating a workqueue for every PCIe port
and removing the single shared workqueue.

Here's the call path that leads to the deadlock:

  pciehp_queue_pushbutton_work
    queue_work(pciehp_wq)                   # queue pciehp_power_thread
    ...

  pciehp_power_thread
    pciehp_disable_slot
      remove_board
pciehp_unconfigure_device
  pci_stop_and_remove_bus_device
    ...
      pciehp_remove                 # pciehp driver .remove method
pciehp_release_ctrl
  pcie_cleanup_slot
    flush_workqueue(pciehp_wq)

This is fairly urgent because it can be caused by simply unplugging a
Thunderbolt adapter, as reported by Daniel below.

[bhelgaas: changelog]
Reference: http://lkml.kernel.org/r/CAMVG2ssiRgcTD1bej2tkUUfsWmpL5eNtPcNif9va2-Gzb2u8nQ@mail.gmail.com
Reported-and-tested-by: Daniel J Blueman <daniel@quora.org>
Reviewed-by: Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
drivers/pci/hotplug/pciehp.h
drivers/pci/hotplug/pciehp_core.c
drivers/pci/hotplug/pciehp_ctrl.c
drivers/pci/hotplug/pciehp_hpc.c