+/**
+ * cgroup_writeback_umount - flush inode wb switches for umount
+ *
+ * This function is called when a super_block is about to be destroyed and
+ * flushes in-flight inode wb switches. An inode wb switch goes through
+ * RCU and then workqueue, so the two need to be flushed in order to ensure
+ * that all previously scheduled switches are finished. As wb switches are
+ * rare occurrences and synchronize_rcu() can take a while, perform
+ * flushing iff wb switches are in flight.
+ */
+void cgroup_writeback_umount(void)
+{
+ if (atomic_read(&isw_nr_in_flight)) {
+ synchronize_rcu();
+ flush_workqueue(isw_wq);
+ }
+}
+
+static int __init cgroup_writeback_init(void)
+{
+ isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
+ if (!isw_wq)
+ return -ENOMEM;
+ return 0;
+}
+fs_initcall(cgroup_writeback_init);
+