ACPI / scan: Add second pass of companion offlining to hot-remove code

As indicated by comments in mm/memory_hotplug.c:remove_memory(),
if CONFIG_MEMCG is set, it may not be possible to offline all of the
memory blocks held by one module (FRU) in one pass (because one of
them may be used by the others to store page cgroup in that case
and that block has to be offlined before the other ones).

To handle that arguably corner case, add a second pass of companion
device offlining to acpi_scan_hot_remove() and make it ignore errors
returned in the first pass (and make it skip the second pass if the
first one is successful).

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

drivers/acpi/scan.c

@@ -131,6 +131,7 @@ static acpi_status acpi_bus_offline_companions(acpi_handle handle, u32 lvl,
 {
 	struct acpi_device *device = NULL;
 	struct acpi_device_physical_node *pn;
+	bool second_pass = (bool)data;
 	acpi_status status = AE_OK;
 
 	if (acpi_bus_get_device(handle, &device))
@@ -141,15 +142,26 @@ static acpi_status acpi_bus_offline_companions(acpi_handle handle, u32 lvl,
 	list_for_each_entry(pn, &device->physical_node_list, node) {
 		int ret;
 
+		if (second_pass) {
+			/* Skip devices offlined by the first pass. */
+			if (pn->put_online)
+				continue;
+		} else {
+			pn->put_online = false;
+		}
 		ret = device_offline(pn->dev);
 		if (acpi_force_hot_remove)
 			continue;
 
-		if (ret < 0) {
-			status = AE_ERROR;
-			break;
+		if (ret >= 0) {
+			pn->put_online = !ret;
+		} else {
+			*ret_p = pn->dev;
+			if (second_pass) {
+				status = AE_ERROR;
+				break;
+			}
 		}
-		pn->put_online = !ret;
 	}
 
 	mutex_unlock(&device->physical_node_lock);
@@ -185,6 +197,7 @@ static int acpi_scan_hot_remove(struct acpi_device *device)
 	acpi_handle not_used;
 	struct acpi_object_list arg_list;
 	union acpi_object arg;
+	struct device *errdev;
 	acpi_status status;
 	unsigned long long sta;
 
@@ -197,22 +210,42 @@ static int acpi_scan_hot_remove(struct acpi_device *device)
 
 	lock_device_hotplug();
 
-	status = acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX,
-				     NULL, acpi_bus_offline_companions, NULL,
-				     NULL);
-	if (ACPI_SUCCESS(status) || acpi_force_hot_remove)
-		status = acpi_bus_offline_companions(handle, 0, NULL, NULL);
-
-	if (ACPI_FAILURE(status) && !acpi_force_hot_remove) {
-		acpi_bus_online_companions(handle, 0, NULL, NULL);
+	/*
+	 * Carry out two passes here and ignore errors in the first pass,
+	 * because if the devices in question are memory blocks and
+	 * CONFIG_MEMCG is set, one of the blocks may hold data structures
+	 * that the other blocks depend on, but it is not known in advance which
+	 * block holds them.
+	 *
+	 * If the first pass is successful, the second one isn't needed, though.
+	 */
+	errdev = NULL;
+	acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX,
+			    NULL, acpi_bus_offline_companions,
+			    (void *)false, (void **)&errdev);
+	acpi_bus_offline_companions(handle, 0, (void *)false, (void **)&errdev);
+	if (errdev) {
+		errdev = NULL;
 		acpi_walk_namespace(ACPI_TYPE_ANY, handle, ACPI_UINT32_MAX,
-				    acpi_bus_online_companions, NULL, NULL,
-				    NULL);
+				    NULL, acpi_bus_offline_companions,
+				    (void *)true , (void **)&errdev);
+		if (!errdev || acpi_force_hot_remove)
+			acpi_bus_offline_companions(handle, 0, (void *)true,
+						    (void **)&errdev);
 
-		unlock_device_hotplug();
+		if (errdev && !acpi_force_hot_remove) {
+			dev_warn(errdev, "Offline failed.\n");
+			acpi_bus_online_companions(handle, 0, NULL, NULL);
+			acpi_walk_namespace(ACPI_TYPE_ANY, handle,
+					    ACPI_UINT32_MAX,
+					    acpi_bus_online_companions, NULL,
+					    NULL, NULL);
 
-		put_device(&device->dev);
-		return -EBUSY;
+			unlock_device_hotplug();
+
+			put_device(&device->dev);
+			return -EBUSY;
+		}
 	}
 
 	ACPI_DEBUG_PRINT((ACPI_DB_INFO,