ACPI: fix a deadlock in hotplug case

we used to run the hotplug code in keventd_wq.
But when hot removing the ACPI battery device,
power_supply_unregister invokes flush_scheduled_work.
This causes a deadlock. i.e
1. When dock is unplugged, all the hotplug code is run on kevent_wq.
2. the hotplug code removes all the child devices of dock device.
3. removing the child device may invoke flush_scheduled_work
4. flush_scheduled_work waits until all the work on kevent_wq to be
   finished, while this will never be true because the hotplug code
   is running on keventd_wq...

Introduce a new workqueue for hotplug in this patch.
http://bugzilla.kernel.org/show_bug.cgi?id=13533

Tested-by: Paul Martin <pm@debian.org>
Tested-by: Vojtech Gondzala <vojtech.gondzala@gmail.com>
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
Reviewed-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>

1 files changed, 16 insertions, 9 deletions

diff --git a/drivers/acpi/osl.c b/drivers/acpi/osl.c
index d916bea729f1..71670719d61a 100644
--- a/drivers/acpi/osl.c
+++ b/drivers/acpi/osl.c
@@ -79,6 +79,7 @@ static acpi_osd_handler acpi_irq_handler;
 static void *acpi_irq_context;
 static struct workqueue_struct *kacpid_wq;
 static struct workqueue_struct *kacpi_notify_wq;
+static struct workqueue_struct *kacpi_hotplug_wq;
 
 struct acpi_res_list {
         resource_size_t start;
@@ -192,8 +193,10 @@ acpi_status acpi_os_initialize1(void)
 {
         kacpid_wq = create_singlethread_workqueue("kacpid");
         kacpi_notify_wq = create_singlethread_workqueue("kacpi_notify");
+        kacpi_hotplug_wq = create_singlethread_workqueue("kacpi_hotplug");
         BUG_ON(!kacpid_wq);
         BUG_ON(!kacpi_notify_wq);
+        BUG_ON(!kacpi_hotplug_wq);
         return AE_OK;
 }
 
@@ -206,6 +209,7 @@ acpi_status acpi_os_terminate(void)
 
         destroy_workqueue(kacpid_wq);
         destroy_workqueue(kacpi_notify_wq);
+        destroy_workqueue(kacpi_hotplug_wq);
 
         return AE_OK;
 }
@@ -716,6 +720,7 @@ static acpi_status __acpi_os_execute(acpi_execute_type type,
         acpi_status status = AE_OK;
         struct acpi_os_dpc *dpc;
         struct workqueue_struct *queue;
+        work_func_t func;
         int ret;
         ACPI_DEBUG_PRINT((ACPI_DB_EXEC,
                           "Scheduling function [%p(%p)] for deferred execution.\n",
@@ -740,15 +745,17 @@ static acpi_status __acpi_os_execute(acpi_execute_type type,
         dpc->function = function;
         dpc->context = context;
 
-        if (!hp) {
-                INIT_WORK(&dpc->work, acpi_os_execute_deferred);
-                queue = (type == OSL_NOTIFY_HANDLER) ?
-                        kacpi_notify_wq : kacpid_wq;
-                ret = queue_work(queue, &dpc->work);
-        } else {
-                INIT_WORK(&dpc->work, acpi_os_execute_hp_deferred);
-                ret = schedule_work(&dpc->work);
-        }
+        /*
+         * We can't run hotplug code in keventd_wq/kacpid_wq/kacpid_notify_wq
+         * because the hotplug code may call driver .remove() functions,
+         * which invoke flush_scheduled_work/acpi_os_wait_events_complete
+         * to flush these workqueues.
+         */
+        queue = hp ? kacpi_hotplug_wq :
+                (type == OSL_NOTIFY_HANDLER ? kacpi_notify_wq : kacpid_wq);
+        func = hp ? acpi_os_execute_hp_deferred : acpi_os_execute_deferred;
+        INIT_WORK(&dpc->work, func);
+        ret = queue_work(queue, &dpc->work);
 
         if (!ret) {
                 printk(KERN_ERR PREFIX