PCI: pciehp: Use per-slot workqueues to avoid deadlock

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>
CC: stable@vger.kernel.org

1 files changed, 4 insertions, 4 deletions

diff --git a/drivers/pci/hotplug/pciehp_ctrl.c b/drivers/pci/hotplug/pciehp_ctrl.c
index 27f44295a657..38f018679175 100644
--- a/drivers/pci/hotplug/pciehp_ctrl.c
+++ b/drivers/pci/hotplug/pciehp_ctrl.c
@@ -49,7 +49,7 @@ static int queue_interrupt_event(struct slot *p_slot, u32 event_type)
         info->p_slot = p_slot;
         INIT_WORK(&info->work, interrupt_event_handler);
 
-        queue_work(pciehp_wq, &info->work);
+        queue_work(p_slot->wq, &info->work);
 
         return 0;
 }
@@ -344,7 +344,7 @@ void pciehp_queue_pushbutton_work(struct work_struct *work)
                 kfree(info);
                 goto out;
         }
-        queue_work(pciehp_wq, &info->work);
+        queue_work(p_slot->wq, &info->work);
  out:
         mutex_unlock(&p_slot->lock);
 }
@@ -377,7 +377,7 @@ static void handle_button_press_event(struct slot *p_slot)
                 if (ATTN_LED(ctrl))
                         pciehp_set_attention_status(p_slot, 0);
 
-                queue_delayed_work(pciehp_wq, &p_slot->work, 5*HZ);
+                queue_delayed_work(p_slot->wq, &p_slot->work, 5*HZ);
                 break;
         case BLINKINGOFF_STATE:
         case BLINKINGON_STATE:
@@ -439,7 +439,7 @@ static void handle_surprise_event(struct slot *p_slot)
         else
                 p_slot->state = POWERON_STATE;
 
-        queue_work(pciehp_wq, &info->work);
+        queue_work(p_slot->wq, &info->work);
 }
 
 static void interrupt_event_handler(struct work_struct *work)