Revert "kernfs: replace kernfs_node->u.completion with kernfs_root->deactivate_waitq"

This reverts commit ea1c472dfeada211a0100daa7976e8e8e779b858.

Tejun writes:
        I'm sorry but can you please revert the whole series?
        get_active() waiting while a node is deactivated has potential
        to lead to deadlock and that deactivate/reactivate interface is
        something fundamentally flawed and that cgroup will have to work
        with the remove_self() like everybody else.  IOW, I think the
        first posting was correct.

Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 232f1a6..d2c439d 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -15,7 +15,7 @@
 #include <linux/lockdep.h>
 #include <linux/rbtree.h>
 #include <linux/atomic.h>
-#include <linux/wait.h>
+#include <linux/completion.h>
 
 struct file;
 struct iattr;
@@ -91,6 +91,7 @@
 	struct rb_node		rb;
 
 	union {
+		struct completion	*completion;
 		struct kernfs_node	*removed_list;
 	} u;
 
@@ -131,7 +132,6 @@
 	/* private fields, do not use outside kernfs proper */
 	struct ida		ino_ida;
 	struct kernfs_dir_ops	*dir_ops;
-	wait_queue_head_t	deactivate_waitq;
 };
 
 struct kernfs_open_file {