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

4 files changed, 17 insertions, 15 deletions

diff --git a/drivers/pci/hotplug/pciehp.h b/drivers/pci/hotplug/pciehp.h
index 26ffd3e3fb74..2c113de94323 100644
--- a/drivers/pci/hotplug/pciehp.h
+++ b/drivers/pci/hotplug/pciehp.h
@@ -44,7 +44,6 @@ extern bool pciehp_poll_mode;
 extern int pciehp_poll_time;
 extern bool pciehp_debug;
 extern bool pciehp_force;
-extern struct workqueue_struct *pciehp_wq;
 
 #define dbg(format, arg...)                                             \
 do {                                                                    \
@@ -78,6 +77,7 @@ struct slot {
         struct hotplug_slot *hotplug_slot;
         struct delayed_work work;       /* work for button event */
         struct mutex lock;
+        struct workqueue_struct *wq;
 };
 
 struct event_info {
diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
index 916bf4f53aba..939bd1d4b5b1 100644
--- a/drivers/pci/hotplug/pciehp_core.c
+++ b/drivers/pci/hotplug/pciehp_core.c
@@ -42,7 +42,6 @@ bool pciehp_debug;
 bool pciehp_poll_mode;
 int pciehp_poll_time;
 bool pciehp_force;
-struct workqueue_struct *pciehp_wq;
 
 #define DRIVER_VERSION  "0.4"
 #define DRIVER_AUTHOR   "Dan Zink <dan.zink@compaq.com>, Greg Kroah-Hartman <greg@kroah.com>, Dely Sy <dely.l.sy@intel.com>"
@@ -340,18 +339,13 @@ static int __init pcied_init(void)
 {
         int retval = 0;
 
-        pciehp_wq = alloc_workqueue("pciehp", 0, 0);
-        if (!pciehp_wq)
-                return -ENOMEM;
-
         pciehp_firmware_init();
         retval = pcie_port_service_register(&hpdriver_portdrv);
         dbg("pcie_port_service_register = %d\n", retval);
         info(DRIVER_DESC " version: " DRIVER_VERSION "\n");
-        if (retval) {
-                destroy_workqueue(pciehp_wq);
+        if (retval)
                 dbg("Failure to register service\n");
-        }
+
         return retval;
 }
 
@@ -359,7 +353,6 @@ static void __exit pcied_cleanup(void)
 {
         dbg("unload_pciehpd()\n");
         pcie_port_service_unregister(&hpdriver_portdrv);
-        destroy_workqueue(pciehp_wq);
         info(DRIVER_DESC " version: " DRIVER_VERSION " unloaded\n");
 }
 
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)
diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
index 13b2eaf7ba43..5127f3f41821 100644
--- a/drivers/pci/hotplug/pciehp_hpc.c
+++ b/drivers/pci/hotplug/pciehp_hpc.c
@@ -773,23 +773,32 @@ static void pcie_shutdown_notification(struct controller *ctrl)
 static int pcie_init_slot(struct controller *ctrl)
 {
         struct slot *slot;
+        char name[32];
 
         slot = kzalloc(sizeof(*slot), GFP_KERNEL);
         if (!slot)
                 return -ENOMEM;
 
+        snprintf(name, sizeof(name), "pciehp-%u", PSN(ctrl));
+        slot->wq = alloc_workqueue(name, 0, 0);
+        if (!slot->wq)
+                goto abort;
+
         slot->ctrl = ctrl;
         mutex_init(&slot->lock);
         INIT_DELAYED_WORK(&slot->work, pciehp_queue_pushbutton_work);
         ctrl->slot = slot;
         return 0;
+abort:
+        kfree(slot);
+        return -ENOMEM;
 }
 
 static void pcie_cleanup_slot(struct controller *ctrl)
 {
         struct slot *slot = ctrl->slot;
         cancel_delayed_work(&slot->work);
-        flush_workqueue(pciehp_wq);
+        destroy_workqueue(slot->wq);
         kfree(slot);
 }