ACPI: Fix resource_lock dead lock in acpi_power_on_device

[Lin Ming <ming.m.lin@intel.com>]

Commit 0090def("ACPI: Add interface to register/unregister device
to/from power resources") used resource_lock to protect the devices list
that relies on power resource. It caused a mutex dead lock, as below

acpi_power_on ---> lock resource_lock
  __acpi_power_on
    acpi_power_on_device
      acpi_power_get_inferred_state
        acpi_power_get_list_state ---> lock resource_lock

This patch adds a new mutex "devices_lock" to protect the devices list
and calls acpi_power_on_device in acpi_power_on, instead of
__acpi_power_on, after the resource_lock is released.

Signed-off-by: Lin Ming <ming.m.lin@intel.com>
---
 drivers/acpi/power.c |   29 ++++++++++++++++++-----------
 1 file changed, 18 insertions(+), 11 deletions(-)

diff --git a/drivers/acpi/power.c b/drivers/acpi/power.c
index eb640874..068349e 100644
--- a/drivers/acpi/power.c
+++ b/drivers/acpi/power.c
@@ -103,6 +103,7 @@ struct acpi_power_resource {
 
 	/* List of devices relying on this power resource */
 	struct acpi_power_resource_device *devices;
+	struct mutex devices_lock;
 };
 
 static struct list_head acpi_power_resource_list;
@@ -221,7 +222,6 @@ static void acpi_power_on_device(struct acpi_power_managed_device *device)
 
 static int __acpi_power_on(struct acpi_power_resource *resource)
 {
-	struct acpi_power_resource_device *device_list = resource->devices;
 	acpi_status status = AE_OK;
 
 	status = acpi_evaluate_object(resource->device->handle, "_ON", NULL, NULL);
@@ -234,12 +234,6 @@ static int __acpi_power_on(struct acpi_power_resource *resource)
 	ACPI_DEBUG_PRINT((ACPI_DB_INFO, "Power resource [%s] turned on\n",
 			  resource->name));
 
-	while (device_list) {
-		acpi_power_on_device(device_list->device);
-
-		device_list = device_list->next;
-	}
-
 	return 0;
 }
 
@@ -247,6 +241,7 @@ static int acpi_power_on(acpi_handle handle)
 {
 	int result = 0;
 	struct acpi_power_resource *resource = NULL;
+	struct acpi_power_resource_device *device_list;
 
 	result = acpi_power_get_context(handle, &resource);
 	if (result)
@@ -266,6 +261,17 @@ static int acpi_power_on(acpi_handle handle)
 
 	mutex_unlock(&resource->resource_lock);
 
+	mutex_lock(&resource->devices_lock);
+
+	device_list = resource->devices;
+	while (device_list) {
+		acpi_power_on_device(device_list->device);
+
+		device_list = device_list->next;
+	}
+
+	mutex_unlock(&resource->devices_lock);
+
 	return result;
 }
 
@@ -351,7 +357,7 @@ static void __acpi_power_resource_unregister_device(struct device *dev,
 	if (acpi_power_get_context(res_handle, &resource))
 		return;
 
-	mutex_lock(&resource->resource_lock);
+	mutex_lock(&resource->devices_lock);
 	prev = NULL;
 	curr = resource->devices;
 	while (curr) {
@@ -368,7 +374,7 @@ static void __acpi_power_resource_unregister_device(struct device *dev,
 		prev = curr;
 		curr = curr->next;
 	}
-	mutex_unlock(&resource->resource_lock);
+	mutex_unlock(&resource->devices_lock);
 }
 
 /* Unlink dev from all power resources in _PR0 */
@@ -410,10 +416,10 @@ static int __acpi_power_resource_register_device(
 
 	power_resource_device->device = powered_device;
 
-	mutex_lock(&resource->resource_lock);
+	mutex_lock(&resource->devices_lock);
 	power_resource_device->next = resource->devices;
 	resource->devices = power_resource_device;
-	mutex_unlock(&resource->resource_lock);
+	mutex_unlock(&resource->devices_lock);
 
 	return 0;
 }
@@ -717,6 +723,7 @@ static int acpi_power_add(struct acpi_device *device)
 
 	resource->device = device;
 	mutex_init(&resource->resource_lock);
+	mutex_init(&resource->devices_lock);
 	strcpy(resource->name, device->pnp.bus_id);
 	strcpy(acpi_device_name(device), ACPI_POWER_DEVICE_NAME);
 	strcpy(acpi_device_class(device), ACPI_POWER_CLASS);
-- 
1.7.10