ACPI / scan: Make acpi_bus_hot_remove_device() acquire the scan lock

The ACPI scan lock has been introduced to prevent acpi_bus_scan()
and acpi_bus_trim() from running in parallel with each other for
overlapping ACPI namespace scopes.  However, it is not sufficient
to do that, because if acpi_bus_scan() is run (for an overlapping
namespace scope) right after the acpi_bus_trim() in
acpi_bus_hot_remove_device(), the subsequent eject will remove
devices without removing the corresponding struct acpi_device
objects (and possibly companion "physical" device objects).
Therefore acpi_bus_hot_remove_device() has to acquire the scan
lock before carrying out the bus trimming and hold it through
the evaluation of _EJ0, so make that happen.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Toshi Kani <toshi.kani@hp.com>

drivers/acpi/scan.c

@@ -95,6 +95,8 @@ acpi_device_modalias_show(struct device *dev, struct device_attribute *attr, cha
 }
 static DEVICE_ATTR(modalias, 0444, acpi_device_modalias_show, NULL);
 
+static void __acpi_bus_trim(struct acpi_device *start);
+
 /**
  * acpi_bus_hot_remove_device: hot-remove a device and its children
  * @context: struct acpi_eject_event pointer (freed in this func)
@@ -114,10 +116,12 @@ void acpi_bus_hot_remove_device(void *context)
 	acpi_status status = AE_OK;
 	u32 ost_code = ACPI_OST_SC_NON_SPECIFIC_FAILURE; /* default */
 
+	mutex_lock(&acpi_scan_lock);
+
 	ACPI_DEBUG_PRINT((ACPI_DB_INFO,
 		"Hot-removing device %s...\n", dev_name(&device->dev)));
 
-	acpi_bus_trim(device);
+	__acpi_bus_trim(device);
 	/* Device node has been released. */
 	device = NULL;
 
@@ -146,18 +150,14 @@ void acpi_bus_hot_remove_device(void *context)
 	status = acpi_evaluate_object(handle, "_EJ0", &arg_list, NULL);
 	if (ACPI_FAILURE(status)) {
 		if (status != AE_NOT_FOUND)
-			printk(KERN_WARNING PREFIX
-					"Eject device failed\n");
-		goto err_out;
-	}
+			acpi_handle_warn(handle, "Eject failed\n");
 
-	kfree(context);
-	return;
+		/* Tell the firmware the hot-remove operation has failed. */
+		acpi_evaluate_hotplug_ost(handle, ej_event->event,
+					  ost_code, NULL);
+	}
 
-err_out:
-	/* Inform firmware the hot-remove operation has completed w/ error */
-	(void) acpi_evaluate_hotplug_ost(handle,
-				ej_event->event, ost_code, NULL);
+	mutex_unlock(&acpi_scan_lock);
 	kfree(context);
 	return;
 }
@@ -1683,10 +1683,8 @@ static acpi_status acpi_bus_remove(acpi_handle handle, u32 lvl_not_used,
 	return AE_OK;
 }
 
-void acpi_bus_trim(struct acpi_device *start)
+static void __acpi_bus_trim(struct acpi_device *start)
 {
-	mutex_lock(&acpi_scan_lock);
-
 	/*
 	 * Execute acpi_bus_device_detach() as a post-order callback to detach
 	 * all ACPI drivers from the device nodes being removed.
@@ -1701,7 +1699,12 @@ void acpi_bus_trim(struct acpi_device *start)
 	acpi_walk_namespace(ACPI_TYPE_ANY, start->handle, ACPI_UINT32_MAX, NULL,
 			    acpi_bus_remove, NULL, NULL);
 	acpi_bus_remove(start->handle, 0, NULL, NULL);
+}
 
+void acpi_bus_trim(struct acpi_device *start)
+{
+	mutex_lock(&acpi_scan_lock);
+	__acpi_bus_trim(start);
 	mutex_unlock(&acpi_scan_lock);
 }
 EXPORT_SYMBOL_GPL(acpi_bus_trim);